Is mid length that much softer shooting than carbine ?

[WAW44]

assume both use h2 buffer and same spring, how big is the perceived difference between a 16 barrel carbine setup , and a 16 barrel mid length setup. Both DI of course. I saw the dwell time videos and other stuff, but is the difference just academic , or does it really make for a better running gun ?

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[DirectDrive]

I don't know if anyone an quantify a smoother recoil pulse, but a 16" barrel sticking out of a carbine handguard looks ridiculous to my eye.
The "dwell length" was set with the original 20" rifle and mid gas on a 16" maintains it.

Welp, there goes my chances for mayor !

 

[RX-79G]

The dwell time includes the time it takes for the bullet to get to the gas port, so it is still shorter than a 20" rifle. But the important thing is that camming action of the bolt carrier was designed with a 20" barrel's port location, so anything shorter than that is going to unlock earlier when there is more residual case pressure. How soft the rifle shoots is essentially a combination of how much gas pressure there is in the gas tube and how much residual case pressure there is, which combine to accelerate the bolt carrier into your shoulder.

Increasing bolt mass with a heavier buffer helps, as does choking off the gas with a tiny port. But neither works as well as just tapping the gas later.


So it not only looks better to use a mid length gas system, but it does work better. Less recoil, less extractor force, slower bolt speed during feeding (one of the reasons for M4 feed ramps.)

 

[DunRanull]

How does the shorter barrel/gas tube effect or relate to the (semi-auto, civilian) M4 carbine? I've got one and havent broken it in yet...

 

[RX-79G]

How does the shorter barrel/gas tube effect or relate to the (semi-auto, civilian) M4 carbine?

While you aren't getting full auto problems, full auto high cyclic rates come from the same problem - low dwell time and higher pressures in both the chamber and gas system. So the action opens earlier, strikes the buffer harder and strips the round quicker.

The reliability improvement of the M4 over the XM177 is more barrel forward of the gas port so the gas flow is more controlled and constant. Plus the feedramps.

 

[Cerberus Group]

Carbine gas system is fairly abusive to the parts involved. Anytime you can ease the force on the system the better.

Mid length with an H2 and a Blue Sprinco spring, or better yet the A5 with a A5H2 buffer and Sprinco Green spring, gets the system closer to the original system cycle design.

 

[Cerberus Group]

While you aren't getting full auto problems, full auto high cyclic rates come from the same problem - low dwell time and higher pressures in both the chamber and gas system. So the action opens earlier, strikes the buffer harder and strips the round quicker.

The reliability improvement of the M4 over the XM177 is more barrel forward of the gas port so the gas flow is more controlled and constant. Plus the feedramps.

Also harder on the bolt lugs and cam pin.

 

[DirectDrive]

The dwell time includes the time it takes for the bullet to get to the gas port, so it is still shorter than a 20" rifle. But the important thing is that camming action of the bolt carrier was designed with a 20" barrel's port location, so anything shorter than that is going to unlock earlier when there is more residual case pressure. How soft the rifle shoots is essentially a combination of how much gas pressure there is in the gas tube and how much residual case pressure there is, which combine to accelerate the bolt carrier into your shoulder.

Increasing bolt mass with a heavier buffer helps, as does choking off the gas with a tiny port. But neither works as well as just tapping the gas later.


So it not only looks better to use a mid length gas system, but it does work better. Less recoil, less extractor force, slower bolt speed during feeding (one of the reasons for M4 feed ramps.)

"Dwell Time" is the amount of time that the gas system is under pressure.
Therefore, dwell time is directly proportionate to the barrel length after the the gas port.
This length dictates the amount of time that the gas system is pressurized.

 

[DirectDrive]

How does the shorter barrel/gas tube effect or relate to the (semi-auto, civilian) M4 carbine? I've got one and havent broken it in yet...

Carbine gas on a 16" barrel ?

 

[Cerberus Group]

"Dwell Time" is the amount of time that the gas system is under pressure.
Therefore, dwell time is directly proportionate to the barrel length after the the gas port.
This length dictates the amount of time that the gas system is pressurized.

This is correct. Shorter barrels won't support a mid length gas system, as there's not enough dwell time to keep pressure up to cycle the action.

 

[JasonTetziki]

Yes OP, mid gas gives a much softer recoil than carbine gas.

 

[arrowshooter]

Years back I shot two identical setups with the only difference being one had mid gas and the other had carbine gas. Off a rest on a bench the mid gas was extremely smooth and the carbine gas bounced up off the rest and I could feel a bit more recoil.

 

[DunRanull]

I've owned several AR15's over the decades and had trouble with one, a semi-auto 177 (Colt). A 14" with the long welded flash suppressor to make it legal in USA. It got dirty easily and jammed up under wet conditions.. Got rid of it and got an AK. None of my other AR's have done this (yet). Don't think I've ever had a mid-length, just shorties and 20"-inchers. Stoner designed the system around the .223 20" barrel. Never have had (yet) any trouble with 20-inchers.
That said- weighing one thing against the other- I trust and generally prefer the AK, tho the AR (even the shorty version) IS "America's Rifle" these days and ammo and parts are far more widely available in the States than the AK. That may be slowly changing with the manufacture of US-made AKs... but it won't change enuff in my lifetime to tip the scales for ME... But then, it's an AK, who needs spare parts?
All that said- I prefer the Stoner-designed 20" AR15 IF I'm going to be using an AR in a defensive situation. YMMV, of course!

 

[RX-79G]

"Dwell Time" is the amount of time that the gas system is under pressure.
Therefore, dwell time is directly proportionate to the barrel length after the the gas port.
This length dictates the amount of time that the gas system is pressurized.

My bad. Though I think it is more useful to look at the system with the barrel before the port as well because that dictates port pressure and residual chamber pressure. Even if you made it so the dwell time was identical between a carbine, mid and rifle, you would still have significant differences in bolt speed with the same buffer.