Barrel Bedding: Yes or No (troubleshooting hot barrel vertical stringing)

[Das Capitolin]

Here's the situation: I have a Savage target action with 28" Criterion bull barrel. The action is fully bedded in a H-S Precision stock using Devcon Liquid Steel, and the receiver fits perfectly. Everything behind the rear action screw (tang) is free floated, along with the front of the recoil lug and barrel nut (tape). There does not appear to be any movement while cinching down the front then rear action screws.

In a second phase at the barrel nut, four inches of barrel were bedded. The first 20 shots (approx) impact as intended, but once the barrel gets heated they begin to string vertically by 2+ MOA. I suspect the long bull barrel is making rifle balance is an issue (front heavy), and there's very slight wobble in the bipod pivot, but since cold shooting is typically fine I'm most concerned that the barrel bedding is causing a problem.

So then, do you recommend bedding any portion of the barrel on a rifle that will shoot 60+ rounds in an hour? I'm troubleshooting the causes, and would appreciate any feedback.

[mattt]

A have a savage 308 with a heavy 32" and a 6.5 with a straight taper30" shoot both off bipod. No stinging.

[MongooseV8]

I have several long heavies, no barrel bedding, no vertical stringing.

[Das Capitolin]

A have a savage 308 with a heavy 32" and a 6.5 with a straight taper30" shoot both off bipod. No stinging.

I have several long heavies, no barrel bedding, no vertical stringing.

Well, I suppose this is feedback.

[dskit]

How long of a shank are you running on that barrel? I've done both (bedding and inch or 2 of the shank and not at all) in the past with Remington set up and have found no benefit to bedding the barrel shank.

Most shanks area around 2 inches, so if you are doing 4, does that mean you are bedding in the area where the barrel tapers? Maybe that's the problem because you are dealing with bedding on angles and not straight lines.

If you feel ambitious, dremmel out all but an inch or 2 of the barrel bedding and see what that gets you.

[kendog4570]

Check your forward scope mounting screw. If it contacts the barrel it can cause erratic grouping. You could also have a barrel that has internal stress that causes movement as it warms up. Having it stress relieved may help, but not readily available, and should have been done at the factory. A new barrel would be another "cure".
I have found most Savage actions have more than .003" run-out at the ring. Even though they have a floating bolt head, I square the ring, lap the lugs with special fixtures, and square the bolt face when re barreling. Check the stock bolt head face for cratering and dishing. Somewhat common on these rifles. A PTG tool steel bolt head helps here. They get a few things right and this is one of them. They still require lapping and squaring.

You could also send it back to Savage but I have heard mixed reviews on how they handle issues like yours.

[dskit]

Check this out as well.

http://www.accurateshooter.com/technical-articles/savage-action-screw-torque-tuning/

[captbilly]

stringing from heat is caused by stress

Think of the entire rifle as an assembly of springs made of materials with different coefficient of expansion. The problem with any sort of bedding is that it forces two materials with different stress/strain and coefficients of expansion to act together. The reason most target rifles are now set up to free float the barrel and even most of the action is that by doing so you allow the barrel and action (which have a single coefficient of expansion) to move freely. So long as the barrel doesn't have some built in stress, or the barrel doesn't heat unevenly, the point of impact should stay pretty much the same with subsequent shots.

There is always going to be some stress in the barrel so ideally you want to do as much shooting as possible with the barrel at a constant temperature. When I used to shoot matches we would always fire of a couple of shots to warm the barrel, then continue to fire at a constant rate to keep the barrel at that same temperature (maybe a shot every minute or two). I don't think many rifles won't string some if you fire enough rounds to get the barrel smoking hot.

[Das Capitolin]

How long of a shank are you running on that barrel? I've done both (bedding and inch or 2 of the shank and not at all) in the past with Remington set up and have found no benefit to bedding the barrel shank.

Most shanks area around 2 inches, so if you are doing 4, does that mean you are bedding in the area where the barrel tapers? Maybe that's the problem because you are dealing with bedding on angles and not straight lines.

If you feel ambitious, dremmel out all but an inch or 2 of the barrel bedding and see what that gets you.

I previously mentioned that it's a straight bull barrel, so it doesn't have any taper. But like you said, it doesn't take much to remove some or all of the barrel bedding. Do you typically suggest bedding the barrel in this situation?

