Excessive heat on AR?

[Robert Kayland]

I recently built my first AR and took it out for the first time yesterday and put 50 rounds through it as a test.

After the first few rounds of each magazine evinced FTF, everything worked perfectly. I shot 3 rounds in quick succession, let it rest for about 5 seconds, then continued that pattern until each magazine was exhausted.

From having shot a lot of M16 back in my Army days and not remembering any untoward heat on the barrel back then, I was surprised that this AR's barrel seemed overly hot and took about 10 minutes to cool down.

Ammo used was Federal .223.

Is this heat normal, or is it a reflection of perhaps lower quality metal used in the upper? I mean, it seemed like, heaven forfend, if I ever got into a situation where hundreds of rounds would have to be fired within a short time frame, the darn thing would start glowing red.

FWIW, here's the info on the upper:

Daniel Defense 16 inch Cold Hammer Forged barrel installed on a CMT Flat Top receiver. 5.56 chrome lined bore and chamber, 1/7 twist, F marked front sight, A2 flash hider, M4 ramped extension and receiver. Standard handguards.

[lilb93]

2 30 round clips and my barrel is pretty damn hot... not hot enought to burn but if it touches you in the wrong place you know it.

[TXDMERC73]

i have the same thing happen to my Bushmaster and i have a HBAR after 2 -30 round mags its very hot. i am thinking about getting aluminum for the fornt handles i will take off the plastic and replace them with aluminum ones see if that helps, and also need a aluminum heat sink underneath.u can add a aluminum railing that also helps keep the barrel cooler or a heatsink on the barrel nut. i am gonn get an aluminum rail for on top my front handle and on bottom it might help keep the barrel cooler.

[Robert Kayland]

Heh, I just saw a post on another forum where the heat issue is discussed, and apparently it's not uncommon for ARs and AKs to get uncomfortably hot when you put a few mags through quickly... they even mentioned soldiers purposely training by using their front hand on the magazines while firing, in preparation for when the barrel became so hot that even with the front guard grips/heatshield the rifle was hard to handle in the standard way.

[Robert Kayland]

Found another interesting item, emphasis on D and E below... apparently, shooting one round every 4 to 5 seconds is the recommended rate of fire... good to know:

GROUND PRECAUTIONARY MESSAGE
ACALA #97-03
DATE: R 051413Z NOV 96
CLASSIFICATION: UNCLASSIFIED (1nn)
SUBJECT: GROUND PRECAUTIONARY MESSAGE (GPM), 97-03 5.56MM M4A1 CARBINE

1. DISTRIBUTION: {MENU} THIS IS A GROUND PRECAUTIONARY MESSAGE THAT HAS NOT BEEN TRANSMITTED TO SUBORDINATE UNITS. SOCOM COMMANDERS WILL IMMEDIATELY RETRANSMIT THIS MESSAGE TO ALL SUBORDINATE UNITS, ACTIVITIES
OR ELEMENTS AFFECTED OR CONCERNED. RETRANSMITTAL SHALL REFERENCE THIS MESSAGE. SOCOM COMMANDERS WILL VERIFY RECEIPT WHEN RETRANSMITTING THIS MESSAGE BY SENDING AN INFO COPY OF THE RETRANSMITTAL TO DIRECTOR,
TACOM-ACALA, AMSTA-AC-ASIR, ROCK ISLAND, IL.

2. PROBLEM DISCUSSION:

A. SUMMARY OF PROBLEM: SEVERAL INCIDENTS OF COOK-OFFS, IN AND OUT OF BATTERY, AS WELL AS BURST BARRELS, HAVE OCCURRED WITH THE 5.56MM M4A1 CARBINE. THESE INCIDENTS HAVE RESULTED IN INJURIES TO WEAPON USERS. THESE INCIDENTS RESULT FROM FIRING NUMEROUS ROUNDS WITHIN A SHORT AMOUNT OF TIME WITHOUT ADEQUATE COOLING.

(1) COOK-OFFS OCCUR WHEN A LIVE ROUND IS LEFT IN THE CHAMBER OR IN CONTACT WITH THE CHAMBER OF A HOT WEAPON AND HEATS TO THE POINT THAT THE PROPELLANT IS IGNITED.

(A) SUSTAINED FIRING OF THE M16 SERIES RIFLES OR M4 SERIES CARBINES WILL RAPIDLY RAISE THE TEMPERATURE OF THE BARREL TO A CRITICAL POINT.

(B) FIRING 140 ROUNDS, RAPIDLY AND CONTINUOUSLY, WILL RAISE THE TEMPERATURE OF THE BARREL TO THE COOK-OFF POINT. AT THIS TEMPERATURE, ANY LIVE ROUND REMAINING IN THE CHAMBER FOR ANY REASON MAY COOK-OFF (DETONATE) IN AS SHORT A PERIOD AS 10 SECONDS.

(C) WHEN THE WEAPON HAS REACHED THE COOK-OFF POINT (OR TEMPERATURE) A ROUND SHOULD NOT BE LEFT IN THE CHAMBER FOR ANY LENGTHY PERIOD OF TIME. THE WEAPON SHOULD BE CLEARED AND THE BOLT LOCKED TO THE REAR TO ALLOW COOL
DOWN.

(D) SUSTAINED RATE OF FIRE FOR THE M16 SERIES RIFLES AND M4 SERIES CARBINES IS 12-15 ROUNDS PER MINUTE. THIS IS THE ACTUAL RATE OF FIRE THAT A WEAPON CAN CONTINUE TO BE FIRED FOR AN Indefinite LENGTH OF TIME WITHOUT SERIOUS OVERHEATING.

