Building an interesting little 338 RCM

[atl5029]

Hello all, been MIA on the forum for a while, but with this new build I'm currently piecing together I had to come back to do some advice collecting. Looking for some load data but I figured I'd tell you all about my new build first. Some of you might wonder why I'd ever build such a gun, some of you might find it cool. No matter what you think, I assure you everything about this build has a reason behind it.

So I building a 338 RCM, a cartridge I have had interest in since it was first introduced. I've been able to find a bunch of brass recently which has been great. While the round may be more or less dead, it seems Hornady still makes brass periodically. This gun is as much an experiment in a niche rifle configuration as much as it is a purpose built rifle. The gun is being built on an older commercial large ring Mauser 98 action. The rifle started out as a Golden State Arms 30-06 i bought from my friend for $100 bucks. I tried to make it shoot good as is, but the barrel was ultimately trash. However, the action is nice and it already had a very nice aftermarket match trigger on it, and I couldn't let a rifle with such a nice trigger be mediocre at best with a crap barrel. Additionally, I thought the intermediate length of the Mauser action would be perfect for a short action round where I could load long, high BC monolithic hunting bullets like the 250gr. CEB Lazer without encroaching on powder space.

The real interesting specs are in the barrel. McGowen Precision Barrels built my barrel after I spoke to them at SHOT show this past January. It's a 16.5" barrel, light palma contour, Q 8.6 muzzle taper and threads, with a 1:6.5" twist. Now I know people are gonna ask, why so short, and why such a fast twist? So why 16.5"? Because I hate carrying a rifle with a long heavy barrel in the back country, and I don't really believe anymore that a long barrel is necessary to hit and kill something at longer range if the optics, cartridge, bullet, and precision of the rifle itself are up to snuff. Does it make it easier, yes. But does it really pay off in the woods, I don't think so. Plus, I plan on suppressing this rifle with the new Q 338 can when it finally comes out, so I wanted the barrel to be as short as possible. And why the super fast twist? Several reasons: I do plan on shooting the very long for weight monos like the CEB Lazer, and out of such a short barrel and small 338 cartridge, I know velocity will be a bit lacking, and the extra stabilization will help at longer ranges. Second, the fast twist will help promote expansion when velocity is lacking. And third, I'm a believer in the terminal effects of fast twist bullets on game. Call me a Q fan boy if you want, but I think some of their developments of fast twist and short barrels make a lot of sense and their testing proves it's efficacy. Lastly, why use the heavier end of bullets, and not the 200-225 grainers the 338 RCM seems to be most balanced with? Very simply, no one seems to make a target bullet for practice less than 250 grains in 338 cal, and you're nuts if you think I'm going to practice with any of the expensive monos or premium hunting bullets in the 200-225 grain range.


Together, I think all of these features are going to give me a unique rifle that has everything I am looking for - something short and light that will be handy in the field and not get caught on branches when lashed to my pack, and something that has the power and ability to kill large game out to extended ranges. According to some quick calculations I did, even if I only get 2400 FPS, with the 250 Lazer, I should maintain expansion velocity out to around 1000 yards.


So now, anyone have load data for 250 grain bullets? Much appreciate any comments on the build or loading tips

 

[sable tireur]

So I building a 338 RCM, a cartridge I have had interest in since it was first introduced. I've been able to find a bunch of brass recently which has been great. While the round may be more or less dead, it seems Hornady still makes brass periodically.

You might quite possibly be one of the very few with an interest in this cartridge since it died about an hour after its release in 2008. This is the same story as the 6.5 and 350 Remington Belted short action mags which achieved more notoriety than the RCM. The devout, diehard few still find that brass is made available every 3 years or so. I don't bother because nostalgia for these cartridges has lost it's draw for me. Better cartridges and brass are available.

Now however, we have the 6.5 PRC made from the same lineage as the RCM but accepted with much greater celebration than the RCM by a significant amount. It also eliminates that despicable p) belt to which so many objected to.

Anyway, cutting to the chase, It's your idea, your rationale and your desire so have at it! Build it, enjoy it and show us the results when you have it finished. We really do enjoy reading about new projects and seeing the finished pictures!

