Fluted barrel

[lysanderxiii]

I figured someone had already “been there, done that.”

The reason the cook-off numbers are so similar is the heat input from automatic fire is so high it out paces conduction of heat away from the chamber area in heavy barrels. What does change is the number of rounds fired after cook-off temperature is achieved. Lighter barrels tend to fire more rounds before cooling enough to not cook-off. Heavy barrels can redistribute heat within the barrel material, as well as dumping heat to the environment, light barrels are more uniformly heated, so can only dump heat overboard.

 

[Varminterror]

But what happens in space, where there cannot be convection, can you just not dump heat?

Have you ever fired a rifle barrel in space?

Obviously, in the void of outer space, there is no contact for conduction nor dynamic mass for convection, so radiation is the primary means of heat transfer from the sun through the void of space to the Earth. When we start shooting cartridge firearms to fight aliens in space, I guess we can worry more about what happens in space than what happens on Earth. The total mass of my body right now includes my glasses. Which do you think is more dangerous - throwing my 2oz glasses at someone at 50mph, or throwing the rest of my 210lb body at them at 50mph? Radiation isn’t the major mode of ejection for heat from a rifle barrel in air. The insulated handguard scenario isn’t free exchange, and has inhibited free conduction and natural convection which occur for an exposed barrel.

 

[bangswitch]

I was waiting for the calculations that shows us how many more rounds per hour a fluted barrel could shoot and stay at the same temp.

Someone has surely done it.

I'm sure someone has, most likely Varmint or Lysander.

Not all the heat comes from the bullet's friction down the barrel, a lot of it comes from the burning powder charge. So, you'd have to take into account
1- the geometry of the barrel (surface area, made up of length and effective diameter/radiating area) and mass
2- the internal bore surface area in contact with the projectile
3- the powder charge (varies with caliber/case size and powder type)
4- rate of fire.
5-??? that I'm forgetting

That's where my empirical calculations work just fine. Shoot a few cylinder or magazine loads and then grab the barrel. The degree of burn you get determines if you need to slow your rate of fire. Grabbing the muzzle end will do, you can't always get the middle (AR handguards, etc.) and you know the breech end will get hot fastest.

Doesn't the military have a standard time or round rate for barrel changes to keep from overheating a barrel on guns with interchangeable barrels (M60, M-2, etc)?

 

[lysanderxiii]

Radiation isn’t the major mode of ejection for heat from a rifle barrel in air. The insulated handguard scenario isn’t free exchange, and has inhibited free conduction and natural convection which occur for an exposed barrel.

"External Barrel and Handguard Temperature of the 5.56mm M4 Carbine", Windham, Jeff, U.S. Army Research, Development and Engineering Center, Rock Island Arsenal found that most heat transfer from the barrel was through radiation. Unless you are forcing a draught around the barrel (as in a Lewis machine gun), or shooting on a fairly windy day, there is not enough air movement for large amounts of convective cooling.

 

[lysanderxiii]

I was waiting for the calculations that shows us how many more rounds per hour a fluted barrel could shoot and stay at the same temp.

Testing described above showed that all barrels took approximately the same amount of time to cool from the maximum achieved temperature to ambient. This would indicate that fluting does not effect cooling that much.

 

[lysanderxiii]

Doesn't the military have a standard time or round rate for barrel changes to keep from overheating a barrel on guns with interchangeable barrels (M60, M-2, etc)?

For the M249 if firing at a rate of 50 rounds per minute (fired in 3 to 5 round burst every 4 to 5 seconds), change the barrel every 10 minutes.
If the rate of fire is 100 rounds per minute (fired in 8 to 10 rounds burst every 2 to 3 seconds), change the barrel every 2 minutes.
If firing continuously at the cyclic rate, change the barrel every minute.

For the M60 if firing at a rate of 100 rounds per minute (fired in 6 to 9 round burst every 4 to 5 seconds), change the barrel every 10 minutes.
If the rate of fire is 200 rounds per minute (fired in 10 to 13 rounds burst every 2 to 3 seconds), change the barrel every 2 minutes.
If firing continuously at the cyclic rate, change the barrel every minute.

