Stress induced POI shift?

[4xforfun]

A friend of mine bought a nice Rem 700 BDL and had it bedded and floated. He found a load that he likes (no idea what) that he said shot pretty consistent 3/4 MOA . He said the tube was hot when he got done zeroing it. He set his scope to zero (Zeiss), but the next week, he was 5 inches low at 100 yards..cold bore! He re zeroed his scope, but after some shooting was 5" high....right where he was the week before. He called me today, frustrated wanting some answers. Best I could do was heat induced movement due to improper stress relief. I suggested a new tube.

Could a trip to one of those shops specializing in stress relief fix the factory tube? He was fine with a new tube,,,,I wanted to give him all of the options.

Thanks,
Tod

 

[watercam]

If it is not a match rifle I do not see a need to shoot more than 3-5 rounds at a time. Let it cool between strings. Otherwise he could consider cryogenic treatment. For factory barrels I have had good luck with it. Not a miracle cure and would not completely solve his problem as no matter how stress relieved a barrel is it will shoot to a different POI when screaming hot compared to cold.

 

[Jay Christopherson]

If I read the sequence of events rights:

1. He shot a bunch of rounds, to the point where his barrel was hot, and zeroed his scope based on that.
2. Next week, he shot a cold bore shot, 5" low @ 100.
3. He re-zeroed his scope based on that, shot a few more rounds, and ended up 5" high.

If that's the case, it seems clear? Sporter barrels aren't made to go through more than a few rounds at a time. On my hunting rifles, if I shoot more than 5 rounds in a row, the barrel will be sizzling and the POI will have shifted up a bit. The first, cold bore shot, is always a bit low. Partly the reason why I always go hunting after having the fouled the barrel. It still hits low a bit, but not as much as a clean, cold barrel.

If he wants a cold-bore 'X', I'd shoot a cold bore shot, adjust my scope accordingly, and then wait for the barrel to go cold again to validate.

 

[4xforfun]

The point is....he won't even consider shooting it this way. Another point ..the POI isn't moving up or down a "bit"...it's 5 moa shift after 4 or 5 shots!!! Not one of you out there would settle for that. If you do, you are a member of the wrong fourm. ;D

Just trying to figure out if a cryro job would be worth a try, or just re bbl. At least he will know what he has when it is done with a new tube. He is not scared to spend money...he has lots. My kind of friend

As far as the wheres and whens on how to zero the gun....been there, done that.

 

[LHSmith]

Mirage from a hot barrel........read today's bulletin.....mirage, caused by heat from the ground, OR barrel will make the target appear higher than it actually is. Try using a mirage shield first to see if that solves the problem. Otherwise, best cure is an good aftermarket barrel that has been stress relieved BEFORE final lapping, preferably with a step up in contour if that will work for him. If the rifle had the typical 3-9x scope, the heat waves most likely went unnoticed.
The cryo rage came and went 15 years ago.....IMHO cryoing a factory bbl. is spending good money after bad. I believe the only provable benefit to cryoing bbls is that they are easier on the tooling.

 

[4xforfun]

Mirage from a hot barrel........read today's bulletin.....mirage, caused by heat from the ground, OR barrel will make the target appear higher than it actually is. Try using a mirage shield first to see if that solves the problem. Otherwise, best cure is an good aftermarket barrel that has been stress relieved BEFORE final lapping, preferably with a step up in contour if that will work for him. If the rifle had the typical 3-9x scope, the heat waves most likely went unnoticed.
The cryo rage came and went 15 years ago.....IMHO cryoing a factory bbl. is spending good money after bad. I believe the only provable benefit to cryoing bbls is that they are easier on the tooling.

Never considered it...BUT....,

1 Although not discussed, the shooter was stating how clear the picture was on his new Ziess. ANY heat mirage caused by a hot tube will distort the sight picture.
2 There isn't enough heat in the world to produce 5 inches of vertical at 100.

3 If there were enough heat mirage to cause 5 moa of vertical you wouldn't know it because the you would not be able to see your target in the first place because of the mirage.

4 Again, if there were, the bbl would be a little puddle of red, molten steel running off of the shooting bench.

I do agree with the whole cryro thing...I think it has it's place, but this isn't one of them. Time to order a new tube.

Donovin. I won't be shooting again till the MN 1000 state matches in mid Aug. I have a big Golf tournement this week end.

Good luck, and thanks to all for the help.

 

[Jay Christopherson]

Tod -

I've seen light barrels do some wild things when there cooking.
Huge ES spreads, huge POI changes, etc...


Donovan

Me too. I've seen a hot sporter barrel spray like a shotgun after getting hot enough. My litmus test for hunting rigs/sporters is usually "can I put 5 shots into a group I like". Anything after that on a hot sporter barrel is gravy. If I can't get the critter in 5 shots, I'm doing something wrong. I have a different set of expectations for my hunting rifles, though.

I will say that I've seen a bad bedding job (read: not stress-free) be the cause of something like this. A friend had a .270 that had a similar issue that we resolved by milling out some of the barrel channel, adding pillars, and re-bedding. When you were shooting it, you could see the barrel clearance change as it heated up (and test with some paper shims).

 

[4xforfun]

Tod -

I've seen light barrels do some wild things when there cooking.
Huge ES spreads, huge POI changes, etc...


Donovan

Me too. I've seen a hot sporter barrel spray like a shotgun after getting hot enough. My litmus test for hunting rigs/sporters is usually "can I put 5 shots into a group I like". Anything after that on a hot sporter barrel is gravy. If I can't get the critter in 5 shots, I'm doing something wrong. I have a different set of expectations for my hunting rifles, though.

I will say that I've seen a bad bedding job (read: not stress-free) be the cause of something like this. A friend had a .270 that had a similar issue that we resolved by milling out some of the barrel channel, adding pillars, and re-bedding. When you were shooting it, you could see the barrel clearance change as it heated up (and test with some paper shims).

Jay,

We had discussed the bedding and action screws in our original conversation. You are correct in saying that a bad bedding job will raise hell with groups. My thoughts were that since the whole high/low/hot/cold thing was repeatable and predictable that it wasn't the bedding or improper tightening of the action screws. I also questioned (politely, of course) his shooting ability, but the fact that almost all of the groups were 3/4 MOA groups.....it didn't matter weather it was the first or fourth group in a series, that his "bench manners" were OK.

I visited with him again last night. Since he hangs around with LR shooters, since his kids ( the kids are in their mid to late twenties) all shoot LR and like to shoot the steel targets out to 750, he is going to go with a new tube. He wants to "keep up with the Jones' ", and is falling in love with shooting...ESPECIALLY LR.

I think that a new tube is right rout to take.

Thanks,
Tod