Many competition shooters of skeet, trap and sporting clays have forcing cones lengthened in their competition guns in an effort to improve patterning and decrease perceived recoil. Personally, I have always stayed away from this with my guns because I believe it harms value, but more importantly I feel it may reduce bridge pressure, thus allowing some gases to escape around the wad, thusly reducing a guns ability to 'shoot hard'. In pigeon shooting, the guns that have lengthened forcing cones seem to be 'feather blowers' and don't seem to kill as well as guns with tight forcing cones. I have no scientific evidence to base this on, just empirical observation. Does anyone know of any scientific evidence which proves the theory that lengthening forcing cones is a BAD idea? or, conversely a GOOD idea?

Lots of debate on this one. Here are a few articles to peruse:

RW article 1

RW article 2

If you're concerned with pressure in the sense of keeping it to a minimum (for older guns), Sherman Bell's tests showed that lengthened cones do usually result in some pressure reduction (few hundred psi) when shooting 2 3/4" shells in 2 1/2" chambers.

Lengthening of forcing cones along with overbore will give very uniform patterns. My Kolar SC has no discernible chamber and the patterns are the most uniform I have ever seen.
Conversely, felt recoil is subjective and there is no scientific evidence that supports the claims.
Removing metal from an engineering perspective on an item designed for specific pressures is not something that i would do or recommend. Many believe that the attributes of lengthening a chamber or forcing cone are worth the effort but I don't believe anyone can supply scientific evidence that it accomplishes any quantifiable change to be worth while and the safety considerations far out weigh any possible gains.
In short, I leave my field guns alone and purchase Target guns with overbore barrels and long forcing cones.-Dick

My pattern testing about 20 yrs ago confirms to me what Dick said. Patterns are better with long cones. The longer, smoother the transition, the better the pattern got in my tests. I tested three cone lengths. A 4" long cone was the longest I tested and it produced consistantly the best patterns.

PS, I would not modify a vintage gun with long cones. The improvement is not worth the devaluation or the cost.

For a serious competitor any mod that "seems", he "believes", or he "feels" enhances performance is a good idea. Whether it's been proven is secondary to what it contributes to the supreme confidence that is so helpful to winning.

FWIW, a theory is just a theory. There may be evidence to support it, but if it hasn't been proven and widely accepted as fact, it's still a theory. Seems intuitive that any scientifically proven improvements to shotgun barrel configuration would be embraced my the makers and users and quickly become SOP. There is ample reading to suggest those barrel mods are an improvement. Most of it is written by people wishing to sell you those mods. You'll have to dig harder to find evidence they don't work. You can't prove a negative...absence of evidence is not evidence of absence. In short, it's not scientific evidence, but acceptance in the public realm that will convince people (or not) of their worth. Browning has been at the forefront of providing competitors with what they thought they needed but, more important, what they wanted. It surely didn't hurt their sales temporarily to increase bore diameters from .729 to .745, lengthen forcing cones and port the muzzles.

Somehow, the 500 yr old maker, Beretta, didn't get the memo. They reluctantly enlarged the bore from .721 to a whopping .733 and called it the "optima bore." Otherwise, they seem to have ridden out the fashion wave for the last 20 years as I've never seen a factory ported Beretta O/U. Meanwhile, many shooters now consider ported barrels to be an absolute deal breaker on a used gun.

I "believe" longer cones than those of 80 years ago are useful for alleviating some of the very slight concern I have for shooting modern factory shells with plastic wads in my Foxes. Anyway, I "feel" it can't hurt and 3 of my Foxes that shoot thousands of modern target loads per year have lengthened cones. Two of my Foxes are bird guns and part of the appeal is shooting and hunting only with factory paper shells loaded with fiber wads in the 1950's. They have the original short cones.

If I were shooting loads with fiber wads in competition I would not want lengthened forcing cones. Gough Thomas Garwood contended that the long forcing cones sometimes allowed gas to escape around the (fiber) wad and weld the shot together.

I wouldn't worry about lengthened forcing cones if I were shooting modern plastic wads with shotcups.

