cooling the bore between shots


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shekarchi
September 11, 2013, 10:29 AM
Hey Guys, this is my first post to thr. glad to be here. I am very new to reloading and just had my first session of testing some handloads. I am hooked- especially after shooting the best group of my life with ammo I made myself. very satisfing... one problem... My experience shows that a hot barrel shoots erratically [this is a hunting rifle- not varmint or heavy barrel].
I came up with a solution that I would like to share. I carry a cooler of ice with some ziplock bags to the range. after 3-4 shots when the barrel needs to cool off I wrap a ziplock bag with ice cubes over the barrel and move it up and down the barrel. in a couple of mniutes I am ready to shoot with a nice cool barrel... have also tried the reuseable ice packs for the same concept [the flexible kind]. I freeze them in a folded position so they will drape over the barrel. this works well also... be sure to coat the barrel with a heavy gun oil/grease to protect against rust from condensation moisture that forms on the ziplock bag on hot humid days.
just an idea...

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YZ
September 11, 2013, 11:09 AM
I did the same with my Tikka at the range.

shekarchi
September 11, 2013, 11:18 AM
I see all these patents for bore coolers [mostly an air pump to move air through the bore but this is much faster- and cheaper... thanks for your comment

jmr40
September 11, 2013, 11:24 AM
I've seen guys keep a towel in a cooler with ice water. Leaving the rifle on the rest they drape the cold towel over the barrel between strings.

I generally take at least 2-3 centerfire rifles and a 22. After shooting all of the centerfires and the 22 for a few minutes the first gun fired is usually cool enough without any help.

On extremely hot days I have been known to keep the truck running with the AC on high and place just fired guns inside for 5 minutes or so.

primalmu
September 11, 2013, 11:31 AM
I would be worried about warping the barrel, as some people say will happen if you pour water down the bore for example. If I'm shooting for groups I'm probably not in a rush, so I'd rather let the barrel cool slowly and, more importantly, evenly.

When I need to let my barrel cool down, I'll stand it up in one of the racks at the range. This lets the barrel act as a sort of chimney and pulls cool air in from the bottom and heat out from the muzzle.

shekarchi
September 11, 2013, 11:32 AM
thanks- another member commented this is not a good idea[cooling rapidly] due to causing problems for the bore- Guess I need to do more research

Arkansas Paul
September 11, 2013, 11:34 AM
I shoot 3 shot groups and then let it cool for 5 minutes of so before doing it again. I've never had problems with accuracy degrading. Taking more than one rifle helps so you're not sitting there waiting.

Welding Rod
September 11, 2013, 12:14 PM
I take 2 or 3 guns and alternate when shooting for tiny groups on paper, but honestly if he gun walks vey much with a hot barrel I just trade it off and get another rifle. A properly manufactured barrel isn't going to walk much.

Mat, not doormat
September 11, 2013, 12:25 PM
Shooting for groups, like load testing, I shoot 3-5 shot groups, then move on to a different rifle, or do pistol drills or something until it cools naturally. I've seen engine blocks and cast iron skillets crack when cooled too rapidly, so I'd not want to try it with a rifle barrel. Even if it didn't crack, (it is good steel, not cast iron after all,) it could still warp, which is no good. Better to cultivate patience than replace a barrel before you have to.

When doing normal practice, that is, shooting from field positions, I go by the rule, "If it's too hot to touch, it's too hot to shoot."

Mat, not doormat
September 11, 2013, 12:32 PM
I should add that I don't spend a whole lot of time on load development. I pick a bullet and a powder, then find the charge that shoots best. If you've gotta try five or six bullets for each weight, and eight or nine powders for each bullet, youre likely to spend all your time on the bench chasing MOA unicorns, and wind up with half (or all) of your barrel's useful life gone before you do anything useful with it.

