FGMM .308 vs FGMM 7.62x51

[KillShot]

I'm about to purchase some Federal Gold Medal Match 175gr from Palmetto State and I noticed they sell sell it in .308 and 7.62x51.

I know the SAMMI pressures are different (65,000 vs 50,000) and the 7.62x51 is a thicker casing but is there any difference in accuracy that anyone has found?

Thanks for any info you can give.

 

[FCS]

Re: FGMM .308 vs FGMM 7.62x51

Same same.

One is tumbled to bright finish (GMM), other is not (7.62X51).

7.62X51 also has crimped primers.

Didn't know that until a customer sent me some brass from 7.62X51 Fed GMM.

 

[08Cayenne]

Re: FGMM .308 vs FGMM 7.62x51

I shoot both with the same dope cards.

 

[Bradu]

Re: FGMM .308 vs FGMM 7.62x51

I'm glad you asked that because I have been wondering about that.

 

[Conrad101st]

Re: FGMM .308 vs FGMM 7.62x51

Non crimped primers would be nicer for reloading.

 

[GlockandRoll]

Re: FGMM .308 vs FGMM 7.62x51

Heck.. now I've got to find out what I bought from them this spring!

My order details show this:

Product Name: Federal Gold Medal Match .308 175gr Sierra MatchKing
BTHP 20rds Item#: 1752, guess I lucked out!

 

[3O8Junkie]

Re: FGMM .308 vs FGMM 7.62x51

I have purchased both, and personally saw no difference other than the 7.62x51 seemed to leave more residue on my lower. It would have a green color to it after shooting a few mags, wiped right off with some balistol for what its worth.

 

[Commander Shepard]

Re: FGMM .308 vs FGMM 7.62x51

I shot the two side by side today out of my 16" EMC. Accuracy was identical, however the 7.62mm stuff seems to be loaded a bit hotter. At 880m I needed 9.8 mils of elevation with 7.62mm and 10.2 with 308 Win. Obviously this data covers only the two lots I happen to have.

 

[LVdubbin]

Re: FGMM .308 vs FGMM 7.62x51

I've always thought that .308 was loaded hotter than 7.62x51...

Which cases are better for reloading? Please excuse me for I'm a newbie at reloading.

 

[Grump]

Re: FGMM .308 vs FGMM 7.62x51

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ShooterMcGavin33</div><div class="ubbcode-body">I have purchased both, and personally saw no difference other than the 7.62x51 seemed to leave more residue on my lower. It would have a green color to it after shooting a few mags, wiped right off with some balistol for what its worth. </div></div>
If that stuff has the modified 4064 powder of newer USGI stuff, perhaps that's an effect of the temp stabilizer or flash reducer (or does it do both--temp stability is reportedly increased...)

Your description confirms my opinionated belief that most of the time "clean burning" is over-rated when it comes to ammo. It's gotta be really bad for me to care about it.

 

[Grump]

Re: FGMM .308 vs FGMM 7.62x51

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KillShot</div><div class="ubbcode-body">[snip]
I know the SAMMI pressures are different (65,000 vs 50,000) and the 7.62x51 is a thicker casing but is there any difference in accuracy that anyone has found?

Thanks for any info you can give.
</div></div>

Um, the sources I have show that even when both SAAMI and USGI were measured with copper crushers, there were differences in methodology which made the numbers NOT identical. One was tested with a hole in the case wall under the piston that drove the copper pellet, while the other used intact cases. Forget which was what and what effect it had.

Same for the 5.56mm/.223 nonsense, which is really just a difference in chamber throats and allowable bullet ogive profile beyond the case mouth. That was the result of going for a heavier bullet and slightly better BC when the military finished its development, as compared to the short light speed-demon bullets used in the prior .224-diameter varmint cartridges just before the then-new SCHV project gave us M193 ammo. Pressure-wise, IIRC the 5.56 is measured with a piezo sensor just in front of the case mouth, while SAAMI piezo puts the transducer at mid-body of the case.

Or something like that.

Then of course there are the problems of comparing 7.62 NATO CUP numbers from the 1950s adoption of the round, with modern SAAMI piezo numbers. Cross-referencing data points can be a booger.

 

[Grump]

Re: FGMM .308 vs FGMM 7.62x51

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LVdubbin</div><div class="ubbcode-body">[snip]
Which cases are better for reloading? Please excuse me for I'm a newbie at reloading. </div></div>
Once the primer crimp is taken out of the GI stuff, no difference.

If you don't have a decrimper, don't want to do the ghetto overdone and wrong-angle decrimp with a casemouth deburring tool, AND don't want to buy a decrimper, then the FGGM .308 is better.

But a few years ago I ran into some (before 7.62x51 FGGM came out) that was not only purple sealed on the primers, but also...crimped. Lightly.

 

[warrenator]

Re: FGMM .308 vs FGMM 7.62x51

I do not reload so I am not sure if it makes any difference for your purpose but the 308 cartridge is dimensionally different than the 7.62x51. I will post a diagram that shows the differences below (this explanation is geared toward understanding the use of 308 vs 7.62x51 ammo in HK and Cetme type actions).

 

[LVdubbin]

Re: FGMM .308 vs FGMM 7.62x51

Thank you Great308. Very informative.