Best,

Mike

Ever seen a pair of forcing "steps"? Sharp, abrupt halt of the chamber area, typically on older guns, likely intended for use with roll crimped, paper rounds.

I've had one set of those worked on. Both barrels were choked full and full, and the choke was let out as well. I probably wouldn't do it to a more modern gun, but, the old girl throws very uniform hunting patterns today, versus the dense, splotchy patterns previous. It works well with either plastic wads or fiber wads, from my limited testing.


Best,
Ted

Beretta did get the memo. I have a Brit market 682 "Sporting" that has factory screw-ins and ports. I got it NIB so I'm pretty sure the factory did the ports. I don't recall that Perazzi did any ports but they are into bigger bores and have had long cones prolly before anyone noticed. That "shoot harder" crap is always fun to hear. What a yuk!

As to the forcing cones - The initial pressure impulse has to be lower and resultant shot deformation lower with longer cones. Is it lower enough to make a difference? How long is long enough? there were "chamberless" guns a century ago. If that is so great why do we still have forcing cones and 12ga bores? I dunno. But I do know that Julius Del George had a Pigeon factory engraved M12 that flat kicked like a MFer until he noticed that it had no visible cone at all. So he had that taken care of and guess what - his $200 purchase instantly increased several fold.

However opening the cones in old gun has a dangerous potential - the barrel thickness may be inadequate to tolerate that bigger ID that the long cone creates. If it gets sent for re-proof it could easily come back in a couple pieces.

Like most of the BS that floats on this and other gun sites, empirical evidence is non-existent for forcing cones, big bores, ports, and a multitude of other "topics of interest". Those are all things that, to my shame, I have participated in with past guns. Abstinence, just like the Repugnicans say, is the best policy and one that I presently endorse.
For guns anyway.

Dr.WtS

I was asked this question some years ago when they became the "in thing" in the UK. I listened to both sides of the argument,I spoke to shooters and to the Proof house who had carried out some unofficial tests and came to a simple conclusion. I dont care what any one say's but at £35 a time I'd do them all day .

Mike, can you point to the specific source of your Gough Thomas reference? I have 3 of his books and I can't remember reading anything about the forcing cone issue--but it could well be I've just forgotten it.

Sure!

May take me a little while.

Best,

Mike

I have my own reamers, hones, etc., for several gauges to lengthen cones. I've tested enough to satisfy myself that patterns get better with a longer cone. This seems to be more dramatic in the little .410. I attribute the pattern improvement to less damaged shot from abrupt changes in the shot path. Since more percentage of the shot load is in contact with the barrel wall with a .410, I think it reflects in the more dramatic improvement. I use a reamer that produces a 3" long cone in a .410. I've tested my barrels enough that I'm satisfied.

I would not do it on a pristine "collectable", but do believe it helps patterns (less fliers) and reduces recoil. Further, if you are starting with a strong gun like a M21, you can shoot an occaisional 3" shell with no problem. When I buy a gun to "upgrade" it is SOP .... chokes, FC's, wood, engraving, refinish, etc.

After more than 100 years of choke bored guns with standard forcing cones that shoot just wonderful patterns, why would we drill out our forcing cones because someone says that it will improve patterns? Does it make patterns tighter? Does it make them more even? Does it add to the center thickness? Maybe Chuck can clarify that. Drilling out forcing cones costs money and takes metal out of the high pressure area of your gun. Why would anyone drill the cones out of a double barrel shotgun unless he were making a living shooting that gun for serious money? My experience is that the "gun rapers" don't shoot very well and are looking for a crutch.

Or someone is stuck in "time warp" and unwilling to consider tech improvements that most progessive manufactures now offer as "Standard" spec for newest guns. I really don't want anyone to "rape" your K32.

Please tell us who you believe are progressive manufacturers.

Considering the thousands of dollars I spent, and the potential damage I did, plying my body with nicotine and alcohol in my youth...I think spending a couple hundred dollars for barrel modifications is clean, harmless fun.