For field shooting, the difference between a.75 MOA load and a 1 MOA load isn't one you can really appreciate anyhow. Find a load that shoots, then crank out a bunch of 'em and get off the bench.

shekarchi
September 11, 2013, 12:33 PM
thanks for all the comments and advice. I work at the university of KY and have posed the question to a metallurgy professor at the college of engineering. will let everyone know what he says...

MtnCreek
September 11, 2013, 01:16 PM
Just my speculation, but it seems to me the barrel would have to be very, very hot before rapid cooling would warp it and if it were that hot, it's probably shot anyway. Again, just my simpleton speculation.

BCRider
September 11, 2013, 01:21 PM
One thing about steel is that it's a very poor conductor of heat as far as metals go. So the inner bore wall can easily be a good 30 to 50 degrees or possibly more hotter than the outside and you won't feel this new added heat for up to maybe a minute before the temperature evens out throughout the wall. The actual time will vary based on the thickness.

So it's possible that you can end up with a very hot inner bore wall inside that is trying to expand the metal while at the same time you're cooling and causing the outside metal to contract with the ice pack.

So first off it would be wise to wait a good 45 seconds to even a minute before you apply the ice pack. Ask your metallurgy friend about the forces that can be generated in the steel when a hot side and a cold side are existing in a wall that is 3/16 to 1/4 thick steel. Or even better put a piece of 1/4 x 1 flat bar in a vise and set up an indicator pointer at the free end attached to something else. Then heat the bar up with a torch to where it's just past being too hot to touch then apply your ice pack to the opposite flat side. I think you'll be shocked at how far the flat bar will curl due to the hot side to cold side expansion and contraction issue. And the length of time it takes before it equalizes and returns to straight.

So all in all if you want to use the ice pack idea I'd suggest that first off you wait for a good minute after the last shot before applying it. That'll reduce the extreme of the hot inner bore to cold outer surface tension in the walls of the barrel. And secondly that you apply the bag to take away the majority of the heat but then let it sit for a good minute or more to let the whole barrel equalize again. Being "just warm" on the inside while cold on the outer wall is just as bad for accuracy as hot.

Another issue that seems to be seldom addressed is the insulating properties of the fore end of the stock. And since you can't ice pack that area of the metal again it's going to take a good minute or more before the coolness you put into the exposed part of the metal can work it's way down into the depth of the barrel channel and the metal becomes a constant temperature throughout.

Another good "table top" experiment to demonstrate the thermal conductivity of steel is to get some steel and aluminium plate that are the same thickness and roughly the same size. On a range element set to high put the aluminium plate down and touch the top and take note of the time it takes before you can't touch it any longer. It'll be literally only a few seconds. Do the same with some steel and you can easily leave your finger tips on the metal for a good 4 to 6 times as long. Another way to test this is with 3 inch lengths of 1/8 diameter welding rod in aluminium and steel and also get a piece of 14Ga copper the same length. While holding the one end stick the other into a propane torch flame. The aluminium and copper will become too hot to hold within 30 seconds. The steel may not get too hot at all. It's such a poor conductor of heat that it actually dissipates into the air before it can get to your fingers.

If you try these easy to do tests you'll quickly realize why I'm suggesting that even with a cold pack that you still want to wait that couple of minutes before shooting again. Otherwise you could have a barrel that is still hot on one side in the barrel channel and cool on the outside where you just removed the ice pack and if you measured it you'd find that it looked like a ski. But once the temperatures equalize it straightens up again. But that can take up to a couple of minutes.

There is actually a lot to be said for the "chimney" idea of shooting a string then rack the rifle with action open so the warmth in the bore can produce a simple chimney effect to let the warm air out the muzzle while drawing in the cool air. It's surprisingly effective.

Inebriated
September 11, 2013, 02:38 PM
I rarely shoot for groups. I zero, and move on to practical field positions.

When I zero, I'm going into it with the expectation that when I take a shot in the field, it'll be a cold bore. So I take my first shot, wait about 10 minute (or until the bore is cool again), then take the next, and carry on until I have three shots. Then I adjust, and repeat. If I'm doing that, I'll usually bring a couple other guns to plink with while I wait.

