Vertical stringing as barrel heats up

M

misterE

New member
So, I finally found a Remington 700 BDL in 308 and got out to shoot it a little today. Once I got on paper, i would shoot 4 or 5 shot groups pretty rapidly, say in under a minute and a half. Noticed that first shot or 2 would be at poa, then they would jump up 3/4 to 1 inch on shots 3,4,5. Now I know this is perfectly reasonable from a sporter weight barrel and does not bother me at all, I was just wondering if free floating the barrel or bedding or both would eliminate some of this. I know that its unreasonable to expect poi not to shift as a thin barrel heats up, but i was just gonna get yalls opinion on what might help a little bit.

Here is some pictures of my groups. In the 6 shot group, i shot 5, walked down to the target and walked back and shot the 6th.
 

Attachments

  • 6groupgameking.JPG
    6groupgameking.JPG
    80.2 KB · Views: 188
  • 4groupfusion.JPG
    4groupfusion.JPG
    95.5 KB · Views: 166
Also shot my best 5 shot group ever at 100 yards today with this rifle! See the thread "why no rem 700 308 in walnut" for pics. So, I'm not at all thinking I have to do something to the gun, just wondering.

Thanks
 
The first thing to do is free float the barrel and bed the action.

The bedding in my 6.5 Sweded M700 was just awful, the barrel touched the sides of the stock in the barrel channel and there was a bedding point in the forend. Clearing that out brought round groups.

But, I have a M96 Swede that I have done all the above and nothing keeps the barrel from walking as it heats up.

If it still walks after bedding and free floating, its the barrel.
 
I've had several rifles which did that vertical-string thing. The usual fix was much like Slamfire's comment. I generally only free-floated the forearm and inserted a shim at the front of the forearm. Only thick enough that it took about a five-pound pull to separate the barrel and forearm to allow insertion.

The most egregious case was my little Sako Forester .243 carbine with a Mannlicher stock. Five shots had each shot one inch above the previous. I found that the Mannlicher stock was a two-piece deal. I removed the barrel band and junked the front piece of wood. Trimmed the front of the remaining forearm. Installed the shim.

3/4 MOA, very reliably thereafter. Not uncommon to put three behind a dime.

No real reason for wild-eyed dispersion in a group from a sporter, if it's properly tweaked and tailored handloads are used. Sorry, but I pretty much take MOA or better for granted in my sporters--and mostly better.
 
I've got a Savage Model 10 in .243 that strings vertically as the barrel heats. It's a very accurate rifle when I take my time, but if I start pouring them downrange, the barrel will get hot and the shots will start walking up the paper. The rifle is free-floated and pillar bedded, but not glass bedded. As it's a hunting rifle and not uncommon for me to only shoot three rounds through it for a whole hunting season, I don't worry about it much. I've got it sighted for the cold bore shot. The critters don't seem to know that it will string vertically.

One interesting thing, though. One summer I wanted to see if different ammo would help it act right, and I bought some factory ammo, and handloaded a bunch of different loads and bullets from 75 to 105 grain. Probably a total of 20 different loads. Later I made a composite target and it shot everything, EVERYTHING into a three-inch group at 100 yards.
 
Thanks for the replies guys. I have never free floated or bedded a rifle, but this is such a fine rifle in my opinion it deserves it:). Also, the trigger has some terrible creep. I'm looking into getting a timney and installing it. Still hard to believe it shot that good! Shot a 5 shot group into 1/2 inch with fgmm. Got the pictures on another thread, can't figure out why I can't post a link to it. Can't wait to see what it does free floated and bedded. I'll be researching the forum for advice on those items but any pointers in advance would be greatly appreciated.

Think I figured it out.

http://thefiringline.com/forums/attachment.php?attachmentid=85696&d=1357160605
http://thefiringline.com/forums/attachment.php?attachmentid=85698&d=1357160605
http://thefiringline.com/forums/attachment.php?attachmentid=85697&d=1357160605
 
big al hunter. . .

I caution folks believing the epoxy bedding instructions and information on www.ballisticstudies.com being good ones. They fly in the face of the track record of match rifle receiver bedding that's been proved best for decades. Examples. . . .

A pad under the barrel chamber for an inch or so is nothing more than adding a bit of fore end contact to the barrel. As the barrel heats up, it'll press harder against the bedding under the chamber and vertical shot stringing will happen. Follow the benchresters way and have no bedding touching the barrel whatsoever.

That part about square bottomed actions such as the Win. 70 needing relief on their sides. . . If that were true, then why were Win. 70 actions full contact bedded without any clearance able to hold zero much better and make barreled actions shoot more accurate than any totally round receiver that twisted out of good contact in a few hundred round with bullets heavier than 160 grains over at least 45 grains of powder?

misterE. . . .

Barrel length and weight has nothing to do with vertical shot stringing. A given barrel whips the same amount and the same frequency regardless of its temperature; barrel steel's rigidity doesn't change unless it starts to melt at much higher temperatures than they'll be shot at. And a light weight, 2.1 pound, 22 inch barrel's just as stiff as a 4.4 pound, 26 inch, medium heavy barrel.

Barrels change point of impact going from cold to hot because they bend. And they bend because they're not stress relieved correctly after rifling or they're fit to a receiver that's not got a squared up face and there's hard contact at one point around the barrel tenon shoulder.