Mike the Ripper

SHOTGUNS AND CARTRIDGES, third edition, page 136

The question then arises, why not a really long cone- five or six inches maybe - by which the pellets would be gently eased back in to the bore? Such cones have been strongly advocated, notably by that doyen of American shotgunners, Elmer Keith. They would certainly lower ballistics (Journee lost 33ft/sec of muzzle velocity by lengthening cones from about 3/8 inche to 1-1/4 inch), but might well achieve a net gain with high-pressure cartridges by the improvemnt of patterns. Superior patterns are worth than marginal values of muzzle velocity.

Years ago, it was the practice of many of our best gunmakers to bore their guns with what could fairly be regarded as a prolonged extension of a normal cone. This was a tapered entrance -- perhaps 9 or 12 inches long - from the cone to the bore proper. In a high-class specimen which I have measured, the bore diameter immediately in from of the cone is .738 inch tapering down to .730 inch at 10 inches form the breech.
But long cones rely absolutely for any merit they possess on the high quality of the wadding. If the wad does not expand adequately immediately on its emergence from the case, a long cone will invite gas to escape past it, and if any considerable amount does so, bad patterns, accompanied by serious balling, are almost inevitable. Here, two of the virtues of the modern full plastic wad stand out conspicuously; the skirt wad provides an efficient gas-seal, and any gas that does escape is prevented by the shot-cup from invading the pellets.

I remember some other remarks by him on this subject - more to the point about balling and written before plastic wads became commonplace

Best,

Mike

I've had forcing cones lengthened on several guns. The only difference ever noted on paper or on the shoulder was my 3 1/2" 10, which had factory cones cut short and slightly off-center. On the pattern board, two ounce bismuth handloads gained percentage points at 60 yards with improved eveness, possibly from fewer broken pellets. No scientific tests but it did seem to make the heavy recoil more of a push than a slap. If the loads lost velocity it didn't matter with the large pellets (BB).

Here's a link to an independent test done on the matter:

http://www.jimeyster.com/testing/documents/Forcing%20Cone%20Test.pdf

"independent?"

take it for what you want, he works on his own.

In my opinion long cones work and reduce recoil and barrel pattern better. Bobby

Fellow Double Gun Fans: In reference to the above study, performed by Ken Eyster at Heritage Gunsmiths in Ohio, I think one can get the idea that changing the radius of the forcing cone may improve patterning (by 10 shot); however, one has to keep in mind this was a very, very small study, utilizing only one gun and one barrel. I am not a statitician, but I wonder if the 10 shot improvement would even lie outside of experimental error parameters. I personally knew Ken Eyster quite well (he is now deceased) and know his son Jim Eyster who has now taken over at Heritage Gunsmiths. Ken did good work most of the time and his son Jim seems quite competent as well. I personally had them back bore several of my competition guns and most of them turned out pretty good. A couple didn't. My point with all this is.....which I knew when I presented the initial question....I don't think we will ever really know if lengthening forcing cones harms or helps our guns until further, large scale, double blinded, without bias testing takes place.

I think it's important that we keep all this in perspective. It's a gun, belonging to the person wanting the cone lengthened, not someone else's grandmother.

I've posted my description of what my patterning results were on this site at least a couple times. It convinced me. I don't have quantitative data, so if you want that, you'll have to do your own testing. While I'm certainly no proponent of taking a pristine high value collectable or even low value rare high condition gun, and modifying it, I will modify my mostly bottom-feeding guns to suit me and sleep well at night.

If something developed a hundred years ago was as good as it could get, you'd be riding in a Wright Flyer when you bought an airline ticket and we'd still be pouring gravel in a large bore and lighting the saltpeter with a torch.

Thankfully, there's something new under the sun everyday.

One thing I can assure you of; "IF" I had an original Wright Flier I would not be modernizing it. I do have several Shotguns which are older than a Wright Flier & I prefer them Un-Modified as well. Its really immaterial to me whether lengthening the cone of one of my 100+ yr old Lefevers, even the lowly H grades, would improve its pattern or not.

