Barrel life, how do you determine your barrel has had it?

[alx01]

Mild?

One magazine at one round per second.
One magazine full automatic.
One magazine at one round per second.
One magazine full automatic.
Ten Minutes.
Repeat 120 round cycle.
Forced air until barrel is cool to the touch
Repeat 240 round cycle.
Continue until you get 6000 rounds

One magazine at 1 round per second get the barrel to over 800 degrees at the hottest point, and one 30 round magazine in full auto right after that will get the barrel over 1200 degrees. That's a pretty rough firing schedule.

You can find the standard test procedure in TOP 3-2-45 - Small Arms Hand and Shoulder Weapons and Machine Guns.

And, the reason the Army is so in love with ball propellants is because it shows the least throat erosion of all the typical propellants, that is also why it is so dirty. 1) the calcium carbonate, a by product of the manufacture process happens to be a good erosion inhibitor, 2) all that solid residue holds the heat off the barrel walls until it cools slightly and condenses out, and 3) ball propellant is heavily deterred and has a low flame temperature.

Good info. Thank you. I didn't realize that barrels reach 1200 degrees under this schedule. It just looked to me that 120 rounds of mixed firing with 10 min break in between and a full cool down after 240 rounds wasn't too bad.

If I recall the same Mil-B-11595E steel is used in many mil barrels including M240/M249 which would experience a more intense firing schedule.

I'm just confused at this point and trying to put two and two together. Wouldn't that imply that M240/M249 wear out barrels significantly faster under a full auto schedule than M16/M4?

[Humpy70]

Actually this is a copy/paste from 3 2 045 as referenced above. Page 15/16 of the document dtd 2007.

(2) Fire three each ten-round targets from each test weapon using the procedures given
in paragraph 4.4 and record velocity and dispersion. The range distances for targets are usually
established in the requirements documents; when they are not specified, refer to test reports on
similar items, or use 50 meters for handguns, 100 meters for shoulder weapons, and 300 meters
for sniper weapons. Velocities should be recorded as corrected to muzzle using any appropriate
instrumentation; the same instrumentation should be used for the duration of the test.

(3) Fire each test weapon in accordance with the firing procedure (number of rounds,
firing cycle, mode of fire, sequence of modes) as specified in the test plan or requirements
document. All firing is done with the weapon firmly hand-held or held in an appropriate mount.
If a firing procedure is not specified, use the firing cycle shown below. Note that the procedure
is based on a typical 30-round magazine and may need to be adjusted to account for specific
magazine sizes.

The basic firing cycle is 120 rounds (the first cycle includes the rounds fired for velocity
and dispersion). Observe a minimum time of 10 minutes to cool the weapon after firing the
120 rounds.

Every 240 rounds, the weapon must be cooled to the point that the barrel can be held in a
bare hand indefinitely (these cycles may have to be modified if they approach or exceed the
cookoff temperature, see para 4.2).

Every 600 rounds (five 120-round cycles), wipe and lubricate the weapon without
disassembly

[lysander]

If I recall the same Mil-B-11595E steel is used in many mil barrels including M240/M249 which would experience a more intense firing schedule.

The steel used by FN for the M240 and M249 is steel made to Drawing C11825998.

This is the proprietary "FN Barrel Steel" FN is so proud of.

[georgeib]

The steel used by FN for the M240 and M249 is steel made to Drawing C11825998.

This is the proprietary "FN Barrel Steel" FN is so proud of.

Is there anything substantial that sets it apart from standard 4150 barrel steel?

[alx01]

The steel used by FN for the M240 and M249 is steel made to Drawing C11825998.

This is the proprietary "FN Barrel Steel" FN is so proud of.

Thank you. I stand corrected. I must have misread Mil-B-11595E spec and made a broader assumption (incorrectly) that all small arms must meet this requirement.

[M995]

One magazine at one round per second.
One magazine full automatic.
One magazine at one round per second.
One magazine full automatic.
Ten Minutes.
Repeat 120 round cycle.
Forced air until barrel is cool to the touch
Repeat 240 round cycle.
Continue until you get 6000 rounds

For the magazines fired in full automatic, did you mean that those magazines were fired in a single continuous burst or in 3-5 round bursts? From what I have read in the 2007 and 2016 versions of TOP-3-02-045, the magazines fired in automatic mode are fired in 3-5 round bursts at approx. 85 rpm. Or is there a newer revision of TOP-3-02-045 with a different firing schedule than the 2007/2016 versions?

[lysander]

3-5 bursts.

[lysander]

Is there anything substantial that sets it apart from standard 4150 barrel steel?

FN thinks so.

I don't what it's composed of so, I can't say.