Hot Barrrel..what's the problem?

B

Buddy Lee

Inactive
Hello All,

Hey, what is the big problem with a hot barrel and what is the big difference between a hot handgun barrel and a hot rifle barrel? I'm serious. Let me explain...

I've been shooting for years. I am ex-SWAT where we use to fire 100's if not 1000's of rounds a day through both our handguns or our rifles. Here on TFL I hear all kinds of complaints from people about hot barrels, almost exclusively about hot rifle barrels. Is this more a complaint about handling a hot object or both handling a hot object and losing accuracy?:confused:

I'm being honest here. The rifles we used were either HK93s, MP5s or HL53s. The handguns were either Glocks, HKs or S&W stainless. We never thought twice about firing hundreds of rounds a day. I worked for a large urban police department and most of our shooting was 50 yards or less. Accuracy from any of these weapons was not an issue. We used the same weapons for years (at least 15 years) with never a complaint about shooting out the barrel.

Why do I mention this now? Well, if you've read any of my other threads, I just recently bought a mini-14 with a Simmons Red Dot system. The gun is fun:D Not great, not bad, just fun! Boy oh boy does the barrel get hot! I'm talking smoking hot, where I thought that I was melting the top barrel guard. I was at a commercial range with limited rapid fire, nothing like I use to fire. The rifle kept shooting ok...it was never great but it didn't throw rounds eveywhere.

I also recently bought both a 357 mag (Taurus tracker 627) and a Glock 21. I put a couple hundred rounds through both of them while at the same range (all within a couple of hours..I shoot my wad and leave). Yeah, the barrels got hot, but you never, or at rarely, hear about this causing problems for a handgun.

So, would someone be kind enough to explain to me in layman's terms what the difference between heating the two different weapons is and why it is a concern for one and not the other?

Thanks,

B.L.

p.s. Yes, I am the kind of guy that gets his oil changed at Jiffy Lube :)
 
I don't believe there is a difference between a hot pistol and a hot rifle barrel.

I do believe that heat accelerates barrel wear though. Maybe not very much, depending upon the alloy, but it does hasten the wear nontheless.

Most materials expand when heated. Metals are no different. They don't expand as much as some other materials, but they still expand.
Now that makes no difference to the outside diameter of the barrel, but there is also some minute expansion to the inside. In other words, the bore becomes a tiny bit smaller.
Even if it's only a difference of say .00001 smaller than the original cold bore diameter, it is still a wee bit smaller.
Your bullet diameter has remained constant so the result is a tighter fit between the bullet and bore. A tighter fit = more friction which = more wear.

The same applies for loosening a fit. For example if you stick a case in your sizing die, put it into your freezer for a while. Once the metal cools, it contracts and sometimes the case will come out easier. in this example, not only does the die material contract creating a larger opening, but the case contracts as well for a looser "fit". Sometimes that's enough to free the case.

That's the way I see it anyway.
 
I gotta disagree with Bottom Gun about one item: A ring expands upon heating. Think of a rifle barrel as a long ring and look at an end view; any line you draw around that circle gets longer.

Back to the question.

The material of the stock and the steel of a rifle barrel expand at different rates with heating. For normal "military accuracy", this change in stress on the barrel is not particularly important. However, for tight-group target accuracy, the change in stress creates a variance in the harmonics of the barrel when the rifle is fired. This increases the size of the group.

You can think of the behavior of a barrel as a spring, with changes in harmonics affecting its frequency of vibration.

Ain't physics wonderful?

Art
 
Sorry, Bottom Gun, but you're wrong - when barrel heats up, both O.D. and I.D. becomes larger in size. I do not need to prove it, because this "phenomena: is used in manufacturing for hundreds of years, for assembly of pieces inside each other - outside piece is heated up, and inside piece is cooled down to allow for initial slide (easy) fit. Example from the gun world - large caliber cannon barrel with liner is assembled in this way. Example fom the automotive world - assembly of valve guides and valve seats into the cylinder head.

