Cold bore point of impact.

[palo]

I have a remington varmint rifle that will put its first shot from a cold barrel 1inch lower than the following shots.
My friend has a tikka hunting rifle that will put its first shot 1in high and 1in left.
This will happen with a clean and fouled barrel.
I would like to know the reason why this happens.
Would a new barrel solve the problem or is it something else ?

 

[jonbearman]

Are you certain it is free floated? Is it bedded? Is the recoil lug seated on the stock or bedded? If it is it sounds like the barrel has a stress point.Is it carbon steel or stainless? If it is carbon I would suggest cryo treatment,if the barrel has alot of rounds down it,replace it.I would try northland supply and get his remage barrel set-up.Then you dont need a smith to do the work.

 

[palo]

The barrel is fully floated in a bellandcarlson tactical stock with the alloy block, I also got it bedded. the barrel is the fluted stainless one. I changed the stock when I got the rifle so I will put the original stock back on to see if that makes any difference.

 

[Ing. Michael W. Mayerl]

The barrel is fully floated in a bellandcarlson tactical stock with the alloy block, I also got it bedded. the barrel is the fluted stainless one. I changed the stock when I got the rifle so I will put the original stock back on to see if that makes any difference.

I suggest you following:

- first make a epoxy bedding in the recoil lug area

If this doesn`t help, put on another scope and test if you have the same problem.
Also check if the scope is mounted right. I suggest to glue the scope in the rings with epoxy. At low recoil calibers you can wax the scope tube before. With epoxy you can get a 100% fit between scope and rings, metal powdered epoxy is best because it gets glas hart. It`s also possible to get a 100% tension free system that also can help.

Clean the barrel best with KG12 bigbore cleaner.


When nothing helps: change the barrel. I don`t use fluted barrels because I get too much trouble with it.

 

[Ing. Michael W. Mayerl]

I forget: also check the rest. Sometimes this could be the mistake too.
Best are bags filled with rice

And also check if the lugs have receiver contact on both sides. If not: lapping.

 

[palo]

Thanks.
I dont think its my rest or scope because if I shoot a few groups straight after the first shot they will all be fine.
If I then let the rifle sit for say 15 mins and shoot again the first shot from the now cold barrel will be 1inch low again.
The rifle calibre is 204 ruger.

 

[fdshuster]

palo: I can't, and am not claiming knowing the answer why your first shot from a cold barrel is at a different point of impact from those that follow, but I do know that when chronographing my loads the first round (cold & clean) will always display a lower velocity,usually by 50 to 60 fps. For that reason I always fire a fouling round before recording the velocities. Several of my barrels are like yours with the first round out of the group, then they are fine. With other barrels it does not seem to matter: first shot fired is in the same hole as the last. Just one of those mysteries of life, I guess, that I've come to accept, and always fire a fouling round for those barrels that require it.

 

[palo]

I was thinking about putting a custom barrel with a 1/11 twist on this rifle at a later date so I was sort of hoping someone would tell me my barrel was the problem.
I wouldnt like to put on a new barrel and still have this problem.

 

[TonyR]

Palo.
Every barrel I have does the same thing with a dirty cold bore but each of them follows a predictable pattern. I don't like to shoot a clean bore until it has had 6 or 7 fouling shots down the bore. I am told that some of the military teams rountinely fire 10 rounds before they shoot for score. As Frank said, it is just part of life, at least in long range shooting.

 

[palo]

Thanks lads.
I guess I must of been lucky with my other rifles so.

 

[whiskey08]

I was chronoing two of my guns the other day, heres what i found. One was a .223 and the other a .308.

First shot on a cold clean bore with both guns was 50-55fps slower. After 3 shots both guns settled into average velocity. I think this is a very possible reason for change in poi on cold clean barrel.

 

[fdshuster]

whiskey08: We agree on the amount of velocity loss when cold & clean. My chronographing was with a 6BRX, but I've seen the same approximate loss with other cartridges as well.

 

[whiskey08]

fdshuster

cool, always good to now im not out in left field. With the JBM caculator 50fps in a .308 and 175mk is about .2moa difference at 200 and exactly .5 moa difference at 500yds. food for thought?