I've taken my time on this batch. Once fired S&B brass out of the same rifle. Steel pin washed and polished with corn cob media after bumping neck back 0.003". Brass was sorted by weight and grouped in 5s to the tenth of a gn (didn't switch to g on my scale).
I worked up loads with HDY 120 SST in preparation for this batch on my ARP 20" Triad Midweight that I built and broke in with S&B 110gr factory ammo. The HDY batch was between 27-28gr of AA2200 @2.295". Found accuracy at the higher end. After reading H's post about pressure testing with the CBB 120 MKT, I figured I would create this ladder for the TMTs at my own risk.
You can see the recipe on the card. All I need now is some good weather over here on the west side of WA, still winter weather here and it sucks (rain). I'll post up accuracy nodes w/o velocity once I test these.
Thanks. I'll also measure case head expansion on each one once I get to 28. I believe xman has a pretty good article on that to measure over pressure signs (along with the normal ways).
I ran the 5-shot per charge ladder yesterday. Concrete bench, lead sled, hand on scope, pressed trigger until round on target. No pressure signs up to 28.4 gr of AA2200 @ 2.295" OAL in my ARP 20" Triad barrel. I did not see accuracy at the top. 27.5 gr was not enough to reliably cycle the action. I have the gas block set to one click higher than S&B 110gr. Accuracy ranged from 1.5"-3"+ @ 100y. Best charge of the day was 28.0 and 28.1. Will play with OAL from here.
I would take 28.1 and test seating depth longer to get that group to tighten up. I'm still working on fine tuning my long range load with the 120 TMT as well, I'm getting close with it. So far I'm at .75 MOA accuracy and need to get it a fair bit tighter to be acceptable for 600M matches.
The 28.1 was a horizontal string, so ya I do want to recheck that charge. I don't think I can go longer, I'm at 2.295" and the tips are touching the front of the mag, unless I get a windowed mag, which I'm not too interested in.
I don't think I can go longer, I'm at 2.295" and the tips are touching the front of the mag, unless I get a windowed mag, which I'm not too interested in.
To test the benefits of loading longer than mag length, you could insert them into the chamber one at a time and see what affect it has on your group size.
Will do and repost results. So many projects and not enough time to shoot. I'm sure the rest you are in the same boat.
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