Failure to Eject due to excessive gas port, UPDATE: Problem solved w/custom gas plug

[DeanD]

6.5 Grendel Carbine, usually ejects forward at 1:00 sometimes to the side but usually to the front, very weak ejection some just go out about 18" onto the bench top. Occasional stovepipe on the empty with fresh round cycled into the chamber. Shooting Wolf 100 gr. ammo, haven't tried the expensive commercial good ammo. My 5.56 AR builds all eject about 4:00 and about 8' away in a nice 3' circle. Only unusual thing I see on the empty cases is a pretty good smeared gouge swiped into the case head from the ejector. Bolt locks back on the last round every time.

Here is what I have in the build:

16" E.R. Shaw 1:9 chrome lined barrel with GI A2 front sight from J&T in Kentucky. Barrel not marked E.R. Shaw but that's what they said it was.
Standard Carbine gas system.
Young Manufacturing chromed bolt. Standard M-16 ejector spring, standard M-16 extractor spring with insert, but no O-ring..was very stiff so I took the O-ring out but no improvement.
Smith Enterprises chromed bolt carrier. Gas key is not leaking.
Standard carbine buffer and spring. Had an H buffer but swapped it for a standard one but no change.
FN M4 upper receiver.
Alexander Arms lower Receiver.
RRA target hammer, trigger, JP springs (red hammer, gold trigger)

Plan on pulling the A2 front sight and checking the gas port hole since it seems to be low on energy ejecting the empty cases and possibly short stroking with the stovepipe jams.
My research indicated a carbine gas system should have a .0625" gas port. Any comments on that?
Is the Wolf ammo weak? Haven't read any reviews reporting poor cycling performance.

[Mustangfreek]

I’d say your on to it. Check the gas alignment and size of hole.

Plus the wolf ammo, if it’s a small hole , the wolf probably won’t run good.

[DeanD]

Pulled the FSB and the gas port hole in the barrel is .093". I keep seeing it is supposed to be .0625" on a 16" barrel with carbine length gas system. If that is correct then I am about 50% oversize and it would have significantly over pressure not under so don't understand the weak ejection. Double checked the ejector spring vs. a new one and it's good.

[Lemonaid]

What does the brass er, steel fired cases look like? A rough chamber can retard ejection.
Acquire/make some dummy rounds and cycle by hand. If that test seems normal then it would seem there is not enough energy in the system.
Either not enough gas (gas port alignment or gas tube problem) or to much resistance of the bgc moving rearward. It may need lots of lube or a reduced buffer spring or buffer weight.)
OR it could be to much gas. I've read some forum threads that put forth that to much gas will let the Bolt unlock early before the case can contract, so that it sticks to the chamber, making it much harder to extract, slowing the BCG down and thus weak ejection.

[Kswhitetails]

Overgassed ejection results often in forward flung cases. They hit the deflector with enough force to bounce forward rather than rearward.

Your gas port is huge. Hit up a H3 buffer or heavier spring or both. That's where I'd start.

[LRRPF52]

Pulled the FSB and the gas port hole in the barrel is .093". I keep seeing it is supposed to be .0625" on a 16" barrel with carbine length gas system. If that is correct then I am about 50% oversize and it would have significantly over pressure not under so don't understand the weak ejection. Double checked the ejector spring vs. a new one and it's good.

.093" on CLGS 16" barrel in 5.56 or 6.5 Grendel is way oversized.

That's why you're having the problems you're having I suspect. Cyclic rate is too fast, which explains the stovepipe malf.

[DeanD]

"Only unusual thing I see on the empty cases is a pretty good smeared gouge swiped into the case head from the ejector. Bolt locks back on the last round every time." Cases have no rub marks per se, I polished the chamber a few sessions ago and the cases look really nice and clean. I don't see the cases hitting the deflector. I had my grandson shoot it while I stood there watching and the cases come out very weak, most to the front but some just land on the benchtop to the side. I may opt for a new barrrel and see what J&T will do to make it right.

[sbowhuntr]

Kswhitails is correct and I would follow his advice, also an adjustable gas block will help too.

[DeanD]

Don't want to mess with an adjustable gas block, I want to retain the A2 front sight. I will just drill the hole out and tap it to 6-32 or so, lightly countersink the hole, screw in a plug from a machine screw, cut it off, peen the plug to swage it into the countersink tight, file it flush and redrill it .062. Don't have to buy anything. Piece of cake. No use throwing a good barrel away because the hole is the wrong size. Old tool & die maker here plugged so many bad holes I couldn't count them. Just hope that fixes the problems. If it is too small I can always drill it a skoshi bigger. I have never had over-gassed problems before just under-gassed.

