Should I drill out my gas port?

[TheSerialHobbyist]

I'm having issues with my rifle being under-gassed and am hoping y'all can help.

It started as a cheap Radical Firearms RF-15 w/ a 16" barrel and worked just fine like that. Then I replaced the barrel with a 22" Satern Liberty SS DF barrel. First, I had extraction issues. That was solved with a new bolt. But now I'm having issues with it being under-gassed.

I've tried every possible fix:

• Different ammunition
• Different mags
• Quadruple checked gas block positioning
• Switched to adjustable gas block that is wide open
• Switched to a "reduced power" buffer spring
• Regular (lightest weight) carbine buffer.
• Checked gas key and rings
• Made sure BCG is properly lubed

But I'm still getting under-gassed symptoms: constant stovepipes, bolt not locking pack, sometimes not ejecting at all because the bolt isn't moving far enough back.

At this point, the only thing left to do that I can think of is to drill out the gas port even wider. Is this a bad idea?

It is already 0.93" (3/32), which is what it should be for a 22" barrel with a rifle-length gas system. But I'm just not getting enough gas, apparently.

Because I have an adjustable gas block (Superlative arms), I can dial it back down as necessary if I end up getting too much gas. Is there any reason I shouldn't do this?

[montana]

If you have an under gassed rifle, the last thing you want is an adj gas block. Adj gas blocks will leak more gas than a standard gas block..
How did you verify the gas block was correctly aligned?
If you insert a cartridge that is known to be the correct size fall out of the chamber easily or does it stick in the chamber..
Do you have an O-ring on the bolt's extractor??
Can you put a cartridge in the bolt by hand and it moves freely in and out?
Does your bolt freely insert into the barrel extension when chambering without hitting any of the locking lugs. Try this very slowly as you cycle the rifle by hand and you will be able to tell..
Does the rifle cycle without problems when done by hand, no rough sections like hitting the trigger?
Did you test the gas tube for cracks or a worn button?
How did you check the gas key?

I like to test all possibilities before drilling a gas port and even then I take my time with the right tools..
If you over size the gas port, then an adj gas block or a way to mitigate the gas will be necessary..

[TheSerialHobbyist]

If you have an under gassed rifle, the last thing you want is an adj gas block. Adj gas blocks will leak more gas than a standard gas block..

Interesting... I hadn't heard that before. But I had the same issue with the original (non-adjustable) gas block.

How did you verify the gas block was correctly aligned?

Careful measurements with calipers to ensure that the hole in the gas block centers over the gas port.

If you insert a cartridge that is known to be the correct size fall out of the chamber easily or does it stick in the chamber..

It falls out easily like it should.

Do you have an O-ring on the bolt's extractor??

I'm not quite sure what you mean... The bolt has the three rings like this: https://www.grendelhunter.com/product/6-5-grendel-bolt/

I've also tried three different bolts: the one that came with the rifle, the one that came with the Satern barrel, and the replacement that Satern sent me because the extractor on the first was too weak.

Can you put a cartridge in the bolt by hand and it moves freely in and out?

Yes, I can put a cartridge in and take it out easily enough, with the extractor gripping properly when it is fully seated.

Does your bolt freely insert into the barrel extension when chambering without hitting any of the locking lugs. Try this very slowly as you cycle the rifle by hand and you will be able to tell..

Yeah, it seems nice and smooth to me. I can't feel or see any issues.

Does the rifle cycle without problems when done by hand, no rough sections like hitting the trigger?

Yep, works just fine if I cycle it by hand. Everything feels smooth.

Did you test the gas tube for cracks or a worn button?

No, I haven't. What/how do I check? The gas tube was new and I didn't notice anything wrong. But I didn't carefully inspect it.

How did you check the gas key?

Just felt it to make sure it wasn't moving and that it was staked properly. Is there something else I should check?

If you over size the gas port, then an adj gas block or a way to mitigate the gas will be necessary..

I don't mind using the adjustable gas block for that purpose. I just want to make sure I'm not doing something stupid by drilling it out.

I've been tearing my hair out for several weeks trying to figure this out and don't know what else to try. If you have points on the things I might have overlooked above (like the gas tube), please let me know!

[montana]

Adj gas blocks can only restricted the gas port pressure, they can not increase barrel port pressure.. Adj gas blocks will leak gas by their design compared to a standard gas block..

The best way to verify an aligned gas port is with a bore scope, but we will assume it is correct.

We will assume the chamber is not tight and is good to go if a properly sized cartridge will fall out after pushing it in the chamber with a slight amount of force..

I was talking about the extractor rubber O-ring that come with some bolts. I have seen them cause malfunctions, especial in the 6.5 Grendel chamber. There can be too much extractor tension..

The best way to check the gas tube button is with a gas tube gauge. Cracked tubes can occur, but we will assume the tube is good to go being new. I will remove them so I can check all sides for cracks..

The best way to check the gas key is to do a reverse torque test of 30 Inch pounds. If the retaining screws are not torqued properly (57 to 58 inch pounds) they will come loose. The screws need to be oiled to get proper torque amount.. If a screw is broke, this will also find it..Be sure to check the gas key for any obstruction by inserting weed wacker line until through the gas key until it comes out into the carrier..

