Barrel heat, effect on groups.

[270WSMANIC]

Ok I have a new douglas barrel on my Browning a-bolt, 24 inch 270WSM. After sighting the scope in, barrel was still a little warm and the day was fairly cool. I fired my last three rounds into 3/4 @ 100yd.
Another day this time temp in high 80's. first 3 shot about 3/4 again. Thats fine I'll take 3/4. After letting barrel cool down a bit 3 more till I had fired 3 or 4 groups. I'm going from memory now groups were something like 1in, 1 1/4in, 1 1/2, 1 1/4. I noticed that each group had 2 touching or nearly touching. Remember these 3 shot groups were fired with a cool down to warm between groups. Chorny showed 130 gr b-tips a bit over 3200 and I was 2 gr below max with mag-pro.
I usually don't look at my groups till the last shot is fired, but on my next group on another hot day; I watched the first 2 go into bout 3/8in and the third shot open to 1 1/4.
It looks like at least on hot summer days I need to shoot 2 and allow cooldown before the 3rd shot. I don't remember needing to do this with the old factory barrel??? Maybe it opened groups on hot days too and I have forgotten maybe chalked it up to me having a bad day at the bench???
I checked to make sure barrel still floated in walnut stock no problem there.
I'll be interested to see what y'alls experiences shooting groups with magnum rifles on hot days. Also wonder if some barrels are more affected by heat then others. Thanks

 

[Schwing]

Are you sure it is the first 2 that are touching and the 3rd that is off? My experience has been that my first "Fouling" shot is off and subsequent rounds hit the same POI.

I am not a big rifle shooter however so others may have more enlightened info

 

[270WSMANIC]

Yes I either shoot from a lightly fowled barrel or if barrel was cleaned fire 2 or 3 before getting serious.

 

[Bart B.]

Barrel steel expands about .000006" per inch for a 1 degree F temperature rise.

Virtually all factory receivers do not have their face squared up with the barrel tenon thread axis. So, every barrel snugged up tight in one bears hardest against the receiver at one point around the barrel shoulder. As the barrel heats up, there's more force on the barrel at that point, And that causes the barrel to bend away from that point. How much depends on how tight the fit is and how hot they get.

A simple fix is to have the receiver face squared up by taking off about .010" of metal, then putting in a .010" thick shim so the barrel clocks back in snug to maintain headspace.

Squared up receivers will shoot most any good barrel to the same point of impact over dozens of shots fired once or twice a minute; or more.

Then there's the occasional factory barrel that is not stress relieved properly. When it heats up, it will also bend. Even if fit to a squared up receiver face.

Hot barrels heat up powder, too. If a chambered round rests in a hot barrel more than 10 to 15 seconds, it'll produce more peak pressure and shoot the bullet out a little faster. Resting there for over a minute or two in a really hot barrel, it will usually produce a high shot on short range targets. And much higher at long range.

 

[270WSMANIC]

Thanks for the info, Bart B. Don't know if the guy that replaced my barrel squared the receiver or not. I guess I have a choice if I want to shoot tight groups on hot days either shoot two shot groups or fire two shots allow for cool down then fire 1 or 2 more into the same group.
It will be interesting this fall in 30-40 degree weather to again try for 3 shot groups between cool downs.
What you said about having a round chambered in a hot barrel for more then 10-15 seconds is something I hadn't thought about . I'm guessing It takes me about that long between shots. The first thing I do after the shot is chamber the next round, it would maybe be better to wait till I get settled into the bags again before closing the bolt.
Again thanks for your input.

 

[usfan]

I notice that shots get more varied as the barrel heats up. It is more apparent in semis like the ar or ak, but if i shoot a lot of shots with a bolt i see it too. If i'm sighting in AND shooting for fun, & let the barrel cool a bit before making any adjustment shots.

 

[CarJunkieLS1]

Could be any number of things that are causing that "flyer" and I wouldn't exactly call a group when it's only 3 shots.

You mentioned you shot on different days so weather is definitely a possibility also what powder are you using is it temp sensitive? Could also be your barrel is getting copper fouled and needs it cleaned out. Some barrels like copper fouling others don't.

 

[Doc7]

How fast does a barrel heat up? I typically wait 10-20 mins between shots when shooting groups. It sounds like I might be able to shoot two shots at each of these intervals? Is it time based or shot based? ie the barrel will not be fully heated yet if you fire a second shot within 30 seconds or so but if you wait a minute now the barrel is heated throughout?

 

[270WSMANIC]

Brand new barrel so not copper fowling.

 

[Bart B.]

Get an infrared scanner app for your smart phone then use it. Some free ones are real good.

 

[CarJunkieLS1]

Have you tried to clean copper out and gotten zero? If you haven't how can you be sure it isn't fouling with copper...if you are sure it's not the copper and not barrel heat. Then it has to be the shooter

 

[270WSMANIC]

Like I said above, brand new barrel maybe 30 rounds through it. Not likely to be copper yet.
Pretty sure it is barrel getting hot and causing 3rd shot to leave group. I have some more ammo loaded up to try again but it won't quit raining so i can get to the farm and shoot.

