Velocity Loss

[chkunz]

Has any one ever measured the velocity loss over the life of a barrel?

 

[joshb]

Not me, yet. I am keenly aware of my body's velocity loss, though.😖 Just waiting for dinner and wasting time. Figured I'd say something as you had no replies.

 

[fgregorio]

I have. Although I've changed projectiles and loads over time, I can compare ladder tests as far as I can remember throughout the life of the barrel.
On my 30 inch .308 True Flite barrel with a life of 11200 rounds at this stage these were the loads for a 2975 fps node from new to now:
Projectile: Optimus HBC coated with Boron Nitride
Cases: Winchester
Powder: Varget
Primer CCI BR2 Large Rifle
Jump: 15thou
Load when new 45.4 gr
Muzzle Velocity: 2975 fps

Load now at 11,200 rds: 47.6 gr
Muzzle Velocity: 2975 fps


Lands moved forward 60 thou and now jump is still 15 thou by increasing OAL by the 60 thou difference.

At 7,500 rds or so I "treated" the first 20 inches of the barrel with abrasives in order to smooth out the "crocodile skin" throat effect. The barrel did regain some of its past accuracy. I have repeated the procedure time and again.
Last scores at 660 yards: 100.7x (out of a possible 100.10x) and 140. 8x (out of a possible 140.14x)
http://forum.accurateshooter.com/index.php?topic=3859845.30

Looking at past ladder tests the VELOCITY DECREASE IS 200 fps or so.

 

[dkhunt14]

I don't believe the velocity loss was from barrel but came from the throat moving ahead and giving more case capacity. I know a good 1000 yard BR shooter that thought he could make his gun better (300 WSM) by throating it out. I believe he throated it out .050. He found it took almost 2 grains of powder to get it back to the node where it shot good. Matt

 

[fgregorio]

I don't believe the velocity loss was from barrel but came from the throat moving ahead and giving more case capacity. I know a good 1000 yard BR shooter that thought he could make his gun better (300 WSM) by throating it out. I believe he throated it out .050. He found it took almost 2 grains of powder to get it back to the node where it shot good. Matt

I agree. And your observation stacks up with mine. More gas would overtake the projectile inside the bore but not enough to assure a loss in velocity. Indeed I am actually missing parts of the lands etc in the first 20 inches of that barrel.

 

[chkunz]

I have. Although I've changed projectiles and loads over time, I can compare ladder tests as far as I can remember throughout the life of the barrel.
On my 30 inch .308 True Flite barrel with a life of 11200 rounds at this stage these were the loads for a 2975 fps node from new to now:
Projectile: Optimus HBC coated with Boron Nitride
Cases: Winchester
Powder: Varget
Primer CCI BR2 Large Rifle
Jump: 15thou
Load when new 45.4 gr
Muzzle Velocity: 2975 fps

Load now at 11,200 rds: 47.6 gr
Muzzle Velocity: 2975 fps


Lands moved forward 60 thou and now jump is still 15 thou by increasing OAL by the 60 thou difference.

At 7,500 rds or so I "treated" the first 20 inches of the barrel with abrasives in order to smooth out the "crocodile skin" throat effect. The barrel did regain some of its past accuracy. I have repeated the procedure time and again.
Last scores at 660 yards: 100.7x (out of a possible 100.10x) and 140. 8x (out of a possible 140.14x)
http://forum.accurateshooter.com/index.php?topic=3859845.30

Looking at past ladder tests the VELOCITY DECREASE IS 200 fps or so.

Thanks for the very detailed response. There is a lot more here than a simple answer to my question, the barrel life and accuracy results are truly amazing! Thanks again for the response.