How to reduce velocity spread?

S

supersonic

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I use 6,5x55 Blaser for both hunting and target-sometimes long range target shooting. I use 139gr Lapua bullet and Accurate 3100powder and velocity is about 840m/s and velocity spread is up to 10m/s. I do not neck turn. I use Lapua cases. I debur the flash hole from inside. I reduced the velocity spread by using magnum primers,with benchrest primers it was even higher. Now I suspect powder..when I look closely at grains..some of them are shorter and some of them are twice as long as is some average length. Thinking about trying Viht 160. But it cost twice as much here. Could it help?
Thanks for any advice.
Best regards,
Petr
 
Petr, are you weighing your charges or throwing them from a powder measure. With slow burning stick powders that tend to have fairly large granules, and especially if they vary in size thrown charges can vary quite a bit in weight. Another thing to try, especially for long range shooting might be to check the capacity of cases with water or methanol or even better a fine grained ball type powder. Select cases that have the narrowest range of capacity might help as well. If you have a variety of primers available you might want to try different brands of primers. The only other thing that occurs to me would be minimizing neck tension variations. If you feel a bullet seat harder or easier than others, set that round aside and use it as a fouler or for short range, non-critical use.
 
I'd also check that your primer seating technique is getting the primers bottomed in the primer pocket without crushing. Either leaving them a tad proud or crushing the primer cake is going to play havoc with consistency of ignition.
 
I am weighing charges. I did not try to check capacity of cases. Neck tension. I will try to do both things. Thanks.
Regards,Petr
 
Primer seating- I was always trying to seat primer against the bottom of primer pocket,so they are a bit deeper inside,not leveled with bottom of cartridge. I did not realize it could make any difference. I am afraid that in case the primer would be left a bit proud,it could be a problem to meassure the cartridge length accurately.i I czech the cartridge length with meassure a adjust later, if some are not accurate. But I can try to seat them without excessive strength.Thanks.
Best regards,Petr
 
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