1:00 ejection & Short stroking ?

[HKGuns]

This is what I've collected from various sources:

SOLGW GAS PORTS:
10.5" Carbine .073
11.5" Carbine .071
12.5" Carbine .068
14.5" Carbine .0625
16" Carbine .0625
13.7" Mid .0785
14.5” Mid .077
16" Mid .076
18" Rifle .0995
20" Rifle .093

Textbook TDP GAS PORTS:
Mk18 10.3” Carbine .070
M4 14.5" Carbine .0625
Mk12 18” Rifle .0995
M16 20" Rifle .093
CRANE 14.5 Mid-Length gas port reportedly .076


AR15 Gas Port Sizes
Disclaimer: These are lists of compiled information from multiple sources. While we make our best effort to test and produce these should be considered for reference only. Any time you start messing with the gas port on your rifle you run the risk of destroying the barrel or causing it to be over gassed. It is much better to slowly work your way up to what you would be happy with.

AR-15 Platform 5.56mm
20"rifle5.56 0.0935
20"rifle5.56 0.096
20"rifle5.56 0.098
16"mid5.56 0.078
16"mid5.56 0.081
16"car5.56 0.0625
16"car5.56 0.065
16"car5.56 0.07
14.5"car5.56 0.067
14.5"car5.56 0.086
11.5"car5.56 0.081
11.5"car5.56 0.089
24" rifle5.56 0.089

And this seems to go with the chart you posted:

The USGI M4 is not 0.070-0.086". The port diameter as spec'd by Colt is 0.0625"/0.063", or 1/16th of an inch.. This is so because of the USGI M16 is listed as 0.092"/0.093" or 3/32nd of an inch. How is this so? Due to port pressure of a M16 is 13,000psi while the M4 ramps up to 26,000psi. If your still boggled, this is the fact that the dwell time factors off a distance of 7 inches from port to muzzle.

Gas passes through a 0.092-inch-diameter port in the barrel, located 13.2 inches forward of the bolt face (with the bolt in the locked position)

The carbine gas port is located closer to the chamber than the gas port of the rifle: 7.5 inches instead of the 13 inch distance on the rifle. The gas pulse therefore enters the gas tube sooner and reaches the carrier group earlier than it does in the rifle length barrel. In addition to reaching the carrier sooner, it reaches it at higher pressure. The gas pressure at the carbine’s gas port is double that of the rifle: 26,000 psi vs. 13,000 pounds per square inch. (ArmaLite)

It is necessary to remember that the 5.56×45 NATO cartridge was designed specifically for a 20-inch barrel on a gas operated weapon with 7 inches of dwell time after the gas port. The 14.5-inch M4 barrel retains the 7 inch dwell length after the gas port.

Armalite Technical Note #48: The carbine gas port is located closer to the chamber than the gas port of the rifle: 7.5 inches instead of the 13 inch distance on the rifle. The gas pulse therefore enters the gas tube sooner and reaches the carrier group earlier than it does in the rifle length barrel. In addition to reaching the carrier sooner, it reaches it at higher pressure. The gas pressure at the carbine’s gas port is double that of the rifle: 26,000 psi vs. 13,000 pounds per square inch.

COLT GAS PORT DIAMETER: (reportedly this is from Colt reference material)

Attachment 67741

Another reference for gas port sizes which is updated: https://docs.google.com/spreadsheets...#gid=766121382

Fantastic information. Thank-you.

[markm]

What the heck is that "AR-15 platform 5.56mm" ports?

Just the sight of those 11.5 ports over .080" is pissing me off.

[JoeBobJoe]

Ran it after opening up gas port, no short stroke ftf, had 1 stove pipe out of 4 mags. I Never had a stove pipe before. Ejection was sharper but not to aggressive around 2:30 to 3:00 still around 4 ft maybe 5 ft. It ejected a few rounds to 4:30 - 5:00 IDK ?, so I also remove O-ring, & ejection stayed at 2:30 3:00 & 4 to 5 feet, no stoppages.
Seems more reliable now. I recorded the ejection before opening gas port up, it was dribbling out of ejection port with a 3 oz buffer & .063 port. Plus could barely throw brass clear bolt was hitting brass as bolt closed.
I didn't want to open it to .093 but a 18 midlenth is .093.
I opened it to.080 first & I wasn't happy.
This is 1 incident with 1 AR, YMMV. Reliability was my goal, it's more reliable now.
I also checked for gas leaks & tried lighter buffers, mags, ammo, different buffer spring, before opening it up.
Only done as last resort.

[JoeBobJoe]

Yeah, I actually was not thinking / saying the extractor force was "too heavy"

I was thinking (based on your description) the cartridge case MIGHT be leaving the bolt face prematurely.

Anyway, - far more helpful than my "thoughts" - somewhere around the forum here is a trouble-shooting flow-chart that can help you approach this in a logical manner. Random swapping/tweaking/removing/replacing, without Variable Isolation, is a good recipe for lots of wasted time and ammo before you learn the actual culprit / culprits

Good luck, and keep us posted.

With the price of ammo, figuring out what is the cause of malfunctions can quickly out price the cost of a new barrel. After looking into usual suspects, & trying various things. I opened up my port from .063, what seems way too tight on a midlenth 16. I opened up my gas port & stopped FTF & my ejection pattern went from 1:00 1:30 ish to 2:30 3:00 ish, & throwing brass 5'. It worked for me. This is a one off, just what I experienced.