 

[atl5029]

You might quite possibly be one of the very few with an interest in this cartridge since it died about an hour after its release in 2008. This is the same story as the 6.5 and 350 Remington Belted short action mags which achieved more notoriety than the RCM. The devout, diehard few still find that brass is made available every 3 years or so. I don't bother because nostalgia for these cartridges has lost it's draw for me. Better cartridges and brass are available.

Now however, we have the 6.5 PRC made from the same lineage as the RCM but accepted with much greater celebration than the RCM by a significant amount. It also eliminates that despicable p) belt to which so many objected to.

Anyway, cutting to the chase, It's your idea, your rationale and your desire so have at it! Build it, enjoy it and show us the results when you have it finished. We really do enjoy reading about new projects and seeing the finished pictures!

Yes the cartridge died so fast that I never really considered this build until a year or so ago when Gunwerks came out with a limited edition gun chambered for it with a integrally suppressed barrel (14inches of barrel, 8 inches of baffles). A buddy of mine picked one up, so I figured I'd jump on the 2 man bandwagon as well and build the budget version. Should be an interesting build, and I'm very excited for it. Gonna pick up some more brass so I don't ever have to worry about it. And I'll definitely report back with how the short barrel/fast twist combo performs at long range.

 

[AZShooter]

Great minds think similarly. I already built a sporter weight 338 RCM and tried a Sierra 300 gr MK bullet in it. It was very accurate and it inspired me to make a long throated version on a LA.

This fired up an idea that came to fruition in 2011. I reported on it a while ago here on LRH. This is repeat:

I always thought a high BC bullet with that much weight from a smaller case using a small amount of powder would be able to fired repeatedly without excessive barrel wear and shouldn't heat up quickly yet perform down range with plenty of energy and minimal wind drift. Ended up making a second 338 RCM but had it long throated so the Sierra boattail/body junction was even with the case's shoulder/body junction and kiss the rifling. It is in a Joel Russo stocked Interarms Mark X. The barrel is a #5 lilja profile 30", 1 in 9 twist. I had Dan Pederson rebore/re-rifle this barrel which was originally an ill fated 1 in 7 twist 7mm lilja. This package shot the 300 gr sierra at 2520 fps with 57.5 gr of RL-17.

Then the 300 gr Berger OTM hybrid showed up! 56.5 gr of RL-17 vel 2550 fps shot very well out to 500 M where I tested it on several occasions. Recoil was not bad for a rifle weighing 14 lbs. Still using Fed 210 Match. It bucks the wind and has lots of energy down range. Recoil is very manageable. Heck even my 7 1/2 lb lightweight 338 RCM wasn't that bad with the 300s. It is a big push not snappy like a larger 338.

Used it for the first time on a coues wt deer. 400 yds impact vel 2244 fps and 3354 ft/lb of energy. Bedded deer was angled facing me. Shot behind shoulder exited between hind legs nicking rear most thigh by 1/2" . It got up and tried to walk downhill. It was moving towards the canyon bottom out of sight. I most likely would have toppled over but I put a second one through it when it offered a broadside shot. Aimed so it would pass behind the shoulders in and out which it did easily. That caused the deer to lie down and die. Neither bullet caused any excessively bloodshot meat just nice 338 cal entrance holes and 1/2" exits. I should have put the bullet into the leading shoulder, bet it wouldn't have caused much meat damage. You can bet I'll do that next time.

 

[atl5029]

Great minds think similarly. I already built a sporter weight 338 RCM and tried a Sierra 300 gr MK bullet in it. It was very accurate and it inspired me to make a long throated version on a LA.

This fired up an idea that came to fruition in 2011. I reported on it a while ago here on LRH. This is repeat:

I always thought a high BC bullet with that much weight from a smaller case using a small amount of powder would be able to fired repeatedly without excessive barrel wear and shouldn't heat up quickly yet perform down range with plenty of energy and minimal wind drift. Ended up making a second 338 RCM but had it long throated so the Sierra boattail/body junction was even with the case's shoulder/body junction and kiss the rifling. It is in a Joel Russo stocked Interarms Mark X. The barrel is a #5 lilja profile 30", 1 in 9 twist. I had Dan Pederson rebore/re-rifle this barrel which was originally an ill fated 1 in 7 twist 7mm lilja. This package shot the 300 gr sierra at 2520 fps with 57.5 gr of RL-17.

