when does barrell heat begin to affect accuracy?


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whatever
June 22, 2012, 11:28 PM
In your experience, how many shots does it take (over what amount of time) for the hot barrell to adversly affect your accuracy? With a .22 ?a .308? a 30-06?

If im shooting one shot a minute out of a target rifle when will the barrell be too hot for accuracy? One shot every 30 seconds?

How long does it take for the barrel to cool down enough to have good groups again?

Sorry if the questipm seems basic , but im just dipping my toe in the water of target shooting and was curious.

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Stack
June 22, 2012, 11:53 PM
This is just an opinion but I have an AR that shoots 1 inch groups at 200 yards when it's good n hot. I think a fouled barrel contributes more to inaccuracy than a warm one does. But, a hot barrel is going to wear faster. A lot faster.

ThePenguinKnight
June 23, 2012, 02:06 AM
As a bit of an generalization on the original question:

How does the temperature of a barrel (and any changes thereof) affect the accuracy of the rifle?

I know my barrel starts throwing shots when i shoot more than two in fairly quick succession, but im not exactly sure why. I could hazard some guesses at these questions, but i would like to see what some smarter people have to say.

harrygrey382
June 23, 2012, 08:06 AM
is it free floated?

TurtlePhish
June 23, 2012, 08:15 AM
I can put a box of 50 through my .17HMR in under 10 minutes and I see no adverse effects caused by heat, and the barrel is still safe to touch. I'd imagine this would apply to most rimfire rifles... Maybe not ones with super-light barrels, though. Barrel on my .17 is pretty thick in comparison to bore diameter.

beatledog7
June 23, 2012, 08:17 AM
Too many variables to be addressed in a single answer.

Generally, about the same time the barrel is getting hot, the shooter is becoming tired or complacent. These shooter factors probably have more effect on accuracy than the temperature of the barrel, so to make an accurate barrel heat test, we would have to remove the shooter from the equation.

jmr40
June 23, 2012, 09:04 AM
It just depends on the individual gun. I've never gotten a 22 RF hot enough to be a problem. With more powerful hunting rounds through lightweight thin barrels you may see groups start to open up after 2-3 shots.

meanmrmustard
June 23, 2012, 09:06 AM
Local long gun comps give shooters 3 shots to foul their barrels. Fouling to the extreme may matter, but I doubt in general.

Heat causes metal to expand, and therefore it becomes somewhat pliable. When the barrel is allowed to cool, things shrink back to normal.

Captain Brown Beard
June 23, 2012, 11:14 AM
As said, it depends on the caliber/barrel type/stock. My Tikka T3 lite 25-06 for example, the group would start to open up on my 4th shot when sighting in. To remedy this, I take a .22 with me to shoot in between 3 shot groups.

If you have a heavy barrel it will take longer for the barrel to heat up, and typically the barrel will cool faster. As said above, I've never gotten a .22 hot enough to make a noticeable difference.

Baba Louie
June 23, 2012, 11:29 AM
What kind of barrel? Thin for hunting, thick for varmints, fluted for weight/cooling, Long for reaching out there, short for (whatever reasons), stainless, carbon, free float, banded, round/octagonal/triangular, caliber/round used?

As others have mentioned, a lot of variables.

Old fact from front loading cannon days, cold barrels shot low/short. Once they heated up range was (more or less) correct. Typically as I recall from old physics class, heat expands cold contracts (except water/ice), differential temps can cause issues between materials (hence free floating).

The stiffer the barrel, usually the longer it'll hold accuracy. But, again, it depends

cfullgraf
June 23, 2012, 11:34 AM
As already said, it depends. It seems like that is an answer for many things with firearms.

I have a 17 Remington bolt rifle with a slender barrel. Accuracy goes to pot after three or four shots in a few minutes. The barrel has to be allowed to cool back to near ambient before accuracy returns to normal.

But, I have a bull barrel 17 Remington AR that I can shoot eight or ten aimed shots (not spray and pray) in a row and accuracy does not change.

But, the bolt rifle is a nice, light carry rifle while the AR is a heavy, "crew served" varminter.

BCRider
June 23, 2012, 12:19 PM
Some thoughts for you to consider.

All barrels will be affected to SOME degree by the temperature which they run at. This is why police snipers in the SWAT or ERT value their cold barrel shot practice. For them every shot which counts is going to be a cold barrel shot. Hunters should check their cold barrel first shot accuracy as well. Since that is how they typically would be shooting when in the woods.

For you/us, as target shooters, we don't worry about a cold barrel so much as we need to find what the temperature limit is for each barrel we shoot. And once we find the best point we'll likely find that on a cold day we can shoot at one pace of regular shots while on a scorcher of a day we need to slow down the shot pace so the barrel can cool back down to the known temperature.

In fact I wonder if this would be a good reason for installing a temperature sensor in the stock of a F class rifle?

As the others have said "it depends". Some rounds will tend to heat more per shot and so need more cooling time. Others not so much. And each barrel will have a temperature where it works best. You will need to test your own rifle by shooting fast enough to raise it until the groups open up and then get a feel for the firing rate which is slow enough to avoid the issue.

Don't discount the stock itself in this. A wood foregrip area can act as a pretty effective insulator and hold heat in the lower half of the barrel while the upper exposed half cools off and shrinks back. Steel is a poor enough conductor of heat that this is a very real possibility. If you get a tendency for the shots to rise as the barrel warms this could be the reason why. Again it all depends on the barrel and rifle design.

But even more important is the consistency of the temperature. Like with most things related to accurate target shooting the key is to eliminate any and all variables. This can and should include the barrel temperature. The way to do this is to warm up the barrel with a couple or four "fouling" shots. From that point on maintain a regular shot cadence so the temperature stabilizes. Likely this will mean around one shot a minute. But to keep things constant make sure it's a minute between shots to within a few seconds. And track your "fouling" shots as well. It doesn't hurt to learn if the barrel POI shifts as it warms during these shots. It's a sign that you need to pay attention to the temperature in order to get your best consistency.

Fat_46
June 23, 2012, 12:43 PM
My main gun "game" is shooting prairie dogs. All of my PD rifles have long, heavy barrels(up to 30" in the case of the 243). Each of them also reacts a bit differently to heat. The 204 starts to string vertically up. The 243 seems to throw an occasional flier. The 260 doesn't seem to notice! 2 weeks ago I went through 47 rounds of 204 in 30 minutes. The barrel was too hot to touch. The neat thing, though, it is was a 5 patch cleanup! A good brushing with Butch's, and the 5th patch was as white as new snow.

That being said, I also have sporter barreled rifles that hate anything more than 3 shots in less than 2 minutes. My 280 is an absolute tack driver for a sporter, but only for the first 2 shots in a short period of time. Load development took 3 times as long for this rifle than most of the others. I also haven't noticed any appreciable effect of fluting.

I'm considering purchasing a laser/infra red thermometer to better track actual temperatures, but haven't pulled the pin on that purchase yet. I think it would be quite interesting to record temperature alongside powder charge, seating depth, ambient air temp, and wind. I wonder what that measurement would do to my graphs?

Baba Louie
June 23, 2012, 03:01 PM
The 260 doesn't seem to notice!For some reason, I Love that comment. ;)

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