Gunsmithing Groups moving after the barrel heats up

[km71107]

I have a 300WM that was put together by a friend. It's a 700 action, Shilen barrel, Tubb recoil lug all pillar bedded in an A4 stock with Badger M5 bottom metal. This thing has issues. Once the barrel heats up, the group will move several inches to the left. I don't know if it's the barrel or if maybe there's a bedding problem. Here's a couple of pics of before and after the barrel heats up. Any ideas?

 

[Wanderlust]

Re: Groups moving after the barrel heats up

Is that a 100m group? I hate to say it but how are your fundamentals?

Most likely, in order of likelihood:
Shooter error- trigger, breathing, eye relief/parallax, bipod loading, etc.
Action torque
Really, really bad bedding job.

I would doubt it's the barrel. But I'll let the experts expound.

 

[2156SMK]

Re: Groups moving after the barrel heats up

Is it a lightweight barrel?

Where we see wandering with heat is when a barrel's bore is not very straight and the contour is straight on the outside.
That causes the barrel to be thicker on one side.
Metal expands as it heats.
When the barrel is the same thickness on all sides, there will be minimal movement of where the barrel is pointing as it heats up.
When you have uneven wall thickness, there is more metal to expand on one side.
NOW, as the barrel heats up, it starts pointing away from the thicker side as the thicker side expands more than the thinner side.
The bullets go where the barrel points them...

 

[km71107]

Re: Groups moving after the barrel heats up

It's a heavy barrel, 1" at the muzzle. I found a place where the stock was rubbing the bolt release and in enough of a bind to make the release stick. I sanded until it cleared, that didn't fix it. I shot these groups after fixing that. It's bedded about 1" past the lug, past that it's floated. There's plenty room around the barrel, so I know it's not rubbing the barrel channel.

 

[2156SMK]

Re: Groups moving after the barrel heats up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: km71107</div><div class="ubbcode-body">It's a heavy barrel, 1" at the muzzle.</div></div>

Have a gunsmith remove the barrel, dial it in according to the bore at the chamber end and tell you how much runout the barrel has.
I bet this one has a lot.

Also, what distance were the two groups in the first post shot at and what size is the orange dot?

 

[Wanderlust]

Re: Groups moving after the barrel heats up

Looks like a 2" pastie.

 

[RobertB]

Re: Groups moving after the barrel heats up

Does it start to walk as you shoot it?

 

[km71107]

Re: Groups moving after the barrel heats up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 2156SMK</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: km71107</div><div class="ubbcode-body">It's a heavy barrel, 1" at the muzzle.</div></div>

Have a gunsmith remove the barrel, dial it in according to the bore at the chamber end and tell you how much runout the barrel has.
I bet this one has a lot.

Also, what distance were the two groups in the first post shot at and what size is the orange dot? </div></div>
They were shot at 100yds at 2" dots. I know the groups suck, I can't shoot worth a damn off of a bipod.

 

[km71107]

Re: Groups moving after the barrel heats up

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RobertB</div><div class="ubbcode-body">Does it start to walk as you shoot it? </div></div>
I haven't noticed. The next time I get a chance to shoot it, I'll try a couple of 10 or 15 shot groups and see what happens.

 

[Redman797]

Re: Groups moving after the barrel heats up

Do you have access to a bench rest? Try shooting from a bench and use bags. What kind of ammo are you shooting? just curious, not that it should make to much difference judging by your target.

Try to have someone else shoot a group on your stick and see if they can replicate the problem.

 

[BravoSector1]

Re: Groups moving after the barrel heats up

KM

Heat the rifle up...10 plus rounds. Move to a new target, plant five, again, move to a new targe, plant five. That round is producing heat, no doubt about it, but it looks like something else is at play.

I remember when I owned a 7mm Mag and .300WM...too much for me. Will put it out ther point blank period. It pushed this 155lb body aroound too much. I shoot a .50BMG today but the muzzle brake does all the work. You've got lateral stringing occuring...which is usually shooter error induced. Take your time...focus on the fundementals. You own the rifle...it doesn't own you.

Eliminate the variables and you'll find the problem. Before you go and shoot in again, blue locktite the receiver/stock bolts to spec, let them sit for 48 hours, then press. See what happens.

 

[km71107]

Re: Groups moving after the barrel heats up

I was on a bench but only had a rear bag with the bipod, I forgot my rest. I was shooting handloads with 208 Amaxs and 76gr of H1000 in Hornady brass with Federal primers. I just started trying to work up a load and this happens every time I get it hot with every load I've tried in it. I'm beginning to think I have a bad barrel. Whatever work it needs, I'll take it to Roscoe. He's local and I've heard he might know what he's doing.....

 

[DirtyRod]

Re: Groups moving after the barrel heats up

Wow. I guess I should stop complaining about mine. My 700 starts to shoot high after about 20 rounds. It's barely noticable at 100 yards but at 500 it goes from 11.25 MOA when its cold to 10.75 after 30 rounds. Fortunately it's very predictable but I went though retightening, reinstalling the scope, a second scope, etc and eventually was told that it's just the lack of stress relieving on the factory barrel but I though the good aftermarket stuff like Shilen would not have this issue. Fortunately mine will still shoot an inch or better at 100 even with the movement so I figured I would just shoot it until I wore it out and adjust for the heat in the meantime.

Definitely interested in what Roscoe has to say about it.

 

[raythemanroe]

Re: Groups moving after the barrel heats up

Video your self shooting so we can see what you maybe doing wrong if anything Do you reload? Work up different loads..Is the barrel floated?

 

[AtOne]

Re: Groups moving after the barrel heats up

May want to double check the scope rings and base for proper torque also just in case.
Sometimes its the simple things.