Seems everybody wants to bore out the cones & bores on these old guns for "Better" patterns, then they turn around & open up those carefully bored original chokes because they pattern "Too Good"

That's about it in a nutshell, Miller. The same people who drill out the forcing cones to tighten the patterns are also drilling out the chokes to make it a quail gun. When I used the "crutch" word, I certainly wasn't referring to Mike Campbell. His drilled out guns are serious competition guns in the hands of someone who doesn't need a crutch.

"If something developed a hundred years ago was as good as it could get, you'd be riding in a Wright Flyer when you bought an airline ticket and we'd still be pouring gravel in a large bore and lighting the saltpeter with a torch.

Thankfully, there's something new under the sun everyday."

Totally false analogy. The simple fact is that the original rapid development of the shotgun pretty much maxed the concept and the following 100yrs merely did some minor tweeks.

In specific I would agree that the .410 has some great room for seeing improvement but who GAF? - I mean, a .410? That's like wanting my smoothbore .22 rimfire to make better patterns.

And nobody has taken a look at how much difference there is between a carefully cut and polished cone job and a stock 649th gun on this reamer production bbl. Which all comes down to me thinking that the general concept may be fine but the individual gun may simply not need its' cone cut. In considering all the results of the mutherfications that I have perpetrated or had perpetrated on gun barrels, there is nothing that would tempt me to "improve" any of the Perazzis that I currently care for. Goes for the M12's too for that matter.

And I still have that 12ga reamer in the toolbox.

And at $50 a whack for a 5min job I'd do'em every chance I got too.

And the more applicable comment about "new" is the one that Will Rogers made - "The only thing new is the history you don't know". Which seems to have bee written for shotgunners.

have a day
Dr.WtS

This thread has mostly referred to patterns. If and when I lengthen the cone of
my Manufrance Idéal it will be only because Mr. Bell concluded that there is a
reduction in pressure when shooting 70 mm shells in 65 mm chambers. (I actually
use 67mm CIP shells in it).

If you are a good shot I am sure you never worry about patterns.

JC

Can you give us Mr. Bell's quote on that one. Larry whatsis said the same thing a while ago. Are you quoting Larry or Sherman Bell? I guess I don't quite understand the meaning of your post.

One would hope that purchasing at the Perezzi level would get you a reamer not on it's 649th tube, but, the only guarantee is death and taxes.

While we are on "minor improvements" Dr. Sane, lets forget, for a moment, the advancements in petrochemical engineering that gave us plastic hulls and wads-do 'ya think a turn-o-the-century P gun would have identical chamber dimensions to one produced, say, yesterday?

I think not. I've seen enough Winchester SX2s to know that the bore and choke dimensions aren't going to be identicle to your model 12.

Let's assume there is a reason for this. It's OK to admit you don't know why.

Best,
Ted

I wouldn't count on lengthening a forcing cone reducing max pressure to any extent. Pressure has peaked & starting to fall by the time the shot gets into the cone. To effect pressure by much the chamber is going to have to be so short as to actually retatrd the opening of the crimp.

Every shell out of a single box of shells fired through the same gun will give a slightly different pressure reading. I Highly suspect had Bell run a lot larger sampling those pressures would have tended to be even more equal than he showed.

I'm sure there have been some dimensional fluctuations over the last 120 or so years but my take would be that they were, if intentional, market hype just like today or inconsequential. I'll omit chamber length since that really has no bearing and was for other reasons anyway. And the simple fact the "modern" dimensioned ammo will work quite well in guns from the turn of the last century is notable.
As you correctly note the REAL advancements have been in the bits and pieces shoved into the gun and not the dimensional standards to which the guns are built. That does not negate the simple fact that guns have been built to a dimensional standard that has not changed in any significant way whatsoever for that whole time. I cannot attest to the Perazzis at that time depth since they did not exist then, but I would suspect that the likelihood of elderly Berettas, Purdys, Greeners, etc., being dimensioned similarly would be quite high.

