Thread: Re-chambering a new factory bbl

Probably needs a gunsmith to answer this one but …. Could a factory 7mmRM bbl be re-chambered to 7PRC.
It would mean loosing a little bit of length off the Knox at chamber end, but looking at the specs on the 2 cartridges it looks like if you chopped the 7mmRM case off just in front of the belt then you’d be close to 7PRC dimensions. The 7mmRM case has more taper so I’d imagine the 7PRC reamer would clean that out. Any gunsmith can comment on this crazy idea ?!

Probably not worth the hassle as most factory rem mag barrels are clapped at the heals with twist rates?d say prc spec would be 8 twist

Unless iv corse you just want to ditch the “dreaded” belt the twist would probably let you down

Yes 1:8 twist would be ideal but a 1:9 is fine for 160-168 gn pills. I’m tossing up ideas for a short (20in) bbl 7mm that’s got more legs than SAUM

Originally Posted by chainsaw

Yes 1:8 twist would be ideal but a 1:9 is fine for 160-168 gn pills. I’m tossing up ideas for a short (20in) bbl 7mm that’s got more legs than SAUM

Very interested in which route you go as I'm thinking of something the same.

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1in9 works for most 180gr projectiles, so don't see why a 1in9.5 which most 7mm barrels are won't work at magnum velocity.
But I'd be chatting to a gunsmith about rechambering
Let alone the wait for brass and factory ammo to arrive in the country.

I am taking the same route but with a 28 nosler . Rechambering a new Remington barrel first and seeing how that thing shoots. I might keep the same caliber on the next tube or jump to theprc if components are more available then.

Yes, discussing idea with one or more gunsmiths is definitely next step. Was hoping a couple on here might see the thread & add some words of wisdom.

In terms of power there is not a lot of difference between the two cartridges. The 7mm PRC has the ability to throw heavier bullets by virtue of the fast twist barrel. Rechambering your 7mm Rem Mag will achieve nothing as the twist rate is to slow for the heavy bullets. Rebarreling is the only answer.

Thanks @gundoc, I understand the difference in twist rates and potential benefits for heavier pills but the 1:9.35 or 1:9.5 twist rate barrels (REM & Tikka) are quite capable in 7RM of producing good accurate loads with 160-168gn pills. My interest and question is more a technical one regarding the engineering aspect or feasibility of modifying a 7RM chamber to convert to 7PRC. Yes one could start with a brand new 7mm blank but I would like to understand the feasibility of the 7RM to PRC change. Looking at SAAMI specs it seems that if you lopped off 7RM cartridge immediately in front of the belt then you’d be close to 7PRC dimensions albeit with less taper & steeper shoulder in the 7PRC. Both differences I assume would be rectified with a 7PRC reamer.
I won’t digress into a performance debate on 7RM vs PRC, but my thinking based on experience with lots of different 7mm cartridges is that the PRC should be less affected in going to shorter bbl (20in). Less taper & more efficient cartridge. Some of the limited data published about 7PRC seems to support this extra potential

The actual operation of setting the barrel back and rechambering is no problem. The breech end would need to be set back by 0.230" (the effective difference in case bodies) which is 3.68 threads, but in order to get the barrel with lettering in the correct place you would need to trim 4 threads or 0.250". This would only leave 7 threads engaging instead of the original 11, which is getting a bit marginal. The alternative is to turn and thread the shortened barrel shank and make a threaded sleeve to give full engagement in the receiver. That is getting back to rebarreling territory time-wise.

Thanks that’s exactly the advice I was seeking. Personally I would not be concerned about where the old lettering end up.