Weird cycling issue... thoughts?

[MWAG19919]

This past weekend I took a low round count course with my MK18. Throughout the class I had no true stoppages with live fire, but a few times when I had to eject a live round from the chamber it was stuck in there pretty tightly. It wasn’t every single time, but the three times it occurred I had to lightly mortar the gun. I can’t quantify the force but it was barely more than the weight of the gun.

The ammo I was shooting was a handload of mine (62 gr FMJ, LC brass). Every single round passed a .223 chamber gauge as soon as it came off the press, and the 2 live rounds I recovered passed the gauge a second time (I could not locate the third round).

The upper is a factory stripped DD MK18 upper with a Toolcraft NIB BCG. I’m not sure if it matters, but the buffer is an A5H0 with a standard rifle spring (I’m pretty sure it’s a BCM spring but it could be Vltor too, can’t remember). I’m also running a LAW folder. I only mention it in case the extra momentum of a heavy buffer system somehow played a role, but I’m thinking that’s not the case because the rounds weren’t out of spec.

Thoughts? I always store the rifle muzzle down and lube it with SLIP2000, so I’m wondering if some lube ran off the BCG into the chamber and gummed it up just enough to make manual extraction difficult. Idk if that’s even a thing, so I thought I’d run it by you gents.

Could it be the BCG? Ik NIB has fallen out of favor due to wear patterns but this one only has a little over 1k rounds through it.

[mRad]

In my experience the chamber gauge is a good check, but ultimately you need to check rounds on the actual chamber of the rifle. There can be variation on tolerances of the gauge just as there can be on the barrel.

Do they drop in freely into the chamber?

How many firings on the brass?

How was the brass trimmed?

When the brass is trimmed sometime a lip can be formed on the mouth that will hang up as well.

Hopefully those questions can help narrow it down, but hand loads are usually the problem or at least the first suspect when it comes to chambering issues.


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[MWAG19919]

In my experience the chamber gauge is a good check, but ultimately you need to check rounds on the actual chamber of the rifle. There can be variation on tolerances of the gauge just as there can be on the barrel.

Do they drop in freely into the chamber?

How many firings on the brass?

How was the brass trimmed?

When the brass is trimmed sometime a lip can be formed on the mouth that will hang up as well.

Hopefully those questions can help narrow it down, but hand loads are usually the problem or at least the first suspect when it comes to chambering issues.


Sent from my iPhone using Tapatalk

I’m with you on suspecting handloads. Tbh I was expecting them to fail the second gauge check when I got home and checked them, but I was surprised when they passed.

The brass was purchased as once fired mixed LC. Sized in a Dillon carbide die prior to trimming in a Dillon RT1500, then neck expanded using a mandrel type die. The rounds didn’t have a burr that I could see, and I crimp them with a Lee Factory Crimp Die anyway.

I just rechecked, and both rounds passed a plunk test in my barrel. They wouldn’t drop free without me tapping the rear of upper onto my palm, so I wiped the chamber with a patch and ran another patch down the barrel. After that the rounds dropped in and tilted out freely.

The upper was cleaned very well after the class and lubed with Slip, but the BCG looked a bit dry when I opened it up this morning. I’m really wondering if the coating on the BCG is causing lube to run off and collect in the chamber

[T2C]

I ran into the same issue when I first started reloading for the AR-15. I also had an occasional issue with reloads for the M1A. I purchased small base sizing dies for reloading ammunition for both rifles and have had zero feeding issues since.

[gunnerblue]

There are very good points made in "Reloads and Reliability" thread. I would also suspect your ammunition and would try out a small-base sizing die. Early on, I experienced some similar experiences and none since using the small-die, specifically a standard Redding small-base and a separate Type S small-base for match type loads.

[MWAG19919]

There are very good points made in "Reloads and Reliability" thread. I would also suspect your ammunition and would try out a small-base sizing die. Early on, I experienced some similar experiences and none since using the small-die, specifically a standard Redding small-base and a separate Type S small-base for match type loads.

I love that thread, but according to Dillon their dies are small-base

[AndyLate]

Has headspace been checked?

I am leaning towards your thought of a cruddy chamber.

Andy

[MWAG19919]

Has headspace been checked?

I am leaning towards your thought of a cruddy chamber.

Andy

Unfortunately I don’t own any headspace gauges

[Leaveammoforme]

I've had that exact "hot chamber" live round manual extraction issue before. I discovered my problem was due to residual sizing lube being left on commercial reloads.

I guess a chamber full of dried run off could cause the same issue.

[MistWolf]

Have you performed a lockback check?