Welding Rod
September 11, 2013, 02:41 PM
We use flame straightening and flame bending in metal work all the time.

If metal is hot enough and is rapidly unequally cooled it will definitely bend. We use this property to accomplish bending and straightening all the time.

But high temp is important, generally around the 1200 degree range, or when you can just barely see faint reddening in low light. Steel does not need to be glowing bright red hot to take a permanent bend. In fact good bending / straightening procedures prohibit this.

The US DOT has a great website the covers recommended heating and straightening procedures for highway / bridge members that are crash damaged.

In their document it is noted that It is generally considered safe to use accelerated cooling once the base metal has cooled to below approximately 600 F, but accelerated cooling from high temps is not done as it can lead to uncontrolled and unpredictable hardening.

A rapid quench from a high temp can lead to hardening, even on mild steel. For this reason I would be VERY cautious about cooling a gun barrel, and I wouldn't even think about speeding the cooling from a very high temp.

jmr40
September 11, 2013, 02:45 PM
I shoot 3 shot groups and then let it cool for 5 minutes of so before doing it again. I've never had problems with accuracy degrading.

Most of the year that works just fine. But in August and September when it is 100+ it takes a lot longer than 5 minutes. Without something to aid in cooling it can be closer to 20 minutes. I've seen several use the wet towel with no issues. I've never had a problem with placing guns inside my truck for 5-10 min with the engine and AC running.

shekarchi
September 11, 2013, 03:07 PM
MtnCreek- I agree that rapid cooling from a VERY hot temp would be detrimental. I would not even think of doing that. But we are talking about a temp of maybe 200-250 degrees... I never shoot so rapidly so as to let my barrel get so hot that I cannot touch it.
My guess [uneducated] is that cooling with an ice-pack after shooting 4-5 rounds so I can start with a "cool" barrel does not hurt the steel... I am waiting for the metallurgy guy to write back. And BC rider, your comment about differences in temp between inside and outside of a bore is absolutely true. Thanks for your comment as well...
its great to see comments from so many people... exactly why I joined this community. Thanks all

Red Tornado
September 11, 2013, 04:51 PM
I've never tried it, but have wondered about spraying canned air down the barrel. It won't leach heat like a cold liquid and seems like it could work. Any one tried it?
RT

MtnCreek
September 11, 2013, 05:25 PM
^ Does the canned air come out cold? If so, condensation may be an issue.

TEC
September 11, 2013, 06:53 PM
Ever try using a thermometer?

Last range session, I tested about 50 rounds of 308 Win fired from my CZ-550 Varmint (heavy barrel) bolt action rifle.

I was using an inexpensive laser sighted IR thermometer, and I have not calibrated the thermometer

http://www.harborfreight.com/infrared-thermometer-93984.html

Measurements were made with the thermometer held about 12 inches from the barrel at a point immediately adjacent to the rifle chamber. During all testing, the barrel felt warm to the touch, but never hot or uncomfortable to the touch. Time between shots, bolt open, was used to unload, inspect brass and replace brass in the shell box, record shot velocity, record barrel temp, reload, and sight the next shot, typically about 2 min between shots.

F Time Comments
79.4 Ambient air temp
85.4 13:48 "Cold" barrel temp
85.2
84.5
84.5
84.1 13:59 Cease fire, reset targets, adjust chronograph



84.5 14:06
84.1
83.9
84.1
83.6
82.8
83.1
82.8 14:21

I have additional temp readings for the session, the highest being 87.8, but I quit recording times with the temps. I believe my barrel was heating as much from being in the sunlight as from the rate of fire of 308 rounds, all about 2550 - 2575 FPS. The CZ-550 Varmint's barrel never got anywhere near "too hot to hold" with what I consider a normal rate of fire while testing various rounds. There was a light, variable wind, but no additional effort was made to cool the barrel between shots. The barrel temps were just about constant throughout the test firing.

it is my belief that while the rate of heat conductivity in steel is, perhaps " slow" in the metallurgical spectrum, that the overall mass of the chamber and barrel, and hence, the total heat capacity of the rifle dictate both the rate of heating and cooling, more so than other factors. At a reasonable rate of fire, with a heavy barrel 308 win, shooting at velocities around 2600 fps, barrel overheating isn't going to be a problem. There is good reason for the military calibers typically not being "over-bored".

