H4831sc velocity question

[phutch30]

Ive been working with some loads using H4831sc/180 gr accubonds and my velocities seem pretty low.

300wsm
brux 4 grove 24" barrel ~35 rds total thru the barrel
CCI 250 primers
fed brass
35-45 degree temp

thru a chroni

68grs - ave-2822
68.5grs - ave-2863
69grs - ave 2871

I realize you may or may not see the velocities posted in reloading guides but I'm pretty far under posted speeds. But Ive never been this far off. Wondering if my chroni is wacked

 

[DrMike]

A chronograph has ruined many fine loads for people. Your velocities are only about 100 fps (~3%) below what might otherwise be anticipated. Eliminate the probable. Shoot a load with a known velocity across your chronograph to ensure that it is recording accurately. Even a 22 long rifle shot across the chronograph will inform you of whether it is working properly or not. If that is correct, measure case volume on a fired case. Your chamber may be somewhat larger than standard specs. Remember, as well, that lot-to-lot variation on propellants account for significant velocity changes. If you just must have that additional 100 fps, up your charge in 0.5 grain increments, watching for signs of excessive pressure.

 

[OU812]

DrMike is spot on. I was working on posting something similar to Mikes post but since I keyboard at the speed of smell DrMike beat me too it. :grin:

 

[bobnob]

I've found H4831SC (called AR2213SC here) to be slower than usual in recent batches, for several years. That may or may not be a factor in your findings too.

In 270 and 25-06 loads, the batches were sufficiently slow that I needed to load a grain or two above book max loads to get book max speeds.

 

[RiverRider]

I'm working with a new-to-me rifle in .280, and I have found that velocities are considerably lower using the loads I had worked up for the previous rifle. It takes 1.4 more grains of H4831 to get velocity back up to 2920 fps using the same powder lot. Fire-formed cases from the new rifle hold about 1.5 grains more water, suggesting that chamber volume is responsible for a good deal of the difference. YMMV.

 

[fwood]

My velocities have fallen off a bit with 4831sc in the last few years, 3095 in the 300wm with 75 gr to about 2930 and really cant stoke it much more but still shooting great groups.

Fwood

 

[.300winmag]

What chronograph are you using?

 

[hunting1]

I am only getting 2870 with IMR4350 and 180 NAB's, so to me this seems legit. Nosler doesn't list many loads over 2900 or usually they are 50-fps +/- faster than my reality. I wouldn't sweat it, shoot what is the most accurate. 69.5 they say 2985 but I haven't got there yet with 180's.