I just ordered two of the 10 dollar m70 barrels from cfs. i read on a 7.62x25 conversion thread that you could ream out the existing chamber and plug it with a peice of roundstock and chamber this plug to whatever caliber you like. I know ak barrels are .311 and 7.62 ammo is .308 but im just building a plinker and accuracy isnt too important. so there would be some space between where the chamber ends and the rifling begins...is this a potential problem? should this short smoothbore area be .311 diameter? any advice is appreciated
The navy did basically that to rechamber M1 barrels from 30-06 to 308. They threaded the the inserts in as otherwise the "plug" or chamber insert has a tendency to pop out when firing.
i see. this plug would be welded in tho.
I have silver brazed in a .308 chamber piece in a .307 (French) barrel It was not satisfactory for several reasons. The "squeeze bore" was too tight and caused serious back pressure. That inspite of all the propaganda that those French barrels are actually ".308" inch... not so !!! Also the insert shrank slightly from the brazing process making an over-tight chamber entrance. The brazing heat and subsequent chill down caused the ordnance steel insert to harden and resist clean-up chambering. I later pulled the barrel from my MAS-49 replacing it with a .308 chrome-lined FAL barrel which worked great.
Threading a plug insert seems a better way to procede. Use loctite with that operation. This assumes a non-full auto application that is cooler.
A grazing cross pin could also solve this issue of anchoring the plug insert. So could an axial set screw (threaded in parallel to the bore) if the insert plug and barrel provide sufficient meat to do so.
The "free-bore" you mention does affect accuracy but should also be large enough to allow passage of the round non-compressed for that .311 cal to .308 barrel adaption to help avoid over-pressure.
added: The conversion from .308 bullet into .311 bore is the opposite issue ie sloppy bore especially with a well used bore. That will give so-so accuracy. It can still result in a fun plinker conversion.
Thanks for the tips. having read your post im thinking i'll probably do a crosspin or setscrew type setup, my welding is nothing to write home about anyways.
I may have asked this before... let's assume an insert is simply a tube that has been reamed on one end. Does the plug/insert work OK with the original freebore, or does the insert need to be rifled up to the point where the original rifling begins?
i could always chop a section of the second barrel and ream it then use it as my plug. just have to be careful that the rifling matches up when its in place.
Or a peice from a 10 dollar demilled rpd barrel from apex if those arent chrome lined they could be cut into sections and reamed to make plugs.
So let me get this straight your going to buy a $10 barrel bore out the end to install a plug then either braze weld pin or srew it so it wont fall out and then also try to match up the rifleing to avoid the aprox 3/4" of free bore and and a worn out pitted barrel ???
You do know you can get a take off barrel for around $30 and rechamber it.
If your going to buy a $120 reamer or have some one do it ( like me) dont wase your time trying to save a worn out $10 barrel that not really the best bore size and likely end up with a possably unsafe cobbled up set up that is very llikely not going to shoot well.
If you have the means to properly machine a barrel and chamber then you might as well just start from scratch.
they do make chmber inserts for 7.62x54 to shoot x25 vI suspose you could chamber it to that or 303 britsh and just install a insert but its still going to not be really accurate.
IMOO UNLESS YOU HAVE THE REAMER YOUR SPENDING A LOT OF MONEY TO GET A SUBSTANDARD RESULT. IF YOU GOT A REAMER THEN IT MIGHT BE FUN TO TRY. IMADE SOME SHOT GUN BARREL INSERS OUT OF A FEW SO -SO BARRELS WITH MY REAMER.
IF YOU NEED A SMALL STUB CHAMBERD i MIGHT BE ABLE TO HELP YOU OUT FOR A FEW BUCKS YOU CAN THEN CUT IT AS YOU NEED. YOUR STILL GOINT TO NEED A WAY TO REAM/ CHAMBER THEBARREL AND IT SHOULD BE PILOTED.
iD AVOID WELDING ON THE BARRLEL IF AT ALL POSSABLE. THE CHAMBER INSERTS ARE OFTEN HELD IN WITH LOCKTIGHT. sorry for the caps.
i looked over many options and well im tryin to do the cheapest and easiest for me. i was gonna use my dads friends lathe to do the chambering and i found a sight where reamers are only $30 to rent so i figured i could make multiple inserts and use them for future projects if needed.