22 inch light weight M14NM match grade barrels shot the same ammo just as accurate as 26 inch heavy match barrels in bolt guns. 20- to 30- shot strings starting with a cold barrel showed no vertical stringing whatsoever with shots fired 20 to 30 seconds apart. Those barrels got really, really hot.
 
Last edited:
My tang safety M77 RL (ultralight) with light profile barrel used to do something pretty similar. I bedded the action (only, not the chamber) and floated the barrel. That corrected the problem. I think it is worth a try. Best of luck and do let us know if you decide to try something similar and how it works out for you.
 
Bart - so in your opinion, bedding and free floating will do nothing to help vertical stringing? Just trying to make sue I understand you correctly because I respect your opinion.

Thanks everyone again for the replies. I think Bart is saying that the barrel is going to bend as it heats up and change poi no matter what. However, won't bedding and free floating eliminate other factors? Such as barrel harmonics issues? Maybe the receiver is moving in the stock? I ask because as I've stated I have no experience with bedding or free floating.
 
misterE, full contact bedding just the receiver does a lot to eliminate vertical shot stringing. Then squaring up the receiver's bolt face will typically eliminate the rest of it. This assumes the barrel's stress relieved properly. Just don't have any bedding touch the barrel.

Long before epoxy bedding was available, good stockmakers would cut out the wood to have a near perfect fit to the receiver, but the barrels were still free floating. With the stock screws torqued to the same setting each time the rifle was used, there was no shot stringing in any direction. Barreled actions so fit to the stock were the best there was for even the most accurate match rifles until the 1950's when epoxies were available.

To see the improvement, be sure to test the rifle's accuracy properly. A popular method is to shoot some few-shot groups with a given rifle-ammo-shooter system then pick the smallest one to base the accuracy on. That's a bad idea 'cause the smallest groups typically happen when all the variables cancel each other out. The biggest group happens when all the variables add up in the same direction. Best accuracy happens when all the variables are as small as possible, so the best group to judge accuracy on is the largest one. If one shoots four 5-shot groups atop one another in one setting, the 20-shot composite will be bigger than any one single 5-shot group. And the smallest 5-shot group shows what the rifle-ammo-shooter does only 25% of the time. Rarely, if ever, are each 5-shot group's center's at the same place; they're scattered about the middle area of the 20-shot group composite.
 
Last edited:
I like my stocks pillar bedded then bedded forward of the recoil lug under the case body and most of mine are synthetic stocks. I've yet to have a gunsmith tell me they wouldn't do it some have said they had better luck not going pass the recoil lug and I've always told them if it didn't work I'd come back and pay you to take it out. Bedding just one part of the total in accuracy.

If I was build a match rifle I may do things different per what's required as to the type of match it's for so it's not a one type fits all.
 
A fully stress relieved barrel, installed in a lathe, heated up to 140 degrees Fahrenheit will droop down approx. .006" --- though a barrel --- whose bottom is insulated by the stock from heat dissipation...will rise vertically
approx. .006" at 140 degrees Fahrenheit. That should not have much effect on accuracy at 140 degrees, but if the expanded barrrel comes into contact with the stock forearm --- it will have an effect on barrel harmonics.
 
Erno86, I don't understand "though a barrel --- whose bottom is insulated by the stock from heat dissipation...will rise vertically"

Where's the heat coming from the stock insulates the barrel from?

Or do you mean a barrel that's got hot will have its bottom in the stock's fore end stay hotter and the expanding metal cause it to bend upwards?

I've never seen any of my match barrels shoot bullet higher (or lower) as they got hot. Even at 1000 yards, they hold elevation for shot impact going from ambient temperature to pretty darned hot after firing 20 to 30 shots in 15 to 25 minutes.

Whatever droop a barrel may have, cold or hot, is negated anyway as the muzzle axis whips quite a bit in the vertical plane. It's typically on its way up and close to the high point when the bullet exits; the best place for bullet exit anyway. Droop doesn't come into play as far as accuracy's concerned, in my opinion.
 
Last edited:
The other responses are probably right, but from what I have been taught verticle stringing could also be caused from breath control. If you are rapid fire in a short period of time it may be caused by you.
 
od green, vertical shot stringing caused by bad breath control's called poor shooting or bad aiming. I think the thread's about holding the rifle still and shots string vertically; typically more with each subsequent shot.
 
Your right, just thinking ,he walked 200 yrds and shot another group and if shooting five or six shot groups say within 1 to 1 1/2 minutes sure the barrell could heat up but later shot the best group after letting things settle down. I'm not claiming poor shooting or bad aming and the Lord know's we all have good and bad day's at the range.
 
Probably gonna get out and shoot a little tomorrow again. This time I will shoot a couple of slow groups just to see what happens. I'm starting to lean towards not doing anything with the rifle as it is plenty accurate enough to hunt with. After shooting that last group with fgmm it just amazed me how accurate this rifle is and maybe it could do even better if free floated and bedded. Last thing I want to do is mess up a good thing. Guess I'm on the fence with it.

It is a thing of beauty - pic -
http://thefiringline.com/forums/attachment.php?attachmentid=85666&d=1357082692

And it will shoot - pic-
http://thefiringline.com/forums/attachment.php?attachmentid=85696&d=1357160605
 
Sorry I keep posting pics of rifle and group, what can I say, I'm loving this rifle!

And I'm finally getting savvy on how to actually post pictures and such. Look out!
 
You must log in or register to reply here.
Back
Top