The critical area for heat damage to a rifle is the chamber's throat and first few millimeters of the rifle's lands, if what I read is correct. The most potential damage is done by rapid firing of "hot" loads in an over-bored caliber rifle. popping off 3 or 4 quick shots in, say, a 243 win with loads in the 3000+ fps range very quickly builds high temps in those critical areas, with the forces of each successive shot acting adversely on those overheated metal surfaces.

Imprudent varmint hunters might "burn out" the throat of a barrel in a single shooting session. But a modest rate of continuous fire with even just a minute or so between shots doesn't worry me at all with the CZ550 Varmint in 308. I'd be much more worried about the potential adverse effects of shooting a relatively quick string, then trying to cool the barrel as quickly as possible to do it again, especially if the cooling were uneven, in a relatively light barreled rifle with hot, over bored caliber loads. That can't be good.

PS. Here's one of the 5-shot, 100 yard groups I shot that Sunday afternoon:http://img.tapatalk.com/d/13/09/12/za4ymuse.jpg

RetiredUSNChief
September 11, 2013, 07:19 PM
My experience shows that a hot barrel shoots erratically [this is a hunting rifle- not varmint or heavy barrel].

I came up with a solution that I would like to share. I carry a cooler of ice with some ziplock bags to the range. after 3-4 shots when the barrel needs to cool off I wrap a ziplock bag with ice cubes over the barrel and move it up and down the barrel. in a couple of mniutes I am ready to shoot with a nice cool barrel.

Couple things here, which stand out to me:

1. You describe the rifle as a "hunting rifle". In my hunting experience (small game and varmint), a hunting rifle doesn't see enough action to significantly heat up a barrel between shots. So this really isn't a concern at all if the primary use of the rifle is for hunting. That said, if your goal is to tweak the most accuracy out of your rifle over several consesecufive closely spaced shots at the range, more power to you. After all...shooting is fun!

2. If barrel temperature increases are enough to affect accuracy significantly over the course of a few shots, as you describe, then the rapid localized cooling caused by applying an ice pack may also significantly affect accuracy, only potentially in a far more adverse way. Rapid localized cooling may cause barrel warpage which might become permanent. So I'd be careful of this.

Just my opinion.

;)

YZ
September 11, 2013, 08:17 PM
I've also experimented with a chilled bore snake. It was slow cooling alright. Abandoned it, too messy and wet.

RetiredUSNChief
September 11, 2013, 09:03 PM
I've also experimented with a chilled bore snake. It was slow cooling alright. Abandoned it, too messy and wet.

Hmmm...now that opens up possibilites, though...

Take a shell casing, fit it up with a nylon tube through the primer hole location, put an O-Ring around the base of the casing...then fit the shell into the breech and pump water through the barrel under pressure until it's cool!

Then swab down afterwards.

Of course, this might be carrying things to the extreme...

:neener:

fletcher
September 11, 2013, 09:46 PM
In their document it is noted that It is generally considered safe to use accelerated cooling once the base metal has cooled to below approximately 600 F, but accelerated cooling from high temps is not done as it can lead to uncontrolled and unpredictable hardening.

In general, that sounds pretty safe to me with regards to cooling.

Making an educated guess, I wouldn't expect there to be any permanent distortion as a result of cooling a warm (not hot) barrel with ice packs, assuming the barrel is of decent quality.

Thermally cycling steel shouldn't result in substantial microstructural changes up to 200~250F would cause warping upon cooling. I certainly wouldn't expect any effect from short excursions to temperatures a bit below the tempering temperature, which is typically in the 750F+ range for 4140 depending on the desired hardness.

