So, I've been working on my 16" gunner, new Grrr build, doing load checks; well, finally got to adjusting my AGB and re-checking loads.
This is just a JoeBob AGB and doesn't have detents but I picked up a couple of them and so far, things are ok. Rather than starting closed and clicking open 1 click at a time, I measured the travel from full open (with the bottom of the adj screw right at the entry into the port/gas flow) to fully closed: 6.5 turns of the allen wrench. I figured I would narrow down to my opening by going "halfsie's": shutting down basically (more or less) 1/2 the full travel distance, do the check, and open or close 1/4 depending on results, etc, in ever smaller 1/2 of the remainder.
I picked factory 123sst ammo as my test rounds, then planned to check the others once I determined the throttle for the 123sst. Fully open of course it locked back sat. Went to 3 turns closed (roughly half-way) and the round still locked the bolt back properly. Went to 4 T closed, 123sst locked back sat. 5 T closed, 123sst locked back sat. OK, now I was at only 1.5 T open on the GB, what to do? I "chickened out" and left it there at 5 closed.... tried a different round, Federal factory 120 MSR. At 5.0 closed the MSR locked back on the mag and not on the bolt catch. So I figured I had reached my max closing amount if not a bit too much. Adjusted back to 4.5 T closed, and the MSR cycled Sat. So now with 2 loads cycling Sat, I tried my 100 Amax and 90 TNT loads, and they cycled and locked back Sat as well. Great! So I'm leaving it at 4.5 T closed (from the full open). Tightened the setscrew down and I'm rockin' and rollin'.
Now for some re-checks of MV from my loads, back to the range and tried them all today, everything cycling sat and my trusty magnetospeed gave me the results:
For 90 TNT (31.2 H335), 100 Amax (29.7 XBR), 123sst (30.8 CFE), 123Factory, 120MSR and 123 Black(factory).
Bullet, Powder, (gr), 1, 2, 3, 4, -- Avg, SD, ES
90 TNT, H335, 31.2, 2675, 2689, 2704, 2696,-- 2691, 12.3, 29
100 Amx, XBR, 29.7, 2653, 2660, 2660, 2638,-- 2653, 10.4, 22
123 sst, CFE223, 30.8, 2427, 2421, 2408, 2413,-- 2417, 8.4, 19
123 sst, Fact , -, 2427, 2439, 2452, 2448, --2442, 11.1, 25
123 HdBk Fact , -, 2375, 2359, 2378, 2361, 2368,-- 9.6, 19
120 MSR Fact , -, 2416, 2426, 2422, 2409, 2418,-- 7.4, 17
Comparing this to my MV checks before adjusting the GB didn't show much change, as Stonehenge had commented on another thread... but I do perhaps see a little tightening up on the 120 MSR as the SD went from 14 down to 7. And there could be some mv gain on the 123sst factory where it had been 2405 but now shoots 2442 Avg (same box of ammo).
It could be that there's no statistical difference as the delta's are relatively small and not consistent across the several loads... perception-wise however I do think it is shooting "more smoothly" than before. I'm pretty happy that factory as well as my fave loads are still doing well however. And looking forward to tweaking the AGB on my 18" faxon Group barrel next.
This is just a JoeBob AGB and doesn't have detents but I picked up a couple of them and so far, things are ok. Rather than starting closed and clicking open 1 click at a time, I measured the travel from full open (with the bottom of the adj screw right at the entry into the port/gas flow) to fully closed: 6.5 turns of the allen wrench. I figured I would narrow down to my opening by going "halfsie's": shutting down basically (more or less) 1/2 the full travel distance, do the check, and open or close 1/4 depending on results, etc, in ever smaller 1/2 of the remainder.
I picked factory 123sst ammo as my test rounds, then planned to check the others once I determined the throttle for the 123sst. Fully open of course it locked back sat. Went to 3 turns closed (roughly half-way) and the round still locked the bolt back properly. Went to 4 T closed, 123sst locked back sat. 5 T closed, 123sst locked back sat. OK, now I was at only 1.5 T open on the GB, what to do? I "chickened out" and left it there at 5 closed.... tried a different round, Federal factory 120 MSR. At 5.0 closed the MSR locked back on the mag and not on the bolt catch. So I figured I had reached my max closing amount if not a bit too much. Adjusted back to 4.5 T closed, and the MSR cycled Sat. So now with 2 loads cycling Sat, I tried my 100 Amax and 90 TNT loads, and they cycled and locked back Sat as well. Great! So I'm leaving it at 4.5 T closed (from the full open). Tightened the setscrew down and I'm rockin' and rollin'.
Now for some re-checks of MV from my loads, back to the range and tried them all today, everything cycling sat and my trusty magnetospeed gave me the results:
For 90 TNT (31.2 H335), 100 Amax (29.7 XBR), 123sst (30.8 CFE), 123Factory, 120MSR and 123 Black(factory).
Bullet, Powder, (gr), 1, 2, 3, 4, -- Avg, SD, ES
90 TNT, H335, 31.2, 2675, 2689, 2704, 2696,-- 2691, 12.3, 29
100 Amx, XBR, 29.7, 2653, 2660, 2660, 2638,-- 2653, 10.4, 22
123 sst, CFE223, 30.8, 2427, 2421, 2408, 2413,-- 2417, 8.4, 19
123 sst, Fact , -, 2427, 2439, 2452, 2448, --2442, 11.1, 25
123 HdBk Fact , -, 2375, 2359, 2378, 2361, 2368,-- 9.6, 19
120 MSR Fact , -, 2416, 2426, 2422, 2409, 2418,-- 7.4, 17
Comparing this to my MV checks before adjusting the GB didn't show much change, as Stonehenge had commented on another thread... but I do perhaps see a little tightening up on the 120 MSR as the SD went from 14 down to 7. And there could be some mv gain on the 123sst factory where it had been 2405 but now shoots 2442 Avg (same box of ammo).
It could be that there's no statistical difference as the delta's are relatively small and not consistent across the several loads... perception-wise however I do think it is shooting "more smoothly" than before. I'm pretty happy that factory as well as my fave loads are still doing well however. And looking forward to tweaking the AGB on my 18" faxon Group barrel next.
Comment