View Full Version : 300 RSAUM in AR Platform?

04-13-2008, 11:01 AM
Does anyone have any info or experience with this rifle? I recently bought the last one at my local shop, but I don't see much about the cartridge anymore. It seem that the WSM line has pretty much wiped them out. This is a heavy rifle, and does not seem very well suited to woods use, but would make a good long range hunting or target rifle. Any input is appreciated.

Louis Boyd
04-13-2008, 01:51 PM
I presume you're referring to the DPMS Panther LR series of rifles.

I recently purchased an LR-260 after carefully comparing the 260 Rem, 308, 300 SAUM and 6.5 Creedmoor options.

The rifle is basicly the AR-10 design with some modifications by DPMS , such as using an AR-15 trigger group (Jewell small pin is a drop in), and AR-15 sight height specs. It's magazines are interchangable with the Knights SR-25 rifle. Not much is interchangable with an Armalite AR-10. It does fit AR-10 stock options (Magpul PRS for example).

The 260, 6.5 CM and 308 cartridges have similar case capacity and pressure, around 56 grains and 60191 psi. The 300 SAUM is whopping 72.5gn and 65000 psi. That's about 40% more available energy. The only problem with any of these cartridges for reaching their long range limiits is that they're stuck with a short action length magazine which just doesn't give enough room for heavy low drag bullets. That problem is worse for the 30s and the 6.5s. The 300 SAUM would have enough energy to drive even a 240 gn matchking but there's just no room for it.

Since you've bought the 300 SAUM this is just my opinion: I'd try using some of the "Palma" weight bullets. Those are 155 grain low drag boattails. There are many including Lapua Scenar, Berger, and Sierra Matchking. The 300 SAUM should brute force those to a supersonic range of 1300+ yards with a muzzle velocity of around 3050 fps. Accuracy should be excellent in lighter wind.

If you bought it as a long range medium and big game hunting rifle I think you made the right choice. For a long range taget rifle I think the 6.5 Creedmoor would squeeze out the greatest range and accuracy. The 308 Win undoubtedly will give the longest barrel life. I picked the 260 Rem since I have other rifles which share the same cartridge. It doesn't give up much of the 6.5 Creedmoors performance.

04-13-2008, 02:35 PM
Sorry, I should have clarified that it is actually one of the now discontinued Armalite guns. The ejection port is enlared, and the lower receiver is actually marked with the cartridge designation, and then a large "Magnum" stamp underneath the "300 RSAUM".

Louis Boyd
04-13-2008, 02:50 PM
I suppose my comments would still apply if the magazine gives the same cartridge OAL restrictions. The only company I know of who made an AR style rifle with a long/magnum action and magazine was Cobb engineering. I think they got bought by Bushmaster. Haven't seen any of their rifles since.

03-30-2012, 03:56 PM
I have one of these rifles. I've been in the US Army for a while and stumbled onto the rifle through friends. The rifle was designed with the Army Marksmanship Unit. During testing they found that .300 WSM isn't designed well for semi-auto fire and they found that the .300 RSAUM performed flawlessly. I love the rifle it will throw 150-208 grain bullets very well, just ensure they are polymer tip or PHP (Like Sierra Matchkings) PSPs get really chewed up during feeding and chambering. Only use the 10 round mags that fit 5 .300 RSAUM rounds, these rounds dont like to be staked any deeper. Under 6.5 inch 5 shot groups at 1150 yards is out of the box performance.

Happy Shooting, Rob

Joe Salt
03-30-2012, 04:16 PM
Bob you said you have been in the Army for a while, First off God bless all you guys and gals for all you've done. If this rifle will shoot 6.5 inches at 1150 yards out of the box, I want one! My 1000 yard light gun sometimes has a had time doing that. Do you know what twist the barrel is.

Joe Salt

04-02-2012, 02:06 PM

ArmaLite was nice enough to put a 1-10 Twist on the Stainless Steel Match Barrel.



Here are two great articles on the rifle.


PS Joe, I love what I do...... its been 20+ years two wars and some other stuff...Its been my pleasure to serve my country!! HOOAH!!

04-02-2012, 02:35 PM
Manufacturer: ArmaLite, Inc.; (800) 336-0184; Armalite.com

Caliber: .300 Remington Short Action Ultra Mag

Action Type: gas-operated semi-automatic rifle

Receiver: forged aluminum upper and lower

Barrel: 24" stainless steel, heavy profile

Rifling: six-groove, 1:10" right-hand twist

Magazine: five-round steel box

Sights: none supplied; Picatinny rail for scope mounting

Trigger Pull: two-stage, 5 lbs.

Stock: synthetic; length of pull, 14 1/2"; drop at heel, 5/8"; drop at comb, 5/8"

Overall Length: 43 3/8"

Width: 1 15/16"

Weight: 11 lbs., 9 ozs.

Accessories: two magazines, instruction manual

Suggested Retail Price: $2,340

Joe Salt
04-06-2012, 09:46 AM
Rob I understand the 300 wsm is the way to go, but it still looks like there is room for improvement. They are definitely on the right track. The 1-10 twist is right, From the looks of thing they need to work more with H-4350 and try some Fed. 210 or 215's with the sierra bullets. I don't own an AR, but always said when they get one that works in wsm I'll buy one! I'll bet the guy that shot 5 shot into 6.5 inches, only done it once and that was pobably his best group. All I'm saying is there trying to sell a product! Wait till they do more tests before you buy one.

Joe Salt

04-06-2012, 11:03 AM

Check this out.


"That initial focus determined that the .300 WSM, while an excellent cartridge in a bolt-action rifle, was not particularly suitable for a semi-automatic rifle. Internally, the sidewalls of the .300 WSM case come straight down forming nearly a right angle where they meet with the flat bottom at the cartridge web. That right angle gives the WSM a smidgen more case capacity, but results in a web too thin to support the case in semi-auto operation. AMU found that in a semi-auto, the WSM cases exhibit some bulging ahead of the extractor groove. Remington’s .300 SAUM, on the other hand, has internal case sidewalls that come down and form a distinct angle before transitioning to the flat bottom surface. That slight bit more web thickness made the difference as far as AMU was concerned, so development was refocused around the SAUM."

Above from Shooting Times Article link above

Joe, your missing out!

Joe Salt
04-06-2012, 02:21 PM
Rob $2,340 thats a lot of bullets and powder for me right now. I'll wait, there will be more tests and I would like to shoot one before I buy one. There is no doubt the 300 wsm is the way to go,and I'm sticking with the H-4350 powder. Just talked with a dealer and if you can get one for that price buy it.

Joe Salt