Had some double feed problems today at the range with my Sig 516. I was using 3 30 and 2 20rd Pmags and Federal brown box 193 55gr. It was 2 live rounds but the first was all the way in the chamber and the second jammed up behind it.  The Pmags are pretty new, about 300 rds through them.  I had only 20 rds of 77gr with me and those went off fine.  I am aware that 2 rds trying to enter the chamber at once is good chance its a bad mag but I have never seen it where the first round is all the way in the chamber. I am positive they are both live rounds. Can short stroking or over/under gassing cause a jam like this? Any Ideas?

Thanks
Mike

it sounds like a mag problem.  is it only accuring with a certain mag or is it happening with all your mags? more info will help in getting a better idea of the problem.

It did it with all 3 of the 30rd and all 2 of the 20rd Pmags I brought with me that day. I would do it every 10-15 rds. I have some old USGI colt mags from the AWB days I can try.

The rifle and mags work fine on the normal gas setting with any ammo. (PMC x-tac 55 abd 62, Fed 55 and 62, Hornady 223 vmax, 77gr SSA). I put my suppressor on, switch to suppressor setting and It was short stroking with PMC x-tac. So next weekend I used Fed XM193 brown box and it did not short stroke like with the PMC but thats when it started doing the double feed thing.  I was going to try fed 62gr but I am hoping I can make it work with the fed xm193 since my stock pile is that ammo.