Check your forward scope mounting screw. If it contacts the barrel it can cause erratic grouping. You could also have a barrel that has internal stress that causes movement as it warms up. Having it stress relieved may help, but not readily available, and should have been done at the factory. A new barrel would be another "cure".
I have found most Savage actions have more than .003" run-out at the ring. Even though they have a floating bolt head, I square the ring, lap the lugs with special fixtures, and square the bolt face when re barreling. Check the stock bolt head face for cratering and dishing. Somewhat common on these rifles. A PTG tool steel bolt head helps here. They get a few things right and this is one of them. They still require lapping and squaring.

You could also send it back to Savage but I have heard mixed reviews on how they handle issues like yours.

I use a 20-MOA rail that's been checked secure to the receiver (with loc-tite, too). All of the scope rings (Seekins) and rail are solid to the Steiner 5-25x, but I'm not ruling the scope out.
If I were having fliers or accuracy issues, I would certainly suspect some of the other items you pointed out (all good advice), but I've managed to print 5 cold shots into a 1.4" group at 330-yards with wind. The problem is when the heat comes.

Think of the entire rifle as an assembly of springs made of materials with different coefficient of expansion. The problem with any sort of bedding is that it forces two materials with different stress/strain and coefficients of expansion to act together. The reason most target rifles are now set up to free float the barrel and even most of the action is that by doing so you allow the barrel and action (which have a single coefficient of expansion) to move freely. So long as the barrel doesn't have some built in stress, or the barrel doesn't heat unevenly, the point of impact should stay pretty much the same with subsequent shots.

There is always going to be some stress in the barrel so ideally you want to do as much shooting as possible with the barrel at a constant temperature. When I used to shoot matches we would always fire of a couple of shots to warm the barrel, then continue to fire at a constant rate to keep the barrel at that same temperature (maybe a shot every minute or two). I don't think many rifles won't string some if you fire enough rounds to get the barrel smoking hot.

If I understand your post correctly, it would have been better to free-float the barrel and pillar-bed the stock? To some extent, this makes a lot of sense. As for shooting the barrel at a constant temperature, my matches and the weather don't always allow for that. I would love it if all of my shots were done with a cold/cool bore, but unfortunately it's closer to 60 rounds in an hour (hence the big thick bull barrel). Taking what you said, I could zero with a warmed barrel, and collect data for warmed/hot barrel conditions.

THANK YOU all for the feedback.

[Das Capitolin]

Check this out as well.

http://www.accurateshooter.com/techn...torque-tuning/

Good article! Thanks for sharing this.

[ar15barrels]

do you recommend bedding any portion of the barrel on a rifle that will shoot 60+ rounds in an hour?

I would recommend against that practice.

I would bet that your vertical deflection is UPWARDS.
Is that correct?

The bedding material will retain heat on the underside, while the topside of the barrel will cool through exposure to air.
This may cause the thermal deflection you are getting.

I would relieve the bedding material and make some room for air to get all the way around the barrel.

[mattt]

What Kendog said.

[LynnJr]

Take two business cards out of your wallet and put one under the front of the action and one under the rear cutting and trimming as required.
This will act as a temporary shim so you can see if too much of the barrel is bedded.
In the future if you hang a barrel of enough weight that you think the barrel needs to be bedded consider a custom action or a barrel block.
I have a 32 pound barrel on my gun and there is no stress on the action because the entire action free floats in air and the barrel is held by a block.
I see you shoot at Palomino in Reno. Say hello to Jan Saras and Robert Hoppe from Lynn if you get a chance.

[dskit]

I would recommend against that practice.

I would bet that your vertical deflection is UPWARDS.
Is that correct?

The bedding material will retain heat on the underside, while the topside of the barrel will cool through exposure to air.
This may cause the thermal deflection you are getting.

I would relieve the bedding material and make some room for air to get all the way around the barrel.

The OP also said that he did the barrel as a second phase of his bedding process. If for some reason he didn't fully torque downe the screws when it set he could be inducing some type of tension on the barrel.

2 phases of glass bedding opens up a lot of opportunities for mistakes. I know that first hand.

[kendog4570]

What Kendog said.

Thanks Shaun.

You can lead a horse to water, but you can't make him drink it.
Messing around with bedding for a rifle that does what is described, is like pouring Rislone and STP into an engine with extreme blow-by and low oil pressure and expecting it to just fix itself. Sounds good, but not likely to produce any good results.
Pretty good bet the problem lies elsewhere.