Home Forums Hunting & Shooting AR and Tactical Rifles Fix for Under-gassed Rifle?

I've put together a rifle for my nephew from a bunch of extra parts, one being a 26" WOA match rifle barrel. I cut the barrel to 20" to make it a bit handier but have kept the original rifle +2" gas system. Got to the range and while it shoots very accurately it seems to be undergassed. Using crappy Wolf steel case ammo to sight the scope, it would either leave the spent case in the chamber, or eject and not load a new round. So it is short stroking, probably because it's missing six inches of barrel in front of the port. I didn't expect this to be a problem, but here it is. It would lock the bolt back with a couple 80gr Amax loads I had on hand but these are single feed. PMC ball with a different mag seemed to work a little better but I think is on the edge. Definitely not a vigorous ejection cycle. I want him to be able to shoot inexpensive ball ammo (not necessarily steel case junk) in it so I need to make it function better with it. New barrel or shorter gas system are out for now, I need to deliver it in three weeks. He'll be hunting coyotes and plinking with it.

So far some options I've come up with are to open the gas port a little (how much?), Wolf reduced weight buffer spring, lighten the recoil buffer (currently rifle A2 style), remove some weight from the M16 style bolt carrier, anything else I'm missing? I really don't know how much weight to remove from the reciprocating assembly to make the improvement so am looking for guidance/experience there. Reversible modifications preferred but I'm looking at everything right now. Appreciate any insights.

Frankly it's no surprise it ended up undergassed with that combination. That's an important thing to consider before shortening an AR barrel, and if you do, you need to be prepared to open the gas port.

You'll need to buy an assortment of wire gauge drills and open up the port in small increments until it runs right. Don't rely on someone else's guess on port size, best results will come from verifying what works on your rifle.

Changing springs, weight, etc to non-standard parts (especially for someone who doesn't know ARs well) is a band-aid fix around the gas port issue and sure to cause confusion and/or problems later.

Fair point, but my available time for iterative testing is short so was hoping parts swapping at the range would be faster.
I decided to go to the mountain and spoke to the man himself, John Holliger at WOA. He wasn't surprised either. He was very helpful and indicated that the port was already larger than normal (~.105") to support the 2" longer gas tube that is fitted, but that I could go as far as .125" which would match the hole in the gas block. I don't think I'll have to worry about a burr because the bore scope shows there is plenty of erosion around the inside edges of the hole. Hopefully I can find all the sizes that I've failed to return to my number drill assortment.

Using slower powder and heavier bullets would also help with the current system but I don't want to handload all the kid's ammo.

I understand that you want to use cheap & somewhat low pressure ammo, but the easiest things to do, aside from opening the gas port size some more, would be to try some genuine 5.56 pressure ammo with a carbine buffer, & with a reduced power recoil spring if you have it available.............it might work.

Obviously, it's not likely to work with the low pressure ammo though & as Yondering said, fixing the gas port size is the surest fix.

Unfortunately, there no book or pat set of conditions that anyone can recommend, just the directional changes discussed already.

This just might be a Bubba Project.............

MM

We resemble that remark...no doubt.

Actually don't want to use low pressure stuff. Just surmising that this steel cased Wolf is based on result and friends comment. It definitely has faster than optimum powder for this tube length. The PMC 55gr stuff functioned the action but ejection was not brisk, so I think it is right on the edge as it is now. I'll check diameter of the port tonight and open it five or ten thou based on where it is. I also realized I may not have the gas block centered, so I will verify that with the bore scope if possible.

He's using an A2 stock so the carbine buffer is out.

Oops................didn't catch that.

You're on your game today, you are.

MM

If that's the standard 223 Bronze stuff, that's still a little short of 5.56 pressure....................

MM

I think it was the standard PMC stuff. I don't consider it low pressure per se but understand where you are going. Hopefully with a little bigger hole, it will handle everything.
The adventure begins....

Switch to diesel.

best suggestion yet.

The PMC 223 ammo is definitely lower pressure than their 5.56 ammo. Same for Federal. If you tune a rifle to just barely work 100% with the 5.56 rounds, often it won't cycle completely with the 223 stuff. Yours may have ended up in that situation from the sounds of it.

Opening the gas port is still the best option regardless.

Tip for drilling the port (assuming you have at least a decent vise and drill press) - find a drill bit that matches your current gas port size, and set it in the hole when you clamp the barrel in the vise; that makes it easy to visualize when the hole is perfectly vertical.
Then to locate the hole, hold that same drill bit backwards in the drill chuck, inserted as far as it'll go. When the drill bit shank will slip into the gas port hole, you've got everything aligned correctly for drilling to the next size up.

Yes; it fixes the root cause. Pretty much everything else is just a pill.

MM

Piston impingement is out.

The barrel is set up in the mill at this time, centered as best I can with what I have on hand. Waiting on a set of gage pins to arrive from Amazon. Needed those anyway and when they arrive I'll finish the setup. Current hole size is some where between .098 and .104. I'm missing a couple number drills from my set so will have to wait on the gage pins to know for sure. Plan is to open it to .110 and see how it does.

John said I could go to .125 which matches the gas block hole. He said removing one or two coils on the spring or a reduced power spring wouldn't hurt, but lighter buffer was less likely to. I think somewhere between .110 and .125 will work and if it doesn't I'll chalk it up to a learning experience. I can always plug the current port and re-drill in the standard position, just to see what happens.

Open the hole to .125 and install an adjustable gas block.

Quick fix is a light BCG and lighter spring, but as noted, its just a bandaid.

But it will show that the gun can work.

I"d open the port until it works, then open it one size more.

I"d only put an ADJ block on if needed after that.

I"ve fired so little of factory ammo of any type I have no clue whats up to speed so to speak or not.

But I'd try it with factory Gold medal match 69s for one, if it functioned with that, I'd be somewhat worried about opening the port personally... might lean to spring or lighter BCG, the bolt that used to? come wiht Colts that had the bottom milled off should be lighter....

I doubt you'll over gas a +2" rifle gas system for 223 pressured ammo. Drill it, just don't go through and hit the bottom.

Ha! I thought of that and will have a piece of drill rod in there to know when I get through. Otherwise sure as you know what, I'd be getting plenty of gas from my dual ports!!

Olympic Arms had a bad habit of just touching the bottom side, according to Mike at DTECH. This caused erratic accuracy in some of their barrels.

Your drill press doesn't have a depth stop adjustment??

MM