Musing on ar15 barrels

[Johnny C]

So, since thinner profile barrels heat up faster and cool faster, I was thinking.

Does the barrel get hotter behind the gas block since that is closer to the "explosion"?

If this is so, does anyone make a barrel that is heavier behind the gas block but pencil thin in front of the gas block?

Would flutes behind the gas block allow faster cooling since there is more surface area in a fluted barrel?

See where I am going with this?

Johnny C

 

[mjelder]

I'm no expert, but logically I would have to say that the barrel behind the gas block doesn't heat any more than the rest of the barrel. The explosion that pushes the bullet out of the barrel is contained and doesn't disperse until it exits the barrel. That along with the friction of the bullet (which is a lot more than most people think) causes the barrel to heat relatively even throughout.

I have had some experience with fluted barrels and I don't really buy into them that much. The extra surface area you get on the barrel for cooling really doesnt make it that much more lighter or that much faster to cool from what I have seen. Maybe others have different opinions on this?

 

[chuddly]

the barrel definatly does get hotter by the chamber. NO QUESTION ABOUT THAT. Go out and shoot your gun until it just starts to warm up. there will be quite a difference from chamber end to the exit end. Who ever says there isnt has never been out shooting that much.

Now once they get up to full temp i dont know if there is enough of a difference to make a real difference but i can for sure tell you that the chamber end heats up much faster.

 

[mjelder]

I still stick by saying that it heats at the same rate, but the end of the barrel would cool faster than right out of the chamber

 

[jrainw]

Whenever I make the M16 glow it starts glowing in the gas block area and then the glow works its way back to the chamber, might have a video but here is a pic from last years 4th of July celebration. 5, 30 round mags and a Beta, don't buy cheap plastic hand guards, they melt.

 

[Johnny C]

POF ARs have a big barrel nut / heat sink, so I thought there might be something to it.

POF-USA Patriot Ordnance Factory, Inc.

Scroll down and you will see it.

Anyway, I wonder if concentric heat sink rings (like on the old Tompson SMG) milled into the barrel aft of the gas block would keep the barrel cool. Could start with a bull barrel for the most largest diameter.

Could be a waste of time,effort and $ though... some would say yes, some would say no.

Like I said, just musing.

 

[SmileDocHill]

That is a very cool (or is it hot?) pic! I'm just really impressed at this.

 

[T4rdV4rk]

It might make sense for the gas block area to heat up before the straight length of the barrel since the gas system is in contact with the gas longer. Also, changes in geometry concentrate thermal energy just as they do stresses.

As for the barrel geometry, you would definitely not want to make the barrel pencil thin at any point. It takes more dye to turn a swimming pool blue than it does a glass of water. Same thing with thermal mass. If you had a very thin barrel, it would get hotter at the thin section as it has less steel to transfer the excess heat to.

Surface area is a big part of heat transfer equation. If you're curious about convection look up Biot, Rayleigh, Grashof. Hope some of this is helpful. And anyone is welcome to correct anything wrong I've said.

 

[jrainw]

I figured that the hot gas at high velocity going through the gas port in the barrel would cause a lot of heat transfer, and the barrel nut and receiver are big heat sinks keeping what should be the hottest end cooler than one would first think.