Sierra 90gr TGK and 748

[300BLK]

First test loads were shot this morning, Savage 110T with Burris XTRII 3-15x.  New Starline cases, F205MAR primers, 29.5, 30.0, 30.5, and 31.0gr WW748.  90gr TGKs were seated in the Forster mictometer die to 2.300", so put the shank of the bullet 2/3 down the neck.  31.gr pushed the bullets out to 2.310" so obviously compressed.  I tried bullets out as long as 2.34", but didn't think there was enough bullet in the case for strength, and they still didn't touch the rifling.

I was shooting @12x at steel plates at 300 yards.  Wind was variable and gusty, so not the best day for real groups.  90gr TGKs were shooting 3MOA higher @300 than Hornady Black factory ammo.  Once I realized that all I needed to do was aim center and watch the wind flags, I shot 5 shot groups.  ALL of the groups were wider than tall, and usually had 3 or more shots inside 2".  30.0 and 30.5gr were shot again, and both were sub 2.5" with the 30.5gr looking closer to 2".

edit: those 1x cases have 1.0gr more capacity 748 than the new cases had

[BluntForceTrauma]

Good info. Thanks!

[300BLK]

Range test #2 for the 90gr TGKs with 748 yielded similar results to the first. While there was noticeably less wind to contend with, those pesky flyers remained at 300 yards. I've loaded these singly, and not from the magazine, so will try shallower seating depths.

748 notes: 30 year old lot of 748 left less carbon in the barrel than did current Benchmark. New 748 is lighter in color, more grey than the old lot, and 4/10gr lighter in ~30gr charge

edit: 90gr TGKs touch the Savage 110Ts rifling at 2.365", next batch of ammo loaded with longer OALs

[300BLK]

Range test #3

Sierra 90gr TGKs touch Savage 110T rifling at 2.365", so this test was only about OAL.  30.15gr 2023 lot of WW748 for all loads, new Starline cases with F205MAR primers

*2.315" OAL, .050" off the lands, 3" for 5 shots at 300 yards*
2.325" OAL, .040" off the lands, 5" for 5 shots at 300 yards
***2.335" OAL, .030" off the lands, 2.25" for 5 shots at 300 yards ***
*2.345" OAL, .020" off the lands, 3" for 5 shots at 300 yards*
2.355" OAL, .010" off the lands, 5" for 5 shots at 300 yards

[popgun]

Do you have a SAAMI spec chamber? It seems you have a long throat with those OAL's to touch the lands.
I realize a 90gr Berger is going to have a little different shape but they are .004" into the lands at a OAL of 2.238" with my chamber.

[300BLK]

unaltered factory rifle

[grayfox]

Berger 90 gr BT? If so it has a tangent ogive, which would make it more in line with the hdy 90 Eldx. G1 BC of 0.409 which is almost = to the eldx, 0.405 IIRC.
So, I would expect it to have a OAL max closer to an Eldx of 2.220-30 in most 6Arc chambers, which puts it about where you are.

The 90 TGK, otoh, has a sleeker, sharper ogive and 0.490 BC, in my chambers it maxes out more like 2.338, one chamber is 2.300 but it is much easier to seat out farther than the 90 BT mentioned. What I would be concerned about (although I hav not tested it to that length) is not having enough shank in the neck to stabilize the bullet during the firing. But if OP is having no issues with that then ok... I wouldn't be going there with my pipes however.