[LR1955]

Don't want to mess with an adjustable gas block, I want to retain the A2 front sight. I will just drill the hole out and tap it to 6-32 or so, lightly countersink the hole, screw in a plug from a machine screw, cut it off, peen the plug to swage it into the countersink tight, file it flush and redrill it .062. Don't have to buy anything. Piece of cake. No use throwing a good barrel away because the hole is the wrong size. Old tool & die maker here plugged so many bad holes I couldn't count them. Just hope that fixes the problems. If it is too small I can always drill it a skoshi bigger. I have never had over-gassed problems before just under-gassed.

DD:

I thought you said it was a ER Shaw barrel? If so, I would get rid of it and buy a better barrel. Shaw makes decent hunting quality barrels but otherwise nothing spectacular.

However, all Shaw barrels I have seen have 'ER Shaw' stamped on them. If yours doesn't, it probably isn't a Shaw. Which means it is a no name brand that is of poor quality. Get rid of it and buy a Group Barrel off of the forum. Will save you a lot more time and you will know you have a decent if not top end barrel.

LR55

[DeanD]

The accuracy is good, the chrome lining looks good, I like the profile and the A2 front sight, all in all a decent barrel except for the gas port hole. I suspect is it a Doublestar store brand barrel and not an E.R. Shaw as they told me. I sent them a message asking about the gas port size of their 6.5 barrels and sure enough they came back and said .094 which is what mine is. Other than the oversize hole it is ok so will try to salvage it and not spend more money. With just Wolf being the only affordable ammo I am losing interest in the 6.5 Grendel although I think it is a perfect cartridge for an AR.

[montana]

https://www.midwayusa.com/product/1003364111

[VASCAR2]

I have the chrome moly version of the Double Star/J&T Distributing heavy profile 16 inch 6.5 Grendel barrel. I have never measured the gas port on my barrel but have considered buying an adjustable gas bolt carrier like Bootleg. I have been very pleased with the accuracy of my DS/J&T barrel. I bought my J&T 16 inch 6.5 Grendel kit to match my duty 5.56/223 AR-15. Other than being a little over gassed I like my J&T upper. My barrel functions fine on factory ammo but is over gassed on a couple of my hand loads.


https://www.brownells.com/rifle-parts/bo...05111.aspx

[DeanD]

Ok, this is what I did, instead of plugging and re-drilling the barrel I made a threaded insert from an 8-32 set screw. Shortened it so it was .005" shorter than the distance from the barrel interface surface to the gas tube hole in the FSB. The existing hole in the FSB is about perfect for threading for 8-32. Drilled a .063" hole in the plug which is what everyone seems to say is the right gas port hole for a 16" carbine barre. Screwed the plug in and lo and behold we have a .063" gas port and it didn't cost anything and only took about a half hour to do. Didn't have to buy an expensive adjustable gas block, got to keep my A2 front sight, the fix is permanent nothing to get out of adjustment. BTW I crushed the threads on the plug slightly so it would screw in nice and tight and won't come loose. Can't go down of course because of the barrel but don't want it unscrewing into the gas tube. I am going to be out of town for a week so won't have a chance to shoot it for awhile but will post followup when I do.

The plug with .063" hole:



Tapping the gas hole, I did have to open up the bottom hole a little to get the tap in:



Screwing in the plug:



Job is done! The allen wrench hex is larger than the .063" hole so that just helps to ensure there is no mismatch from the barrel to the hole in the plug.

[Lemonaid]

Well done! You could make more with different i.d. hole sizes and have options for more/less gas. Like carburetor jets.

[montana]

Nice job, I love it. Great pictures and info.

[VASCAR2]

I might have to do that to my 16 inch carbine gas 6.5 Grendel. I know people have used gas bushings in mini 14’s for years but I never really thought about it on a fixed sight AR-15.

[DeanD]

What I like is the only alteration was threading an existing hole. I can always drill the hole a bit larger if necessary. Must say those set screws are hard. Annealing it first would help or getting a cheap softer set screw. I finished drilling the hole after grinding the screw down, getting it hot and letting cool slowly several times probably annealed it a bit.

[DeanD]

I like the carburetor jet analogy. Part of my motivation here was to teach my grandson how to fix things with what you have or can make. He is a total AR fan and 6.5 fan.

[FRB6.5]

Stainless set screws would likely be a bit softer to deal with if had to make more.