Gunsmithing Tapered-bore question

[dragoon]

In WW-II , the Germans had an anti-tank gun that had a tapered-bore . The advantages were increased velocity and accuracy . The downside was the tungsten projectiles wore the bore out in about 300 rounds ... My question is - could a tapered-bore be used to decrease barrel-length without losing range or accuracy in a precision-rifle ? Has anyone tried this ? For example , could the ballistics of a 26" barrel be achieved in a 16" , easier-to-handle package ? This would make silenced-rifles easier to transport . I think copper-jacketed rifle ammo would be a lot less abrasive than the tungsten AP shells they used .
2.8 cm sPzB 41 - Wikipedia, the free encyclopedia

 

[RTH1800]

IIRC, the German gun utilized a flanged projectile. The flanges folded back as the bore diameter decreased. This would be the only practical way of sealing the bore that I can think of. If you do not have access to flanged bullets I see no way it could work. If you have other ideas I would be interested in hearing them.
RTH

 

[Ledzep]

Yeah, I believe they had a couple squeeze bores. IIRC a 75-55mm cannon and the 28-20mm pzb41. Extremely specialized ammunition. The tungsten never touched the barrel, the pressures involved just eat barrels.

 

[pmclaine]

Use a projectile like a hollow base wadcutter that will expand under barrel pressure yet be able to constrict as the barrel tapers. Just make it pointy.

 

[dragoon]

Not a number-crunching rocket-scientist , but why couldn't normal copper-jacketed ammo work ? The barrel could be roller-forged around a polygonal mandril , a la H&K ( or a Whitworth rifle ) with a taper . For a 16" x .30 bore , the taper wouldn't be as dramatic as field-artillery . My wiki link mentions going from 28mm to 20mm in about 5' . With our modern technology , it seems that we could find a happy medium that would give a reasonable barrel life .

pmclaine's hollowbase idea seems reasonable , but wouldn't that degrade aerodynamics ? I thought about a sabot , but that would make the end projectile lighter , losing energy and possibly range as well , and making it easier to deflect .

 

[MarinePMI]

Already done. It's referred to (IIRC) as a swaged bore. CZ rifles have this in their rimfire rifles (to a minimal degree) and is part of the hammer forging process (mandrel is made to take the muzzle end down to .221"-222" IIRC).

I have seen (back in the 90's) where some barrels were made for .22LR that swaged the round down to .204" and .172" calibers. If memory serves right, the .204" bore was the most beneficial (balance between increased pressures and velocity gains).

The big challenge is the increase in pressures when doing this. With the headaches involved, it seems more practical to just go to a different cartridge if higher velocity or smaller bore is desired....

 

[dragoon]

My thought is that maybe one of the barrel makers has some input on the manufacturing versus practicality - if the idea has any merit , using established , off the shelf ammunition . The idea is to minimize the length of the .30 cal. precision-rifle , without decreasing its efficiency . Imagine the lessened burden of dragging a silenced Mk13 , without the extra weight and unwieldiness of 12" of barrel .