US Military choice of .300 WinMag over .338 Lapua

[bwaites]

I always found this to be a strange decision. Most of our Nato allies are using the .338 Lapua in their long range rifles, and it seemed that with the upgrade of the Remington to the PSR, that it was a logical time to move to the larger cartridge. SEALS and other Special Forces operatives had used it, and everyone seemed to love the ballistics.

Then the stories started to circulate that the .300 WinMag approved by SOCOM had performance bordering on the .338. That made no sense, but I decided that there might be more than one way to skin a cat and maybe they had found some magic.

This past weekend I got the chance to spend hours with some of the most knowledgeable weapons system guys out there. Guys who had spent literally years shooting, coaching, and building high performance systems when the subject came up. One of them offered that the .300 WinMag that was being used wasn't really a SAAMI WinMag, and that the cartridge being used wouldn't fit any factory chamber out there. He told me it was loaded much longer than SAAMI. That made sense, the first reasonable thing I had heard.

Then I picked up Sniper mag today, and a lot more of the story came out. The military wanted 2850 FPS from a 220 grain bullet. The way to do that was load out to 3.50 inches, well longer than the 3.34 SAAMI allowed. They also bumped acceptable pressure from a max of 65,000 to 68,000 PSI at 70 degrees. I'm not sure what that translates to at 125 degrees in the Sandbox, but I'm guessing its a LOT higher. They also had to use a smaller firing pin than normal in a tighter than normal channel. They almost created a .300 WinMag Mag!

All of those make sense, and I guess there really is no free lunch. You want more velocity from a given barrel, you have to have more pressure. I just found it interesting that the military made those compromises to get what they wanted vs. just using the .338 Lapua.

When the decision was made, there was much ballyhoo about the fact that .300 WinMag was already in the supply chain, but that was all BS. The .300 WinMag in the supply chain isn't the .300 WinMag that was decided on for the system! This system creates a cartridge that requires doublestruck brass, since its so hot that primers may blow otherwise, especially in the heat! Interesting stuff, that!

[Michael]

bwaites - Interesting info and thank you for sharing. I have spoken to a couple of my buddies in the last few months on this; one who is a former sniper and one in the small arms procurement realm, and they couldn't give me a satisfactory answer. Still wondering about this break from the NATO standard.

[mongoosesnipe]

I read about the development of the round and platform a few months ago it's be a out the 338 in the same way 6.5x284 became popular in f class taking a bullet with the same bc and fire it at the same velocity and it will fallow the same path

The load it's self of a 220 vld at 2850 is not all that hot, hodgdon data for retumbo pretty much gets it done I can push the 208 amax at 2900 fps with published data

That being said the 338 will hit harder at any given range but on soft targets you don't need to hit all that hard and it can be fond with a smaller, lighter and theoretically cheaper gun

[bwaites]

And the 6.5-284 got soundly spanked in F Class by the 7mm WSM's and similiar just like the .338 spanks the .300WM. Its a little cheaper to load .300WM, though.

[maverick5582]

The 6.5-284 is rough enough on barrel life. The last one I tossed @ 1200 rounds. "It's not unusual for a 7mm WSM to "go south" after just 700-900 rounds, though some barrels will last longer." That could get to be an expensive habit.

[bwaites]

The 6.5-284 is rough enough on barrel life. The last one I tossed @ 1200 rounds. "It's not unusual for a 7mm WSM to "go south" after just 700-900 rounds, though some barrels will last longer." That could get to be an expensive habit.

Yup, now think about barrel life in a WinMag at 68,000 PSI at 70 degrees being shot in 120+ temps!

[mongoosesnipe]

And the 6.5-284 got soundly spanked in F Class by the 7mm WSM's and similiar just like the .338 spanks the .300WM. Its a little cheaper to load .300WM, though.

bc and velocity will give you the arced path the bullet flies, but when it comes to staying on said path the heavier the bullet the better it can buck the wind

it doesn't mater what sort of wiz bang cartridges come to market, the three rules still apply

[nincomp]

In 2009, there was a presentation given at the National Defense Industrial Association (NDIA) conference that had a section about the development of the MK 248 MOD 1 .300 Win Mag cartridge. The presentation includes some comparisons of this new round (using a 220 gr Sierra Matchking) vs. a couple of .338 Lapua loadings.

The presentation also discusses the development of the 7.62x51 MK 316 MOD O sniper load. Eventually it was discovered that the propellant chosen for this cartridge is good old IMR 4064. Although this powder has been around for decades, it is very temperature stable.

http://www.dtic.mil/ndia/2009infantrysma...ii8524.pdf

[BjornF16]

What is the connection between IMR 4064 and AA 4064?

...and is IMR 4064 more temp stable than Varget?

[LR1955]

What is the connection between IMR 4064 and AA 4064?

...and is IMR 4064 more temp stable than Varget?

Bjorn:

Not sure about differences in stability or burn characteristics between AA and IMR 4064's. I do know that if you asked ten High Master shooters if they would rather use IMR 4064 or Varget, 9 would choose Varget. IMR4064 had very large granules of powder and was very difficult to meter consistently from powder measures. And, many believed it was too slow for the more popular cartridges. I think this was more myth than fact but when shooters get a notion about something, I won't argue over it. Reloader 15 and Varget meters way better and both seem to be more versatile over a wide range of cartridges and bullets.

4064 was very popular with the 30-06. 46 grains of 4064 if I recall correctly, for the more popular match bullets of the time. Probably because the other choices were too fast or too slow and 4064 gave a greater case fill due to its size.