For the M240 if firing at a rate of 100 rounds per minute (fired in 6 to 9 round burst every 4 to 5 seconds), change the barrel every 10 minutes.
If the rate of fire is 200 rounds per minute (fired in 10 to 13 rounds burst every 2 to 3 seconds), change the barrel every 2 minutes.
If firing continuously at the cyclic rate, change the barrel every minute.

The M2A1:
If the rate of fire is less than 40 rounds per minute (fired in burst of 6 to 9 rounds at 10 to 15 second intervals) change the barrel daily.
If the rate of fire is mores than 40 rounds per minute (fired in burst of 6 to 9 rounds at 10 to 15 second intervals) change the barrel every hour.
If firing continuously at the cyclic rate, change the barrel every half hour.

 

[Jim Watson]

Unless you are forcing a draught around the barrel (as in a Lewis machine gun),

I am kind of surprised that nobody has set up an AR like a Lewis gun. The handguard is already tubular, not much trouble to extend it past the muzzle and ventilate at the breech.

 

[Varminterror]

Testing described above showed that all barrel took approximately the same amount of time to cool from the maximum achieved temperature to ambient. This would indicate that fluting does not effect cooling that much.

For the M4 being assessed - a 14" barrel with 7" of the chamber end encapsulated in the handguard.

 

[lysanderxiii]

For the M4 being assessed - a 14" barrel with 7" of the chamber end encapsulated in the handguard.

According to the test report, the barrels were instrumented with thermocouples on the barrel surface, except during the endurance test, which necessitated the removal of the handguards.

This tends to agree with anecdotal evidence from here and other threads on this subject.

 

[lysanderxiii]

I am kind of surprised that nobody has set up an AR like a Lewis gun. The handguard is already tubular, not much trouble to extend it past the muzzle and ventilate at the breech.

You need an open back end too. Doable, but a rather restricted opening.

 

[Varminterror]

I haven’t seen one of these in about 15 years, but I had a dozen or so customers ask for these in the past.

Ungainly, but man, they would get SUPER hot, very clear they were moving a lot of heat.

 

[GooseGestapo]

If fluting has no benefits, why are machine gun and auto cannon barrels fluted?
Sniper rifle barrels are fluted as such to maintain stiffness, but to also reduce overall weight.
To see a Bradley Bushmaster cannon in use is an awesome thing. The barrels in fire fights become cherry red at the breech. The stream of fire is incredible!
There’s a YouTube video of an engagement of two Bradley’s operated by Ukrainian personnel engaging a Russian T90 main battle tank. The bushmaster cannons rake away the external antennas, camera’s, and sensors blinding the tank. They also jam the turret leaving the tank vulnerable, and the crew evacuating the tank. It’s later blown up by a FPV drone.
Yes, fluting works.

 

[Varminterror]

Sniper rifle barrels are fluted

Conventionally, rifles issued by the US for snipers have not and are not fluted. The M82 and the McMillan Tac-50 being exceptions, of course, a weight reducing effort for an anti-materiel weapon. But the M40, M24, M2010, etc are not fluted barrels.

 

[jmorris]

I haven’t seen one of these in about 15 years, but I had a dozen or so customers ask for these in the past.

Ungainly, but man, they would get SUPER hot, very clear they were moving a lot of heat.

View attachment 1247583

I can see that being much more effective at dissipating heat than a couple .050” deep cuts in steel.

 

[FL-NC]

The US mil experimented long ago with fluted barrels for the M16 family of weapons for cooling purposes. I wasn't part of the test, but the conclusion was that the miniscule difference in temps wasn't worth the effort and $ of the extra machining processes, and the effects it would have on mounting the M203.

 

[Miami_JBT]

Only gun I have that has flutes is a FNAR.

 

[lysanderxiii]

The US mil experimented long ago with fluted barrels for the M16 family of weapons for cooling purposes. I wasn't part of the test, but the conclusion was that the miniscule difference in temps wasn't worth the effort and $ of the extra machining processes, and the effects it would have on mounting the M203.

See Post #45