Heat Issues with M4 style barrels...

[btward79]

New to the AR scene, gun scene in general. Looking to build an AR, I get to pickup my lowers on the 18th wooo hoo!

I have already done hours of research on this stuff, apparently not enough as I still have questions...

While talking to a gun dealer he mentioned that the M4 style barrels (the ones with the indent on the barrel where a grenade launcher attaches to) are more susceptible to heat issues, ect because of that indent section on the barrel.

Now this does make sense, due to heat transfer, it's going to get hotter there. Is it an issue though if I don't have anything attached to it? Warpage, ect...

I'm looking at this upper kit at the moment... it looks to have that indent on the barrel, I'll call tomorrow to double check.

http://ar15-kits.com/contents/en-us/d1_AR15kits.html

16" barrel ARM-4 Military specifications Kit

[J_Rock]

You will never be able to fire fast enough in semi-auto for this to be a problem.

[Blacktail 8541]

You are worrying about nothing. If you shoot enough to worry about excess heat transfer it will happen with any barrel.

Welcome to the board.

[btward79]

Thanks!

More folks keep chiming in with your thoughts.

I have to admit, when he was telling me this, while it made sense in theory. I thought to myself, I said, self, the military uses it so whats the problem...

[Cal-Irish]

Dont worry about it.

[aplinker]

The heat issue isn't with the indentation, but with the thin section under the handguards.

Yes, it does cause POI to migrate with extreme rates of fire, but most people don't shoot that much/fast and, if you do, just get a different barrel profile.

[btward79]

The heat issue isn't with the indentation, but with the thin section under the handguards.

Yes, it does cause POI to migrate with extreme rates of fire, but most people don't shoot that much/fast and, if you do, just get a different barrel profile.

I doubt I'll shoot that many that fast as well, considering the cost of ammo these days.

You'll have to forgive me for my ignorance but what is POI? Also, the thin section under the handguards you are refering too, is this with all of the barrels or only the m4 style barrels?

[aplinker]

POI = point of impact

Most of the goverment-styled profiles are thin under the handguards...

a typical M4


A 20" gov't


SOCOM has added thickness since SOF often shoot more/rapidly and still need to maintain accuracy.



go here for schematics of all kinds of barrel profiles:

http://ar15barrels.com/profiles.shtml

CMMG has photos of many of them.

[bellson]

New to the AR scene, gun scene in general. Looking to build an AR, I get to pickup my lowers on the 18th wooo hoo!

I have already done hours of research on this stuff, apparently not enough as I still have questions...

While talking to a gun dealer he mentioned that the M4 style barrels (the ones with the indent on the barrel where a grenade launcher attaches to) are more susceptible to heat issues, ect because of that indent section on the barrel.

Now this does make sense, due to heat transfer, it's going to get hotter there. Is it an issue though if I don't have anything attached to it? Warpage, ect...

I'm looking at this upper kit at the moment... it looks to have that indent on the barrel, I'll call tomorrow to double check.

http://ar15-kits.com/contents/en-us/d1_AR15kits.html

16" barrel ARM-4 Military specifications Kit

HI BT,

Three things to remember:

1. M4 Barrel profile is skinny under the handguards, the indent in front of the sight block is nothing.

2. M4 Barrels are lighter than the heavy ones, by about 2 lbs. If you are going to carry the rifle, you should remember that.

3. It generally takes me about 80-90 rounds, firing quickly (aimed shots) to get my M4 barrel hot enough to perhaps effect accuracy, maybe 1 moa. Me bouncing around and jerking the trigger has a much greater effect than the heat.

M4 is a good trade off between weight and rigidity. The heavy part up front has more to do with harmonics than anything else.

Good Luck,

BTW: My favorite upper is a Del-Ton Mid-Length. And it is heavy by comparison.

[dieselpower]

Just to add some BS to this. Heat loss is due to surface area. The M203 cut out helps heat loss in the same way fluting helps. More surface area, more heat loss. If the area in question was tapered down slowly, the heat loss would be less, since the area is decreased. The M203 cut out is a sharp drop with a flat face on one side and a quick taper on the other. This is a greater surface area, so more heat is dissipated then a barrel without.

In the long run, it doesnt make a notable differance on a 16" barrel.

[aplinker]

I would disagree about the government-based profiles being good choices.

I would much rather have a lightweight or, if I were shooting scoped or static, a medium contour. Putting the mass and the thickness at the back is a much better design.

Of course, you'll want to add or subtract to the thickness if you move away from a 16" barrel, to maintain rigidity.

Just to add some BS to this. Heat loss is due to surface area. The M203 cut out helps heat loss in the same way fluting helps. More surface area, more heat loss. If the area in question was tapered down slowly, the heat loss would be less, since the area is decreased. The M203 cut out is a sharp drop with a flat face on one side and a quick taper on the other. This is a greater surface area, so more heat is dissipated then a barrel without.

In the long run, it doesnt make a notable differance on a 16" barrel.

That cut-out adds about 1% to the total surface area of the barrel. I'd call that nothing. Remember, the reduction in circumference has a reduction in surface, even though you gain for the cut-out. The total gained is tiny compared to the rest of the surface. This isn't the same for a cut down the length of the barrel.

[Sicarius]

I wouldn't worry about it at all. As said with Semi auto... it is a non issue... even with full auto, the m4 profile can take it. Granted a medium contour would be nicer but heat wouldn't be my first concern with a gov profiled barrel. 10 round mags aren't going to help heat the barrel either.
Kevin

[dieselpower]

I would disagree about the government-based profiles being good choices.

I would much rather have a lightweight or, if I were shooting scoped or static, a medium contour. Putting the mass and the thickness at the back is a much better design.

Of course, you'll want to add or subtract to the thickness if you move away from a 16" barrel, to maintain rigidity.





That cut-out adds about 1% to the total surface area of the barrel. I'd call that nothing. Remember, the reduction in circumference has a reduction in surface, even though you gain for the cut-out. The total gained is tiny compared to the rest of the surface. This isn't the same for a cut down the length of the barrel.

totally agree, its nothing...thats why I said it was just BS, but 1% is better then 0%...lol

[B Strong]

With a M4 profile, the barrel can get hot enough to effect point of impact of your rounds, but it takes full auto fire to actual damage the barrel, and the gas tube will melt before you can get to the point where the barrel will fail.

[a1fabweld]

I've never liked M4 barrel contours just because there is no purpose for the notch. If I could strap a grenade launcher on it, different story. They are trendy though.