338 RCM

gregsjt

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Jan 31, 2015
Messages
160
Hey Everyone,

I was reading through the post that elkholic started about his new 338 SM, I also read through the 338 Max thread and it got me thinking, does anyone use the 338 RCM? Seems like the 300 PRC / 375 Ruger case is pretty hot these days, I mean I think its great, no belt, no rebated rim, short enough to use long bullets, etc. The 338 RMC, made from the same case just shortened, came and went with no fan fare and no following. It seems like it would make a great short barreled, longish range hunting round. Does anyone use it, have you used it, what was your experience.

Thanks,
Greg
 

Forcedoutage

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Dec 31, 2018
Messages
477
Location
TN
I looked real hard at this case but decided to go with a 338 SST. That being said, I believe the 338 RCM is very close in performance hand loaded right. I was a little surprised to see the lack of support for the RCM. I see nothing but positives in a true short action 338.
 

gregsjt

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Jan 31, 2015
Messages
160
Yeah, i was looking at some of the published data and its pretty close to Win mag levels, except all the data was produced from a 20" barrel. Pretty impressive to me!
 

AZShooter

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Dec 12, 2005
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2,722
Location
Tucson Az
I have two. Ordered a reamer with Sammi specs when it first came out. Made a SA Ruger with McMillan Ultralight stock into the 338 RCM with a 22 inch #2 Lilja SS barrel. Used 225 gr accubonds and RL-17 @ 2750 fps to kill two cow elk.

At one point I seated some 300 gr Sierra bullets for single shot to see how they performed. At 200 yds I had some very tight groups as I worked up the load. That got me thinking of a second 338 RCM with a slight change to the chamber. I sent an tired 30" #7 SS profile barrel which had a Mark X LA reciever to Danny Pederson to have it rebored from 7mm to 338. At same time I shipped the reamer with a dummy round and requested the throat be lengthened for the longer magazine. Had excellent results.

When Berger came out with their 300 gr match hybrid, I switched to that bullet. Mild recoil with this 13 rifle which is in a Joel Russo laminate stock. With such mild powder charges of 54.5 gr of RL-17 velocity 2455 fps the barrel slowly gets warm and throat wear is minimal.

I took it out once on a coues wt hunt. Put that bullet through a deer that was bedded at just under 400 yds. It went in near leading shoulder and exited near offside hip. Little meat damage. The high BC of that 300 gr Berger minimizes drift and it packs a great deal of energy with 3000 ft/lb at just under 450 yds.

I read here that Broz used that 300 gr Berger on quite a few animals at LR. I quote:
"bedded cow at 816 yards. Impact velocity was 1975 fps. Cow was slightly facing away. Entrance was in the crease behind the near shoulder. Exit was far shoulder. I was kind of surprised that the exit was only 1 1/2" or so. But this exit is deceiving. Note the bone fragments on the hair around the hole. Inside was total destruction and the exit shoulder was a loss. Elk died quick and clean. I am pleased."

I decided to have the SA mag box lengthened to 3.1" for a useable OAL of 3.050".
Worked up a load for the 300 gr Berger that fits and feeds from magazine. Ended up with: 54 gr of RL-17 fed 210 standard primer 2349 fps. Took it along on a bull hunt a few years ago for stalking the wooded slopes. Ended up not using it but did get a bull with a different rifle.

At 8000 ft for elk that slow heavy bullet in the SA Ruger retains energy well with 3000 ft/lb at 375 yds and if I used Broz's low impact velocity of 1975 fps as a minimum velocity for good expansion, the rifle is good out to a bit over 550 yds which is more than I would shoot at an elk. To date I have taken 27 elk and none were shots more than 300 yds.

While Hornady brass is a scarce these days it can be found. I suppose the 6.5 version could be necked up. I see ADG has 6.5 PRC available.



Here is the SA Ruger "tanger"


The heavy long throated 338 RCM:

 

J E Custom

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Joined
Jul 29, 2004
Messages
10,723
Location
Texas
Hey Everyone,

I was reading through the post that elkholic started about his new 338 SM, I also read through the 338 Max thread and it got me thinking, does anyone use the 338 RCM? Seems like the 300 PRC / 375 Ruger case is pretty hot these days, I mean I think its great, no belt, no rebated rim, short enough to use long bullets, etc. The 338 RMC, made from the same case just shortened, came and went with no fan fare and no following. It seems like it would make a great short barreled, longish range hunting round. Does anyone use it, have you used it, what was your experience.

