Do I have a problem?

[Firewater]

Shot my new piston AR for first time. When clearing the gun found gas residue on first couple of rounds still left in mag and the round cleared from chamber. I never had this issue with old DI gun.

[tombogan03884]

Probably venting from the chamber.

[fightingquaker13]

I will post a no comment. But I would ask about the brand and the ammo you fired.
FQ13

[Firewater]

Hornady 55gr VMax

[Firewater]

Same rounds I use in my DI system.

[Sponsor]

[fightingquaker13]

Any problems with other brands? I'm not the guru here, just trying to ask the simple questions so the gurus have the facts. What brand of rifle (unknown)? What brand of ammo (known), have you had this problem with? Have you had this problem with other brands (unknown)? Did your DI weapon have the same problem with the same ammo, and was it ok with other brands (both unknowns)? Sorry for sounding all academic, but the more variables we can take off the table, the easier it is to fix the problem. FWIW.
FQ13

[Firewater]

Same ammo both guns. DI is Bushmaster Varmitter and the piston is SR556UFB on a Black Rain lower. No problem in the DI gun.

[tombogan03884]

Tomorrow some one who has experience with piston systems will give you a definite answer. but I would guess that because gas isn't venting onto the bolt through the DI system it is venting back from the chamber when the casing ejects.
Some one else with a piston system posted that it seemed to shoot dirtier than DI but didn't post details.

[billt]

Both of my LWRC piston guns shoot residue free. With that said I'm shooting 25.0 grains of AA-2230-C under a Winchester 55 Gr. FMJ. I'm just guessing at this point, and would suggest trying different brands of ammo. Slower burning powders are apt to cause this in piston weapons. That's a problem with factory ammunition. You have no idea of the burn rate of the powder they load with.

I know this is a big deal with the Springfield M1-A. So much so Springfield has published a list of .308 ammo you should not use in the weapon. I know Hornady TAP is on the list. If the powder is too slow the gas system can be subjected to too much residual pressure when it opens. This can cause bent op rods, along with a whole slew of other problems. M-1 Garands are effected by this to a even worse degree. Federal has recently come out with gun specific loads for both the M-1 Garand and the M-14 / M1-A in .30-06 and .308. They utilize powders that are of a mid range burn rate. This is much easier on the gas system. I would try some Lake City M-193 Ball, or else some M-855 from either Lake City or else IMI. IMI M-855 is excellent ammo that runs well in both the M-16 / AR-15 as well as the Galil. This is what the IMI M-855 looks like if you should run across it. It is also avaliable from Wideners. Hope this helps. Bill T.

http://www.wideners.com/itemdetail.cfm?item_id=9020&dir=18|830|845

[Firewater]

Thanks for the info. Will try different ammo