Big bore rifle conversions?

[BattleRifleG3]

Being as I'm a fan of pump action arms over lever actions, I keep trying to find a way to set up a big bore big dangerous game pump. Dixie slugs are something like that which work in a regular rifled barrel shotgun. My idea was a bit different. Something I could very well actually make on my own from past experience making barrel inserts for shotguns. This could take one of two forms.

1.) Take an existing round whose rim diameter is about the same as that of a 12ga shotgun shell, ie that could be fed and extracted through the shotgun system. Make either a new barrel or a barrel insert for that round, which would only be loaded to pressures the shotgun was designed to handle (14,000psi for 3.5"), perhaps using black powder or substitute.

2.) Design a round shaped like shotgun shell with the bullet receded in the front. Would be pretty easy to make each shell on a lathe, or even cast them. The shell would be bored at the diameter of the bullet, which would be the width of the powder column. A barrel insert could then be used that had a flat surface to mate with the flat edge of the cartridge. The pressures of this round could be as many times the original 14,000psi as the ratio of the cross sectional area of the round over the 12ga cross sectional area. 458 caliber for example could be up to 42,000psi. The smaller the caliber, the higher the pressure could be. 375 caliber could be as much as 53,000psi. I doubt I'd go under 375 caliber in something as low velocity as this. Actually the 375 Winchester would be a good comparison, being loaded at the same pressures and being only slightly smaller. Checking pressure specs again, the 458 caliber version would be similar to the 450 Marlin. 475 or 50 caliber versions would have to work with lower pressures, 33,000psi or 30,000psi respectively.

So think this might be a good idea?  Apart from caliber, it would make available every option of existing 12ga pump shotguns, and if the latter concept were used, the shells could be treated in much the same way.

[Ramrod]

Stick with the low pressure idea. With the high pressures you are talking about, even if your barrel could take it, I think the lockup of the bolt would fail. (catastrophically, as the scientists say).

[BattleRifleG3]

Here's the thing with the lockup:  Force on the bolt = pressure x cross sectional area.  The 12ga has a large area.  The smaller the internal area of the round used, the lower the force per unit pressure, so greater pressures could be used.

14,000psi applied to 0.4185in^2 = 5860lb

5860lb / 0.1647in^2 = 35570psi

Hmm, not sure where the 42000psi came from before, but still the allowable pressures are much higher than the shotgun ones because the area is lower.

Course the black powder idea still has appeal, especially if it allows use of existing reloading supplies and the ability to use 50cal+ rounds that already have the sporting exemption.  Any rounds come to mind that have an OAL and rim diameter similar to a 12ga?

Of course it seems there's a good chance that regular 3.5" slugs would do at least as well.  At least something to look into.

[Graybeard]

Shotguns are designed to work at below 15,000 LEAD units of pressure. LUP is not comparable to CUP or PSI really. They are not made to handle the pressures you're talking about. I recommend you forget the idea. I know of no one who would intentionally take a pump gun for dangerous game anyway. Yeah I shot one a lot but I'd not trust my life to it on danerous game.

[BattleRifleG3]

Wow, LUP, CUP... I'm constantly amazed at how many new wierd units people come up with that make lives harder.

I had the impression that the 14,000 I read was psi, but as in anything I could well be wrong.  Glad you pointed out the LUP thing.

Guess it's time to read some more.  And some more.  I'm sure I'll figure out the design of a lifetime on my deathbed.

I really shouldn't be dreaming too hard on pumps as much as I brag about my speed with a bolt action (though my accuracy is nothing to write home about.)

I hope that, in spite of many reality checks on why some things haven't been done already, that we can come up with something new and useful.  But if not useful, at least safe.

[BattleRifleG3]

Just checked Dixie Slugs website, they list 10,000psi as being within the limits of a 3" mag.  That lines up with my numbers, which say 11,500 for the 3" and 14,000 for the 3.5" mag.  Considering that low pressure rifle rounds start at about 30,000 with most around 45 and many all the way up to 60, 14,000 doesn't seem far fetched for a 3.5" magnum shotgun.

Still learning though.

[Ramrod]

The L.U.P and C.U.P came from the way pressure was tested in gunbarrels in the "olden" days. There was no good cheap way to measure P.S.I. So a lead pellet of known dimensions was subjected to the breech pressure directly through a hole to the testing apperatus. The lead "crusher" was then measured for deformation, and as you might expect, the more pressure, the more deformation. The chart went up to about 15,600 L.U.P. At higher pressures copper crushers were used, hence C.U.P.

[Graybeard]

I have no clue where you came up with that math above that makes you think the higher than shotgun pressures are OK but I think you're bad wrong on it. Just my opinion but let me explain.

