Gunsmithing Barrel Walking

[mbeavers1]

Probably know the answer to this, but hate junking a good barrel.

Have been shooting a lot the last few weeks and have really noticed my Bartlein M24 6BR barrel stringing vertically. Gun zeros perfect at 100yds and dope has been trued out to 1000 yds, hitting 600yd waterline for MV then 700, 800, 991yd waterlines for BC. Lapua brass, 29.8gr of Varget, berger 109s. Barrel has about 1500 rounds on it, but more in cooler months.

Shooting the last couple matches, several of which where smoking hot (Oklahoma last weekend was 100F+ with little shade). I am finding my barrel stringing vertically through a 10rd stage. For instance, 500 and 545yd stage with 10ea 10" circles from modified prone. Dead center on first, but shots 2-5 string perfectluly vertical and hit target hanger for final 5 shots.

Confirmed similar results out at 900 yds, approximately 0.4mil elevation change at 900yds. This was exaggerated but can be partly explained by mirage.

Plans this week are to heat test by:

1) confirm 0 at 100yds
2) rip off 10 rds at one paster, reload, 10 more at a second paster, and probably a 3rd mag at a 3rd.

Goal is to see if i get repeatable results and max vertical with a smoking hot barrel. Yes, i know this may be a bit hard on thr barrel but my barrels are consumables.

Im thinking I just got 'one of those barrels' because I have not seen this with any of my other Bartleins (not blaming by any means...sometimes you just get them). Any thoughts?

 

[Krob95]

Guy at the range this past weekend was having a similar issue with his bartlein 6.5cm barrel. But he was using imr4350. He would shoot and chamber a round and let it sit chambered for a few minutes before firing and was experiencing a vertical stringing effect. He told me about the issue while I was waiting on my rifle to cool down and I suggested his ammo was getting heat soaked and to not chamber the round until he was ready to fire and it seemed to "fix" his stringing issue.

That being said, if you’re letting that ammo sit any more than a few seconds in the chamber after round 5, it's possible it's getting heat soaked causing the powder to heat up and velocity to increase. I would run the entire test over a chrono if you have one and see if the ammo is speeding up as the chamber gets hotter.

 

[Lawnboi]

Make sure to chrono while testing if possible to eliminate the above variable

 

[mbeavers1]

Guy at the range this past weekend was having a similar issue with his bartlein 6.5cm barrel. But he was using imr4350. He would shoot and chamber a round and let it sit chambered for a few minutes before firing and was experiencing a vertical stringing effect. He told me about the issue while I was waiting on my rifle to cool down and I suggested his ammo was getting heat soaked and to not chamber the round until he was ready to fire and it seemed to "fix" his stringing issue.

That being said, if you’re letting that ammo sit any more than a few seconds in the chamber after round 5, it's possible it's getting heat soaked causing the powder to heat up and velocity to increase. I would run the entire test over a chrono if you have one and see if the ammo is speeding up as the chamber gets hotter.

Spends very little time in chamber since I only close bolt once on target.

Between stages, i was using a wet towel and a chamber chiller to get barrel back cool. It would go back to the initial POI and repeat process.

Good point on chrono though.

 

[djarecke]

Just curious: what action are you using. Have you had this problem before on this action with other barrels?

 

[FCS]

Using a mirage band on barrel?

 

[mbeavers1]

Impact. Not that i have noticed and even with this barrel I dont remember it doing this in the cooler weather. Even down here at Navasota, it hammered in June and July. I shot 97 and 98%.

I shot last Sunday at Navasota and shot at a square at 500yds and it drew a perfect vertical line across 10rds. The first time I noticed it was in New Mexico and King of Coal which was also hot...

And maybe it isnt the barrel, but i find it strange that if it was the load/seating depth that it would walk perfectly vertical. A load issue would be more likely a flier, not repeatable vertical stringing.

My guess is that this is happening because my barrel is timed to TDC by my smith (correctly so!) so the barrel is following its natual curvature. If it wasnt timed it would be going all over the place. This is what leads me to think its a barrel stress issue.

