doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Gun reboring and regulating.

Gents,
The general principles of regulation are very well known due to double rifles, which have far more ambitious goals for regulation than shotguns ever will.
Regulation depends on:
- construction of the barrel set (static convergence, length of barrels, straightness, muzzle area)
- projectile velocity profile in the barrel (charge of powder, type of powder, projectile characteristics, friction on the barrel walls)
- inertia of the gun + projectile (how much does it move while the projectile goes down the barrel)
- to a lesser extent, how you hold the gun (same as above)

Even though indeed the tubes should be straight through manufacturing, I am sure that someone somewhere fixed up regulation by mucking with the barrel assembly.
Pretty much *all* double rifles are done this way : the breech and the forend loops impose a fixed geometry on the barrel assembly towards the breech, and only the muzzle wedge is adjusted to make things work. The barrels *have to be bent* (in a small way)to make this work.
Another way is to modify the muzzle profile. This is heretical to double rifle people but well known recent examples exist.

By and large, the shotgun makers should know how to build a shotgun to make this work without mucking around with anything post assembly in a "correct by construction" methodology. Of course, the way you define correct is interesting, i.e. how good is good enough...
Additionally, the regulation cannot be perfect for every load anyways.

Best regards,
WC-

Mike;
There is one thing I can most definitely agree with you on. That is that we simply need to discuss this like Men, no sniping etc. I will try my level best to do so. All that I can go with is like they say in a court of law, The Preponderance of the Evidence.
Let me state that carefully one more time.
My copy of the L C Smith Plans & Specifications is copyrighted 1981 by F Brownell & Son. I pre-ordered this book when notice was sent out of its up-coming publishment. It came with a facsimile of the title block of an actual shop drawing attached inside, declared the book to be #1328, Autographed by William Brophy & dated Nov 15, 1981. Sometime shortly after receiving this book in studying over the drawings therein I noted the barrel specs which I have cited. I became curious as to just how some of my guns compared to the Smith specs, so set about to find out. Measuring the space at the breech & muzzle is extremely easy. I picked about three sets of barrels to compare, don't even recall exactly which ones now. The first thing that struck me was that just taking the spacing of the two ends & considering the lengths of these barrels they all showed a total convergence of from 011" to .012" per inch of length or virtually identical to the Smith specs. Next I carefully measured & marked regular intervals along the length of the barrels (about 2" intervals as I recall) until I came to the area of the barrel flats where it was no longer practical. A careful measurement of the outside of these barrels compared to the measurement across their outer widths did indeed show that as far as their OD's went they had the same convergence on a linear basis as their two ends had exibeted. There is of course still the factor that the bores are not necessarily concentric with their OD's. I did take all this into consideration. I did do the sight check & to the best of my ability & knowledge they were about as straight as they could be. At this point I am not totally certain whether I used the concentric circle or the back lighted window, though I do more commonly use the frame shadow line & this is most likely what I used. While these are the only ones I have ever measured to this extent I have looked down the bores of many sets of barrels over the years to see if I could spot one that had those swamped in barrels, as I have Heard this "Theory" for years. Do date I have not encountered a single barrel set which showed this swamping.
That in a Nutshell is the preponderance of my Evidence.
Now I am ready to honestly & manly review any evidence you can present which actually shows a set of barrels to have been constructed in this manner. I promise to give it my utmost attention & consideration with no snidey remarks.
Best I have to offer.

Mike,

Sorry to drop out like that, but have been busy all day with Mother's Day meal and company and such.

Have enjoyed all the back and forth, but still await an answer for the question I put forth (twice). From post #366059:

"I mean, why in the world would a barrel man put two barrels together with a converging angle, which is to counteract the recoil which pulls the gun to one side or the other, then make the bores parallel?"

The shot charge will be leaving the muzzle guided by the direction given it from the last bit of bore, right? If there was, say, 6 inches, of parallel bore the shot charge would leave basically in the direction given it by that last 6 inches, right? Then, why build in convergence, which you admit exists? The parallel bores would nullify the convergence given by the built in angle.

Think with me through this a minute. The shot charge begins moving down the left bore, and the gun begins to rotate left because of the recoil being off-axis to the centerline of the gun. The angle of convergence will counteract that rotation if left alone. But, now the shot charge hits a bend in the bore and begins to move back left, the opposite direction from where it needs to be directed.What is the reasoning in this? Help me out here.

SRH

From 366066



Does that answer the question you asked? If it didn't I need more feedback on what I am missing.

Stan this is about the maker setting the convergence of the tubes. If, as you and Miller argue, both tubes are straight and since Parker muzzles all touch then the convergence is not set by the maker on a two-frame Parker, it is set by geometry. The two-frame designation sets the distance between the centerline of the bores at the breech, the touching muzzles set the centerline of the bores at the muzzle. Parker doesn't set the convergence, geometry does. If the tubes are straight and the muzzles touch then all two-frame Parkers with 26" barrels have the same angle of convergence. If the tubes are absolutely straight then all two frame Parkers with 32" barrels have the same convergence angle. The 32" angle is different than the 26". It is only by curving the barrels that Parker would be able to set the angle of convergence on those guns because, for whatever reason, they built their guns with touching muzzles. Could we just focus on two frame Parkers for a little bit. Once we have a meeting of the minds on Parkers we can go on to guns that don't have touching muzzles and other variables.

