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Open L1A1 gas port?

Invictus77

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Drilling the port out is sometimes legit, but not the first step I would suggest. Maybe you have gone through the other simpler issues, IDK?

To your specific question, I do not recall ever drilling out an SLR/L1A1. Can that angled port be done without pulling the GB?
 

Jeff in Pa

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I had to drill my L1A1 barrel ( brand new barrel, NEVER drilled) and it was easy to drill. As always, make sure you do NOT hit the "bottom" of the barrel with the drill bit. Use a high quality drill bit too.
 

Perku-t

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Opening the port in the barrel is not the first cure for short stroking try to close the gas evacuation/ regulator first and look for leaks that would prevent full direction of gazs on the piston.
Are you reloading or using factory ammo ?
Does the bolt drives free ?
Have you checked if springs in the stock are clean and lubricated ?
 

Nathaniel01

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It’s been a few years, so I figured I’d reassess. Ran like a raped ape until I opened up the gas- left it in the fully closed position and no problems. Regulator is a little wiggly, gas tube a little wiggly too.
Happy it ran but wish it weren’t fully closed. Was shooting mix of Malaysian and MKE Turk.
 

biyf

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Wiggly is what it should be. Sounds like the gas port might need to go up one more size. Before you do that, suggest going through everything else first. Try a different lower if you have it to eliminate a binding recoil spring or other lower issue such as out of spec FCG. Try the piston drop test and make sure it falls free. Measure the gas port as-is now, check the gas tube threads, make sure the gas tube pin is installed, etc. I had a recent build which I had to drill out to .110 to get to reliably function with the gas port on 4, but I drilled it out one bit size at a time over several months as I was able to get it out to the range for test fire. Harbor freight has numbered drill bit sets for $20, quality is not great but they worked just fine for this job.
 

gunplumber

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I would buy a quality cobalt or carbide bit. I do not recommend HSS. If HSS breaks off, you are screwed. If cobalt or carbide break, you have a chance of shattering bit and getting chips out.

It is common for worn ga systems to need to be opened up. It was a standard REME task. a "1" or "2" was stamped on left side of sight ear to indicate stgep 1 or two.

Nominal is .098 (2.5mm) I start with a #36 (.106)(2.7mm) then a 7/64 (.109) or a # 35 (.110) (2.8mm)

Yes, you can fabricate a go/nogo gauge for the gas block - sometimes out of roundness occurs from extensive blank fire. and sometimes the fit between the gas regulator and outside of gas chamber can become worn.

But drilling up to .110 is no big deal. After that, if it still won't cycle on 4, there is likely something else wrong.

This is for full length barrels. Shorter barrels need larger ports. .116 for 17-18 and .118 for 16.
 

4markk

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I lock mine into the drill press at the proper angel and use a cobalt bit with cutting oil. The current hole will guide the angle, so set it with a smaller bit first.

As was stated, it's a bitch if you break a bit off. Also put a dowel in the bore so you don't go too far and scar the bore on the other side.

The red line in this photo represents the gas port in an L1A1.

L1A1 Gasport.png
 

gunplumber

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And while I'm not saying you're "wrong" to lock it in, I deliberately drill it by hand and not locked in the mill, because I want the bit to have some flex to find it's happy spot of least resistance.

Nice image by the way, it took me a long time to do all that light blue fill on those original prints.
 

4markk

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And while I'm not saying you're "wrong" to lock it in, I deliberately drill it by hand and not locked in the mill, because I want the bit to have some flex to find it's happy spot of least resistance.

Nice image by the way, it took me a long time to do all that light blue fill on those original prints.
Did I get that image from you? I have a lot stored on the computer and have long forgot where they all came from.

I used to also grab photos of full-auto FALs (transferable, pre- and post-Amy samples) when they came up on auction sites as well. Knowing we would need them for reference some day.
 

def90

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Should be the same as drilling an AK gas port. I use my cordless DeWalt drill and use one of the long bits AK Builder sells.. just go on McMaster Carr and find the same long drill bit type but in the correct diameter. Takes a bit of touch, high speed and slow feed to get it started, once started it should just follow the existing hole.
 

Nathaniel01

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Thanks for all the replies. Got it zeroed perfectly, so took it to RBGC FAL match. I started with the 600 yd side match, and after it started to get hot, it crapped out. Ejection was weak even with the gas port closed. Glad I took a backup rifle!
I’m going to get some cobalt bits and get this thing fixed!
Thanks for the excellent tips!
 
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