I mean, it's a (hopefully) straight round tube and the choke area is concentric to the rest of the tube. Admittedly the quality production of such a device does potentially pose some difficulties but the concept is about as complex as a rock.

have a day
Dr.WtS

PS - the only comment that comes to mind on the topic of long cones reducing pressure when people are too stupid to use the correct ammo is DUH! The pressure spike reduction would have to be marginal, but an effectively longer chamber is a longer chamber no matter how you may construe it.

As I recall, Sherman Bells comments about pressure versus chamber length mention the inconsequential differences as Wonko says. I'm still waiting for the Bell quote that says anything contrary. Very few quality makers have gone to longer cones, again contrary to what some posters state. Long cones are absolutely risky in repeating shotguns considering the prevalence of separated hulls today. They can also be risky in break open guns used by those who don't check their bores every shot before loading another shell.

I'll say it again, I'm certainly no proponent of taking a pristine high value collectable or even low value rare high condition gun, and modifying it, I will modify my mostly bottom-feeding guns to suit me and sleep well at night.

Actually, I don't bother to touch the cones or chokes of most of my guns. I just received a nice little 20g Grade 3 NID, factory SST, ejector. back from restoration by Gunter Pfrommer. (Yeah, I know some of you will want to fight about restoration too. Well this one had one leg in the junk pile already). It doesn't have, nor will it get, long cones.

I don't advocate anyone modify their vintage gun with long cones or open their chokes (my modern tight and tigher 28"/28g Repro will keep its chokes and cones as is). But, I do know that there is a performance advantage to be had. To say such things don't exist is just ignoring facts. To say they are only for someone of a particular level is as rediculous as saying you need to shoot a predermined qualifying score before you're allowed to own a certain gun.

If anyone wants to pursue testing of long cones for themselves, I have a couple reamers I would modify your test barrel with to support your curiousity.

If long chamber cones are so desirable ,why dont the manufacturers do them as standard? Has any asked Beretta, Ruger, Galazan, Mossberg ,Remington ? Has any one asked the cartridge loaders the same question?

My suspicion on why it's only done by some performance gun makers is that it bucks the manufacturer standards organization specs (SAAMI, or other foreign orgs). SAAMI specs include the cone. Most of the makers you mentioned are likely SAAMI members, except maybe Galazan.

Krieghoff choose to go the long cone route a long time ago. I think someone mentioned Kolar did as well. Possibly other target gun makers have as well.

Caesar Guerini and Beretta offers modified forcing cones on their target guns:

Caesar Guerini
Beretta 682

Baserri claims they have eliminated the forcing cone entirely with their Tri-Bore barrels.
Baserri

Question is whether they believe it works or they think their customers want it.

SAAMI is of course only a recommendation, not legally binding. Also I believe their recommendations for the cone are for a "Minimum" cone size. Any maker shoud be quite free to lenghten theirs to their hearts desire & still be able to say it was to SAAMI Specs.

I do not contend that longer forcing cones do not improve barrel performance. What I said was is that there is no empirical evidence to substantiate that claim. If someone is happy with the reamer results - cool. Forcing cones are difficult to eyeball and a crappy one could be difficult to detect but one improved by recutting could be a boon. To my eye, the Perazzi cones look very rough but the results on the board and targets completely negates any desire on my part to change that.
So I currently have nothing that feels the need of the time and expense involved. Maybe if I could qualify for it I might be tempted hahahaha or not

Dr.WtS

I would tend to agree . . . except for the fact that I don't believe he ever recorded an INCREASE in pressure as a result of a lengthened cone. There was always some decrease. I do agree that in order to determine how much of a decrease one is likely to get, you'd need to fire several shells (all the same loads) through the unaltered cone, then do the same through the altered cone and take an average.

Since SAAMI is only a industry org, it's obvious they have no legal authority. On the cone length, the only information I have is a hard dimension, in this case an angle with a reference length for the finished cone.

Hello 8B,

Here are some quotes from the article related to different tests involving a
comparison of same shells before and after the lengthening:

"Modifying the 2,5 inch chamber with a long forcing cone dropped the breech pressure slightly to 11,045 psi (from 11.125 psi), The pressure at the cone dropped more significantly to 7500 psi (from 8,100 psi), or almost down to 2,75 inch pressure value."

