From a gunmaker's point of view, why is it an attribute of a best gun that there is no through lump in the floorplate, as opposed to lower quality guns which may show the lower part of the barrel lug through an opening in the floorplate?

Is it because of aesthetics mostly, or has it something to do with fitting? Is it easier to fit up a double with an underlug that is visible through the floorplate?

It certainly looks cleaner when it is hidden above the floorplate, IMO, unless there is some very well executed engraving on and around the lug and opening.

It is interesting that some American makers did not make guns with through lumps and some did. Same for Britain. From what I have seen most Continental makers did, except for their best.

All pertinent opinions welcome but, would any gunmakers/doublegunsmiths please address this?

SRH

Well, I'm not a gunmaker, nor am I a gunsmith. But, I did have a discussion about through lumps with a Purdey representative at the 2000 Vintage Cup at Orvis Sandanona. We were discussing hammerguns with and without through lumps. The Purdey rep told me that Purdey never did, nor ever would produce a hammergun with through lumps. I asked why, he told me it was a matter of strength, through lumps make for a weaker action.

We must have spoken to the same guy. The man at Purdey's that I spoke to about it said that when the lump swings down into the action floor It was a sign of best craftsmanship that you could fit the lug so tightly there was almost an airtight surrounding of the barrel lump On closing.
If you think about the technology that was being used to produce the early best guns making that square box in the bottom of the action was quite a feat, and a real sign of craftsmanship.
But it's also one more of those best gun treats that you can't actually see either.

Definitely not a case of, "Hey dumbass, When you carve out that blind hole, don't cut all the way through." LOL!

Ithaca added one when they brought out their Magnum-Frame NID in 1932.

Regular Frame --



Magnum Frame --

Interesting you should say that. This past weekend a friend's Boucher dumped some powder from a shotshell somehow into the lug mortices when a roll-crimped case came apart. Just a few flakes of powder were enough to prevent the gun from closing and it wasn't a sorta maybe thing. If flat would not go at all and the locking bolt wouldn't even think of swinging shut.

Beware of getting a little grass seed or cattail duff in there.

That would seem to refute the business about strength.

It does add additional bearing surface to the frame/barrel set interface.

Engineers put lightening holes in just about everything.

Why would a shotgun frame be any different than, say, a bridge when designing for bending load? They don't always make those solid you know...

Wonder why Purdey didn't tell Ithaca about that before they made such a huuuuuge mistake? Must be a big pile of cracked Ithaca Magnum actions somewhere, eh..........

Not!!

SRH

ClapperZapper,
The holes do go all the way through, they are just covered by the bottom plate. Having the lugs go through allows a slightly thinner action, while being strong enough to meet the requirements.
Mike

IMHO (engineering), this is far more about aesthetic and fashion than about action strength. I am unaware of any stress issues around the barrel to frame joints. If the barrel lugs are circle jointed to the frame, the bulk of the load in firing is straight tinsel on the frame and compression on the lug; both in relatively thick section areas. I don't see any particular strength advantage for either design or the need for any. Note that this is not an area in which even low quality guns fail.

DDA

researcher: extraordinary photos above...

are they digital or 35mm film?

ed,

Take your off topic questions to the private message feature, or start another thread, please.

SRH

In regards to strength . . . I recall an analogy offered that I either read or heard many years ago . . . A 175 lb. mountain climber has two ropes that he uses when scaling a vertical rock wall, one rope is rated to support 1000 lbs. of weight, the other rope is designed to support 2000 lbs of weight. Which rope for the climber's needs is safer? Answer: They are both safe, as both will easily support his weight. Next question: Which rope is stronger? The answer is obvious, the 2000 lb. rated rope is stronger.

You could use the above analogy when comparing the strengths of a gun with or without through lumps.

I don't see how through lumps are one whit weaker than non-through lumps where a floor plate is employed. The through lumps would make for slightly better reliability as well.

We are talking about the front lump I gather. Because the rear lump is always machined through, its concealment being the triggre plate, at least that is how it has been in the all the SXSs I have come across.

Solid pin boxlocks are by definition machined through, and the coverage of the front lump is via the bottom action plate. Some of the very best boxlocks are made this way, including some double rifles.

Let's take a look at these two pics . . .
Picture a testing lab with a machine to test the strength and rigidity of these two frames without the barrels or butt stock mounted. One end of the machine clamps onto the knuckle at the front end of the action from the water table down to the bottom of the action, the other end of the machine clamps onto the both sides of the action at the rear. The machine then twists the frame. Assuming both frames utilize the same exact makeup and tensile strength, which frame, in your opinion, will offer the most rigidity, strength and resistence to bending, the top frame without the through lump or the bottom frame with the through lump?

I know I prefer the through lump for my guns. I have had the same problem with guns without it as mentioned earlier with a small amount of debris preventing the closing of the action. And it’s much easier for me to thoroughly clean the pin/ hook area when the gun has a through lump. Action strength is a non issue with me.

WS, Is twisting really relevant to a shotgun?

In horology, blind lumps would be called a "complication" for all the same reasons.
I don't discount salesman's rhetoric in their promotion.

I've never heard of a gunmaker checking to see if the front lump and inside floor have an exceptionally tight fit - or of anyone caring about it.

Perhaps they did/do, but it sounds odd.

Not having a through-lump should make the bbls easier to fit and require less time overall.

When you put the bbls back on face, there's less work to be done, too. And there's no ugly gap on the through lump like you see here:

https://www.gunsinternational.com/guns-f...un_id=101130969

The strength argument is odd, too.

Scott used through-lumps on their sidelocks from the 1870s to at least the 1930s.

I've seen them on old, rising-bite .450NE & .470NE Rigby sidelock DRs & 12g shotguns, too. I'm pretty sure Rigby is using them today on their new rising-bite shotguns and DRs.

So if through-lumps weaken actions, why?

I suspect through lumps were more of a PITA overall. I bet makers got rid of them because of the extra work they required and to tidy up/modernize the look of their guns.

OWD

"I suspect through lumps were more of a PITA overall. I bet makers got rid of them because of the extra work they required and to tidy up/modernize the look of their guns."


That's interesting, as most guns with through lumps are considered cheap. I had always thought the same as you, a little more time and skill to get it right.

Good point.

On some guns -- cheap & expensive -- I'm certain the through lump made the action easier to machine.

I wonder if a big maker like Webley & Scott machined similar rough actions for all their sidelocks and then sent the actions on their way for building -- one would become a 3rd-tier gun, another a Premier? But they all started out the same way. Makes sense.

On other guns, I bet makers used through lumps to enlarge the hook/hinge-pin radius without making the action much deeper (Rigby double rifles).

OWD