7.62x25 in an Rifle made for 7.62x39?

[boots-]

well i stand corrected ive never heard of fire forming with projectiles, im gonna check it out, sorry for the mis information.

 

[Trigger_The_Rookie]

One should keep in mind that the already close tolerances of the brass' OD and the chamber's ID are what allow the combustion pressure to expand the brass and seal the expanding gases. If you have excessive airspace between the brass and chamber the case will rupture and the path of least resistance will be backwards. It'll likely be more than just lubricating oil splattered into your eyeballs.

 

[H Wally]

One should keep in mind that the already close tolerances of the brass' OD and the chamber's ID are what allow the combustion pressure to expand the brass and seal the expanding gases. If you have excessive airspace between the brass and chamber the case will rupture and the path of least resistance will be backwards. It'll likely be more than just lubricating oil splattered into your eyeballs.

Too add to that, consider that without adequate seal in the chamber it's very possible for the gasses to vent Both back around the bolt face, and even through the bolt. There's a reason why many rifles have a small hole drilled on one side of the receiver ring just back from the bolt head/face, and many bolts have vent holes that face down into the mag well when the bolt is in battery.

Sooo... add to that the fact that it would not likely perform well, if at all.... I'd be disinclined to even attempt it unless I was out of every other option. And I'd likely wrap the cartridge in tape to center it.

 

[ButtWhat]

This topic and related topics is covered in depth by member Dr.Lector and other gurus on several threads

http://www.canadiangunnutz.com/forum/showthread.php?358829-AR-upper-in-7-62x25
http://www.canadiangunnutz.com/forum/showthread.php?117863-Shrink-that-Krink!/page19

 

[TERMINATOR101CA]

7.62x39 will never be more scarce than x25 which is already harder to find.

 

[TERMINATOR101CA]

You can absolutely fire form with live projectiles. Plenty of examples in YouTube and Google. Generally shoulder forming but that's academic with the cartridges the OP asked about.

Chamber insert is still the way to go when viable. I was simply pointing out that voids between your case and the chamber walls are not always catastrophic (and certainly not with the pressure differences between x25 vs. x39 - 40,000 vs 51,000 psi).

Yes you can fireform , but never with steel casings, at least I wouldn't try it . Brass is much more forgiving , and still ruptures when fireformed to extreme dimensional changes from original chambering.