I would not expect a thermal gradient substantial enough to cause permanent warping from casual cooling using the ice packs, but stranger things have happened.

Of course this could vary depending on the alloy, the heat treat process used to obtain its final state (e.g. stabilization, existing stresses), dimensions/geometry, etc.

Let us know what the metallurgy professor says when you hear back. I would definitely be interested in hearing his thoughts.

WVRJ
September 11, 2013, 10:56 PM
I tried cooling my 308 by putting it over the duct in my house and running the central air.The rifle is very accurate,but after a couple of 5 shot groups,accuracy would fall off.After cooling it,the POI had changed by well over an inch.Tried it again...same result.I would conclude that this was caused by uneven cooling.The barrel was warm in the stock,but cool to the touch where the metal was exposed.In my early reloading days,I loved to shoot a lot of rounds and see the result of my work.Nowadays,I just take a couple of guns out at a time.Or even better have a buddy so there's somebody to BS with while they cool.Sporter barrels will do crazy stuff when they're hot,and if you try to sight one in hot,it'll most likely shift POI when it cools down,especially if not free floated.There's my 2 cents worth,even ifn it hain't worth 2 cents.

USSR
September 11, 2013, 11:13 PM
one problem... My experience shows that a hot barrel shoots erratically [this is a hunting rifle- not varmint or heavy barrel].
I came up with a solution that I would like to share. I carry a cooler of ice with some ziplock bags to the range. after 3-4 shots when the barrel needs to cool off I wrap a ziplock bag with ice cubes over the barrel and move it up and down the barrel. in a couple of mniutes I am ready to shoot with a nice cool barrel...

My take on this is, carrying a cooler of ice while hunting would be a real drag. Suggest you try the method I use which results in merely a warm barrel; One shot and then dress out the animal.:rolleyes:

Don

TEC
September 11, 2013, 11:14 PM
Hmmm...now that opens up possibilites, though...

Take a shell casing, fit it up with a nylon tube through the primer hole location, put an O-Ring around the base of the casing...then fit the shell into the breech and pump water through the barrel under pressure until it's cool!

Then swab down afterwards.

Of course, this might be carrying things to the extreme...

:neener:

Won't work for rapid fire, but I experimented with a dummy 243 round filled with #9 lead shot. Put it in the mag of my BAR 243 and loaded a live round over it. My thought was that an auto loader that immediately ejected hot brass, and then chambered a cool load with lead in the case was a way to quickly introduce a more effective heat sink in the hot chamber. Let the chamber cool a bit by thermal conduction to both the chamber wall and the dummy round, then work the action once to eject the dummy heat sink and go live. If nothing else, it will slow you down if you have the irresistible urge to pull the trigger again too quickly!

IWAC
September 11, 2013, 11:18 PM
I used alcohol on a piece of toweling to rub on my barrel, thinking evaporation would help cooling, but I didn't really like that too well. I then bought a (Coleman, I think it is) battery powered air matterss inflation pump. I got some 1/2" tubing, hooked one end to the pump and shoved the other end into the breech of my rifle. Works as well as anything.

Centurian22
September 12, 2013, 07:55 AM
TEC: interesting results but I must point out a couple facts based on the temp gun. It has a distance to sight ratio of 6:1 meaning at 12 inches its averaging the temperature sensed over a 2 inch circle. Also the accuracy is +/- 4 deg. F or 2% (which would be about 1.7 deg. F) seeing that all (or almost all) of the readings fall within this error range and I doubt the part of the gun you were trying to sense was more than 2" wide, I wouldn't put much faith in the numbers. Possibly try again with the sensor just and inch or two away and see if it alters the results.

To the OP I personally wouldn't chance the rapid cooling myself.

boogieman
September 12, 2013, 08:03 AM
This thread was somewhere else also and disappeared.
It all depends on temperature and carbon content of the steel used. But in short if you heat steel and rapidly cool it then you increase the hardness. When you spot cool you get spot hardness. You can drastically change the harmonics in a barrel and lead to failure of the barrel. If you have to cool it down quicker then use the fan method. Water is probably the very worst thing your barrel could contact. At least you could dip it vertical so that the cooling is even.