 

[mbeavers1]

Using a mirage band on barrel?

Not sure I know what a mirage band even is...so no.

 

[mbeavers1]

And for the record, I am not blaming anyone here regardless of the cause...unless its me. I have multiple other similar barrels from the smith that all hammer without this quirk. I know sometimes these things happen.

I just want to know what is causing it and if it can be solved because I hate tossing a barrel that has probably another 1500 rounds to go (though I may never regain confidence in it again )

 

[pineoak]

Guy at the range this past weekend was having a similar issue with his bartlein 6.5cm barrel. But he was using imr4350. He would shoot and chamber a round and let it sit chambered for a few minutes before firing and was experiencing a vertical stringing effect. He told me about the issue while I was waiting on my rifle to cool down and I suggested his ammo was getting heat soaked and to not chamber the round until he was ready to fire and it seemed to "fix" his stringing issue.

That being said, if you’re letting that ammo sit any more than a few seconds in the chamber after round 5, it's possible it's getting heat soaked causing the powder to heat up and velocity to increase. I would run the entire test over a chrono if you have one and see if the ammo is speeding up as the chamber gets hotter.

That has happened to me... where I took a while longer to "settle in" for a shot at the middle end of a long string (re grip rear bag, squeeze more fill to where I like it; wipe sweat, etc.)...

and I have a random shot that is higher up on the steel than the previous 7 shots, but then after they go right back onto the center/waterline.

I KNOW it wasn't me pulling the shot, and it was perfectly centered/windage.

This explains it.

I've had it happen before and wrote it off as random.

THANK YOU guys for educating the rest of us.

 

[rlsmith1]

And for the record, I am not blaming anyone here regardless of the cause...unless its me. I have multiple other similar barrels from the smith that all hammer without this quirk. I know sometimes these things happen.

I just want to know what is causing it and if it can be solved because I hate tossing a barrel that has probably another 1500 rounds to go (though I may never regain confidence in it again )

If you predator hunt don't throw it away, just stick it on a hunting rifle. If you're shooting a 10 shot string at an animal something else is wrong!

 

[pineoak]

If you predator hunt don't throw it away, just stick it on a hunting rifle. If you're shooting a 10 shot string at an animal something else is wrong!

Maybe the caliber is too small for the animal, and you're just pissing it off...

 

[Buzzinga]

Clean the barrel down to metal. Get a current "jam" setting for your bullet, and load 'em there. Let two other people shoot your rifle without telling them about vertical stringing issues and see if it still has problems.

 

[mbeavers1]

Clean the barrel down to metal. Get a current "jam" setting for your bullet, and load 'em there. Let two other people shoot your rifle without telling them about vertical stringing issues and see if it still has problems.

Cleaning can see, another very good shoot shot it and it was high.

What does jamming do here?

 

[kthomas]

How good is your rear bag technique?

I've noticed recently that I've had some vertical stringing, more so with heavier recoiling rifles. I've gotten sloppy with my rear bag technique, and really need to focus on that and make it a priority when shooting, especially with .30 cals.

The first place I look when experiencing issues is at myself, the shooter. If that doesn't address the issue, then I explore other potential causes.

 

[mbeavers1]

@kthomas Thats an interesting thought and one I would like to eliminate. Generally, I think its solid but...I have been looking for an excuse to get a more dedicated rear bag with light fill instead of my Weibad tater tot with heavy sand fill. I know the sand does require me to readjust nearly every shot.

Will say I dont have that issue with my 22 Dasher which has the exact same set up (minus the barrel).

 

[kthomas]

@kthomas Thats an interesting thought and one I would like to eliminate. Generally, I think its solid but...I have been looking for an excuse to get a more dedicated rear bag with light fill instead of my Weibad tater tot with heavy sand fill. I know the sand does require me to readjust nearly every shot.

Will say I dont have that issue with my 22 Dasher which has the exact same set up (minus the barrel).