"When the long-coned figures are in, we see a drop of only 220 psi, to 8545 psi at one inch but again, a nice fall-off of 800 psi to 5500 psi at the forcing cone."

"The much-anticipated data with the long forcing cone was a pleasant surprise. The breech pressure returned to 6385 psi, virtually identical to the longer chamber figure. At the front of the chamber the number is 4700 psi, which is even lower than in the long chamber".

But, having re-read the article I must now keep in my memory bank (don't know for how long it will stay) Mr. Bell's last remark:

"But I might have the forcing cones lengthened, assuming the barrel wall thickness will allow it. I wouldn't bother for the slight pressure benefit but as a fussy handloader, I hate it when my hulls have that nose-cone shape. I have no proof, but I think patterns will be better when the shot charge has a smother, unrestricted ride into the bores".

I other words I am leaving my Manufrance Idéal as is and shall continue to shoot 67 mm CIP shells from it galore.

And thank you for making me re-read the article and mend my ways.

JC(Alway Learning)

For those who may find the partial Bell quote confusing, let me say that the "nose cone shape" of the lip of a shell is not from a short forcing cone, but from firing the shell in a chamber actually shorter than the case. Short forcing cones don't do anything to a shell.

8B, you are spot on on that (as usual). Thanks for clarifying.

JC

P.S. For those interested the complete article is in "The Double Gun Journal",
Volume Twelve, Issue 4, Winter 2001. jc

At least with plastic shells, you seem to get some "nose-coning" after you've used the same hull several times. I can notice a definite difference between once or twice fired hulls and 8 or 10 times fired hulls. And that's in 2 3/4" chambers.

I doubt I'd have cones done for the relatively little pressure reduction either, but it was an interesting result of Bell's tests.

I am firing a shell in a chamber actually shorter than the case and I get no "nose-coning". Clearly 67mm shells in 65mm chambers are nothing to worry about.
And no SAAMI shells for me thank you!

JC

I'm using a full 2 3/4" paper in a 2 9/16" chamber and I get a little shredding of the hull in the I.D. of the crimp. I load them twice and toss them. There's a definite indication of the chamber being short on the hull outside as well. I'm running a measured 6500psi load.

JC, at one time I assembled quite a collection of fired hulls. I discovered that some 67MM hulls were as long as some 2 3/4" hulls (none of which actually measured as long as 2 3/4"). If you measure your chamber and measure your hull, you may also find the hull isn't actually any longer than the chamber. I was surprised at the amount of variation.

Hello Larry,

I did a comparison also and there were marked variations between different shells. I have a photo somewhere that I'll post if found.

JC

If one is planning on regularly shooting an American vintage SxS, and it has/had "short chambers," I see no harm in opening it to a standard 2-3/4" chamber AND adding longer forcing cones at the same time (assuming there is enough barrel thickness). I have had my gunsmith do so to several of my SxS shotguns.

Pressure is lowered at least marginally, and the useful life of the shotgun is probably extended. It does no harm...

gold40

I copied this from the Ceaser Guerini site someone linked to:

"The DuoCon forcing cones are a unique dual conical long forcing cone system designed by Caesar Guerini to produce optimum performance and maximum versatility. The first conical section maximizes chamber pressure and permits the use of fiber wad ammunition. The secondary 4.5" long forcing cone section reduces recoil and increases pattern uniformity."

It is interesting that we again get to GT Garwood's contention that gas bypasses the fiber wads in a long cone. I added the underline and italics

If anyone is planning to lengthen forcing cones, I propose we run a pattern test. Dr. Jones is willing to run analysis provided ten samples of each gun & load are taken. Less than ten doesn't meet the statisticalneeds of good research. Anyone want to do this?