(E) THE SUSTAINED RATE OF FIRE SHOULD NEVER BE EXCEEDED EXCEPT UNDER CIRCUMSTANCES OF EXTREME URGENCY. (NOTE: A HOT WEAPON TAKES APPROXIMATELY 30 MINUTES TO COOL TO AMBIENT TEMPERATURE CONDITIONS).

(F) THE USER'S MANUAL (TM 9-1005-319-10) FOR THE M16 SERIES RIFLE AND M4/M4A1 CARBINE STATES, "THAT IF A MISFIRE OCCURS IN A HOT WEAPON, REMOVE THE ROUND FAST (WITHIN TEN SECONDS). IF THE ROUND CANNOT BE REMOVED
WITHIN TEN SECONDS, REMOVE THE MAGAZINE FROM THE WEAPON, POINT THE WEAPON IN A SAFE DIRECTION AND WAIT FOR 15 MINUTES."

(G) CAUTION SHOULD BE TAKEN BY THE USERS TO KEEP THEIR FACE AWAY FROM THE EJECTION PORT WHILE CLEARING A HOT WEAPON.

(2) COOK-OFFS OUT OF BATTERY RESULT FROM A ROUND WHICH COOKS OFF WHEN THE BOLT IS NOT LOCKED OR A ROUND WHICH COOKS OFF AS THE USER IS TRYING TO CLEAR THE WEAPON.

(3) BURST BARRELS RESULT WHEN THE WEAPONS ARE FIRED UNDER VERY EXTREME FIRING SCHEDULES AND THE BARREL TEMPERATURE EXCEEDS 1360 DEGREES FAHRENHEIT. WHEN THE BARREL REACHES THESE EXTREME TEMPERATURES, THE BARREL STEEL WEAKENS TO THE POINT THAT THE HIGH PRESSURE GASES BURST THROUGH THE SIDE OF THE BARREL APPROXIMATELY 4 INCHES IN FRONT OF THE CHAMBER. THIS CONDITION CAN RESULT IN SERIOUS INJURY.

B. PARTS, ASSEMBLY, OR COMPONENTS TO BE INSPECTED: NA

3. USER ACTIONS. {MENU}

A. TASK OR INSPECTION SUSPENSE DATE (IF APPLICABLE): N/A

B. REPORTING COMPLIANCE SUSPENSE DATE: N/A

C. INSPECTION PROCEDURES: N/A

D. CORRECTION PROCEDURES: RANGE PERSONNEL AND USERS SHOULD AVOID EXCEEDING THE MAXIMUM AND SUSTAINED RATES OF FIRE DESCRIBED IN THE USER'S MANUAL FOR THE M16 SERIES RIFLES AND M4 SERIES CARBINE. USERS SHOULD BE TRAINED ON
THE CAUSES AND HAZARDS OF COOK-OFF. BETWEEN FIRING SCHEDULES, ADEQUATE WEAPON COOLING TIME SHOULD BE ALLOWED
__________________

[TXDMERC73]

yes thats true but you can modify some ways to help keep the barrel cooler another good way is that end grip thats mounted under the AR front handle that also helps handling the barrel when its hot

[Guns4Fun]

Buy a set of m4 double heat shield handgaurds. They work much better than the standard carbine handguards.

Or put a rail on it with a vertical grip. But depending on how you hold the V grip, your hand might still get hot.

[ungawa]

Two or three mags fast and the rifle will get pretty hot. But you still have some way to go.

I have an M16 and shoot 100-round Beta mags through it no problem. But I give it a rest or swap uppers after 100 rounds. Here is some additional info I have noted from other sites:

ARDEC Engineering Support Directorate

Rounds to Cookoff

M16A1/ M193 Ball= 150rds @ 85rpm

M16A2/ M855 Ball= 170rds @ 85rpm

M4/ M855 Ball= 190rds @ 78rpm

http://www.uzitalk.com/forums/showthread.php?t=25367

In our barrel testing done at MGI, we found that normal gov't profile type barrels would begin cooking off between 180-200 rounds. Medium profile barrels went a little longer, around 210 rounds. HBAR type barrels made it to around 240 rounds, before cooking off.
This was in normal ambient temperature conditions.

In high-temp(150 degrees ambient temps) the rounds fired before cook-offs started were about half to two-thirds the number in normal temps.

In many circumstances, it took 20-30 seconds before cook-offs began, with the round in the hot chamber.

This test was done with changing 30-round mags as fast as possible, so there was a couple seconds of "rest" between each magazine change. It also was done with M4 plastic handguards in place, and not an alloy ventilated handguard.

Belt-fed may reduce the number of rounds till cook-off, because of more continuous firing than mag changing, but the alloy ventilated handguard might offset some of that too.

Of course, all tests will have somewhat differing results, because no two testing conditions are exactly the same.
But, you could use these numbers as a guideline, and check your actual results against these.

So, as expected, the duration of fire is based on the rate of fire. 12-15 rpm goes about forever. Cyclic could get you into trouble with Beta mags before the second mag is done (less than 30 seconds). A little less than cyclic with 30 round mags and you can probably get the old combat load (210 rounds) out without cookoff based on MGI's data (but not the Army's). But if you're firing that fast you're either goofing off or have serious problems that bullets can't solve.

Like I said, I stop at 100 rounds in full auto (rapid or cyclic). More than that and the gun starts to really smoke and it smells like a rifle should not smell.

[Magnum Banana]

Keep firing until it catches on fire. That is the safe limit. Oh wait you said AR not AK.

[Berks_Iraq_Vet]

Doing a convoy live fire prior to deploying to Iraq, one of my NCOs was firing his M-4 (semi automatic). After a few mags, rounds started cooking off. He had to drop his mag and wait for weapon to cool down. First time I ever saw that happen.