sudden velocity increase mystery

[Erik Cortina]

You don't get higher velocities with less pressure. Pressure is what get's the bullet moving!

Having said that, what is your accuracy like? If it's still accurate, then just order another turret and go, if not, lower your powder charge and get back to the velocity you were before, and there you go.

As for why, I believe that jamming more into the lands will create more pressure, therefore more velocity. One barrel has 800 rounds, which has a longer throat (erosion), therefore less speed than the one with 200 rounds, which has a shorter throat.

But it could very well be Aliens! ;D

 

[people]

Joe Zullo many of us do not clean untill accuracy goes. I have a 223 I use for PD and I never clean the tube any more. I will clean the action but that is it. My service rifle will do 300 to 400rds before accuracy goes. My bolt 308 it is many many I do not remember any more. So I do not clean them until accuracy goes. Now my Kimber 10mm I get about 50 shots or so before accuracy is gone to the point I have to clean. I can see it starting to drop around the 20rd mark. When it is clean and I do my part I can shoot one inch groups at 25yds. Granted that is when I do my part. Most of the time they are around 1.5 to 2.5 inches. At 50rds I am lucky to shoot 6” groups.

 

[camac]

Joe Zullo many of us do not clean untill accuracy goes. I have a 223 I use for PD and I never clean the tube any more. I will clean the action but that is it. My service rifle will do 300 to 400rds before accuracy goes. My bolt 308 it is many many I do not remember any more. So I do not clean them until accuracy goes. Now my Kimber 10mm I get about 50 shots or so before accuracy is gone to the point I have to clean. I can see it starting to drop around the 20rd mark. When it is clean and I do my part I can shoot one inch groups at 25yds. Granted that is when I do my part. Most of the time they are around 1.5 to 2.5 inches. At 50rds I am lucky to shoot 6” groups.

This is an interesting topic in itself and no doubt we would get responses from both sides of the fence and some "sitters as well. I personally clean often and believe in the barrel burning calibers that you will extend barrel life by doing so. By the time accuracy goes, pressure is already up and it is hard to get all the fouling out as it is really built up and ground in

 

[juliomorris]

Joe how often i clean depends on he gun and when the accuracy starts to drop of. That was a new rifle and i hadn't developed a cleaning routine for it. I now know i need to clean after about 50 rounds because of the velocity/pressure not because of the accuracy it was actually grouping a little tighter.

 

[zullo74]

Thanks for the reply Julio. I shoot F-class and a typical match for me is 60 rounds for record and about 10 rounds for sighters. I clean after each match. It normally takes my gun about two or three rounds to settle back in. BTW, it's a 6mmBR . I use the same routine when I shoot .308 Win. Every 500 rounds or so I wash out the copper fouling with Sweet's 7.62 and use a brush on the throat to clean out the carbon ring.

 

[camac]

You don't get higher velocities with less pressure. Pressure is what get's the bullet moving!

Having said that, what is your accuracy like? If it's still accurate, then just order another turret and go, if not, lower your powder charge and get back to the velocity you were before, and there you go.

As for why, I believe that jamming more into the lands will create more pressure, therefore more velocity. One barrel has 800 rounds, which has a longer throat (erosion), therefore less speed than the one with 200 rounds, which has a shorter throat.

But it could very well be Aliens! ;D

You are quite right Erik but it is pressure over length of time that gets velocity. A high peak pressure but then low over the rest can have a slightly lower velocity vs high peak pressure (such as incorrect seating depth). In load development I think I often see (by changing seating depth and then building load again) I sometimes get a higher velocity for same "peak" pressure. I think this is because the load initiates better for a smoother pressure curve. Those of you with quickload might be able to run a few quick comparisons. I am definately not sure on this and with no pressure testing equipment am going off pretty rough indicators.

Either way though the big consensus of opinion are on seating depth or barrel cleaning - both easy to fix and try - would love to hear the results.......

 

[constructor]

Not sure about less pressure but, open a new lb of powder and shoot your normal charge for vel. leave the powder container open for a week, load the same charge wt and test the vel again.
I see a 100fps difference in dry and wet powder often but that doesn't explain the difference in the 2 rifles.

 

[rogn]

There is some suggestion mentioned her at times that when a barrel is broken in there is often a velocity increase that occurs at the 150-250 round count. No pressure changes mentioned, just an increase in velocity.

Some barrels don't shoot until they have fired several rounds. I had one 6x44mmBR barrel by a well respected manufacturer that would not begin to shoot/group until it had fired about 15 or more rounds thru a cleaned barrel. Clean gave 6" groups at 600 yd but the groups would shrink to a reasonably consistent 1.5" after several fouling shots. It seemed to maintain that level up to 60 rounds. Never went beyond the 60. With todays premium reading components, I simply retired it.

 

[338 dude]

I don't think that is it, because I have another gun that uses the exact same round. I use the ammo in either gun, as they were both built with the same reamer. Both are loaded long, and seat the bullet when the action is closed. One has 800 rounds thru it and this one has 200. The one with 800 had an increase of 8 fps, which I attributted to the higher temps.
Thanks for the input...

Every barrel is an individual with different results many things could attribute to this I chalk it up to maybe your barrel was not 100% broke in at only 200 rounds but it also could be your cleaning regimen carbon ring environmental’s or many things

 

[joshb]

“The only difference is I annealed it before this firing.”
A change in your process resulted in a different outcome. Hmmm! Go figure?

 

[Mad_Charlie]

Those 11 year old posts sure do sneak up on a fella, I wonder how OP made out.