Opinions on 338 rcm?

[wvfarrier]

I am thinking of a 338 rcm (if I can find brass) or 338 Federal in ar10. I would prefer 338 rcm but the brass is unobtainium. It also has far superior performance over 338 Federal. Anyone tried it?

 

[45-90]

I am thinking of a 338 rcm (if I can find brass) or 338 Federal in ar10. I would prefer 338 rcm but the brass is unobtainium. It also has far superior performance over 338 Federal. Anyone tried it?

No, I haven't tried it, but it would be easy. I have the KAK magnum bolt, & reciever.
Brass can be made from 6.5 PRC, mandrel up, run through FL die, trim length, or any PRC case or Ruger 375, with more work, trimming and neck turning.
I'd buy a 338 Federal barrel and rechamber with 338 RCM reamer, 10 twist if one is available. KAK was chambering for 300 WSM, don't know if they have a RCM, others probably do...18" to 20".

 

[LRRPF52]

A big consideration you need to look at with RCM and its .532” case head and larger body diameter is chamber wall thickness. For a limited round count occasional hunter, it should be fine but it would do better in a chromoly steel barrel vs stainless I think.

Have a really tight-fit thread job between the extension and the tennon. It’s a 62,336psi MAP cartridge, so that helps that it isn’t a 65,000psi like most magnums.

In order to get that additional 200fps over the 338 Federal, you will generally need all the propellant and pressure you can get, though I lean on optimum propellants over chasing pressure.

The other problem is magazines. Due to the case diameter, it might not stack and feed as well.

338 Federal is the easy answer here if you must have a 338 AR-10.

Is this for hunting?

 

[45-90]

A big consideration you need to look at with RCM and its .532” case head and larger body diameter is chamber wall thickness. For a limited round count occasional hunter, it should be fine but it would do better in a chromoly steel barrel vs stainless I think.

Have a really tight-fit thread job between the extension and the tennon. It’s a 62,336psi MAP cartridge, so that helps that it isn’t a 65,000psi like most magnums.

In order to get that additional 200fps over the 338 Federal, you will generally need all the propellant and pressure you can get, though I lean on optimum propellants over chasing pressure.

The other problem is magazines. Due to the case diameter, it might not stack and feed as well.

338 Federal is the easy answer here if you must have a 338 AR-10.

Is this for hunting?

KAK was selling barrels and uppers in 300 WSM with .555" has and .535" rim dia running full power loads.
Then the .510 whisper case body at .585" head and lathe cut to .535" rim with new extractor cut, for AR 10...that gets a bit thin.
I wouldn't worry about the 338 RCM at a mere .535". Found barrels are available, plus I already own the AR 10 .535 bolt and upper reciever wide cut.
Easy build that wouldn't need full power loads to easily beat the 338 Federal.
I may build one just for fun, as my next project, ...18" or 20" barrel? Probably 20" can always cut it down.

 

[wvfarrier]

A big consideration you need to look at with RCM and its .532” case head and larger body diameter is chamber wall thickness. For a limited round count occasional hunter, it should be fine but it would do better in a chromoly steel barrel vs stainless I think.

Have a really tight-fit thread job between the extension and the tennon. It’s a 62,336psi MAP cartridge, so that helps that it isn’t a 65,000psi like most magnums.

In order to get that additional 200fps over the 338 Federal, you will generally need all the propellant and pressure you can get, though I lean on optimum propellants over chasing pressure.

The other problem is magazines. Due to the case diameter, it might not stack and feed as well.

338 Federal is the easy answer here if you must have a 338 AR-10.

Is this for hunting?

Shits and giggles mostly. I like oddball stuff and an AR10 in the rcm would qualify

 

[wvfarrier]

KAK was selling barrels and uppers in 300 WSM with .555" has and .535" rim dia running full power loads.
Then the .510 whisper case body at .585" head and lathe cut to .535" rim with new extractor cut, for AR 10...that gets a bit thin.
I wouldn't worry about the 338 RCM at a mere .535". Found barrels are available, plus I already own the AR 10 .535 bolt and upper reciever wide cut.
Easy build that wouldn't need full power loads to easily beat the 338 Federal.
I may build one just for fun, as my next project, ...18" or 20" barrel? Probably 20" can always cut it down.

I had one of their 24" uppers (no longer available) in 300wsm. It was a lot of fun but the shoulder angle on the wsm seemed to create feeding issues periodically

 

[45-90]

Yep, still can buy the 300 WSM 19" uppper from KAK industry's. They list 2 mags as better preforming one on there site.
The 338 RCM has a 30° shoulder like the 6.5 CM, so it should be easier to feed...sounds intriguing to me. Custom barrels have quite long wait times. Could build one from s blank or buy an instock 338 12 twist 18" 338 Federal, and rechamber, to 338 RCM.

 

[45-90]

AR 10 in 338 RCM?...I is just been finished mine.
7 lbs 11 oz fluted 18" barrel, with a serious muzzle brake, without optics.
Brass made from 6.5 PRC.