Barrel temp - how does it affect groups when testing loads?

[lukester]

I'm sure I can find good info on this somewhere, but thought I'd throw it to some of those who I know can help me. I'm testing loads for my Ruger m77 chambered in 6mm Remington. So, when I head to the range w/ five or more cartridges in each of 5 or 6 different loads... do I need to spend time waiting for the barrel to cool between shots and/or groups? Seems like I can wait for what seems like forever and can feel no appreciable difference to the touch.
I assume there's a difference between the first cold round and everything that comes after that, but what about once it really heats up?

Thanks,
Lkstr

 

[Offfhand]

Responses to this are going to be intresting, I can't wait. Thanks for asking.

 

[John Wayne]

I'm sure you'll get some very complicated answers, but here's a simple solution that has worked for me:

How fast the barrel heats up and cools depends on many factors including barrel weight, outside temperature, bullet weight and velocity, addition of fluting, etc.

If the barrel is too hot to touch with your wrist (along any portion of its length), it is likely to affect accuracy. Some guns may not be affected, or affected as much by the barrel heating up, but it ain't gonna help.

 

[788Ham]

I plan on being there awhile if I have, say the same amount of ammo to shoot that you are using. I'll shoot 3 rounds, then let the barrel cool, opening the bolt of course to allow air flow. IMHO, this doesn't let the barrel heat up so hot, as to start throwing the rounds at the target end, fire the other 2 when cooled, then wait until cool again before firing the next 5 in the same sequence. I've never done this, some guys at the range will take a can of freon and spray the barrel to aid in this cooling process, like I said earlier, I allow time for cooling. As far as not noticing appreciable difference: I check my barrel about 3"-4" ahead of the breech, and then about 12" further down, if I can't leave the back of my fingers on the steel for a couple, maybe 4 seconds, I wait until I can. I figure the barrel doesn't have to be "stone cold" to start shooting again, but do allow maybe 5 mins. between strings. YMMV

 

[Walkalong]

Shoot one or two to foul the bore and heat it up a little. After that just don't let it get to hot. (uncomfortable to touch) If it won't shoot warmed up, and even a little hot, it isn't worth having unless it is strictly a hunting rifle where you might shoot it once or twice a day.

 

[Blackrock]

I shoot a Rem 788 in 6mm Rem on prairie Dogs and I just keep an even rythem going when range testing. I shoot 3 to 5 shot groups, walk 100 yards downrange to check target and do it again.
When shooting on the dog towns I rotate with my daughter and a friend and we all will shoot 10 round strings and switch out. But Ihave been known to put 50 rounds out in less than a half hour.

 

[USSR]

Shooting F Class, we shoot 25 - 30 rounds in 30 minutes. We warm them up with 5 - 10 shots before shooting the 20 shots for score. The barrels do get warm. Of course, most of our barrels are of a heavy profile and act as a heat sink. Once a rifle barrel heats up, any stresses in the barrel are amplified. To answer your question, I would fire 1 or 2 cold bore fouling shots, then wait 5 minutes between shots for group purposes.

Don

 

[cfullgraf]

Barrel profiles will have an effect on how frequently the rifle can be shot over time before accuracy degrades.

I have a 17 Remington with a slender barrel. Groups expand dramatically after about 3 to 5 shots in a short period of time. Free floating the barrel has helped. For multiple groups, I pretty much have to wait for the barrel to cool to ambient before shooting the next group.

I get short on patience but USSR's timing sounds reasonable for most rifles.

My rifle is a great walk-about varminter but would never make it in a prairie dog town.

 

[Tuckerp229]

Barrel temp - how does it affect groups when testing loads?
I'm sure I can find good info on this somewhere, but thought I'd throw it to some of those who I know can help me. I'm testing loads for my Ruger m77 chambered in 6mm Remington. So, when I head to the range w/ five or more cartridges in each of 5 or 6 different loads... do I need to spend time waiting for the barrel to cool between shots and/or groups? Seems like I can wait for what seems like forever and can feel no appreciable difference to the touch.
I assume there's a difference between the first cold round and everything that comes after that, but what about once it really heats up?

Thanks,
Lkstr

This question drove me nuts as well. Temperature surely affects group size and location but I have discovered that temperature affects each gun differently. I solved this question by the use of an infra red thermometer. It is quick, accurate and does not touch the barrel. It costs less than a typical box of rifle cartridges and you can buy them here, consistentcrimp.com

** Full disclosure, this is my company

 

[jamesicus]

When I was a (much younger) competitive high power rifle shooter I mostly shot the National Match Course (V ring targets* - metallic sights) in practice and matches. I was issued a Military premium grade M1 match rifle which I used most of the time, although I used my personal Winchester model 70 heavy barrel match rifle on occasion. Both rifles were tack drivers at 600 yards which was my forte.

National Match Course:

200 yards - ten shots standing (offhand) slow fire in 10 minutes (preceded by two sighters).

200 yards - ten shots standing to sitting rapid fire in 60 seconds.**

300 yards - ten shots standing to prone rapid fire in 70 seconds (preceded by two sighters).**

600 yards - twenty shots prone slow fire in 20 minutes (preceded by two sighters).

The barrels were really hot after the rapid fire strings, but the rifles maintained their cold barrel accuracy, even at 600 yards - I cleaned numerous targets at that range with both my M1 and my bolt rifle.

* The "A" target used at 200 & 300 yards had a 4" V ring and a 12" five ring; the "B" target used at 600 yards had a 12" V ring and a 20" five ring.

** The M1 service rifle was loaded with a partial clip of two rounds while standing, and reloaded with a full eight round clip during firing. Bolt rifles were loaded with five rounds while standing, and reloaded via a five round stripper clip during firing.

James

 

[qajaq59]

In my experience it depends on what you are using for a rifle. My Savage 99 featherweight in .308 will heat up really fast, forcing the POI up after only 3 rounds, unless I really let it cool off. But my Win 94 doesn't seem to care how many rounds go thru it. It's easier in the end to just let it cool off between groups, if you are firing for the best load.

 

[243winxb]

Keep it Cool for Long Barrel life.

When the round cooks off,( thermally induced firing) you barrel is to HOT. Other wise 3 minutes between is ok. Watch for a barrel (factory) that walks the point of impact as it heats, 20 shots of rapid fire is a good test High power scopes (36x) will Magnify the heat waves coming off the barrel making you aiming point dance. Place a wide piece of thin card board, or thick paper on the barrel from under the scope to within 2" of muzzle to reduce heat waves in the scope. Don't let it slip forward, ever.

 

[Tuckerp229]

My experience is that every rifle, or at least rifle brand or type handles heat differently. For example I have a Remington 700 in 30-06 circa 1975 that starts to "walk" after 3-4 shots. My bushmaster AR15 CAR model preban with heavy machine gun barrel can handle fully two rapid fire mags before POI starts moving and then it is only a bit.
In general I have found that off the shelf commercial deer rifles ten to meet their respective design requirements, say 2-5 shots before POI changes significantly. The Mil Spec rifles tend to hold POI longer as one would expect given the design requirements for military contracts. The latter finding has been substantiated by a AR15 custom builder that tried the barrel temp gauge to test his custom barrels. He was pleasantly surprised how little barrel temp affected the POI of his products...especially because he had always supposed that barrel temp was affecting POI.

Knowledge is power.

Of course bullet type, powder type and number of grains all play into the results. Finally ambient temperature affects heat build up and cooling time.
In the end I have found that each rifle has its "character" with a given load recipe. It pays to know what that "character" is if you want good consistent hits and also to save ammunition costs normally wasted by firing without any way to measure barrel temperature.