Bullet Speed.

[LONG RANGE CAPT]

For the last couple of years both I and DAN534 have been shooting identical 7.62 AE Accuracy Internationals (24 inch barrels), and loading 155 SMK's over 46gr Vit 140.

 

All hand loading has been done separately at respective homes and all ammo had been shooting around the 2805 fps mark in both guns.

 

However in recent months we have both seen an increase in the velocity, both now shooting between 2850 - 2860 fps.

 

To ensure this wasn't a one off anomaly, I reloaded a test batch using new brass. Again ever thing seated to normal specs but the rounds are still at the 2850 fps mark.

 

Group sizes haven't changed and are still shooting sub 0.5 MOA in both guns.

 

Estimates on rounds through both guns are around 4000 rds.

 

What reasons could there be for this increase ?

 

Has anyone else experienced similar velocity changes ?

 

 

Kind Regards

 

Rob

[Barrelsniffer]

What about temp when doing your velocity checks ??...Neck tension on cases ??

[SteveW]

Different powder batch??? After 4000 rounds maybe the rifling is a little smoooother

[Ronin]

Different powder lots - this is slightly faster?

 

Carbon in case neck - increasing tension - faster speed??

 

 

Just guess's really.

[ds1]

If not powder 3 thoughts

 

1.are you using the same chronograph. Worth checking against another chronograph. I use a Chrony and am aware that the opening hinge is not the best method for consistant results from session to session, but will give reliable data for one session.

 

2.have you measured ogive length of bullets- I dont use smks but Lapua Scenars changed a while back when I measured one lot against another - possible with Sierra?

 

3.change in primer type (not probable).

[foxing2night]

I would put my money on powder batch?????

 

All the best Darrel