Then the 300 gr Berger OTM hybrid showed up! 56.5 gr of RL-17 vel 2550 fps shot very well out to 500 M where I tested it on several occasions. Recoil was not bad for a rifle weighing 14 lbs. Still using Fed 210 Match. It bucks the wind and has lots of energy down range. Recoil is very manageable. Heck even my 7 1/2 lb lightweight 338 RCM wasn't that bad with the 300s. It is a big push not snappy like a larger 338.

Used it for the first time on a coues wt deer. 400 yds impact vel 2244 fps and 3354 ft/lb of energy. Bedded deer was angled facing me. Shot behind shoulder exited between hind legs nicking rear most thigh by 1/2" . It got up and tried to walk downhill. It was moving towards the canyon bottom out of sight. I most likely would have toppled over but I put a second one through it when it offered a broadside shot. Aimed so it would pass behind the shoulders in and out which it did easily. That caused the deer to lie down and die. Neither bullet caused any excessively bloodshot meat just nice 338 cal entrance holes and 1/2" exits. I should have put the bullet into the leading shoulder, bet it wouldn't have caused much meat damage. You can bet I'll do that next time.

That's pretty awesome! So what do you think is the best powder for the 338 RCM and the heavier bullets? RL-17 seems to be really popular. And you're using just regular LR primers for these, not magnums?

My barrel is about half your length, lol, but I'm excited to see what kind of results I get.

 

[gregsjt]

Love the idea, long barrels are ridiculous for hunting. Let us know how it goes.

 

[sable tireur]

Love the idea, long barrels are ridiculous for hunting. Let us know how it goes.

This is a Long Range Hunting website so the potential for some of the hunters to use longer than average barrels is very high. This all depends on what style and type of hunting is being pursued. Not everyone runs around in the woods. Some folks hunt the wide expanses of the plains and others, like myself, hunt the longer distances of the open desert. Sometimes longer barrels are a benefit.

 

[gregsjt]

This is a Long Range Hunting website so the potential for some of the hunters to use longer than average barrels is very high. This all depends on what style and type of hunting is being pursued. Not everyone runs around in the woods. Some folks hunt the wide expanses of the plains and others, like myself, hunt the longer distances of the open desert. Sometimes longer barrels are a benefit.

Doesn't matter where you hunt, if your rifle is ever slung across your back or in a scabbard short is your friend. You can make up for the velocity loss with high bc bullets, laser range finders and a couple more clicks of elevation on your scope.

 

[sable tireur]

Well my friend, we'll just agree to disagree since your points are wrong in general.

Have a great day!

 

[nksmfamjp]

This is interesting. Tagging to see result's. Make sure you have a long enough mag and a throat that uses the magazine.

Would love to hear the logical path of slow monos at high twist rates equals good perfromance. That seems counter-intuitive, but following intuition alone would have stopped most breakthroughs in technology.

Where will you ever find brass? If you find it, it will surely be on sale! These rifles were like 50% off at CDNN a couple years ago.

Better get Quickload to help you guess what bullet.

 

[AZShooter]

Yes RL-17 is the only powder I ever used with this round. It was made for the short fat cartridges like the RCM. Only tried 210 non mag primers. When chronographing loads I had some very low ES and sometimes got identical velocities! Looking forward to reading your results.

 

[martinakl]

Following. This kind of reminds me of the new "8.6 BLK" cartridge but a magnum version. Something my mind automatically jumped to when I read about the 8.6 BLK. "Neat, but I'd need more speed"

8.6 BLK (blackout) is a .338 that uses 6.5 Creedmoor brass as the parent cartridge (shortened). Barrels are 1:3 or 1:4 twist rate. It'll run subsonic and supersonic ammo.

 

[2Old2Care]

Started down this rabbit hole myself. I have 200 new cases and a set of dies, now if I could find one of those 'half-off' rifles I'd be in business. Just thought it would make a dandy Alaska float trip companion for moose and black bear while being handy. Light is right at my age and even in a lightweight rifle I don't think the recoil will be that significant. Yes, I know that if I need ammo while up there that I'm likely screwed, but at least it will be a handy club.

 

[Ray Gross]

I have been working on a similar idea necking up 6.5 PRC brass to 30 cal. Should get a barrel put on in the next month or so.

I chose to neck up from the PRC rather than down from the 338 RCM because I wanted to use Lapua brass.

What are you using for sizing dies?