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25-06 IMP
Gunswapper
Member Posts: 1,058 ✭✭✭
I have a Remington 700 rifle in the shop. The only markings I see on the barrel is 25- 06 IMP. He has been using 25-06 Remington ammo in it and says it does not fire every time. Is he using the correct ammo? Is it safe to fire the 25-06 ammo in the gun? Has the rifle been re-barreled? Is there a source for 25-06 IMP ammo? Any info will be appreciated!
Comments
Well yes, and no. He has a rifle with an Ackley improved chamber. You are usually good with the factory round in an Ackley improved chamber, but with the straighter wall of the Ackley chamber, maybe it's letting the factory round slide too deep into the chamber and sometimes the firing pin can't dent the primer enough to fire?
" Is it safe to fire the 25-06 ammo in the gun"..............probably, if head space is 'on'
"Has the rifle been re-barreled?"..............no other markings, then yes
" Is there a source for 25-06 IMP ammo?".................no, you make brass by firing standard .25/05 ammo and then reload the fire formed brass.
if the rifle "does not fire every time"...........a head space check is in order, standard .30/06 gages work.
MW has answered the questions. But, I would also suggest to try other brands of ammo. A few thousands difference at the shoulder could make the difference in reliable firing. Checking the firing pin protrusion is also suggested. The Ackley Improved chamber is SUPPOSED to have the same headspace as the standard cartridge allowing standard factory ammo to be used.
This is a quote from some Ackley material I have on file. Please read carefully:
Rimless improved chambers, when properly headspaced, allow the shooter to fire the factory parent cartridge in the new improved (oversized) chamber safely. This is because the cartridge is headspaced on the junction of the neck and shoulder. Traditional Ackley gauges utilize a go gauge that is .004″ shorter than the factory or SAAMI go gauge. Because only a small point on the shoulder is in contact with the chamber it is easy to crush the shoulder as the bolt closes. When fired the brass stretches to fill the new improved chamber. This is what is known as fire-forming.
Here are the illustrations for this process:
The fireforming headspace is the junction of the neck and shoulder of the standard cartridge case. The rim of the case is in full contact with the bolt face.
I my opinion, as happens frequently with inexperienced amateurs, the original standard cartridge chamber was simply recut with the Ackley Improved reamer leaving a little too much headspace. It's possible that the headspace was checked with the extractor and ejector in also. Bad idea since it shifts the headspace incorrectly.
The correct method is to set the chamber back one thread first then recut the chamber using the proper gauge to check the headspace. Your chamber should be checked by a qualified gunsmith using the correct gauges, then probably set back and the chamber corrected.
Enjoy!
Second the previous post.
Properly done, the Ackley Improved re-chambering usually requires setting the barrel back one thread so the improved chamber will support factory spec cases when fire forming. Done the 'lazy' way often/usually ends up with a chamber too long to do this.
I'm wondering if he had a bad lot of Remington ammo that was out of spec. Just a possibility. With the chamber altered to IMP a small defect in the standard 25-06 case would make a difference.
I had a machinist re-chamber a 257 Roberts to AI and he made the same mistake. Cut the barrel back a thread and did it again. He just couldn't understand that using a 257 Rob headspace gauge wasn't correct. After the second attempt, I just left it that way and bump the neck out with a 6.5 neck expander and then size long with the 257 die. Using 257 Rob FL would likely result in a case head separation IF it did actually fire.