 

[warrenator]

Re: FGMM .308 vs FGMM 7.62x51

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: LVdubbin</div><div class="ubbcode-body">Thank you Great308. Very informative. </div></div>

Glad to help

 

[Grump]

Re: FGMM .308 vs FGMM 7.62x51

Hmmm...first info I've ever seen that reported differences in CASE dimensions.

The chamber differences have been beaten to death. Few people ever bother to look at a set of calipers with the maximum chamber difference dialed in. It's like the thickness of a sheet of paper, about.

 

[Beef82]

Re: FGMM .308 vs FGMM 7.62x51

Never heard of an external case size difference either, not sat saying it isn't possible.
Cut with a larger chamber makes sens for comabt arms for two reasons, wider production tolerance, and most importantly the ablity to run extremely dirty. Soldiers don't reload so as long as the case survives once its fine. Really seems that if 7.62 cases were .012 longer to the shoulder those of use with bolt guns would be given all kinds of fits trying to chamber surplus rounds, and I haven't had any.

 

[Doctawho]

Re: FGMM .308 vs FGMM 7.62x51

Anyone notice much accuracy differences?

 

[EZTundra77]

Re: FGMM .308 vs FGMM 7.62x51

So the consensus is that 7.62 x 51 FGMM is fine to shoot in a Rem. 700 .308. I have heard repeatedly that it is fine to shoot NATO rounds through a Rem 700 .308. But the above diagram seems to contradict that. It would seem that the cartridge in a NATO round would be too long for a .308 chamber. Is FGMM even the same size as NATO ammo. That is to ask: Does 7.62 x 51 FGMM even count in terms of the above diagram?

 

[EZTundra77]

Re: FGMM .308 vs FGMM 7.62x51

I think that the diagram that "The Great .308 post is very helpful". However, I think that it might not reflect the difference in FGMM .308 vs. FGMM 7.62. I think that the digram is comparing commercial .308 (i.e. FGMM .308) vs. milspec NATO rounds. I am still trying to figure this out myself. I have FGMM w/ 175 gr. Sierra MK in both .308 and 7.62. I contacted Federal and they said that both FGMM's' have the same ballistics. Supposedly, the are loaded different to create the same amount of pressure. Federal seemed to insinuate that the case dimensions and the wall thickness was the same. This leads me to believe that FGMM 7.62 x 51 is not an actual milspec NATO round, even though they sort of claim that it is. I think that this federal rep. might not have known all of the facts, but here's the response I got from them:

ORIGINAL EMAIL EXCHANGE W/ FEDERAL.

Esmin,
The wall thicknesses are the same the hardness of the brass may be slightly different. The two different numbers on the packaging probably come from averages of loadings over time so they are very close. The ballistic coefficients are the same. We test both rounds in the same P&V barrels so that is not an issue. We test for accuracy using the same accuracy barrels. We load our cartridges to pressure levels not to the amount of powder in each case so if there is a difference in amount of powder it is only to get the pressures at the correct levels. The main advantage of the 762x51 cartridge is the case is built to withstand the higher pressures generated by military type firearms. The case is also not as shiny and we stake the primers to keep them from backing out. Other than that the really are virtually the same load.
Thanks
Federal Premium
-------------------------

 

[Grump]

Re: FGMM .308 vs FGMM 7.62x51

Please understand that all those colorful pictures above apply mainly to the problems inherent in the H&K style roller-locked action.

I think of it as a roller-locked, recoil-unlocked, blowback action.

The newer FC cases I have are virtually identical to 1980s-vintage LC M852 cases, as well as first-gen LC Special Ball and regular Ball cases. Right down to the water capacity of fired cases. Their velocities are close enough to almost completely overlap the variations between different strings fired with the same ammo.

But the FGMM if you don't want to de-crimp primers.

 

[Mute]

Re: FGMM .308 vs FGMM 7.62x51

I've had the same reliability and bullet drop for both the .308 and 7.62 FGMM rounds out of all my rifles (bolt or semi). IOW you're good to go with either.

 

[KevinB-KAC]

Re: FGMM .308 vs FGMM 7.62x51

Insignificant difference for bolt or DI guns.

In theory Modern .308 has a higher pressure than 7.62x51 NATO, but the dimentions are negligable.

All KAC guns have a .308WIN Chamber - we run both just fine.

Piston guns and the Hk G3 type guns have reported issues, but I've never seen it, and run .308 Match ammo in both.

 

[EZTundra77]

Re: FGMM .308 vs FGMM 7.62x51

Well all of this leads me to the following question: Why does federal make FGMM in both calibers if they perform the same? Is it just to appeal to H & K gas gun users?

 

[bogeybrown]

Re: FGMM .308 vs FGMM 7.62x51

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Doctawho</div><div class="ubbcode-body">Anyone notice much accuracy differences? </div></div>

I asked Federal about the difference, and explained that I didn't care about case construction, primers, powder, whatever. My sole concern and question was whether the 2 rounds were ballistically the same and whether I would have a POI shift going from one the other. Below is the reply I got back from Federal:

"They are basically the same round. The .308 is held to a slightly tighter accuracy spec at 200 yards. I believe the 762 is <1.8 inches and the .308 is <1.5 inches at 200 yards. Your point of impact should be very close.

Thanks
Federal Premium"

Not sure it that helps