Barrel heat causes POI to walk

Snav · Apr 17, 2018

I have a Rem 700 mountain rifle in 280 rem that has an issue I've ignored for a long time. When I shoot from the bench (summer), if I shoot a five shot group at normal pace 10-12s it walks right up towards 2 o'clock. However if I let the barrel cool with the bolt open for 45-60s I can cut cloverleafs. I've never worried about it as the cold barrel shot is where I need it and in the winter it probably(untested) doesn't move so much.

If I start poking at it to find the problem where is the place to start?

Bountied · Apr 17, 2018

Snav said:
I have a Rem 700 mountain rifle in 280 rem that has an issue I've ignored for a long time. When I shoot from the bench (summer), if I shoot a five shot group at normal pace 10-12s it walks right up towards 2 o'clock. However if I let the barrel cool with the bolt open for 45-60s I can cut cloverleafs. I've never worried about it as the cold barrel shot is where I need it and in the winter it probably(untested) doesn't move so much.

If I start poking at it to find the problem where is the place to start?

Your barrel profile. Skinnier barrels will shift when hot.

TheOriginalMexicanBob · Apr 17, 2018

Does it have a lightweight barrel? If so, that's the issue...it can't get rid of heat fast enough between fast follow-up shots. Lightweight barrels are for easy carry and taking one shot from a cold barrel. A heavier and/or a fluted barrel should cure the walking group problem but at the expense of more weight to carry.

Some rifles are simply more prone to it than others...looks like you got one on the more prone end of the spectrum.

iH8DemLibz · Apr 17, 2018

When it comes to hunting rifles, the only shot that matters is the first shot.

wilcam47 · Apr 17, 2018

https://www.300below.com/firearms-cryo-barrel/

Biggfoot44 · Apr 17, 2018

The simple answer is don't shoot quickly. Not snarky, will be fine for hunting that way .

Plan B is Welcome to the world of Adventures in Bedding .

Glass bed the action, and +/- 3 inches in front of action will * Probably * cure you issues .Almost certainly stop the walking . Probably more forgiving of different loads .

John from MD · Apr 17, 2018

Check the barrel to see if it is free floated or not. If it isn't, try free floating the barrel.

Snav · Apr 17, 2018

Biggfoot44 said:
The simple answer is don't shoot quickly. Not snarky, will be fine for hunting that way .

Plan B is Welcome to the world of Adventures in Bedding .

Glass bed the action, and +/- 3 inches in front of action will * Probably * cure you issues .Almost certainly stop the walking . Probably more forgiving of different loads .

That's how I've been using it, hence the lack of moving it up priority list.

d33rhunt3r · Apr 18, 2018

What Biggfoot suggested is what I was doing with my Ruger Hawkeye. As the barrel heated, the POI was shifting significantly. I started to wait about 30 minutes between shots and was able to get it zeroed that way. Eventually, instead of going through the bedding and such, I elected to trade mine in for a better option.

Magnumite · Apr 18, 2018

Is the second shot significantly away from the first shot?

Snav · Apr 27, 2018

No, Walks about 2" towards 2 O'clock in a five shot string.

John from MD · Apr 27, 2018

Take a piece of leather or rubber about 1/8 thick about 1 inch long by 3/8 to 1/2 inch wide and place it under the barrel at the forward part of the stock and try it. Your elevation will change some but, if it stops the walking, you can adjust the elevation out with the scope.

GunBum · Apr 28, 2018

What John from MD said...

I have a Remington 700 Mountain Rifle in 7-08 that did the same thing. Free floating had a bad effect on accuracy. I guess the skinny barrel didn’t like hanging unsupported. The fix that worked was to add a pressure point at the front end of the stock.

outrider58 · Apr 28, 2018

Anybody try a harmonics dampener? Like thy he ones the ast Simms makes?

John from MD · Apr 28, 2018

outrider58 said:
Anybody try a harmonics dampener? Like thy he ones the ast Simms makes?

Sometimes they work but not too many people like the aesthetics.

