MV increases with every shot

[desertbull]

What can cause MV to increase 15-20 FPS after each shot? I have never had this problem with H1000 before.

New 300 WM

28" Criterion Barrel

212 ELD-X
77.5 grains H1000

cold bore shot 2895 FPS
2nd shot 2923 FPS
3rd shot 2975 FPS
4th shot 3003 FPS

2-3 minutes between shots
75 degs F

 

[Trnelson]

What equipment are you using to record your velocity? Optical chronographs can show a spread within your posted numbers with changes in light.

 

[Clucknmoan]

What can cause MV to increase 15-20 FPS after each shot? I have never had this problem with H1000 before.

New 300 WM

28" Criterion Barrel

212 ELD-X
77.5 grains H1000

cold bore shot 2895 FPS
2nd shot 2923 FPS
3rd shot 2975 FPS
4th shot 3003 FPS

2-3 minutes between shots
75 degs F

Is it showing increasing pressure signs as velocity increases?

 

[desertbull]

What equipment are you using to record your velocity? Optical chronographs can show a spread within your posted numbers with changes in light.

Plain Jane Chrony but its never given me these type of readings before and there was not a cloud in the sky.

The readings correspond with a vertical string on the target, so the actual numbers might not be dead on acurate but the increase in MV seems to be legit. I also shot my 7RM and it did not do this.

 

[desertbull]

Is it showing increasing pressure signs as velocity increases?

No.

Obviously there has to increasing pressure to increase velocity but there are no danger signs on the brass or with bolt lift.

Im just puzzeled that it would do this with H1000. Maybe I got a bad bottle. I have had it for a year or so and just opened it, but its been stored indoors in my closet at 77-79 degrees.

I do have verticle stringing (1/4"-3/8") per shot on the target at 200 yards also.

 

[Clucknmoan]

How many rounds down the barrel?

 

[Barrelnut]

Was this with a squeaky clean barrel? On some of my rifles, once cleaned, the velocity will get faster and faster for 6 or so shots. IMO it is the barrel getting fouled and creating a better pressure seal with each shot. Once I get to 6 or so it will level out. That's when I start doing my ES/SD testing.

 

[desertbull]

110 rounds

 

[desertbull]

Was this with a squeaky clean barrel? On some of my rifles, once cleaned, the velocity will get faster and faster for 6 or so shots. IMO it is the barrel getting fouled and creating a better pressure seal with each shot. Once I get to 6 or so it will level out. That's when I start doing my ES/SD testing.

That crossed my mind too. Seeing as that it is a new barrel I am hoping it is just not settled in yet.

Barrel was not squeaky clean but I did use some foaming bore cleaner and a few patches.

 

[Clucknmoan]

^^ Thats what I was wondering. Hopefully theres enough down the barrel to let it foul.

 

[LoneTraveler]

This is interesting. The chronograph is telling you what is happening.
Now the hunt to find what is causing it.
Have you tried shooting one shot, Clean the barrel. Shoot one shot and clean for a series of 5 shots. See if it will shoot the same FPS from a clean bore.
The barrel may be collecting bullet material, or collecting powder residue and the change is starting the velocity and pressure change upward.

I ran into a similar incident with Win. 748 powder in a new factory 223 Rem. 700 Rem.
After 1 shot a Kano Kroil wet patch and a brown residue covered the patch where the jag held the patch in contact with the bore. Did not have my chronie with me at the range that day.
Good Luck in finding the cause and a cure for this problem.

 

[Rich Coyle]

You mentioned, "There was not a cloud in the sky." Were the rounds in the sun?

 

[blinderthanascope]

sounds like they set in the sun and heated up as you was shooting, 3min between shoots rise in velocity, maybe yes no try it again and keep the rounds cover or in the shade, I was shooting 4320 in my dasher with what I thought was a good load, shot some at 45 deg then some at 75 got sticky bolt ejector marks primers flat, you know the story

 

[Bullet bumper]

I am leaning towards barrelnuts advice due to the steady advance . However sometimes we find that a few things are contributing to variations but they are minor things that are hard to pin down
If it was a sunny day and the ground light in color reflection can cause chrony errors .
Try a dark blanket or tarp under the chrony .
Also if you were watching wind flags to shoot off then the round can be in the chamber heating up by varying amounts of time before the shot is taken . Try to have the bolt open will waiting for the right flag condition and close and chamber when you see the condition appearing on the flags .
Others have covered other forms of heating .
Also H1000 is not immune to heat adding pressure just better than some others .