 

[Delmar]

I doubt that copper fouling is the culprit unless there is some serious issues in the bore, but the barrel is not likely worn in with only 30 rounds, either. We are assuming of course that the action is properly bedded to the stock, scope mounts and rings are good.

 

[Trent]

I had an old Weatherby MK IV in 270 that would predictably climb high and right as the barrel heated up. It was so bad, after five shots I'd be off the target on a 12" target at 100 yards. The first shot was on the money each time.

I ended up trading that rifle off. It would have made a good one-shot hunting rifle, but we don't have rifle hunting rights in IL, so it was kind of worthless to me as a one-shot hunting rifle.

I also have a 300 win mag Savage, which I sent the action to Krieger when I shot out it's original barrel. The new barrel is capable of holding a tight group in f-class events - tight enough to clear high master scores. That requires 20 rounds in 20 minutes, and generally in the summer when temps are .. ugly. I have to use a mirage shield on the barrel or I can no longer see the target. Sometimes takes an hour for the barrel to cool back down to ambient after a string (remember, this is a 300WM and that's a lot of powder burning... it gets damn hot.)

So the answer to your query;

#1 yes it is normal for some rifles to "walk" as they get hot
#2 yes it is normal for some rifles not to "walk" as they get hot

How to affect this:

Get the barrel squared to your rifle's action.
Get the barrel bedded (or freefloated) - sometimes this will help (although not as much as you'd like probably)
Get a new barrel

(That last is expensive, but required, if your barrel has uneven stress relief and squaring it up / re-bedding don't help)

 

[Bart B.]

Trent's info is good except for bedding the barrel.

Barrels vibrate away from any hard object touching them. That includes a pad between the stock fore end and barrel. As pressure amounts vary on fore ends with shooting position and recoil, anything touching both barrel and fore end transfers that pressure to the barrel. It's never constant.

Totally free floated barrels don't have such accuracy degrading from external forces.

 

[270WSMANIC]

Bart B, you mentioned the barrel vibrating away from any hard object they are in contact with.
You wouldn't believe how many of my ole shooting-hunting buddy's I have caught at the bench resting the barrel directly on the front bag, they then wonder why they are shooting high. Also if using a tree, log,rock,fence post as a rest; put your hand against the rest not the rifle.
As I said in my original post the new barrel is free floated 2 dollar bills go easy between barrel and barrel channel.

 

[270WSMANIC]

Thanks for the post Trent, You mentioned getting a new barrel. This is a new Douglas barrel with about 30 round through it , maybe further break in will help???. Having the action trued to the barrel might help. If, however limiting myself to 2 shot groups in scalding hot weather, and maybe 3 shot groups in cool weather will keep it sub moa wonderful. Anyway I need to do some more shoot'en and its so hot and rainy here that it may be a week or 2. Wva is the hottest state in the country this time of year, or it sure seems like it.

 

[Bart B.]

How much clearance does the barrel have when its fired in a benched shooting position?

Fore ends bend in benched positions from rifle weight and shooter weight on the stock. That barrel bends several thousandths when fired.

 

[270WSMANIC]

Bart B, I would never have thought of those fine details. I see what you mean though if I put enough pressure on the stock to nearly close the barrel gap and the barrel then expands slightly when fired could be enough to push the bullet just a bit.
Just thought of something else, I wonder how much barrel clearance I still have after the first 2 shots and the barrel is hot enough to burn my hand??

 

[Bart B.]

I mentioned earlier in this thread how much barrel steel expands. Doubt it will be a problem.

1/16th inch is the minimum barrel clearance to the fore end. More for flimsy plastic stocks.

 

[TwoEyedJack]

One of my rifles does the opposite. When I was developing a load, I would print three bullseyes on one piece of paper and shoot 15 rounds (5 per bullseye) within a few minutes. In every case, each subsequent group got smaller. When the barrel is good and hot, it shoots around 1/2". The first group from a cold barrel runs closer to an inch. The rifle is a Ruger #1V in .223.

 

[270WSMANIC]

My two dollar bills in the barrel channel gap would be much less then that 1/16 min. Might need to do some sanding on that barrel channel.

 

[Delmar]

Also depends on what your stock is made of. If its a dense material, 2 bills might be enough. If its flimsy, a lot more clearance is needed.

 

[Zeke/PA]

Barrel heat does in fact effect group size!
I notice it especially in my Ruger # 1'S.
My #1's are very accurate with reloads but if I try to shoot for group too fast, I pay the price.
The # 1's are accurate enough that I can kill a deer easily with a neck shot at 300 plus yards!

 

[Delmar]

I would expect that on a Ruger No1. The barrel is not freefloated