I would take Reloader 15 over 4064 and Varget over Reloader 15, for any cartridge. But none of them are good for the Grendel due to their lesser bulk density than ball powders.

LR55

[BjornF16]

Thanks Gene...I was thinking more along the lines of 308 Win based upon the slides nincomp posted...

I'm currently loading 43.0 grains of Varget for my 24" Savage 308 Win and 43.8 grains for my 20" 5R R700 pushing 175 SMK's...both getting roughly 2600 fps.

Are AA and IMR really the same company?...they seem to have some of the same numeric designations for powders...

[LRRPF52]

The Navy really pushed the .300 WM against the Army SOF requests, and it drove the direction SOCOM went with it.

I didn't mention it up at BoomerShoot, but I had a lengthy discussion about it with someone privy to the process that took place, and a lot of feathers were ruffled over the ordeal, to the point that there will be more division in how weapons are procured within SOCOM. SF wanted .338 LM pretty badly, and I understand that they are looking at .338 LM still. Squeals wanted .300 WM.

Barrel life is an issue with the guns for formal training, as well as unit sustainment training. This is one area where .308 shines, even though it has no legs when it comes to .338 LM territory.

.300 WM is a known problem for barrel life and cheating SEAL Sniper students out of qualifying in their course, although this was addressed several years ago if certain SEAL authors are to be believed. Webb claims they started using chronographs to document throat erosion and velocity loss from jump, which resulted in erratic velocity shifts at distance.

.300 WM would be nowhere on my list for a long-range rifle, but it got a boost in its life with the Remington MSR contract. I think belted magnums need to go the way of the gun, but that's just me.

[nincomp]

I found more information on the .300 WinMag MK 248 MK 1. I am not completely sure if this is the current round though.
- Propellant is Hodgdon H1000
- Velocity 2850 fps at 70 degrees F
- Velocity difference from -20F to 165F 75 fps or less.
- Average chamber pressure at 70 degrees F less than 68,100 psi (with whatever the method the military uses)
- Average pressure at -20F and 165F not to exceed 71,500 psi.

All of the specs at : http://usarmorment.com/pdf/300WM_load%20data.pdf

edited to add: Based upon posts by civilians who have shot the round, the comments range from "damn" to "Good Lord, I'll never shoot that stuff again!!"

[mongoosesnipe]

i am not sure exactly what they are doing to get enough powder in the case to make the magic happen because hodgdons load data lists compressed charges with h1000for similar bullet weights with less velocity and way way less pressure

[bwaites]

i am not sure exactly what they are doing to get enough powder in the case to make the magic happen because hodgdons load data lists compressed charges with h1000for similar bullet weights with less velocity and way way less pressure

But what if you move the bullet out .15?

[mongoosesnipe]

0.15" less bullet in the case equates to 173.66 cubic mm which comes to 2.66 grains of water capacity these calculations are assuming a purely cylindrical base to the bullet since I don't have a 220 smk laying around so I am just going to swag and say 10% of the cylinder call it 2.4 grains water difference so I am not sure of h1000s exact density but say 3 extra powder

[nincomp]

Bwaites has a good point about the OAL. The OAL for the MK 248 Mod 1 is longer than the SAAMI spec:
SAAMI max= 3.34"
MK 248 MOD 1= 3.50"

The max average pressures are different too, with multiple specs for the mil round:
SAAMI: 64,000 psi
MK 248 MOD 1: 68,000 psi @ 70 Degrees F
but up to 71,500 psi @ -20 and 165 degrees F.

[nincomp]

In contrast to MK 248 MOD 1 .300 Win Mag loading, the MK 316 MOD 0 7.62x51 loading is pretty mild. As was mentioned by others, loads using powders like Varget can safely push the same bullet to higher velocities. .

Are AA and IMR really the same company?...they seem to have some of the same numeric designations for powders...

They are not the same companies. Hodgdon owns both IMR and GOEX and sells Winchester powders under license. Accurate Powders, Ramshot, Montana X-treme, and Blackhorn are owned by Western Powders. Accurate Powders, Ramshot, Hodgdon, IMR and Winchester do not actually manufacture powders, but they do create the specifications for them. As far as I know, the only two smokeless powder manufacturers in North America are General Dynamics in Canada, who makes extruded powders like the IMR series, and St. Marks Powder in Florida (also owned by General Dynamics), who makes ball powders like CFE 223. All of the US companies sell smokeless powders manufactured by one or both of these manufacturers. Most of the US companies also sell powders made in other countries.

IMR 4064 and Accurate 4064 are different powders with different specs, but they have fairly similar burn rates. What gets confusing is that both of these powders happen to be manufactured at the same place, but again, to slightly different specifications.

Confused yet?

[Joseph5]

The Navy pushing for it makes sense since weren't they the prime users of the MK 13. It mentioned in the article in Sniper that the MK 248 Mod 0 and Mod 1 both being loaded to 3.5 inches and originally shot out of a 26.5 inch barrel of the MK 13. The barrels for the MK 13 are made by Lilja but I am thinking they would be chambered by whoever is assembling the rifles. They could be using a reamer with a long free bore on it to accommodate the increased length. The Remington M2010 and MSR barrels are only 24 inches in length which necessitated the increase in pressure to maintain the specified velocity. I can't remember where I read it but the article stated that the MK 248 MOD 1 brass were un-reloadable after being fired because the primer pockets were so loose.

[nincomp]

Does anyone know if the 308 will still be used by snipers or has it been relegated to Designated Marksmen. The choice of propellant of the MOD 316 was partly driven by the need for it to be compatible with M14 and AR10-based rifles.

If both .308 and .300 Win Mag are to be used by snipers, how is the choice made between them?