Have a "new" (NOS technically) SIG 516 I finally got around to shooting today. It was a SIG lower with a 14.5" chrome lined 516 upper. I wanted to zero my irons and Aimpoint T-1. Used 40rds of Mk318 and 40rds of M855 "green tip". Once the zeroing was done I just plinked at some clays I had set up on my 100yd berm.
The M855 didn't miss a beat. The Mk318 was constantly short-stroking or at best failing to lock back, even on the "adverse" gas setting.
I thought Mk318 was a little hotter than M855? Got me to thinking about a thread I had posted last year about a Hodge barrel and different types of ammo using an LMT EBCG. I looked back at it and saw where the Mk318 had about a 50% failure to lock back on an empty mag, the highest of the rounds I tested that day; fired and cycled well otherwise (unlike today). Of the three types of rounds I tested then (Mk318, Mk262 IMI "Razor", and M855A1) it seemed to have the least "oomph" for cycling. Did not test regular M855 that time like I did today.
So this time there was a piston gun and no EBCG, Razor ammo, or M855A1, just plain old M855 and Mk318. It would seem that the Mk318 still seemed to lack a little in energy to cycle the system. Yes, it was a piston gun this time, but Mk318 was consistent in being the "weaker" round for cycling purposes.
While I didn't compare lot numbers, the Mk318 I shot today was a different batch than what I shot last year. It is disappointing as I have >1,000 rounds of it socked away and it's a damned good bullet terminally. Thought I'd throw this out there and see if anyone had similar experiences.
FWIW, both batches of Mk318 (last year and today) were Federal "white box" T556TNB1.....there was no "X" prefix anywhere. The M855 I shot today was Federal XM855 from a 1K round bulk pack.
EDIT: gonna have to try some Mk262 "Razor" and M855A1 next time.
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