Just jumping in as I've got a 6gt barrel spun up for my AT-X. I just started breaking it in, and am at 38 rounds down the tube so far. I'm using Eagle Eye ammo with the 105 Hybrid for this process, and then will reload the Alpha brass when I'm done with this box. I'm guilty of using factory ammo to get the first 50 - 100 rounds on a barrel.
So far, I started by shooting 5 groups of either 4-5 rounds between cleaning. Every one had a single flier that opened the group up to around 3/4 MOA. Once or twice, it's probably me sucking, but I got suspicious when it was all 5 groups. I seated another group of 5 down .005 from factory and that next group was in the .4s with no more fliers. I seated another .005 down (.010 total) and it was just over a half minute- again with no fliers. So I went ahead and seated the remaining rounds .005 down from what they came at (I'm now at 1.947 CBTO).
I did try one group at .005 above factory, but it was a consistent pattern that was opening up, so I figure the -.005 is the sweet-enough spot. I disassembled one round and got 33.5gr of a powder that looks a lot like either N150 or Reloader 16. I was thinking I'd see Varget or H4350, but it was definitely not.
I'll get some velocities as I get closer to finishing this stuff. Unfortunately, all I have to start with is 107 SMKs or 108 ELD-Ms.
Right now:
105 hybrid
33.5gr unknown powder
Unknown SRP
Alpha OCD brass
1.947 (new) CBTO.
Rifle is an AT-X with 27" Krieger M24, 1:8, with .237/.243.
And so begins my 6gt journey.
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Shots 3, 4, 5, and 6 on the barrel.
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Shots 11 - 15, my first 5 shot group during break-in in. The single uncalled flier became a trend until I played just a smidgen with the seating depth.
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