More Powder, Less Velocity

[js2013]

Using Precision Rifle Powder, CCI-200, Starline 308 brass, Sierra 169, 24 inch barrel, 80F, same setup same day, results repeatable from one previous test.
Results - velocity averages 5 rounds;
43.2 - 2628
43.5 - 2585
43.8 - 2590
44.1 - 2598 (extreme spread 4fps)

My guess is not all powder is not being ignited, and as powder is increased (compressed?) then it's even harder to ignite. Anyone have a better explanation or anything to add? Curious what would happen going to a hotter primer or perhaps a longer barrel.

 

[Dimner]

I have had that same experience with SW match rifle and ramshot hunter and cci200s. Both ball powders.

Cci 200s are rather mild in my opinion, too bad I have 12k of them. But the 200s seem to do fine with SW precision since it's a stick powder. The only other thing I can think of to check is if you are near or at a compressed load. When near a compressed load, I have noticed there are a few charge weights where some of the string are compressed some are not.

 

[Fast14riot]

How many fouler shots before measuring velocity. Also, is there an outlier in the data causing the higher avg? I usually shoot two ladders round robin. One going up and the other going down.

 

[Jager]

You're burning 99+ percent of your powder in that 24" barrel. Going to a longer barrel or a different primer is unlikely to make a difference in what might seem like a velocity peculiarity. And - depending upon the case volume in your Starline brass - your ladder is right around the 100% fill ratio threshold. Meaning, as @Dimner noted, some of your charges - even those of the same nominal charge weight - may be compressed while some are not.

Most likely, though, is that you're just observing a simple statistical wrinkle emerging out of the small sample set. Shoot more rounds and my guess is you'd see things settle out and the "peculiarity" would go away.

 

[Webster]

Using Precision Rifle Powder, CCI-200, Starline 308 brass, Sierra 169, 24 inch barrel, 80F, same setup same day, results repeatable from one previous test.
Results - velocity averages 5 rounds;
43.2 - 2628
43.5 - 2585
43.8 - 2590
44.1 - 2598 (extreme spread 4fps)

My guess is not all powder is not being ignited, and as powder is increased (compressed?) then it's even harder to ignite. Anyone have a better explanation or anything to add? Curious what would happen going to a hotter primer or perhaps a longer barrel.

What's the ES for all of the loads?

 

[js2013]

What's the ES for all of the loads?

About 30 for the other loads

 

[std7mag]

RL17 does the same thing.
Seems like there is an optimal charge weight, beyond that velocity starts to drop.

 

[Doom]

Please post your individual data.