Jerry, I think that advice is good maybe 95% of the time. Maybe even more. But I don't think it would be a good idea, for example, to take an Ithaca Flues 20ga, especially if it's one of the lighter ones, and punch the chambers to 2 3/4" and lengthen the cones. At the least, I'd certainly want to take some wall thickness measurements where I intended to have metal removed if I were to contemplate such a modification. You're certainly not making the gun any stronger by removing metal. And while MOST vintage American guns are pretty stout, some aren't. We've already heard of Flues frame failures, usually light 20's. The problem, at least in a couple cases I recall, appears to have been "light" promo ammo (which is not really light in terms of pressure, nor velocity), 2 3/4", in short chambers. If enough metal were removed to extend the chambers to 2 3/4" and lengthen the cones, I think one might have a legitimate concern whether even ammo at pressures appropriate to the pre-modified gun might not cause problems.

With regard to reducing the wall thickness, lengthening the chamber will push the corner of the chamber/forcing cone further forward. Since the outside of most sxs guns has a taper from the breach end, this definitely reduces wall thickness. However, I haven't run across a gun with a tapered outside that was steeper than the longest forcing cone reamer I have. Therefore, the minimum wall thickness will still be the corner of the chamber/forcing cone, regardless if the cones are lengthened with my reamers. I believe someone stated that modifying cones on a British proof gun doesn't take it out of proof? If so, this would be the reason, IMO.

It might be useful to remember that all "fiber" wads are not "created equal" when it comes to obturation. Cork wads, for example, do not obturate much, at all. Fiber wads can obturate a bit better, especially if they are properly lubed and/or "ventilated" (see Zutz). By and large the best obturators are felt wads, with obtuation levels varying according to the quality of the felt and the wad lubricant that is used (See Greener, Churchill, et.al.).

Chuck, it's correct that lengthening the cone doesn't take a British gun out of proof. But lengthening the chamber does. That's where the peak pressure always occurs.

Going back to my post about Flues frame failures, lengthening chambers would only increase the likelihood of those if, as a result of the longer chambers, someone were to use higher pressure shells. But most gunsmiths that specialize in doubleguns, I think, would like to see a minimum barrel wall thickness of .100 at the mouth of the chamber. I don't know whether another 1/4" added to the length of a 20ga Flues chamber would put you below that mark, but I think it would be something to consider.

Thanks Larry. I recall in some past posts in threads where there was concern of reducing minimum wallthickness with a long cone. I was pointing out that it just doesn't occur with a lengthening of a forcing cone on most doubles, since that outside taper is so much longer than even my reamer for a 4" cone in a 12g.

Who'd have thunk this little subject would get a bunch of old men seeing red enough to insult each other? I'm sorry if I did that, myself, to anyone on this subject.

This is great stuff to know! I was not aware of the proof distinctions between chamber lenngthening and forcing cone lenghtening.

In my opinion, British Proof is a load of manure once the gun exits from the proof house. Brits are famous for grinding the wall thickness from the outside, leaving the inside "in proof". A hundred dollar wall thickness gauge is worth ten times what a proof stamp is worth. Also in my opinion, two identical shotguns, one original 2 1/2" chambers, the other drilled out to 2 3/4", if fired with progressively stronger 2 3/4" bullets, the drilled out gun will burst first. Of course, the drilled gun will recoil less.

I sure have a lot of doubles with original chambers and forcing cones with wall thicknesses way below .100" at the end of the chamber.

Fox A grade 16ga, 26" barrels, 2-7/16" chamber, 0.085" and 0.086" minimum wall thickness at the end of the chambers, .734" and .734" diameter at the end of the chambers, 5/8" long forcing cones, #4 barrels, gun weighs 5lbs 9oz, serial 302XXX.

Parker VH O Frame 16ga, 28" steel barrels, serial 134XXX, 2-9/16" chamber, .082" and 0.085" minimum wall thickness at the end of the chambers, 0.730" and 0.732" end chamber diameters, 3lbs 2oz unstruck barrel weight, gun weighs 5lbs 14oz.

