Barrel temperatures

N

nhkuehl

Guest
I've seen a couple of articles on monitoring barrel temperatures with an infrared thermometer or temperature strips, but no mention of the actual temperature limit you shouldn't exceed. Once I can't grip the barrel with my bare hand I consider that too hot and that can happen with just the sun on a blued barrel. What is the upper safe limit for barrel temperatures to protect barrel life? - nhk
 
I'm surprised no one has given a temperature guideline. During practice or load development I shoot 5-shot groups and space the shots in 1 minute intervals and then 5 minutes between groups, or 30 rounds per hour under an overhead cover. That generally keeps the barrel where I can grip it. Sunlight, air temperature and wind affect the barrel temperature as does barrel thickness and surface area. Cartridge and powder make a difference too. I did some searching online for temperatures and found several studies that looked at rate of fire, but didn't include actual temperatures. It seems the temperature in the bore is much higher than the external temperature and that varies with barrel thickness. Over time I have some degree of heat checking in all my barrels. - nhk
 
Piece of plastic trash bag to cover barrel to the tennon.... Then lay a saturated bath towl or cham wow..! Hehehe... This will pull BTU's out of that barrel very fast and wont get water all over the gun, or no more than a little condensation on the barrel for a few seconds aft removal of the towl / plastic.

Works VERY well and fast... GREAT out on the varmint fields...

Yes, I too use the grab test ... Pretty accurate... Don't run that rig HOT..! Just killing that tube..! FAST.!

cale
 
How do any of you know that running "hot" is "killing the barrel?"

"Hot" to your hand is 200-250degrees.....

Steel softens then melts at 2000-2500degrees....

just sayin'

al
 
I remember a time when an accidental touch test ironed the ridges flat in the palm of my hand and fingers, the barrels were still considered serviceable. I cannot
tell you how much it degraded accuracy, no way to test.
 
What's hot?

alinwa said:
How do any of you know that running "hot" is "killing the barrel?"

"Hot" to your hand is 200-250degrees.....

Steel softens then melts at 2000-2500degrees....

just sayin'

al
Click to expand...

Correct, and the outside temperature will be lower than the inside temperature until it has set for awhile and normalized. At what temperature does fire checking start in the bore or is it a combination heating and cooling that hardens the surface and makes it brittle over time? - nhk
 
And is it possible that fire checking or fire cracking could be LESSENED by keeping the barrel hot?
 
alinwa said:
How do any of you know that running "hot" is "killing the barrel?"

"Hot" to your hand is 200-250degrees.....

Steel softens then melts at 2000-2500degrees....

just sayin'

al
Click to expand...

Simply have seen it........... In particular AR platform(s) on HOT day's with ACTIVE PD mounds....

One in particular.... AR heavy barrel, up to the hunt... Rounds in tube was right around 500 rds... Add another 300 rds in a 1-2 hour period in 100 deg weather and basically no cool down time..... That barrel wasn't a tomato stake afterwards BUT was coppering HARD and wouldn't hold KNOW loads to under 1".... A barrel that I knew would do sub 1/2 MOA right before the shoot.... Trust me... Later, bore scope showed major cracking and bronze colored throat up 1 1/2" long...
The barrel simply just got too hot in a short period...

Another.... .220 Swift (yes, hard on barrels "anyway") with about 100 rds in HOT temps.... Original throat was not "shot out" but the 100 rounds in short order just about devoured the throat up a full 1", then started coppering hard, wouldn't quit no matter what....

It's the temps AND the small lands of barrels that CAN quickly erode .... Have seen it...It does happen.

The temps AT THE THROAT can get REALLY high..... Have no way of measuring it.... Just say'n... WHY run it hot..?
THERE are good ways of pulling the heat out of a tube quickly, helping to preserve a good shoot'n tube...
The next barrel may not be as good..$$$

Anyone........?
cale
 
Oh yea.... There are TONS of stories about WWII German Model MG42's.......... DESTROY'N barrels in SHORT order...
Yes, a machine gun and accuracy is not a high priority.... Yes, they could have hit temps to make the barrel steel damn near melt...... Many probably did...! Still, Heat KILLS.!

""And is it possible that fire checking or fire cracking could be LESSENED by keeping the barrel hot? ""

Hummmm...??? Al, you mean to cause damage, being HEATED then Cooled, then HEATED.... Repeat in short order...... ..Hum, interesting...?..

Still, have a way of cooling other than time before the barrel is just TO hot to touch....... And Or several rifles / barrels ready for the varmint hunt... Always has worked for me.

cale
 
alinwa said:
And is it possible that fire checking or fire cracking could be LESSENED by keeping the barrel hot?
Click to expand...

I doubt it.

My experience. My 9" twist .22-250 Savage LRPV shot slightly bigger than caliber groups at 100 yards with the 75g Hornady HPBT. During load development I was very careful with it. 1/2 hour or more between 5 shot groups. I had a lot of rounds through it but never got it hot. It was shooting remarkable groups, so I decided it might be fun to enter the local ground hog matches in the factory class.

Then I shot three ground hog matches with it. Between my inexperience and desire to do well, I ended up shooting 15 rounds, 10 spotting rounds and 5 for score in each of 3 relays for 3 matches - the 15 shots were in 6 minutes so the barrel got quite hot - too hot to keep my hand on. (Finished 1st, 1st, and last in factory class in that order.) The third match the rifle just wouldn't shoot - after the match I shot a 5 shot group at 100 yards, it was over an inch.

Borescope examination showed the throat looked like the bad example in the Hawkeye adds. I mean a dry lake bed is mirror smooth by comparison. It was really ugly. At that time I wasn't set up to take bore pictures like I can now. It was ugly. That was the bad news. The good news was that barrel is what caused me to get started chambering. Wasn't that long ago I was on here trying to figure out how to set that barrel back an inch and a half and ream a new chamber. I did. Shot a ground hog in the heat at 280 yards in a 7 to 10 mph cross wind with it last Monday. My best shot so far. (55g NBT leaving the muzzle about 3640 fps).

The throat erosion mechanism as I understand it is that the gasses in the throat are at near plasma temperatures as the bullet exits. The huge delta T between the gas and the surface layer heats the surface of the steel white hot almost instantly tapering to red hot in less than a mil. That surface layer expands relative to the layer just below it that hasn't had time to get more than a couple hundred degrees hotter than it was before the shot and creates tremendous shear stress, then it cools almost immediately to a bit hotter than it started but with a lot of shrinking while doing it. Repeat that cycle long enough with hot enough gasses and pretty soon the scales appear and flake off resulting in throat erosion. Anyway - my theory is that the hotter the barrel gets as one keeps shooting, within practical limits, the deeper the white to cherry red layer that expands and contracts to cause cracks gets, and the deeper it cracks as a result. Deeper cracks can't be better than shallower cracks IMO.

YMMV.

Fitch
 
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