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Posted: 1/7/2017 8:11:19 PM EDT
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I started this project last year with the thought that a gas operated 9mm should be a smoother ride than the clunky blowback bolts, but is obviously a challenge. I reload 9mm major for USPSA, so ammo isn't a concern. I am currently running 7.0 of WAC with a 115 jhp. My first try had the gas system about 1.25" farther forward than it is in the pics below. It was decent, but the gun cycled too slow compared to blowback rifles. As a match gun it must be able to cycle quickly. I then started doing some more thinking and some research. That led me here with some past threads found through Google searches.
I've shortened the gas system about as much as I can figure how to do it. I'm getting plenty of gas and the gun runs fine, but still a couple of feed issues. I'm thinking I need to cut a ramp at the bottom of the barrel extension to smooth that out. Another problem is some cases aren't ejecting 100% and getting caught. I might need to open the bolt up a bit more as I just used a .223 bolt and opened it a little. Never knew about using a 5.45 bolt until a few days ago reading on here. Another problem is that using a Glock mag lower and the mag keeps getting sucked up into the upper and jams the bolt. I may need to glue a stop collar or something onto the mag to hold it in place. Any suggestions on this? I had to cut (grind) the bottom of the bolt carrier body and bottom 2 locking lugs to clear the Glock magazine feed lips. Anything I'm missing here? shorty gas system. I turned the area for the gas block kind of an elliptical from the barrel to avoid severe bends in the gas tube. 
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| I would suggest getting another bolt...the angles I see cut on the back of them mean that it is no longer locking and the bolt is slamming into the barrel extension on firing...the only mod to locking lugs should be a slight angle to the very corner of the two lugs on the bottom where they drag over the cartridge......just to keep them from hanging on the case rim...on a single stack mag it is on the inside...on a double stack it will be on the outside, we machine it into the 45 bolts.....but on a custom I just hit the corner with a Cratex wheel. I cant see all the lugs but what I see is a little unsafe. |
| I already have another bolt to use, so that's in the works. No doubt I went a bit far with those in the pic. My next issue is feeding from a Glock mag. I'd like to not cut on the locking lugs at all, but they won't clear the feed lips without thinning them down. If nothing else I may have to try it with a Colt mag adapter lower. I did find that a new PSA lower I had in the cabinet has a little tab to prevent the mag from being over inserted, so that issue is easily remedied. |
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The bottom center of the barrel extension is a huge obstacle. Leave as much as you can....but take the peak formed by the feed ramp cuts out.....you'll have a lot better luck feeding.
Another little tip.....get the top of the round where it is almost in line with the bottom of the bolt pocket.....or at least above the open space between the bolt...that will eliminate most of the nose up in the extension failures to feed. |
| I am thinking that I may have to abandon the Glock magazines for now. Seems to be a little bit of a challenge with trimming the bolt locking lugs and I am thinking the colt mags might be an easier solution. Looks like I will need to trim the ears on the magazine block to clear the bolt carrier group, though. |
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