Fox XE 16ga, 30" barrels, serial 301xxx, .072" and .080" minimum wall at chamber ends, 2-7/16" chambers, .733" and .733" end chamber diameters, gun weighs 6lbs 3oz

Parker DHE 16ga, 32" steel barrels, serial 212XXX, 0.090" and 0.092" minimum wall thickness at chamber ends, 2-9/16" chambers, .735" and .736" diameter at chamber ends, barrel unstruck barrel weight 3lbs 11oz, gun weighs 7lbs 4oz.

Lefever H grade 16 gauge, 28" twist barrels, .090" and .092" minimum wall thickness at chamber ends, 2-5/8" chambers, .729" and .728" diameter at chamber ends. Gun weighs 6lbs 4oz

Ithaca Flues Grade 4E 16 gauge, 28" Krupp fluid steel barrels, 0.091" and 0.092" minimum wall thickness at the end of 2-5/8" chambers, daimeters of .728" and .730" at the end of the chambers, gun weighs 6lbs 6ounces.

Parker DH 12 bore, 28" Damascus barrels, 1 frame, .086" and .090" minimum wall thickness at end of the 2-5/8" chambers, gun weighs 6lbs 14oz. Serial #84XXX, My Skeets gauges are in capable of measuring the diameters at the end of the chamber.

Bissel Birmingham boxlock, 20 gauge, 25" steel barrels, made in the 1920s, .084" and .092" minimum wall thickness at the chamber ends, 2-1/2" chambers. My Skeets gauges are in capable of measuring the diameters at the end of the chamber. Weighs 5lbs 7oz.

Best,

Mike

Those dimensions are good reason to not lengthen the chambers, IMO.

I just wanted to make the point that many old doubleguns left the factory with substantially less chamber end wall thickness than .100"

I may want to trade or sell one of these light guns someday and would certainly hate for the general perception to be that they were too thin in the chambers. Bore gauges and wall thickness gauges are becoming ubiquitous and things that didn't used to get checked get checked now.

Best,

Mike

Here is another data point:

AYA #1 20 bore sidelock, factory 2-3/4" (70mm) chambers, 30" barrels, built and proofed in 2006, .092" and .091" minimum wall thickness at the end of the chambers. Skeets gauges unable to measure chamber diameter. Gun weighs 5lbs 13oz.

Best,

Mike

Drilling out a gun with .090 wall thickness at the end of the chambers is absolutely silly. Paying someone to do it is way more than silly.

Just for the record, I am not advocating chamber lengthening. I am contending that old light SxSs shipped from the factory with chamber end wall thicknesses substantially less than .100"

I don't lengthen or have lengthened chambers or forcing cones in my old doubles.

Best,

Mike

Edit - what I meant to say: I don't lengthen or have the chambers or forcing cones lengthened in my old doubles.

Couple more data points:

My shooting student Joe Wood checked his minty Webley 700 6lb 4oz 12 bore, .092" and .090" minimum wall thickness at the end of the chambers. Factory 2-3/4" original chambers.

One of his DH 12 bore 1 frame Damascus 28" barreled guns weighs 6lbs 8oz and has .092 and .095" at the barrels. Original 2-1/2" chambers.

eightbore, your engineering terminology is grating on my nerves.
The rest of you make sure your guns are mechanically sound and just shoot them.
Leave well alone, Greener did most of the experimenting and research and got well paid for it, don't pay someone to experiment and don't waste your life experimenting, get out afield hunting fishing and shooting. Your a long time dead.

They're all unsafe, Mike. Sell them immediately. How many of those guns (other than the AyA) were made after 1930? By that time, we'd switched to higher pressure shells. Lengthening chambers AND shooting higher pressure loads might be a bad combination.

Eightbore, re your comment on British proof . . . the drilled-out gun you suggest would likely burst first (and I think tht's a good bet) would have to be submitted for reproof--where it might have failed without endangering the shooter.

Will you take them off my hands please Larry?

And all of them were before 1930 and have the original sub-2-3/4" chamber lengths. And I shoot reloads in them that have a maximum pressure that doesn't exceed the cartridges they were designed to shoot.

But Joe Wood's 2-3/4" chambered 700 is certainly post 1930 and intended, designed, and built for the American market.


Best,

Mike