Discussion Forums

Andrew Murray

I was checking over some velocity for a load I did up earlier for my 308

Specs:
168gr A-Max
Winchester Brass
MagTech Primer
42.5 gr AR2206H
71mm COAL

The velocities are as follows
1. 2710 fps
2. 2691 fps
3. 2736 fps
4. 2673 fps
5. 2673 fps


I'm curious as to what could cause such a huge spread!!

I'll attach a photo but the group was 0.4MOA. (Bottom Left) This was with a barrel mounted chronograph, POI seems unaffected.


The rifle has shot consistenly sub 0.5MOA groups with this load but today you will see that the other groups were shocking! Just huge to the point I thought that I had dropped the rifle and damaged the scope or something.



I'm using Lee Balance scales which to be honest I've questioned before but I was very careful, even triple-checking the loads by removing the pan from the beam and bouncing the beam after it came to rest; an incredibly long process!

I'm hesitant to lay blame with the scales, but anyone offering an (affordable) accurate alternative would be appreciated simply to speed up the time involved.

Is it possibly the brass? Is it fouling? Could this have caused the groups to widen? Is it possible the chronograph acted as a harmonic balance that caused the groups to come back down?

Lots of questions...

On a side note, my SMLE was re-barreled in 303 and is shooting like a gem. Looking forward to taking a walk with it in the near future.