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12/6/2019 7:27:02 PM
Posted: 3/16/2011 9:58:20 AM EST
My new XM177E1 is short stroking. What size do I need to open up the gas port?

Link Posted: 3/16/2011 10:00:41 AM EST
[Last Edit: 3/16/2011 10:03:46 AM EST by Hal143]
.093 is milspec. What buffer weight are you using ? Maybe try an H1 or H2

My Rifle has a short-stroking problem - the gunsmith says it may be a gas port problem. What are the correct sizes for the gasport?

A: Courtesy of Rick McDowell of Competition Specialties, NRA Life, USPSA Life, Master ( 105 E. Cass, PO Box 451, Osceola, Iowa 50213 Phone: (800)369-4481 / (641)342-2011 )
I have an Extraction Problem, is this related? How can they be fixed? The below gas port dimensions are the ones that I have accumulated while working on AR's for years. When someone is having problems with short stroking and their gas port is not within the below ranges, that is usually the main problem. On individual rifles I have varied both bigger and smaller with port sizes, but these were definitely exceptions, or there was no other choice due to poor quality parts we were working with.
For example;
11.5" barrel, .750" barrel diameter at the port, 3.850" from muzzle; Port should be approx. .086" to .094" in diameter. The smallest I have seen the port on these short barrels is .081" and it worked with some military ammo but not with some faster burning rate, commercial ammo. With the .086" port the military ammunition worked better but the commercial still wasn't getting enough pressure to work the carrier properly. The .094" port would work with both the high port pressure military ammo and low port pressure PMC ammo. Anything over .094" will cause short stroking/timing problems from too much pressure to the carrier and under .086" might cause short stroking for lack of pressure. To know if the port should be changed or not will depend on a few other things. Is the chamber narrower than it should be? Is the chamber rougher than it should be? Are the rings worn and allowing gas to blow by? Is the carrier key allowing gas to blow by? Etc., etc. Eliminate these variables first! With a smaller diameter barrel at the port, the gas port sizes will usually be a little smaller as well, given the barrel length is still the same.
Link Posted: 3/16/2011 10:38:53 AM EST
I'm running a standard buffer. I'll try a 1 or 2 and see what happens.

Link Posted: 3/16/2011 2:27:00 PM EST
If you have to buy one get an H2 or H3.
Being you have standards already, you can make an H1, H2, or H3 by adding or subtracting tungsten weights.
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