Velocity question...

Bill2662

Private
Minuteman
Feb 14, 2012
13
1
6
Westford, New York
Shootong 175 smk’s average velocity was 2666. But weren’t grouping. Reworked the load and backed the coal down to 2.8. Now up to same charge weight and velocity is average 2700fps. Grouping good and no pressure signs. Surprised in a velocity increased though. Any thoughts? Same can of powder.
Initial load the bullet was .020 off the lands. New load is it at .060 from lands. Curious because I figured moving away from the lands would also slow it down a bit.

Rifle:
Vanguard 308
24” barrel
1:12

New Load:
175smk
44.5g Varget
Fire formed Hornady Match brass
Fed 210 Primers.
2.8 COAL
.060jump
2700fps avg.

Old load
175smk
44.5g Varget
Fire formed Hornady Match brass
Fed 210 Primers.
2.840 COAL
.020 jump)
2666fps avg.

Alt. 1880
Temp 66
Basically the same both days out.
 
Last edited:

918v

Manipulated by Variables
Belligerents
Jul 15, 2007
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Miserable CA
I’m getting those velocities with 43.5grs in 164gr Hornady match brass out of my 26”
 

ShtrRdy

Gunny Sergeant
Belligerents
Sep 17, 2011
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High Plains
If you seat the bullet more into the case it will decrease the volume inside the case. This will raise the initial pressure and increase the velocity.
 
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abn31c

Sergeant of the Hide
Belligerents
Minuteman
Apr 10, 2018
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By seating deeper you are giving the bullet a running start, think freebore. Roy Weatherby was a fan of this theory. Also as ShtrRdy say more initial pressure.
 
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Bill2662

Private
Minuteman
Feb 14, 2012
13
1
6
Westford, New York
Makes sense. Not going to worry about it, was just curious how I was at that velocity 1/2g under the max load. If I remember right win cases hold a bit more than hornady. Either way thanks all. No pressure signs and groups are good so no worries. Might go back down to 44g play with seating depth.
 
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Doom

Private
Belligerents
Mar 24, 2013
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South of the Mason Dixon Line.
By seating deeper you are giving the bullet a running start, think freebore. Roy Weatherby was a fan of this theory. Also as ShtrRdy say more initial pressure.
With the same charge and deeper seating you also have less air in the case. The air is a dilute that reduces the peak temperature and pressure of the fired charge. Small effect but still there.