We were issued british 7.62mm ammo when we first arrived in Iraq (U.S. M1A1 company). The ammo cans were a little thinner, so the belts wouldn't fall over in them, but that also meant that they didn't quite fit right in the mounts.

1. The ammo wouldn't reliably cycle the M240 unless the gas port setting was adjusted. Does British ammo have less powder in each round?

2. The headspace on the M240 was off with the British ammo and caused frequent jams - it seemed that the British ammo was slightly longer. We worked around this by just not tightening the barrels down all the way. Unscrew the barrel lock lever 1-2 clicks and the weapon would stop jamming.

By changing the gas port setting and loosening the barrel, we were able to get the British ammo to work, but I was surprised that NATO countries would have partially incompatible ammo in the same caliber.

Any comments?

Correction: in bold above

Well, the fact that you could adjust things and it all worked well means it wasn't incompatible. What were the markings on the ammo? Was it RG as in Radway Green? If so, I want to say I've had it related that it is a touch on the larger side of the NATO spec as you found with the bullets not being seated quite as much. Some of that could be how the british want their GPMG's to seat the bullets tighter in the barrel throat than the US specs are done to.

I don't know the markings on the rounds off the top of my head. If I go through my photo collection, I could possibly figure it out, but I don't want to spend the work on that right now.

There was one loader that would ALWAYS tightened his barrel down all the way and have repeated jams. The guy just couldn't understand why it was supposed to be loosened.

I have been involved in similar debates about NATO 5.56mm ammo, and I expect the same explanation applies to 7.62mm. While supposedly made to the same STANAG specification, there are minor national variations to suit national weapons, so although NATO ammo is more or less interchangeable, some types work better than others in particular guns.

So what's the difference between a M240 and a L7, L37 (etc)?

L7 et al are inch pattern. Ironically the M240 is a metric pattern MAG.....

RORG 7.62x51mm is set up for inch pattern FALs and MAGs.

Simon

From memory we balanced guns at or about 6. 6 was the standard setting for gas as per pamphlet.

Little confused about this, the M240 barrel doesn't screw in, do you mean that when you pressed down on the lock lever you didn't press it down all the way?

(correction: I think we're talking about the same thing)

The barrel lock lever twists about 70 degrees to lock the barrel into place. As it does, there are about 5 audible "clicks." If you tighten the lock lever all the way, then push down so you can loosen or two "clicks," the barrel is loosened somewhat and your headspace is (field-expediently) increased.

Correction - The barrel doesn't twist, just the barrel lock. Tighten the lock lever all the way down, then loosen up 1-2 audible clicks.

I'm confused as well. Unless the barrel assembly of the M240 has changed markedly in the past 10 years, the barrel can only be put in one way, with the gas port aligned with the receiver. The barrel lock rotates around the barrel, or it did, engaging the buttress threads in the receiver thus pulling the barrel in and fixing the headspace. So you see, it isn't the barrel that is rotating, it is the barrel lock.

You're right, the barrel itselt doesn't twist. I misspoke.

Thanks Biscuitjam for raising this topic. I noticed before that the 7.62mm ammo cans for the M240/GPMG are narrower than the ammo cans for the M1919. I then realized they used different .30-cal rounds. That said, does the US Army still use the older .30-cal cans and can these fit on the M240 ammo tray on the M1? Thanks.

When did that happen?

I have some U.S. ammo cans stenciled for linked .30 caliber, and some stenciled for linked 7.62 Nato, and they both appear to be exactly the same. The lids even interchange. The 7.62 Nato was usually packaged in two one hundred round cartons with a canvas carrier bags, this fills up the extra space used by the older .30 caliber cartridge.

I also have some of the older WW2 cans, the kind that will attach to a M1917A1 tripod, now those are different.

Say, Tomas, did you get your threads crossed? Ammo cans are another thread.

From cruffler.com; a discussion of 7.62x51 variations from different nations.

http://www.cruffler.com/trivia-June01.html

I mentioned the sizes of ammo cans briefly in the first post here.

Thanks for the link. I'll be reading up on it later.

Correction noted.

Thanks for the link Shep.

Bob: As usual, my observation was sparked by a model kit. I have not seen actual .30-cal ammo cans, only .50-cal.

Are you sure about that Simon? The first L7s came in quite a bit later than the X8/L1 an we've been buying L7s directly from FN for a long time (at least a quarter of a century), which we didn't do with L1s. I can't believe the Belgians keep a complete line of imperial spec parts just to run off a few hundred GPMGs for us once in a while. AFAIK there was also never an issue with RG 7.62 not working in Belgian FALs or vice versa, so ammo compatibility wouldn't necessarily have been an issue even had there been an 'inch pattern' L7.

I thought GPMGs were still made by Manroy

http://www.manroy.co.uk/manroy/GPMG.HTML