Severe elevation change?? during a string of fire.

[Jim See]

So I put together a 6xc for PRS matches. At my last shooting sesion I noticed the point of impact going up during fireing, so tonight I did a little test;

Starting from a clean barrel it printed 100y groups in the .2 range, but as the round count thru the tube grows so does the elevation. Tonight it went from a perfect 100 yard zero to 3/4 min high over 50 shots,(spread out over time so barrel heat was not an issue.) During this shooting session I would shoot at 100 dial up to 600 back to 100 ect for 3 pairs of groups alternating 100 to 600. first 100 yard group spot on, First 600 yard group was 1/4 min high, second 100 yard group was 1/4 min high, second 600 yard group was 3/4 min high, last 100 yard group 3/4 min high, last 600 yard group 1 minute high. conditions were excellent.

The gun is holding very good vertical with-in the 600 yard groups them selves. varying from 2.5" to 1.25"

I left the 600 yard dope on the gun and in the am I will shoot it again at 600.
Wondering if anyone has dealt with a barrel like this acting similar?
Fouling wise at the last cleaning with about 80 rounds on it there was a good bit of copper in the last 3" of barrel the rest looks great.

 

[Immike]

I had a heck of a time this spring with a new brux that felt rough inside and wouldn't shoot well. With help from Don Rabun we ran a few patches with Hollands witch brew several strokes (30) and after several shots it settled down and shot fine.

 

[Jim See]

I have about 250 rounds thru this one. I just got off the phone with a friend who works for the company that makes the scope I'm using. Apparently this could be an issue with my zero stop not set properly, which by the way I described it to him, I did set it wrong and that may be the issue causing me grief. I'll fix it and give it another run.

 

[Kings X]

Jim,
I would look at scope ring aligment - lap them true.
And the action bedded in too tight. I like free sides and nothing in front of the rear of the recoil lug touching. I like to see the stock fall off the barreled action.
Oh ckeck for guard screws binding also.
Hope this helps.
Richard

 

[Carbide]

Are you using a double base powder? Are you running over chronograph at the same time?

 

[Jim See]

I'm using H4350. good chrono readings.
Richard, the gun is bedded as you suggested; front and sides of lug taped for clearance, bolts have relief around pillars. The rings were not lapped but I did bed the scope itself into the ring bottoms before final instal, only because I didn't have a 34mm lapping bar. I'm going to check the zero stop issue today.

 

[tclaunch]

I shoot with someone that had this very issue. His barrel was a Broughton, it would climb as it heated up. Tim North had him send it back in to be heat treated again and the problem went away. Your barrel might have stress still present or possibly the bore is drilled off center at the muzzle and the thin side allows the thick side to take over when hot. I`m repeating things I hear from other shooters. Just things to consider and good luck!

 

[Kings X]

If I thought it was stress in the barrel - i would ship it to 300 Below for cryo.

 

[Jim See]

I had a long talk with a buddy who shoots 6x47 lapua and has many competitors shooting the same. He said he and others have seen some vertical climbing issues as the barrels heat and the rounds warm up in the chambers, (using H4350) but mostly only in 6mm cartridges. He has not seen it in his 6.5's. So by chance we both tried varget in our guns yesterday and it is looking very promising. with heating the barrel I only seen what could be interpreted as a 1/4moa change in 50 rounds starting from a clean barre. More testing to follow.l

 

[Bob Sebold]

Jim, wondering if you found out the problem yet. Saw those photo's you sent to Dad. Nice buck! I will bet money it's your scope. If you have a colimater (not sure on spelling) you can check to see if the scope tracks correctly. Nine times out of ten, my problems stem from the scope. Rita & Olaf are both sending in nightforce's cuz they drift. I had one that would not click for elevation then jump about a minute when it did move. Most frustrating thing ever, those scopes. The other thing you could do if possible is try another scope on the gun to see if it does the same thing. That said, often I get some change in impact, bullet rise, when shooting competion. I always figures that was just because things started heating up. You know I don't let the gun cool when I shoot! Only a click or two during a string. Let us know what you figure oout.

Bob

 

[Jim See]

I did have scope issues that are now being rectified but they were less severe with the varget load than the h4350 load??? go figure??