Do you load for a Uintah Precision bolt upper? (Maybe in 6mm ARC?)

[cas6969]

Sometime last year I ordered a bolt upper from them in 6mm ARC. Since buying loaded ammo seemed to be the only way I could get brass, I did, and have been fiddle farting around with that since then. I finally loaded a few test rounds for it the other day and it didn't go great. Well... it actually it shot pretty dang good, but I had primer dimple "inversion". Not like signs of high pressure and starting to get primer flow, but defined squared off stick out.

Now I'm unsure what to blame:

I've seen mention that these uppers do this with warmer loads.
(though I mostly read about it in earlier, AR10 sized guns).
Is that the problem?

I used Hornady's Bolt Gun load data.
Is that the problem?

(Hornady 108gr ELD-M, with a 70+% up the scale load of AA2520. They don't list this bullet weight for the gas gun loads, despite it being the same bullet I've been shooting in the factory ammo (using same COAL))

Or just regular old the book doesn't match the reality of my gun"?
Is that the problem?

I don't expect you to have the answer per say, but it'll be a while before I get to play with it again, so I thought maybe someone with experience with these uppers (maybe even with this round) would have some input and ideas.

 

[cas6969]

That said.... no chrono data so I have no idea what they were doing Vs the factory ammo.

My initial plan was to mostly shoot 95gr Ballistic Tips in it, so if I end up have to shoot them with gas gun loads, it's not a big deal at all. I only tried the 108's because the factory stuff shot well.

 

[Mike_in_FL]

Well... it actually it shot pretty dang good, but I had primer dimple "inversion". Not like signs of high pressure and starting to get primer flow, but defined squared off stick out.

Read the 1st post, using CCI 400s? https://www.snipershide.com/shooting/threads/6mm-arc-bolt-gun-loadings.7158760/

 

[cas6969]

I'm now using "AR" primers, but I've only had a chance to try a couple loads with them, seems to have helped, though I don't believe I went too far into the bolt loads with them. Been too busy with other things. (I forgot I even started this thread)

 

[cas6969]

It's funny, every time I google Uintah and 6 ARC, this thread is near the top of the results, and every time I see it I realize that I forgot I even started it.

With that, I figured I'd update it to maybe help someone else out. As I said in the post above, I started using "AR" primers. With standard SRP's I was getting "primer prolapse" at 3/4 up the scale for gas gun loads, basically near starting bolt gun load data. I got ahold of some Federal AR Match primers and carefully worked my way up, to approaching max book loads for CFE223 and Lever'lu without any problems.



I will say this upper/caliber combo has been the most fickle thing I've ever dealt with. Usually your search for accurate loads on a "ladder" is "not good, okay, better, pretty good, good, great", then back up in size.

This thing is "awful, awful, awful, awful, almost amazing, awful, awful, awful.." "How can .3 grains of powder make it open up 2+ inches!"

Today I learned it really likes 29.2 grains of powder for some strange reason. Two different powders, two different bullet brands/weights, four combinations of same, they all liked 29.2
And didn't like anything else.


ETA: A day later, more frustration today.

"...almost amazing..."

Example:

29.2gr