need info on 125 NBT loads

[Recusance]

I want to start loading 125gr NBT's for my whisper.

I have AA1680 on hand, and it works in my other loads like 220 and 110 loads.

what charge would you recommend and OAL ?

going for max velocity in a 16" AR 15 barrel.

Thanks.

[N310toN170]

125 GR. NOS BT 2.060" IMR 4227 16.5 @1818- 17.7C @1965

IMR 4227 is the slowest powder Hodgdon's site lists, given that all powders are their own; AA1680 is even slower than that.

125 GR. NOS BT 2.060" AA1680 @ 18.2 grains is ~100% case capacity @ ~1900 fps but at only an ~80% burn rate:

http://www.quarterbore.net/forums/showthread.php?t=9319

[pomofo]

I load them at 2.150", with great accuracy at 20.2, 20.4, and 20.6 grains of 1680.

[N310toN170]

I gave this a bit of research and have to agree that 2.150" COL does make good sense with just over 7mm seating depth, enough to provide strength when impacting the feed ramp. This also increases the case capacities, just slightly. 20.2gn appears to be almost exactly 100% full and within a safe pressure threshold. It also increases the powder burnt percentage leading to a 'cleaner' load as well as more consistent results.

I would have to caution against anything at or above this until building up to these thresholds to factor variables like primer selection, neck pressure, rifle personalities and environmental intemperance.

The results look promising with a reduced jump to the lands and velocities around 2100 fps...results may vary, normal disclaimers apply.