Velocity fluctuations

[Bunnypunter]

I have been reloading my .308 Savage with 168 Amax, 42g Varget, Win cases and primers. I threw it on the crony the other day and was getting a serious amount of fluctutaions in velocity. Anywhere from 2656-2744. I weigh each charge on an electric scale. Where are I going wrong on this? How do i keep my velocity within a managable range?

 

[Greg Langelius *]

Re: Velocity fluctuations

Unless your Chrony is at least 12-15ft downrange from the muzzle, the escaping gas from muzzle blast can cause velocity deviations that have nothing to do with your bullet's actual velocity.

 

[1lnbrdg]

Re: Velocity fluctuations

That's a fairly light load of Varget for a 168gr bullet in most rifles.

I'd try working up just a little bit and see if you can find an accuracy node with a better extreme velocity spread.

 

[CajunAR]

Re: Velocity fluctuations

with the "lighter" loads i noticed alot more spread than with the hotter loads.

I chrono'd another set of 5 yesterday to confirm some previous velocity readings and i was SHOCKED that 4 out of my 5 shots were duplicates...probably just a fluke, but that might have been the best feeling i've had since i started reloading ~2 years ago.

Rilfe:

DPMS SASS

Round Recipe:
43.5gr Varget
CCI Large Rifle Primers
Fully trimmed, and prepped 1-2 fired Federal Premium Brass
178gr Hornady AMAX

***this round technically over pressure according to the Hornady manual, but it shoots great and i JUST started noticing some extractor marks, i may have to back it down, but i'll test it a few more times first***

 

[Bunnypunter]

Re: Velocity fluctuations

I got great accuracy when I shot a 5 shot group at 300 yrds. 4 shots into a quarter and 1 flier, my fault. So I'm stuggling to grasp why velocity would be off when 'm grouping that well. I'll try a hotter load and see what happens. It is shooting sweet within 300 yards but any further out it is throwing off my range card. I'll post results ASAP. Any thoughts on Varget and how may grains to use behind a 168AMAX? Thanks for your advice.

 

[mk12bill]

Re: Velocity fluctuations

Myself and a few guys I know are getting really good results with 44gr Varget with the 168 Amax and a 210m primer. I'm using win brass. I get 2640 fps out of a 24" barreled 10fp, SD is 12

 

[Deadshot2]

Re: Velocity fluctuations

It sounds like you have a "measuring" issue rather than an ammo issue. Some chronographs are just plain fussy about lighting conditions, how steady your tripod/mount is, and even reflections off the bullet.

Some shooters will blacken the bullets they're "clocking" with a magic marker to increase the contrast when it passes over the sensors.

It's also important that the bullet pass over the chronograph parallel to the sensor supports.

Assuming that all the usual suspects are dealt with, powder weight per charge, neck tension, uniform bullet weights/lengths, seating depths, etc, the only real question is "how accurate is your speed measuring tool and method.

As for Varget and A-max's, I use 44.4gr in a winchester case at 2.800 OAL. Works good for me in my 5-R Milspec 24" bbl.

 

[NCHillbilly]

Re: Velocity fluctuations

I use an RCBS electronic powder dispenser,and although it does a great job for making a lot of "good" loads,it will still vary +/-.1 grain.If you are looking for absolute exact charges,you'll need to throw .5 gr light and hand trickle up to your desired weight.Military brass is known to be a little inconsistent as to case weight an wall thickness also.I've actually shot better groups and had lower sd with Win and R-P cases.