You seem to be trying to compute back thrust or some such there. Most shotgun recoil lugs are rather tiny due to the low pressure shotguns operate at. BUT back thrust is not by any means the only concern. Barrels are not designed to within stand the pressures you're talking about. Even a proof load for a shotgun would be well below your minimal pressure listed. By well over 10,000-12,000 units whatever we want to call them.

Some SxS and O/U double guns have been safely turned into rifles. BUT the have far more steel to begin with and more added and the lock up is far stronger.

Not my body parts in danger here so I really have no stake in this but I think you're on a dangerous mission. I can't stress that enough.

[Shorty]

Battlerifle,
You want a pump action, big bore?  Look for a Colt Lightning, large frame (Express Model).  They were made from 1887 to 1894 in cal's up to .50-95 Express.  Of course, you'll have to pay somewhere around $3000 for one.    :eek:

[MGMorden]

I wouldn't personally trust any round that would generate more pressure than a shotgun load.  I've often thought that a pretty neat looking slug load could be made using a brass case of the apporopriate size and a slug seated just like a bullet would be.  As I said though, it would just be neat looking; the performance would be a clone of a standard slug round.  And that's where I think you're going to hit the problem: a slug round is pretty much maxing out safe shotgun pressures.  

If you want a pump rifle then Remington makes the 7600.  Never shot one and have little personal opinion on them but I do have an uncle who has hunted with the older model (the 760) for quite a while now.

[BattleRifleG3]

The higher pressure would be sustained by the barrel insert and the case itself, which would be steel.

Rest assured I'm not about to go packing this stuff together just on an idea.  I'm a few months short of an engineering degree, and the numbers I'm tossing out are just preliminary estimates.  Hand calculations aside, I'd run a stress analysis computer simulation assuming worst case scenarios.  I'm someone who isn't satisfied without a decent factor of safety.  Even so, I don't shoulder and fire strange untested guns.  I've already done a few remote rifle tests firing from behind cover and then checking for any signs of yielding.

Nonetheless, the more I read up the less I really think I could top Dixie slugs.  I at first thought that they'd be an expensive specialty item but after looking further I spend the same on 300 RUM.  I still think a big bore pump rifle would be nice though, but I'm currently leaning more towards the black powder idea, and on a power level more suited to eastern brushbusters than dangerous game stoppers.

I hope I'm not scaring folks here with my unorthodox suggestions.  I'm basically brainstorming and bouncing ideas off of folks whose experience I respect.  I'm holding on to hope that there are still new things to be made that will be worth making.  I seriously go through hundreds of these bizarre concepts and once in a blue moon do I actually end up building something, and it's usually much more mainstream and always at least as strong as what's out there already.

ACTUAL gunsmithing projects of mine have included building a target stock for a 10/22, FCG and magazine conversions of Saiga rifles, assembly of an AR-15, and still in progress is an AK build in 35 Remington (yes, all the numbers check out and yes it's been done before.)

I'm probably a little smarter than I let on, I'm just not afraid to ask questions or share ideas, even if they sound stupid.

[Ramrod]

Hey, if nobody ever tries anything we would never have anything new!
As far as dangerous game goes, penetration is probably alot more important than velocity. And expansion is really not necessary in a big bore. So, how about a sabotted .577 or .600 FMJ at max shotgun velocity? This would be close to the old Black Powder Express rounds used before the turn of the century.

[BattleRifleG3]

Concept 1 would be about as powerful as a 50 cal modern black powder muzzleloader.  It would just use metallic cartridges and be pump action.

[BattleRifleG3]

Just did an analysis.  The shell for concept 2 will just barely hold on its own, without a shotgun barrel around it, at 35,000psi.  Rearward force would be the same as the 3.5" shells and the stress on the shotgun barrel would only supplement that sustained by the shell.

Not conclusive by any means, but suggests that it could possibly work.

[willysjeep134]

The only problem with concept 2, atleast if anybody were to try it commercially, woul be people chambering standard 12 gauge rounds in the modified barrel. It could be disasterous, unless you made the sub-caliber super thick cartridge and chamber much shorter than a standard shotgun shell so a regular shell wouldn't fit in the modified barrel.

[grendel]

I have read of more then one Pro hunter using a pump shotgun as their "Social" shotgun.  That is the gun they pickup when they have to trail "Thin skinned" dangerous game in to brush (ie Lion and Leopard).
 
Next I suggest you go dig up some of Ross Seyfried's writings in Rifle and Handloader mags.  It might not take much more then putting a GOOD (but expensive and custom) barrel on a shotgun to turn it into a close in big bore (72 cal AIR for a 12ga) stopping rifle.  As I also recall  from reading some of his articles (it has been a year or two though) a slow twist and the right style slug plays a large part of this equation.
 
Grendel

[BattleRifleG3]

I thought of the disasterous chambering of a standard shell too, and yes a shorter chamber seems like a good idea.