SleazyRider
September 12, 2013, 08:33 AM
Great question. My hunting rifle needs to be accurate only once or twice each year, and that's usually on a cold December morning when touching the receiver or barrel with an ungloved hand will send chills down one's spine. And that is how I like to sight it in---cold barrel, cold action, and cold ammo. One or two "cold" shots at the range, leaving my rifle and ammo in the trunk of my car the previous night.

The problem with cooling down a warm rifle, in my estimation, is consistency. By that I mean everything---barrel, action, ammo, and magazine---needs to be cool and at the same temperature.

rbernie
September 12, 2013, 09:07 AM
There is actually a lot to be said for the "chimney" idea of shooting a string then rack the rifle with action open so the warmth in the bore can produce a simple chimney effect to let the warm air out the muzzle while drawing in the cool air. It's surprisingly effective.This bears repeating; it's simple, free, and it's effective because it cools the bore and not the outside.

I also use a bore snake before I rack the rifle sometimes to remove hot carbon bits and to allow the snake to absorb some of the heat.

shekarchi
September 12, 2013, 06:19 PM
thanks everyone for your comments- still have not heard from the professor. will let you know what he says. if he ever answers that is...

shekarchi
September 12, 2013, 06:22 PM
USSR
haha
I wasnt talking about hunting with a cooler of ice
I never heat up the barrel when I'm hunting because I only shoot once...

YZ
September 13, 2013, 09:06 AM
I tried cooling my 308 by putting it over the duct in my house and running the central air.The rifle is very accurate,but after a couple of 5 shot groups,accuracy would fall off.After cooling it,the POI had changed by well over an inch.Tried it again...same result.I would conclude that this was caused by uneven cooling.The barrel was warm in the stock,but cool to the touch where the metal was exposed.In my early reloading days,I loved to shoot a lot of rounds and see the result of my work.Nowadays,I just take a couple of guns out at a time.Or even better have a buddy so there's somebody to BS with while they cool.Sporter barrels will do crazy stuff when they're hot,and if you try to sight one in hot,it'll most likely shift POI when it cools down,especially if not free floated.There's my 2 cents worth,even ifn it hain't worth 2 cents.
It sounds like you shoot your rifle right outside your air conned house. Lucky you.

I have actually abandoned active cooling while practicing. I take long breaks, change targets, piddle with supplies, or shoot a handgun in between. Cooling by waiting.

shekarchi
September 13, 2013, 12:13 PM
Gentlemen I heard back from Associate professor of materials Science. I guess whoever said there is a chance of warping the barrel is probably right...

Here is his reply to my question about using ice-packs to cool a hot barrel...
Have a great weekend all

[I]Interesting question … I looked into this a bit and it seems that most barrel steel is 4140 steel, heat treated to relieve stress at 600 C and then slow cooled. So if you were to heat the barrel by rapid firing, it should not be a problem (I am not sure, but I doubt that firing would raise the temperature to 600 C) since the elevated temperature should not affect the steel microstructure and hence mechanical properties such as hardness would remain the same.

However, the method of cooling could possibly induce stresses and/or warpage in the barrel, which you of course want to avoid. Standard heat treatment would be followed by slow (air) cooling, with no stress buildup. If you were to accelerate the cooling in a uniform way, you could also avoid inducing stresses in the barrel. However, if you were to cool one part of the barrel quickly, with the rest of the barrel cooling afterward (and more slowly; also with some heat transferring back to the already cooled region), then yes, I think you could warp the barrel. Perhaps not enough to see, but this might have an influence on shooting accuracy.

If you do want to try your rapid cooling idea, you probably want to test this method on a barrel you would not mind warping. Basically, I think there is a real possibility you could affect your barrel's accuracy.

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