Do you buy it or try to avoid it?

There are many vendors of once fired brass on the web. Some will state that the product that they are selling might / or might not be, MG / SAW brass. Seems like it is a roll of the dice thing nowadays as to what one might wind up with when buying OF brass.

Thoughts?

Possibility of case head separations from excessive chamber dimensions.
This alone keeps me from buying MG brass.

Can`t say that I blame you one bit in your opinion.

I try to avoid it as well.

I check the insides of my casings on all of my OF brass and in some, the inspection results are ugly.

Does the military segregate the MG brass from the rifle brass? I'd be surprised if it wasn't mixed when it came from the various ranges. I've also read that SAWS aren't as hard on brass as older machine guns such as the M60.

I read the M240 was the reason for thickening up the 7.62x51 brass.  Other than dimensional differences and caliber, what are the differences between the M240 and M249 design?

I've bought a couple 1000 round lots of once fired brass that the dealer says "some SAW brass mixed in". In the 1000 cases they were typically about 50 SAW cases. Most of the SAW cases showed no problems with stretching or damage. A very few were banged up or showed stretching. Most of the SAW brass had the ejector marks on the case head. SAW ejector marks are shaped like a watermelon slice rather than the normal horseshoe mark left by M16's or AR's sometimes. I wouldn't NOT buy "some SAW brass may be mixed in" brass if the price was right and knowing there would be some quantity of it in the mix. But there should be the same amount of attention and checking all military once fired brass as there would be SAW brass. Seems I find from 5 to 25 military once fired cases with the classic stretch mark inside and bad enough that they might separate if loaded again. I wouldn't buy ALL Saw brass though unless it was very very cheap and expecting to do a lot of case inspections on them. Having loaded a lot of military surplus brass it's a gamble on all of it. Seems some brass is very good with no issues and looks almost like it was fired from a bolt rifle while other lots have nicks and dings, more than normal cases that are stretched, rim damage, and ejector marks. Some military rifles seem to have very good headspace and cases aren't damaged while other rifles must be in poor condition with bad headspace and do lots of damage to cases.

I don't know when we (US) started using M240's.  Back in the mid/late 70's we were still using M60's and M14's were I was stationed and the GI brass was thicker/heavier than civilian/commercial .308 brass.

MG brass is fine.  I'm on my 8th loading of 1000 pieces of TAA 7.62N brass.  Start all of your loads about a full grain lower than you would with commercial brass as the case capacity isn't quite as much with the thicker brass.  I don't have any trouble getting loads to shoot very well, the brass is cheap, and if I lose some shooting it through a semi then no big deal.

All surplus 7.62x51mm is likely to be machine gun brass unless the head stamp says M118LR. Even ammo fired through M14's gets the crap stretched out of it because of it's chamber dimensions and the fact that the bolt opens so quickly after being fired. The brass is getting yanked out of the chamber before it has had time to contract.

It's not unusual to have to resize the brass twice to get it to gage properly. I use 2.0 full grains less powder when loading Lake City when compared to Winchester brass. Even then I'm at maximum charge weights, you should start closer to 3.0 whole grains lower than what you use in commercial brass and work up.

This stuff is tougher and thicker than commercial cases, but it works fine especially in semi-auto rifles provided you resize to minimum SAAMI headspace. I load them four times then recycle. They have been overly stressed on their first firing and therefore deserved to be retired at a early age.