175 gmm = +/- xm118 lr

[nf1e]

Just for my own information, I pulled 10 rnds each of 175 GMM and XM118 LR from 2011 randomly from the stash.

For what it is worth, after pulling bullets from casings and weighing components this is what I found.

Both appear to use Reloader 15 as powder.

GMM adverage power charge 43.5
XM118 " " " 43.2

Bullet weights were the same.

XM118 bullets sealed at cartridge neck.

XM case weight is approx 3 gn heavier 404.1 than GMM 401.3

Primers both appear to be 210M.

This was done because at 200 yds. the impact has been identical.
Chrono at 12' is the same for both.

Conclusion 6 of one half a dozen of the other.


Semper Fi
Art

[Litt'le Lee]

yep--I've been preaching RL-15 as the powder to go to for 7.62x51--I use Nosler J-4 155 Palma bullets in my Garand built with a 308 med match barrel--built by West Texas Ord--it shoots !!!

[Sunray]

You can't tell anything about a powder or primer other than their colour by just looking at it.
Both powder changes can and very likely will be slightly different in another ammo lot.

[nf1e]

You can't tell anything about a powder or primer other than their colour by just looking at it.
Both powder changes can and very likely will be slightly different in another ammo lot.

Re 15 has a distinctly different appearance than any of the other suggested powders for the GMM and XM118LR.
By all accounts during 2011 both utilized the 210M primer. As they were both produced by Federal, I can't imagine them using any other primer.
Nothing is 100%, but this is my best thought.

[pmclaine]

I was lead to believe that early in the desert war it was found the RL-15 ammo had overpressure issues in the heat and future rounds would be loaded with IMR 4064.

There is a build sheet out there that shows the Navy MK316, used by spec ops for their long range round loaded with 41.7 to 8 of IMR4064 under a 175MK with Fed Match Primers.

The load sleuthers Ive followed like 41.7 to 8 of IMR 4064 under a 175 SMK with 42.7 for a 168 to clone FGMM.

Just some extra info to add.

[nf1e]

I was lead to believe that early in the desert war it was found the RL-15 ammo had overpressure issues in the heat and future rounds would be loaded with IMR 4064.

There is a build sheet out there that shows the Navy MK316, used by spec ops for their long range round loaded with 41.7 to 8 of IMR4064 under a 175MK with Fed Match Primers.

The load sleuthers Ive followed like 41.7 to 8 of IMR 4064 under a 175 SMK with 42.7 for a 168 to clone FGMM.

Just some extra info to add.

Thanks for the information. I sure hope I don't even get close to the temperature the guys saw in the desert war. Temps I witnessed in Viet Nam were enough to take care of me for this lifetime. I had heard that. I was just surprised at the similarity between GMM and M118lr that were both produced in 2011 when RE15 was the choice. Now that I have semi-retarded, I may have too much time on my hands.

Art

[Chris F]

I have a friend that was involved in the fielding of M118LR and I can fill in some blanks. During the development of 118LR, all types of powders were tested, and the Vihtavuori rep told me that one of their High Energy powders was a lock to be selected. Ultimately it was a US manufactured ball powder that was selected and the back channel reason given was during time of war, they wanted an assured supply of powder which a foreign manufacturer could not guarantee. The first few lots of LR were HOT and the USMC put out an edict that it was to be fired in bolt guns only. At some point, ATK (parent company of Federal) took over the operation of Lake City and shortly after, a press release came out that after careful testing, M118LR would be loaded with Re15. At the same time, M118LR was tamed down a bit (official word was to match the ballistic cam in the Unertls which were tuned for M118 SB. I found it ironic that Re15 was selected since it's a Bofors powder manufactured in Sweden.

My understanding is that XM'118LR's are rejects (unlike XM118 which was experimental), so I'd be cautious about drawing conclusions about M118LR from that.

[nf1e]

Thanks Chris. No conclusions to be drawn. I just happened to have a bunch of each and made the comparison and thought it was interesting.
Better than 90% of my shooting is with hand loads anyway.

[Col. Colt]

Any idea how the newer rounds trajectory is compared with the original XM-118 from Vietnam for the XM21/M21? I'd like to find a load for my ART scope without buying up expensive 70's ammo! CC

[emmagee1917]

Any idea how the newer rounds trajectory is compared with the original XM-118 from Vietnam for the XM21/M21? I'd like to find a load for my ART scope without buying up expensive 70's ammo! CC

Chronograph the '70s load and weigh the bullet . The same weight bullet of the same profile type moving at the same speed will have the same trajectory , or at least close enough that you wouldn't be able to tell in the field or on the range . May have to tweek the charge or seating depth for the best accuracy .
Chris

[nf1e]

Got out and ran a few ammo tests this morning at the request of a gentleman on another forum that was interested in the Atomic 168 gr match ammo that had been marketed by CMP. Atomic was a bit slower than any of the others at 12'.
Ran 10 rounds of each through my brandy new XM21 with Med weight 20.5 inch Bula Defense barrel cut and target crowned. All were 1moa or better at 100yds. Temp 40 deg.

Results: Atomic 2423
175 GMM 2526
XM118LR 2500
ZQI 2742

http://i1180.photobucket.com/albums/x413/nf1e/IMG_0914_zps3b5gi5hb.jpg (http://s1180.photobucket.com/user/nf1e/media/IMG_0914_zps3b5gi5hb.jpg.html)

http://i1180.photobucket.com/albums/x413/nf1e/IMG_0915_zpspqhajspo.jpg (http://s1180.photobucket.com/user/nf1e/media/IMG_0915_zpspqhajspo.jpg.html)

Semper Fi
Art