The best way to drill out the gas port is to check the port size with pin gauges and then gradually increase the port size until satisfaction. Be sure to insert a metal cleaning rod so you don't go too far and hit the opposing side of the bore across from the barrel gas port..I use chucking reamers as they bore a perfect hole..Many here on the forum have used drill bits with complete satisfaction..

Some bolt carriers are not gas efficient and don't have proper tolerances in their 3 bores.The bolt tail O.D. to boat tail bore I.D. in the carrier is the most important. The gas ring bore is also important for gas efficancy. The last is the shoulder bore that determines the bolt shoulder support tolerance..If you can find another known bolt carrier that is proven to test in your rifle, it can help a lot with diagnosing a gas problem.

I assume your gas tube is the proper length..

No need to tear your hair out lol, just take your time and do the process of elimination to find and fix your problem..

[TheSerialHobbyist]

I see, thanks!

Going through each point:

1. I don't have a bore scope or anything that would act as one, but I'm pretty certain it is aligned.

2. I don't think the bolts I have use an o-ring on the extractor.

3. I don't have a gas tube gauge, but it looks okay visually. I can blow through the gas tube, with it on the block, and only feel it coming out through the block. If I close the bleed-off valve and plug the gas block hole with my finger, no air will go through. If I fully close the gas block, no air will go through. If I leave the bleed-off open and plug the hole, air will go through the bleed-off valve.

4. Just checked the gas key. Didn't move at 30 inch pounds. The staking isn't perfect, but it seems to be holding just fine. I don't have weed wacker line, but checked it with a length of 3D printer filament and it seems fine.

5. I don't have pin gauges, but I checked it with calipers (and drill bits as go/no-go) and it seems to be right at 3/32. So should I drill one size up? The next largest drill bit I have is 7/64.

6. I actually do have a new bolt carrier coming, though it isn't proven. Maybe it will work better. But the bolt carrier I have is the original one, which worked fine before the barrel swap. Theoretically, I could pull the bolt carrier from my other AR If I need to. But again, this one worked before the barrel swap.

7. Yep, gas tube is the proper length (rifle length). Is there anything I should double-check there? Like the exact distance it comes into the upper receiver or something? I did a rough measurement when I did the swap and it is in approximately the same place as the original gas tube was.

I guess my main question is: is there any downside to opening up the gas port, then reducing flow with the adjustable gas block? I can't think of any reasons why that would be an issue, especially since this Superlative Arms gas block has a fancy bleed-off instead of just restriction, but I want to be sure before I go drilling into a $300 barrel.

[TheSerialHobbyist]

Actually, I just realized something that may explain things. It turns out I may be very, very stupid...

The Superlative Arms adjustable gas block instructions say this:

CLICKS OF ADJUSTMENT:

0: CLOSED (NOT RECOMMEND TO FIRE CLOSED, YOU MAY SEIZE THE SCREW)
1-17: RESTRICTIVE MODE (NOT RECOMMEND, YOU MAY SEIZE THE SCREW)
18: FULLY OPEN, FULL PRESSURE (ACTING LIKE A NON-ADJUSTABLE GAS BLOCK)
20-48: BLEED OFF MODE (RECOMMENDED - UNSUPPRESSED / SUPPRESSED)

I opened mine up all the way to max (so 48 clicks), thinking that would give me maximum pressure. But looking at it again, I think I might be an idiot and that is actually maximum bleed off.

If I'm understanding it correctly, 1-17 lower gas pressure by restricting flow. 20-48 lower gas pressure by bleeding off gas. 18 is normal, full flow and what I should have it set at.

Does that make sense? Have I just been using the gas block improperly this whole time?!

[montana]

Actually, I just realized something that may explain things. It turns out I may be very, very stupid...

The Superlative Arms adjustable gas block instructions say this:



I opened mine up all the way to max (so 48 clicks), thinking that would give me maximum pressure. But looking at it again, I think I might be an idiot and that is actually maximum bleed off.

If I'm understanding it correctly, 1-17 lower gas pressure by restricting flow. 20-48 lower gas pressure by bleeding off gas. 18 is normal, full flow and what I should have it set at.

Does that make sense? Have I just been using the gas block improperly this whole time?!

This makes me laugh because of the things I have done in the past, forehead slap. This is also why I hate giving advice, there are so many variables that can be over looked and why I say drilling the port bigger is the last resort.. A lot of people want quick answers without going through a process of elimination..It can be difficult to find others problems when the rifle isn't in front of me..This is why I try to encourage people to find problems through the process of elimination..One thing to remember when working on firearms, you are going to make mistakes..That said, it looks like you may have found the problem, well done..Enjoy the process and never, ever, get in a hurry..Hope it works out for you..

[TheSerialHobbyist]

Thanks so much! You were a big help, it was your statement that "gas blocks can only restrict pressure" that made me think about it again and realize that the way I adjusted the gas block didn't make sense.

I'm almost certain that that was probably the issue, but I won't be able to get to the range to test it until next week. I'll report back then to confirm.

Thanks again for your help!

[montana]

Your welcome, good luck!