unintended auto fire from new 5.7 upper

[cav1993]

Wondered if others had this issue with the 5.7 uppers? I bought a new 5.7 upper and mounted it on a 5.56 DPMS lower- Using FN blue box ammo, the first two trigger pulls sent single rounds down range without any issue. However, the next trigger pull fired a four round burst-Necks of the cases were completely blown out-The range came to a standstill and the range master nearly blew a gasket(appropriately)-I switched lowers to one my buddy has his 5.7 upper mounted on-the next(and last) trigger pull sent 5 rounds down range-Sent the upper back to the guys at AR 57(who were very responsive) for what I assume is a firing pin issue.

Realize this can happen with semi autos, but has anybody else seen this with the 5.7s? Thanks

 

[m1garand30064]

Re: unintended auto fire from new 5.7 upper

Sounds like the primers on those must be very soft. The firing pin must be making just enough contact to set off the round and causing an in chamber detonation. This is a very dangerous thing and it could seriously screw up both you and your gun.

Reloaders (such as myself) who shoot their loads in semi auto guns such as M1a's and AR-15's use CCI #34 and #41 primers to prevent this from happening. They are extra hard mil spec primers.

Be careful!

 

[cav1993]

Re: unintended auto fire from new 5.7 upper

BW-Thanks for the post-Based on those thoughts I'll contact FNH and ar 57 to find out more about the primers utilized in their factory rounds and whether they recommend one round vs another for the ar. interestingly my friend nearly exclusively uses the blue box stuff(ss197 sr 40 gr vmax)for his ar setup and it's the ammo sold by the ar 57 webcite but agree it would be something to look into-thanks

 

[cav1993]

Re: unintended auto fire from new 5.7 upper

FWIW-Talked to the guys in tech support at 5.7-they are very helpful-they utilize mostly the blue tip ss197sr ammo but feel any commercially available factory ammo would be ok in an ar set up-He had already looked at the bolt I returned and agreed the firing pin was malfunctioning and has already sent a replacement.

 

[ecdbcd]

Re: unintended auto fire from new 5.7 upper