Thanks,
Greg


Like others, I decided to build a 338 RCM when they first came out and ammo and cases were available. I wanted a small, light and compact powerhouse and got it. I built mine on a Model 7 Remington action with a 22" barrel and the rifle weighted in around 6 pounds. You can still find 300 RCM brass and neck them up If your brass supply is slim.

The little rifle shot extremely well but had to much muzzle rise for follow up shots so I installed an Assassin side port brake and the problem went away and so did lots of recoil with the 225 grain bullets.

Having several WSM's I had looked at the 325 WSM but the 8 mm bullet selection was poor so I decided on the 338 RCM

The 338 RCM doesn't quite match the 338 Win Mag, but it is close. Mine likes the 200 grain Accubond @ just over 2900 ft/sec using a case full of H414 (Just below 61,000 Psi) I also seat the bullets at mag length minus .030 for freebore and assured feeding. (It's primary use was for bear)

I also tried the 250 grain bullets but didn't see any benefit in performance.

J E CUSTOM
 

Seabeeken

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Apr 30, 2013
Messages
271
Location
Communist state of maryland
I have the Ruger Alaskan version and I love the thing. I tested at length the 185 tsx. The rifle loved both N-550 and A-4350 giving .5”. With N-550 I was slightly over 3000 fps. This week I will be testing the 186 SH bullet and I think this will be an awesome combination. Biggest issue I have is the short mag length. Since the mag makes for a long jump to the lands, the copper bullets work well since they like that. My 185 is jumping .1”. The hammer 186 should get closer due to the nose design. I’ll post results when I shoot them.
 

Seabeeken

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Joined
Apr 30, 2013
Messages
271
Location
Communist state of maryland
I have the Ruger Alaskan version and I love the thing. I tested at length the 185 tsx. The rifle loved both N-550 and A-4350 giving .5”. With N-550 I was slightly over 3000 fps. This week I will be testing the 186 SH bullet and I think this will be an awesome combination. Biggest issue I have is the short mag length. Since the mag makes for a long jump to the lands, the copper bullets work well since they like that. My 185 is jumping .1”. The hammer 186 should get closer due to the nose design. I’ll post results when I shoot them.
After loading the SH bullet if find I can reach the rifling within mag length due to the design of the ogive. I have them now set to .020 off jam
 

Calvin45

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Apr 13, 2019
Messages
935
Location
Nipawin, Saskatchewan, Canada
I’ve had the though that the rcm cases should be awesome for magnum ar-10 platforms. I’ve also had the thought that the .338 rcm in particular could be fun as a novelty...semi auto but done as a bull pup with a short barrel, call it an Alaskan PDW.
 

Baker Alvin

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Joined
Dec 7, 2014
Messages
59
338 Federal, 336-06 A Square, 338 RCM, and 338 Win Mag have them all. So far I've Used all but the 338RCM so far,. I am following this thread.
 

TimberNinja

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Joined
Apr 5, 2021
Messages
3
Location
Montana
Hey All, new here and soaking up as much info as possible. The 338 RCM seems like a highly underrated caliber and I’m on the band wagon. I want to build one.
The factory ammunition numbers I’ve found appear to not be repeatable because they used a proprietary powder that’s not available. I understand it’s been designed for short barrels. A 22” to 24” barrel looks to be the sweet spot, and a brake sounds like a requirement. From the guys who have built 338 RCMs, anything you wish you would have done differently? Thinking 225 grain pills with H1000 would be some bad medicine for elk.
 

Calvin45

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Joined
Apr 13, 2019
Messages
935
Location
Nipawin, Saskatchewan, Canada
Hey All, new here and soaking up as much info as possible. The 338 RCM seems like a highly underrated caliber and I’m on the band wagon. I want to build one.
The factory ammunition numbers I’ve found appear to not be repeatable because they used a proprietary powder that’s not available. I understand it’s been designed for short barrels. A 22” to 24” barrel looks to be the sweet spot, and a brake sounds like a requirement. From the guys who have built 338 RCMs, anything you wish you would have done differently? Thinking 225 grain pills with H1000 would be some bad medicine for elk.
You’ll want a significantly faster burning powder. About the slowest powder hodgdon lists in their load data is win760. But most of the best powders listed for that cartridge are what would work best in a .308 win. 748, 4064, 4895, varget, 8208xbr. It says magnum but the case to bore
Ratio is about the same as a .308.
 

Seabeeken

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Apr 30, 2013
Messages
271
Location
Communist state of maryland
Ive tested a number of powders in mine. N-550 gave excellent accuracy. I tested RL-15 today and it did well but pressured out quick as did CFE-223 and N-540. N-540 had amazing ES/SD. I was looking at quick load and Win 748 looks as if it may be the best powder. I'll test it next week.
 
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