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.
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.
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
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.
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’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.
I’m not entirely sure what you mean, but if you mean checking to see whether the bolt locks back on the last round fired, yes I have previously. It’s how I developed my handload. I’ve learned that out of all my rifles and “pistols” the MK18 is the only one that’s picky about ammo. All the other ARs I load for lock back on light .223 loads even in cold weather, but for the 10.3" with 0.070" gas port I need ammo loaded near or at the top of the published charge weights for the bolt to stay open at colder temps.
However, the issue I had this past weekend was only with manual cycling of the action. A couple rounds were reluctant to eject manually, but it wasn’t every time. I wouldn’t even go so far as to say they were stuck; I mortared the gun mainly to prevent pulling back on the CH at an angle. The actual mortaring was quite light. I’m not sure if those particular rounds would’ve cycled with live fire, but my educated guess is they would have since I had no issues during live fire throughout the day.
I suppose I could’ve fired those rounds to see, but I didn’t want to risk putting them back into the gun until I double checked them on the case gauge again.
Without annealing every piece of brass, you WILL get variations in shoulder bump. There’s simply differing amounts of “spring back”. Now if the round chambered, the bolt could have bumped that shoulder back enough that it checks out in your chamber gauge. You want your die set so that it’s averaging in the middle of the min/max headspace. Too little sizing, and you get sticking rounds. Too much sizing/bump, and you’ll get separations.
Could just be a chamber on the tighter side too that’s playing a role in this.
I shoot too much .223 to anneal by hand like I do on bolt gun ammo. I don’t have the live round extraction issues that you’re experiencing. The Giraud annealing machine would be sweet, but I’d have to have more issues with .223 to justify the expense.
Would it matter that it passed a .223 chamber gauge and the chamber is 5.56?
Shouldn’t be any difference in what the gauge measures for shoulder bump.
What drop-in gage are you using? Typically they tell you three things: is the shoulder pushed back far enough, and is the case too short or too long, requiring trimming?
The JP and Sheridan gages are the only factory ones that will tell you if you’re sizing enough for cartridges to freely drop into the chamber. As mentioned, the chamber is your ultimate case gage, and a round dropped in should also fall freely when you point the muzzle up.
Dillon sizing dies are NOT small-base – they don’t size down far enough because of 550 shell plate thickness and contact with the heads of the brass buttons. Use your micrometer and check how swollen your cases are about a quarter-inch above the case head. If you’re using range pick-up brass (or cases once-fired from a GI chamber) and your DD chamber is tighter then you’ll need a small-base die (or size with the Dillon dies on a single-stage press).
The NiB is not your problem. I do not personally go as far as this particular ‘internet expert’ but he lubes the holy living crap out of his and claims it is just fine:
(Not suggesting you or anyone lube your BCG like sotar dude does)
Do you have a spare nitride BCG that you can use instead just to see? I always keep a spare BCG just in case situation when I go to the range.
I have NiB on one AR but it only has about 600 rounds through it. I bought it from Palmetto State Armory a few years back. For my spare BCG I have Toolcraft BCG and my main AR has BCM parkerized BCG in it. I have only had to replace the gas rings on BCM BCG.
