Green Mountain Barrels and Mid Length Inquiry

[sentinel77]

Hi, so I've been wanting to build a m4 clone but was swayed by popular trend to instead go with a 14.5 middy. Seems like it's a softer shooting setup than a 14.5 carbine. I stumbled upon Green Mountain's GM-M19, which is their only 14.5 midlength barrel. Does anyone have experience with this particular barrel or with Green Mountain barrels in general? What type of accuracy and barrel life should I expect out of this barrel if I do choose to go with this option? Lastly, what is a reliable gas port size for a 14.5 midlength barrel? I know it's not a standardized gas length for 14.5, and thus, manufacturers have different gas port sizes, but I'd like to know the general consensus on proper port sizing. Mil spec port size for a 14.5 carbine is 0.063 IIRC, and that's been proven to be reliable. What's a proven port size for 14.5 midlength without being overgassed? Thanks in advance!

[Clint]

I believe there is a thread on here where someone asked GM what there port size was and they responded. It was quite large.

[JediGuy]

If you email them, they will provide the port size. You can see on this thread that their 11.5” pencil barrel has substantially more gas than is needed.

[JediGuy]

https://www.m4carbine.net/showthread.php?218386-11-5-Carbine-Length-Barrel-for-Suppressor-95&p=2777204&highlight=

[26 Inf]

Hi, so I've been wanting to build a m4 clone but was swayed by popular trend to instead go with a 14.5 middy. Seems like it's a softer shooting setup than a 14.5 carbine. I stumbled upon Green Mountain's GM-M19, which is their only 14.5 midlength barrel. Does anyone have experience with this particular barrel or with Green Mountain barrels in general? What type of accuracy and barrel life should I expect out of this barrel if I do choose to go with this option? Lastly, what is a reliable gas port size for a 14.5 midlength barrel? I know it's not a standardized gas length for 14.5, and thus, manufacturers have different gas port sizes, but I'd like to know the general consensus on proper port sizing. Mil spec port size for a 14.5 carbine is 0.063 IIRC, and that's been proven to be reliable. What's a proven port size for 14.5 midlength without being overgassed? Thanks in advance!

AS I've said before, GMB's are my go to barrels (unless something as quality is deeply discounted). The only GMB mid-lengths I have are on 16 inch barrels. Accuracy at 100 yards is easily MOA with a magnified optic, from a rest. At 200 I generally shoot about 6 inches with a Vortex Spitfire, that is on me and the optic, not the rifle.

[everready73]

Green mountain makes quality barrels at a good price but their port sizes are large

Optimal size on a 14.5 middy for general use is right around .076-.078 IMO.

I don't know for sure what the GM spec is but betting it is .080 or higher.

If you want to go with them get a gas tube or insert from Clint at Black River Tactical

BCM makes a 14.5 middy with correct port size.. I believe SOLGW offers one as well