Blacksmith101 · Apr 28, 2018

Some links to get you started, there are lots more to read:

Barrel Harmonics
http://www.varmintal.com/amode.htm

Heat Induced Barrel Movement
http://www.stocks-rifle.com/barrel-movement.htm

Barrel tuners
http://www.stocks-rifle.com/harmonics.htm

http://www.varmintal.com/alite.htm

sxs · Apr 28, 2018

Snav said:
No, Walks about 2" towards 2 O'clock in a five shot string.

Sounds pretty common for a light barreled rifle. Floating may reduce stringing a bit or change the stringing direction somewhat. The real solution, as intimated by others, is to use a firearm with a heavier barrel. My 700 in 30.06 gets sighted in with much slower shooting rate (1 or 2 minutes between shots) and shoots around an inch or inch and a half at 100 yds using my handloads...about 2 - 2 1/2" if I use factory Core Locked (my go to factory load). No obvious stringing when shooting a 5 shot group at this rate of fire. My rifle is glass bedded with the barrel floated. FYI, first shot from a clean barrel often looks like a 2 to 3" flier compared to subsequent shots from a fouled barrel. I always discount the first couple shots when doing final sight in for deer hunting and leave the barrel fouled until after hunting season for just that reason unless I end up hunting in the rain or something. When done for the year, I do a thorough cleaning.

I also have a Rem 700 Varmint in .223 also glass bedded an floated. I get consistent groups under 1". Never noticed stringing in this firearm, but again, I don't fire it very quickly either. The Varmint barrel is a heavy, but not bull, barrel.

Doco Overboard · Apr 28, 2018

I would start looking at bolt lug contact surfaces. You can have receiver locking surfaces that are square to the bolt lugs but one of the bolt lugs are slightly longer than the other.
When the receiver begins to warm, the contact surfaces begin to engage each other differently. Also, inconsistent contact at the face of the receiver will do the same thing.
A wood stock that is susceptible to swings in moisture content can have a profound effect on consistency too. Thats why plastic stocks are the go to for manufactures these days. Cheap and reliable.
Properly sealing a wood stock in the barrel channel and receiver mortise were the first steps taken to improve bedding. If it's been wet a few times it may start to act up by wanting to change shape a little bit as the entire assembly warms. Even just by taking it outside and being in the sun a little bit can have an effect.
Sounds to me you have just a few minor details that are not working well together collectively and once you know the cause you can address one detail at a time.

Bountied · Apr 30, 2018

outrider58 said:
Anybody try a harmonics dampener? Like thy he ones the ast Simms makes?

I have a RAS tuner and a Harrell tuner. The RAS is on a AR build and looks like a brake. The Harrell's tuner is on a 6.5CM that I have not tuned yet.

With the RAS tuner I got much improved groups about 1/2" MOA down from 2-4". I tried different brakes/muzzle devices until I found out about tuners and they really work. As I was tuning it per instructions you can see the groups open and close with each successive turn of the tuner. I shot a 1" group at 200yds with Fiocchi 77gr ammo.

lazarus · May 8, 2018

Resurrecting a little. Floating, glass bedding, dampers, etc are all ways to improve things. The biggest issue is that barrels aren’t perfect in their metallurgy. So when they heat up or cool down the metal along the length expands at fractionally different rates. Now, if you are lucky, it doesn’t affect POI much. But in most cases with a lightweight barrel it will shift it an inch or two no matter what you do unless you’ve gotten a specially stress relieved Barrel (I think faxon are among them now, but at some $$).

My Sako Forester .308 can manage holes touching 3 shot groups at 100yds, but then the barrel heats up and it walks the shots an inch or so out. I think also to the 2 o’clock. I just deal. It’s a family heirloom (ish) and frick it, it’ll shoot sub MOA with several different factory loads all day long. So long as you are only shooting a round every 5-10 minutes. Or no more than 3 rounds rapid. If you just want it hammer stuff down range it opens up to about a 1.5MOA rifle with the right ammo. Also perfectly acceptable.

My 6.5 grendel with a fluted heavy barrel which I just got back to the range a 2nd time actually has better repeatable accuracy as I can hammer 20 rounds out in 5 shot groups at 1.25 MOA in the course of about a minute of shooting and still keep going. But it to if I go real slow with the right ammo seems to be about to manage sub MOA...but only JUST sub MOA.

Barrel heat causes POI to walk

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