Bullets fired from red hot machine gun barrel behave in the same way as they were fired from the oversized smooth bore barrel.
 
Its not just heat

The products of combustion are rich in carbon dioxide, carbon monoxide, nitrogen and its oxides, ammonia and water. All but water are capable of hardening steel as in carburizing and nitriding. In barrels, this is one of the mechanisms of "checking". The process is one of diffusion and without going into Fick's Law and other technical info, the basics on the rate of this process involve heat, pressure and gas concentration. You cannot do much over the gas concentration and pressure is almost a given as light loads only decrease pressure by a few percentage points.

What happens at the time of firing is the heat, pressure and concentration force these gases into the steel. Hotter barrels tend to allow deeper penetration into the steel, hardening it to the point of being brittle. The pressure and fit of the bullet cause the barrel to expand ever so slightly much like a snake eating a rat. This stress is greatest at the bore and with the higher hardness and corresponding loss in ductility, the bore eventually check.

Since the diffusion does not extend but a microscopic depth, the much greater ductility in the rest of the barrel prevents crack growth.

Heat just makes barrels live shorter lives. Chrome plating is nearly impervious to diffusion, hence the increased lifespan. Eventually the chrome wears away and then erosion starts.
 
Thanks everyone for your replies. Does having a stainless steel barrel make a difference? My mini 14 is a stainless steel model.

Also, if heat and gasses effect any barrel and chamber, why do we hear more about this with a rifle than a handgun? You can find threads on hot barrels in "The Art of the Rifle" but I did not find one in any handgun section.

By the way, when I said accuracy was not an issue, I was talking military accuracy. Most of our shots were timed and on the move. All the guns were more accurate than we were considering what we were doing when we were taking the shots. Before anyone asks, yes, we did have target zones that we had to hit (approx. 14" by 10")...heck the mini-14 would qualify in this scenario.

Finally, I'm talking Field Support and Entry SWAT members, not High Ground. High Ground guns were much, much more accurate and had to be dead-on when the barrel was cold, since most shots would be taken with a cold barrel.

Thanks again,

B.L.
 
Does having a stainless steel barrel make a difference?
Click to expand...

No. There is no concrete evidence that SS wears longer or shorter than chrome/moly or carbon steel barrels.

Highpower guys change our barrels every 4-5000 rounds.
 
if heat and gasses effect any barrel and chamber, why do we hear more about this with a rifle than a handgun?
Click to expand...

rifle rounds create much more heat :eek: than handgun rounds.
simple really, rifles get hotter because they fire hotter ammo.

stinger
 
Great dissection and dissertations above.

Handgun barrel shows less accuracy loss due to heating than rifle barrel for two reasons. (at least)

1. Accuracy of handgun generally falls in the realm of lousy rifle at best. So derrogation of accuracy is likely to go undetected.

2. Handgun barrel is short and stiff. Frequency of vibration is much higher and amplitude is low. Changes in the vibration are less with a given amount of applied heat.

Sam
 
I agree with Stinger that the major difference is that handguns simply do not use as much powder so they do not get as hot. Also, they use fast burning powder and most heat stays in the chamber area, and many handgun barrels are in the open (e.g., revolvers) and cool faster.

The accuracy question is not really so much about hot barrels as about what a barrel does when it gets hot. The normal stresses in a barrel from manufacturing plus the configuration of the stock will affect whether the barrel actually bends under heat. In a conventional rifle, the bottom of the barrel is in a stock which does not allow the barrel to cool; the top of the barrel is cooler and thus will expand less, so the barrel actually bends.

The main factor in barrel heating, of course, is not the number of rounds fired, but the time between shots.

Jim
 
KeithJ, I think your analysis is more appropriate to the long-term "lifespan" of a barrel, rather than what happens during any one string of shots. You definitely brought out some excellent explanation of what goes on during that lifetime.

:), Art
 
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