Thanks Miller. Just finished up Mother's day at the in-laws and look forward to continuing the discussion tomorrow.

Mike, I have to believe the tubes are straight unless a mistake was made by whoever stitched them together. If they were anything but straight there would be reams of material written about the fine art of bending them and then the incredibly difficult task of joining prebent tubes. There is nothing. In your discussion comparing 26" and 30" barrels have you considered the difference in barrel flip? Seems to me the shorter the barrel the greater the flip and vice versa. In my way of thinking that could easily explain how these two different lengths with very different convergence points still shoot to the same POI at distance. To reinforce the concept I have heard that guns firmly set in a bench rest shoot vastly different than shooting offhand.

Joe barrel flip is up and down, not left and right. Garwood reported that it most frequently appears on long barreled sub-bores.

As far as anchored barrels/guns: If the barrels didn't rotate when the shot is fired then the barrels could be made parallel. If barrels/gun with normal convergence were fixed where they could not rotate then the right barrel would shoot far to the left and the left barrel would shoot far to the right.

Kind of an awkward example, but what would a Parker concept gun look like if it had a pair of blunderbuss barrels mounted up and touching. Do the 26's and 32's touch by design, or pure random luck based on the tubes that got dropped off that morning. Maybe they can be machined to touch as well as change or preserve some convergence angle.

Chances are after being designed and tested someone jigged up a method for production, rather than adjusting bend, choke and convergence angle for each barrel set that was made. Still wondering, if it can't or is barely seen, how did they place, align and preserve the intentionally bent tubes through the makers process.

Edit to add, "flip" I believe is the recoil/rotation/what ever. The gun movement on firing likely has many influences and I can't see it limited to vertical.

Craig "barrel flip" has a specific meaning. It is phenomenon that causes SxS barrels to shoot low. Garwood wrote that it most frequently manifests itself in long barreled sub-bores. By arguing that barrel flip is up and down I am not arguing that the barrels aren't rotating in the horizontal plane as the shot goes down the barrel, they are.

Parker barrels left the factory touching at the muzzle. I suppose there have been exceptions but I have never seen one.

Burrard wrote he felt it was a mistake to have barrels of different length fitted to the same gun as Barrel Flip would cause them to hit to a different point "Vertically". He did not confine this to sub-bores but was speaking primarily of the 12 gauge, which was at the time of his writing "THE" gauge in the UK.
This I believe was not what Joe was speaking of. Perhaps the best term here would simply be Barrel Displacement. As I read through these posts I believe we are all pretty well in agreement that the barrels are moving during the load's travel down the bore, otherwise there would be an unacceptable amount of crossfire, as the barrels whether straight or bent do converge.
Now let me Speculate a bit. I believe it is a False Assumption to believe that the barrels of every given length, every weight of gun & every load fired has to end with the same degree of convergence. Maybe I am misinterpreting here Mike but I seem to be getting the feeling you are saying this has to be so. I have gone back & re-read your link to the Parker Board. Let me say this as kindly as I can, but I can see absolutely nothing there other than the speculation that barrels of different lengths having the same breech spacing & still touching at the muzzle "Must" have been bent so the last section of the barrels at the muzzle would have the same convergence. This is as far as I can see an unproven hypothesis.
In studying the history of barrel making one finds their configurations were Set, well back in the Welded barrel era. At this point a barrel was generally made to be round at any point, though contoured down its length. Metal for the flats was welded on. It was also found that flats needed to be put on the mating surfaces of the breech ends of the two barrels to bring their centers closer together, else they would indeed crossfire. Of all the barrels I have ever checked this on I still find that the web between the two barrels is not equal to twice the the wall thickness at the extreme breech end of the barrels, thus Gunmakers are still building to essentially the same criteria. All the writings I have seen would indicate that standard practice was to make the barrels as straight as humanly possible & to set them at a converging angle, no doubt worked out over time by trial & error. The "Very" limited amount of barrels which I have personally checked show that "Those" barrels were indeed made in this fashion.

There are people joining the conversation late. I think these are things that Miller, Stan, and I all agree on. All are in reference to side by sides. I will quote it the next time someone chimes to argue something with me that I am not disputing.

1. The barrels converge at the muzzle because recoil moves the barrel/gun as the shot charge goes down the barrel. The convergence is needed so the gun will shoot where it was pointed at the time the shot charge started down the barrel.

2. As the shot charge goes down the right barrel the barrel/gun rotates to the right. It also rotates up. This necessitates both convergence of the barrels and that the axis of the bores point down relative to the axis of rib. Of course firing the left barrel gives left rotation, muzzle rise will be the same.