This is a thread over at the firing line gunsmithing forum:

http://www.thefiringline.com/forums/showthread.php?t=250213

Interesting work. I'd have tried barrels longer than 22 inches myself but since the owner is running a red dot perhaps he intends to use his 45/70 double for quick work at close quarters.

Wow! I hope Ruger marketing is paying close attention! What a door opener that would make in many calibers. roger

Is a shotgun hinge pin and locking mechanism designed to take the torque of many high power 45 cal boolits in rifled barrels?

I have done that analysis for another break action 45/70, the Handi Rifle. There are a few things to calculate:
1) Hoop stress in the barrel
2) Latch pin shear
3) Bending moment section modulus on breech face
4) Latch stress

The hinge pin is often hooked or captured by a lug on the barrel with holes on either side in the receiver. This causes the calculation to be in double shear, as the pin would have to shear in two places.

The locking mechanism sees a possible force [if brass cases were slippery and parts had no mass] that is a function of two things:
a) The geometry of the hinge pin relative to the breech face. That is if they were in line [pin through the bore] there would be no force up or down on the latch.
b) The distance from the latch to the hinge pin.


On the topic of gun strength, most of the gun culture is dum'r-thn-uh-box-a-rocks, and opinionated based on "what the gun was designed for". AR is an oasis of intelligence, but you can't count on everyone here.

The Red Label action has Trunions to pivet on, just above the center of the bottom barrel.
The locking lug surfaces on the rear of the mono block again, is just above the center of the bottom barrel.

Many of these were dconverted to 375 H&H rifles in the 80's, by Jaeger, Searcy and myslef.
I would make a new mono block from 4140, heat treat it and then final fit the block.
The barrel blanks were threaded into the monoblock, rather than soldering.

The hard part is making the new hammer spring struts, to convert the hammer from a rebounding type to a top lever recocking type.
Also you need to reduce the firing pin diameters to prevent flow back.

James Wisner
Custom Metalsmith

apropos of nada, I did a google search some time ago and turned up a gunsmith in, IIRC, Virginia, who does a 45/70 conversion on side-by-sides.

tried to search him again, and can't find him.

I thought he was in TX. He would only do it on guns with a third lockup, preferably a Greener crossbolt, and only to 45-70. IIRC it was less than $1000, done with eccentric barrel inserts to regulate.

Looked for him again and can't find him on the web. Perhaps a few projects blew up and he's no longer with us....

that's gotta be the guy, the "eccentric barrel inserts" rings a loud bell. as usual, I'm at least half wrong- Texas not Virginia

as I recall, the price was on the low end for the work, too, as you state.

I think I got his name off the Guild page.

thanks.

If you ever find him, please PM me with the info, I have the perfect candidate. A Henri Pieper 12 with a Greener crossbolt and a front set trigger. Probably had a set of Cape barrels at one time.

quote:

Originally posted by tnekkcc:
on the topic of gun strength, most of the gun culture is dum'r-thn-uh-box-a-rocks, and opinionated based on "what the gun was designed for". AR is an oasis of intelligence, but you can't count on everyone here.

You certainly have a way with words ,Oliver. Nice avtar!!!! roger

My question was asked because I do not know how double rifle locks are built, or particularly how they differ in design from shotgun locks.

Specifically with regard to handling the torque imparted by firing a heavy slug in a rifled barrel.

I have wondered about this for a while and am sure there is someone on here who can address the question.

quote:

Originally posted by 1 Shot Hunter:
My question was asked because I do not know how double rifle locks are built, or particularly how they differ in design from shotgun locks.

Specifically with regard to handling the torque imparted by firing a heavy slug in a rifled barrel.

I have wondered about this for a while and am sure there is someone on here who can address the question.

What about handling the torque?
You want the peak torque calculated if the gun is restrained?
You want to compare this with the barrel threads torque?

You want to know if the gun will fall apart from stress from the torque?


I can tell you that in reaction to recoil, put a shotgun butt up against a brick wall, and the recoil can break the stock at the wrist. I have wrecked a hot rodded .410 that way.

The reaction to free recoil in a rifle is a few fps back and some twist.

The internal forces in the gun are small when the only load is to accelerate the mass of the gun.


Are you thinking that if we restrained the gun in a vise, we could break the stock from rearward recoil AND twist? And maybe bend some metal?

I know that O/U shotguns tend to loosen up after many thousands of rounds. I don't know if it's only the trunions that wear, or the latch, or both, as my Berreta only has a few thousand rounds through it and still feels about as tight as new.

Since the recoil of a heavy caliber rifle round can be, in my estimation, greater than that of a typical 2-3/4" 12 ga target round, I would expect the loosening to occur with fewer rounds. Then you add the torque of rifling into the equation...

Are big bore double rifles built with a more robust pivot pin, which might be supported 360 degrees around, rather than the trunions that are supported 180 degrees or less (allowing the shotgun to easily be assembled/disassembled in the field)?

BTW, I am sure shotgun barrels are tightened into the monobloc while it is mounted in a vise, as opposed to stressing the trunions and latch during final barrel tightening.

I am not a gunsmith nor a mechanical engineer, so feel free to correct or ignore me if I am wrong.

A good quality break action shotgun does not throw all the load on the hinge pin like a H&R single shot rabbit gun. My double and O/Us have locking surfaces on the underlug that rotate into recesses or holes in the receiver and take up at least part of the longitudinal thrust. Does a Red Label?

In the second place, a 20 ga shotshell has something over twice the casehead area of a .45-70 so even a top .45-70 SAAMI load is not treading very hard on the safety margin, when figured as force against the breechface. I can't figure the effect of rifling torque.

A lot of study goes into locking bolts, what Greener called "holding down bolts" but the load on them is not really very great. Greener said that one of his guns could be fired safely with the bolts removed, the action held shut with "a turn of common cord."

Greener attached a lot of importance to his crossbolt extension. Gough Thomas said it did not add as much as claimed, and HE was a mechanical engineer.

I think the Ruger conversion pictured and the ones by the 'smiths named are likely just fine.

Didn't Butch Searcy get his start building double rifles on shotgun actions?

I built a double O/U on a SKB small gauge shotgun action once & it worked very well. They are soft soldered barrels in the monobloc & a good crossbolt locking mechanism. It was a 30/40 krag and had a wedge "regulator" in between the barrels & at the muzzle. Shot very well IIRC.

quote:

Originally posted by Jim w.:


A good quality break action shotgun does not throw all the load on the hinge pin

I tried to relate the force on the latch to chamber pressure, and my father, a gun designer, pointed out that there was no force on the latch or hinge that was proportional to the chamber pressure. The latch and hinge pin stress' were a function of bullet friction and recoil on the barrel mass.

It took me a while to get my mind around that.

Maybe I did not get my mind completely around that, as I see I blathered on about hinge pins and latches in my post above