.300WM a "heat leaning" group?

[PPP MMM]

First two-three shots and all is perfect, but as soon as the barrel heats up there is a vertical string and then it starts to lean left and stops between 4 and 10 o'clock.
Three different powders, two different primers and two different bullets. The same pattern invariably appears. The only difference is the size of the individual groups and the velocity.
I'm not an expert on this, but it looks to me like some kind of tension in the steel of the barrrel. The barrel is a button rifled CM 26"/RH10"/19MM(.75") @muzzle, fully floated right from the glass bedded receiver with a 2.5MM (0.1") gap each side.

What one can do? Is there a remedy, or to throw away the barrel?

Thanks.

Shoot better
Peter

 

[Charles E]

I don't know of a for-certain cure, but if the manufacturer agrees & is willing to do it, it might be worth another stress relief. There have been barrels that had thermal characteristics where this solved the problem, and I imagine ones where it didn't; those tend not to get reported.

 

[Danny Brooks]

I'm curious about...

... the load that you are shooting to get these results. What bullet, powders, cases and so on. What velocity are they leaving the barrel and is this a Win Mag or a Weatherby?

Danny

 

[PPP MMM]

Danny

.300Win.M.- Some loads are very hot indeed.
Fed.215-IMR 4350-180SPBT/3203fps.
Fed.215-IMR 4831-180SPBT/3060fps
Fed.210-IMR 4350-180SPBT3030fps
Fed.215-H1000 -200SPBT/2970fps

First 2-3 shots into the center 20-30MM/100M, then the next 5-6 rounds would rise in a vertical string 35-40MM high and then the next 5-8 rounds would start to go left to 10 o'clock and made a string of some another 25-30MM long facing between 10 and 4 o'clock.

So a group that starts at 20-30MM/100M for three shots eventually ends up at nearly 100MM/100M for 15 shots. Let the barrel to cool for an hour and the same pattern will happen again.
An absolute accuracy isn't that important as it's a throw around hunting rifle and its very unlikely to shoot more than 4-5 rounds while pig hunting, but it's frustrating just knowing what it's going to happen if more consecutive shots will ever to be fired.

Shoot better
Peter

 

[jerryhm]

I've seen this happen before with a 300 win mag, it was caused by a bedding problem. Try a "stress free" rebedding of the rifle.

 

[msalm]

I had the exact problem in one of my dad's rifles. It was a Win 70 Featherweight in 7mm-08. I bedded the stock, re-crowned, and free-floated the barrel...it got MUCH worse at that point as the barrel was more free to walk while heating up. I dropped it off at Badger Cryogenics in Baraboo and a week later the rifle was shooting strings of 5 and 10 shot into 1 1/2" at 100 yards. Before that treatment it would shoot maybe 3 rounds into the group and then walk up and to the right a full 6-7 inches. I believe those barrels are hammer forged and have more tendency to have stress, but I'd bet that's your barrels' problem too...stress.

Cryo the barrel and your problem will disappear (IMO anyway!).

 

[Dog's Elvis]

I'm not sure why you need more than 2-3 shots from a hunting rifle, but then I don't know what you're shooting at. Fifteeen round groups from a hunting rifle suggests - to me - that you have too much time and money on yur hands (and makes me jealous, I suppose, but I'd use the time and money differently). I'd not worry about this unless I was trying to make a long range gun out of it, but if that's the case I would shoot different bullets, among other things.

 

[PPP MMM]

Gog's Elvis

Ha.ha,,,,,,There is never enough money, women, sex, rifles and time, but living in the "sticks" makes a shooting life just that little bit more interesting. If one hunts mobs of pigs on open plains in a good season a fifteen shot group is OK, but sometimes a tight group of thirty shots would be even better.

Shoot better
Peter

 

[PPP MMM]

Problem solved-and barrel lapped

it might be worth another stress relief. There have been barrels that had thermal characteristics where this solved the problem, and I imagine ones where it didn't; those tend not to get reported.

,,,,,,,,,,,,,,,,,,,,

I got the barrel back after it was double stress relieved at 600*C for 2hours each time and the result is absolutely amazing.

I don't know why, but for some unexplicable reason I've decided to lap the barrel in my lapping jig that I've made some 15 years ago, but until now I've never used it.
I won't go to the too many details of my "lapping jig" at it always upsets some. The only thing is the entire lapping is done vertically and the stroke is udjusted on the jig to stop the teflon slide,( 2MM exit at the muzzle and 8MM at the throat) uses a foam rubber to dump any rod vibrations and the rod is "guided" by fired case with the head bored out and hold in the chamber by an offset M8 screw in a barrel extension theaded to the barrel that itself has a rod guide with clearance of 0.1MM made of teflon. The barrel extension has a 30x30MM long slot milled in as an oil adding, foam holding and observing window.
The jig makes everything perfectly lined up in a V and every stroke is exacty as the next stroke. After the tight spots are removed the entire stroke can be done in the same speed and without upsetting the lap.
Every lap was casted individually after the previous lap was loose and finish. 600 grit that's added every 20 strokes, no indexing and just honning oil (as I had nothing else here). Last 40 strokes was done with the same lap and grit and oil added every 10 strokes. All up 4 laps and 160 pulls.

It may be different to what your are doing but it worked beyond my expectations.

The result 178A-Max. 7-12MM/100M/3070fps for three five shot groups, with 23-32MM/100M for three ten shot groups. Not bad for a 5Kg throw around hunting rifle.
Now I may have to start to worry about the damn thing.

Shoot better
Peter

 

[Lynn]

Pppmmm

Peter
It looks like you did three things but never said which one cured the problem.

You had the barrel heat treated not Cryo-ed.

You changed the bullets and load.

You lapped the barrel.

Which cured the problem?
Lynn

 

[PPP MMM]

Lynn - Most likely the

Peter
It looks like you did three things but never said which one cured the problem.

You had the barrel heat treated not Cryo-ed.

You changed the bullets and load.

You lapped the barrel.

Which cured the problem?
Lynn

,,,,,,,,,,,,,,,,

Double stress relieve. As the barrel now stopped "walking" altogether with any load tested.

The cold barrel was accurate (for my needs) to start with, but very sensitive to the temperature and after only 3 shots it would start "walking" away, but in unique and somewhat "predictable" way.

Because the "walking" would take virtually the same pattern with any load I would be incline to say, that there was some steel stress involved in this and the double stress relieve was the cure to the "walking problem". However, it would be hard to say, that a single stress relieve wouldn't be as just as effective.

The barrel lapping? The barrel had more than 250 rounds through it and it was probably "broken in" already as it had only two extremely fine "tight" spots. The first lap even with the 600 grit remove those "tight" spots very quickly.
I don't have a borescope so I have no idea what the bore looks like, but I know for sure, that every stroke with the lap and the rod guided all the way in the jig was exactly the same and lapping in the vertical position would distribute the oil/loose grit more evenly than a horizontal lapping would.

The load?, just lucky I guess. I don't compete, so I don't load for super accuracy and 20MM/100M is all I'll ever need. I don't trickle and I only use a RCBS powder thrower with my own designed insert that gives me less than 0.2gr maximum spread measure with any, even the corsest powders.

Shoot better
Peter