Colt 6920, LMT SPM 14/16, M4 Viability

[grizzlyblake]

Here's the Crane info on carbine vs mid-length on a 14.5" barrel. Digest it however you will.

https://soldiersystems.net/2018/05/1...d-performance/

[AndyLate]

Here's the Crane info on carbine vs mid-length on a 14.5" barrel. Digest it however you will.

https://soldiersystems.net/2018/05/1...d-performance/

Unfortunately, the link focuses on extended barrel life, which is not directly related to gas system length. The reduced cyclic rate for a midlength gas system should not be shocking to anyone with much AR experience. Again, the linked article does not address increased or decreased wear and breakage of parts caused by gas system length.

[indianalex01]

Here's the Crane info on carbine vs mid-length on a 14.5" barrel. Digest it however you will.

https://soldiersystems.net/2018/05/1...d-performance/

Appears that you posted this without really reading it. Doesn’t really support what you said. Try to keep things factual vice opinion. Thanks.

[grizzlyblake]

Here's a link to the actual Crane slide deck report.

https://partner-mco-archive.s3.amazo...1527866983.pdf


I'm using the other poster's term "violent" to refer to the measured difference in bolt speed, with the mid-length being slower.

The mid-length gun's bolt speed is 22.6% slower than the carbine-length gun.

The mid-length gun's action cycles 15.9% slower than the carbine-length gun in full auto.

I guess it's semantics, but a slower cycling gun seems "less violent" to me. Less malfunctions seems "less violent" also.

Averaged overall bolt speeds and differences in bolt speeds are presented in Table. The P-Values of
bolt speed results for both suppressed and unsuppressed fire are less than 0.05, so there is a statistically
significant difference between the two gas systems. Bolt speed is uniformly lower for mid-length gas
systems when compared to carbine-length gas systems. Mid length bolt speed was 2.13 fps, or 12.4%,
lower than carbine-length for suppressed fire and 3.23 fps, or 22.6%, lower for unsuppressed fire.

Averaged overall cyclic rate of automatic fire and differences in cyclic rate for all round
counts is presented in Table. The P-Values of all cyclic rate of automatic fire results are less
than 0.05, so there is a statistically significant difference between the two gas systems for
these parameters. Mid length cyclic rate of automatic fire was 62.7 rounds per minute (rpm),
or 7%, lower than carbine-length for suppressed fire and 127.2 rpm, or 16%, lower for
unsuppressed fire. Averaged cyclic rate of automatic fire for ambient temperature testing
are similar to overall results.

Carbine-length gas systems experienced a total of 65 malfunctions directly attributable to the
weapon and 13 unserviceable parts. Mid-length gas systems experienced a total of 30 malfunctions
directly attributable to the weapon and 9 unserviceable parts. The total numbers of malfunctions
directly attributable to causes other than the weapon and the total numbers of unserviceable parts are
summarized below in Mean Rounds Between Failure (MRBF).


Results:
12,600 rounds of testing for comparison:
- mid length gas systems experienced a total of 30 malfunctions
- carbine length gas systems experienced a total of 65 malfunctions
- no significant differences between the two gas systems in muzzle velocity
- no significant differences between the two gas systems in terminal velocity
- decrease in bolt speed and cyclic rate of automatic fire for mid length
- no significant differences between the two gas systems in precision or barrel erosion
- high and low temperature testing showed no significant differences (malfunctions,
ROF) between two gas systems
- Recommended for use
- Recommended continuation testing for mid length.

[indianalex01]

Here's a link to the actual Crane slide deck report.

https://partner-mco-archive.s3.amazo...1527866983.pdf


I'm using the other poster's term "violent" to refer to the measured difference in bolt speed, with the mid-length being slower.

The mid-length gun's bolt speed is 22.6% slower than the carbine-length gun.

The mid-length gun's action cycles 15.9% slower than the carbine-length gun in full auto.

I guess it's semantics, but a slower cycling gun seems "less violent" to me. Less malfunctions seems "less violent" also.

The term that a few of you are using “violent” is a very poor choice. The Carbine gas system is a soft shooter and very reliable. I have never had an M4 fail in action and it’s a fine weapon. M16A4 is also a great weapon

[grizzlyblake]

Yeah, I don't think people are having 6920s fail all over or anything, but the Crane testing does show the carbines gas malfunctions at a higher rate.

Malfunction Carbine-Length / Mid-Length
Failure to fire 10 / 7
Failure to feed (from magazine) 22 / 10
Failure to eject 20 / 4
Bolts fails/hold rear 7 / 3
All other malfunctions 6 / 6
Total-Above malfunctions combined 65 / 30
Mean Rounds Between Failures (MRBF) 581.5 / 1,260.0

[1168]

The term that a few of you are using “violent” is a very poor choice. The Carbine gas system is a soft shooter and very reliable. I have never had an M4 fail in action and it’s a fine weapon. M16A4 is also a great weapon

You never had any failures to extract with them back in the day when they had lighter buffers and weaker extractor springs? Or any other stoppages related to bolt speed? Or were you not using them back then?

I agree that its a fine weapon today.

[MountainRaven]

Here's some light entertainment comparing a GI-type M4/M4A1 with a commercial/civilian-type AR.

[RUTGERS95]

Here's a link to the actual Crane slide deck report.

https://partner-mco-archive.s3.amazo...1527866983.pdf


I'm using the other poster's term "violent" to refer to the measured difference in bolt speed, with the mid-length being slower.

The mid-length gun's bolt speed is 22.6% slower than the carbine-length gun.

The mid-length gun's action cycles 15.9% slower than the carbine-length gun in full auto.

I guess it's semantics, but a slower cycling gun seems "less violent" to me. Less malfunctions seems "less violent" also.

lol, you still are failing here. can you catch your mistake?

oh and the percents look great until you actually look at them

[RUTGERS95]

You never had any failures to extract with them back in the day when they had lighter buffers and weaker extractor springs? Or any other stoppages related to bolt speed? Or were you not using them back then?

I agree that its a fine weapon today.

no, ,not a one. what tie period are you referring to?