6.5 CM Velocities

[OverInfinite]

I have been reloading a while, and this last year I loaded up some 140gr Berger Elites with 41.5gr IMR4350 & CCI 200's inside Hornady Brass loaded out to 2.825" OAL
We are at roughly 5,000 ft of elevation. I shot the loads out of both a Ruger American Predator 22" barrel and a Ruger Precision 24" barrel.
Both shot great groups, under an inch, the weird thing is the predator had velocities of 2750 FPS with an SD of 11 and the precision shot 2735 FPS with an SD of 13.
Not that its an Issue, my question is WHY? why is my longer barrel shooting slower velocities? Is it just purely down to throat length between the two rifles?

 

[Mag_7s]

Have you measured the throat length between the two rifles? Some barrels are just "faster" than others, meaning you can have two barrels from the same manufacturer say Bartlein, identical length, twist, contour and chamber and one can be 50fps faster or slower than the other.
This is just my thought, im curious to hear others opinions.

 

[S-3 ranch]

Have you measured the throat length between the two rifles? Some barrels are just "faster" than others, meaning you can have two barrels from the same manufacturer say Bartlein, identical length, twist, contour and chamber and one can be 50fps faster or slower than the other.
This is just my thought, im curious to hear others opinions.

I was thinking the same thing.
in my old 270 I loaded 61gr 4831 = 3140’s
new = 3088 - 3090’s

seems logical

 

[OverInfinite]

I know my precision is about 0.020" longer to the lands compared to the American. That said, they both have some LONG jumps to the lands with the loads above.

 

[OverInfinite]

Something I never considered but just thought about, is my american is close to 7 years old with 1,500+ rounds through it. And my precision is less than 2 with less than 500 rounds through it. Would that make a difference? How often does velocity increase with barrel life?

 

[Mag_7s]

Something I never considered but just thought about, is my american is close to 7 years old with 1,500+ rounds through it. And my precision is less than 2 with less than 500 rounds through it. Would that make a difference? How often does velocity increase with barrel life?

Round count does make a difference. The bore of a rifle is continuously changing, undergoing the most change during the first 100 -200 rounds. Generally the barrel picks up speed during this time, and flattens off somewhat. As per how the barrel degenerates over round count will depend on the cartridge, string volume and how hard the load is pushed. I am not so sure on barrels slowing down with high round count and something I'll have to research.

 

[wind gypsy]

plenty of variance barrel to barrel. Do you clean them often and make sure to clean out the throats? Only other thing i can think of is a carbon ring in the predator.

 

[OverInfinite]

plenty of variance barrel to barrel. Do you clean them often and make sure to clean out the throats? Only other thing i can think of is a carbon ring in the predator.

I am not thrilled to say I am not a proper break in or clean shooter. For break ins I clean every 10 rounds or so for the first 40 rounds then I clean after every other reload. So 200 rounds and do a clean. I do clean the throat thoroughly.
Thanks guys for all the info, sounds like there is some normalcy to the guns. I have noticed my predator always seems faster than most manuals. Just lucky I guess.

 

[Bellmoa]

I had a Predator in 6.5 creedmoor a few years and noticed the same thing. My barrel would regularly have higher velocities than published in loading manuals. It ended up staying consistent through the life of the barrel.