I've noticed that this issue is exacerbated with heavier recoiling cartridges. I can get away with my sloppy rear bag technique with my 6BRA, but not so much at all with my .308 or .300 Norma. 6.5 Creedmoor can exploit this flaw as well, but not to the same extent as the .30's.

A dedicated rear bag would be a big help. I personally really like the Precision Underground bags. I don't think the barricade type bags make great rear bags, they just aren't optimized for that prupose.

 

[Krob95]

I don't know man, my heavy fill tater tot works awesome as a dedicated rear bag as well as a positional bag. I've gotten better results with it vs a traditional rear bag.

 

[kthomas]

I don't know man, my heavy fill tater tot works awesome as a dedicated rear bag as well as a positional bag. I've gotten better results with it vs a traditional rear bag.

I don't have a tater tot, but I do have a fortune cookie and mini fortune cookie.

I don't think barricade bags make great rear bags from my experience. They can certainly be made to work, but not optimal.

Perhaps @lowlight and @Enough Said can share some insight on this, as they see lots of shooters, rifles & gear and techniques.

 

[mbeavers1]

I don't have a tater tot, but I do have a fortune cookie and mini fortune cookie.

I don't think barricade bags make great rear bags from my experience. They can certainly be made to work, but not optimal.

Perhaps @lowlight and @Enough Said can share some insight on this, as they see lots of shooters, rifles & gear and techniques.

The only benefit of the tater tot or mfc is that its uber flexible for odd positions or poor bipod height selection. I can lay it flat and get my buttstock very low or flip it on end to really jack the rifle up. Fully understand thats may not be ideal, but I can usually get fully locked in and stable.

 

[kthomas]

This article may be of interest to you:

The Taylor was Here Rear Bag

Follow Sniper's Hide and pick up the latest information on all things precision rifle related. Sniper's Hide Training is for the serious tactical marksman.

www.snipershide.com

 

[mbeavers1]

This article may be of interest to you:

The Taylor was Here Rear Bag

Follow Sniper's Hide and pick up the latest information on all things precision rifle related. Sniper's Hide Training is for the serious tactical marksman.

www.snipershide.com

Nice! I do have a ColeTAC bag like that. Will give it a shot this week

 

[kthomas]

Nice! I do have a ColeTAC bag like that. Will give it a shot this week

I think that's a good plan. Just keep in mind that it may take some work to get proficient at it. I still have to be very mindful and work at it every time at the range. Its currently the biggest flaw in my fundamentals.

 

[FCS]

Mirage band attaches above barrel to redirect heat away from optical path of scope.
Definitely worth having, especially on hot and humid days that tends to exacerbate mirage effects.

Improvised rifle mirage band

If you shoot a rifle match with a long string of fire, you’ve most likely encountered a mirage caused by a hot barrel. At best, it makes shooting more difficult requiring the scope’s ma…

rifleshooter.com

I’ll dig out F-open rifle and put mirage band on it, post a picture. Might be a weekend before ai get to that.

 

[mbeavers1]

3ea 10 shot groups shot back to back (30 straight shots) with no cooling at 100 yds. Repeated with same results. Think i have my answer

 

[Krob95]

What's the answer?

 

[mbeavers1]

What's the answer?

The simplest one...the guy behind the barrel. Mechanics must have not been on point and got in my head.

1) definitely not ammo heating up. 1st 30rd group had an SD of 6 and the second had an SD of 5.

2) Wouldnt say in any of those groups that there was an upward trend with heat. Barrel was so hot after 30rds that i couldnt touch it.

 

[obx22]

I’m a rimfire nut, so take this with a grain of salt:
Mechanically speaking, I can only think of a few reasons for vertical stringing:
Ammo heating (cooking) in the chamber.
Barrel warpage possibly from irregular stress relief.
Bore dimensional change due to heat allowing slightly higher velocity (which should show on the chrony).
Bedding change in the stock from the heat, this would obviously dissipate very slowly. Also if the barrel is making any stock contact at all, then climbing is to be expected as things heat up.