How many mags do you fire off in rapid fire before you let your barrel cool down?  I did about 3 prety fast before the handgaurds started somking. I didn't just dump the mags rapid fire back to back.  I was shooting rapid fire groups of about 2-4 to see how tight of a group I could get. (In case you're wondering, the groups were all over the place but it was still fun.)

I have a 16" M4 profile barrel and wanted to know how hot I should let it get before giving it a chance to cool.

I make it a point to torture test every new gun to make sure it will be reliable when hot. Any gun is reliable when cold, but if it's still problem-free when hot you know that it should stand up to anything you can throw at it in a defensive situation.

After the first 200 (gentle and slow) rounds through my new Colt M4 carbine I let it cool down and then cleaned the barrel. Once it was cool I dumped four mags (120 rounds) through it as fast as I could pull the trigger and reload. My goal is to get as close to the maximum rate of fire as possible.

In the end of the four mag dump the handguards were hot to the touch and the barrel was steaming-but it still ran perfectly. I let it cool to the point where I could touch the barrel with bare hands and then repeated it six times without cleaning (840 rounds total plus the 200 initial rounds).

As far as I'm concerned if an AR can't handle that without a malfunction it's a piece of junk.

You dump 1000 rounds for every AR? That seems like a lot of barrel life being shot away.

~AbM

A friend and I put two BETA mags through a M16 in about four minutes, 100 round dumps each. We wound up melting the gas tube but the barrel (Bushmaster 14.5-inch Heavy) was/is fine. After replacing the gas tube the rifle works just fine and is just as accurate as before. I wouldn’t worry about a good chrome lined barrel.

I’ve found a good way to let them cool is by just setting them in a milk crate you use to haul stuff out in.

[img]http://volcano.photobucket.com/albums/1103/Monster11/arf/de084a17.gif[/img]

I know it sounds excessive, but it's necessary to ensure reliability.

Currently I only have three ARs, two preban 20" Colt 6601 HBARs and the new 16" Colt M4 carbine. Even though the HBARs have never been a serious part of my home defense plan I still need to make sure they are completely reliable.

The reason is that several times per year my ARs get loaned to my father's PD for use as patrol rifles. Whenever a normal shift is augmented with extra troops (Labor and Memorial Day weekends for example) they don't have enough long guns to go around. That's why I'm such a nazi about reliability. I wouldn't be able to live with myself if one of my rifles went down when one his guys needed it.

Recently my father's PD got four new Colt LE6920 carbines, but they still don't have enough since the new Colts replaced some of their aging Mini-14s that were literally falling apart. The old man is looking into buying surplus DRMO M16s from Uncle Sam, but the process has been long and tenuous.

   I've done 13 30rd mag dumps, somewhere within 5 min.  the upper was a 16" HBAR bushmaster.  i melted the part of the handguards where the gas tube meets the front sight base, which makes ff ras a necessity.  the gas tube did not melt and the weapon still functions well.  i have put about 7-9k thru it in the last 4 months... i lost track of how many rounds.
   so what i am saying is.... don't worry.

   Stainless

Will heating a barrel up that much hurt its accuracy permanently?

This is why I never buy USED RIFLES!

First of all thanks for all the replies.

So basicaly what you saying is as long as I am reasonable about it(I.E. don't dump like 20 mags back to back) I shouldn't worry about getting my barrel too hot?

Exactly. Don't worry about it.

Although the maximun rate of SUSTAINED fire should not exceed 12-15 rounds per minute...That's ONE round every FOUR seconds.

HUNTER.

Every time you fire a rifle, the bullet/gases plasma erodes the throat of the barrel.  When the barrel becomes too hot, the throat erosion is greater per round fired.

Bottom line is that barrels are seldom worn out in the rifling, it's the throat of the rifling that is worn, and the bullet has to jump father forward before it engages the rifling.  The longer that the bullet jumps forward without spinning, the less accurate the bullet will be, due to the rifling marring at bullet engagement.

Chrome lined barrel are less susceptive to erosion, but will still erode.  The downfall to chrome lined barrels is that most plated barrel are less unified in the lands and groves than a non chrome barrel, due to the variable thickness of the chrome plating as it apply down the bore.  If you plan on dumping mags in your rifle, chromed line is that way to go, but if your looking for a tack driver, a non-chromed barrel that is not mistreated will be a better solution.

Note: The determination of how accurate a barrel will be is determined by first the blank. Then how trued to bore line it’s turned, and then finally the reamed chamber.  In some cases, a chromed line barrel will out shoot a non-lined barrel, if the non-lined barrel is poorly produced.

P.S. The smoke that you were getting off the barrel was just CLP burning off the surface of the barrel.