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Firing Problems S&W M&P 15

Posted: Sat May 12, 2012 3:21 pm
by kimber4570
I have Two (2) S&W M&P-15 300whisper/300blackout rifles (just purchased both of them from different shops). Both guns work flawlessly with Remington 300 AAC Blackout 125gr and PNW Arms 300 BLK 147 gr. When using Remington 300 AAC Blackout 220 gr, both guns will fire the round but not chamber the next round. I have got one of them to fire two rounds before having problems but that's about it. It just seems strange that BOTH of these guns are doing the same thing with the same ammo.
Has anyone had this problem?
And any ideas as to what could be happening?
Or should I just send both guns back to S&W?

Thanks in advance

Re: Firing Problems S&W M&P 15

Posted: Sat May 12, 2012 9:40 pm
by mdyer
I bought one new a couple weeks ago. I've only fired Remington 220 subs in it and hornady 208 subs it cycled both fine. Ejected well threw the empties 5-6 feet. No problems yet.

Re: Firing Problems S&W M&P 15

Posted: Sat May 12, 2012 9:53 pm
by FarmerTed1971
Put a can on it?

Re: Firing Problems S&W M&P 15

Posted: Sun May 13, 2012 11:41 pm
by kimber4570
Just put a 9mm can on one of the MP 15. Works great with the subs now. Only problem is I was told with the 9mm can I should not shoot any super sonic loads. So leave it on and shoot only subs or just keep taking it on and off, I guess. I am going to try the Hornady 208 subs first. If they work I will retire the remington rounds and not worry about it. If they don't I think I will be sending both back to S&W.
Thanks for the help.

Re: Firing Problems S&W M&P 15

Posted: Mon May 14, 2012 6:36 am
by Weber
You can open your gas port some...

Re: Firing Problems S&W M&P 15

Posted: Sun Mar 31, 2013 10:26 pm
by Ed@DarkStorm
Have you tree different buffer weights?

Firing Problems S M 15

Posted: Sun May 05, 2019 4:14 am
by Enfoto
I had backfiring problems in tandem with a big power loss. check the timing, mine was off by a tooth.