Stuck cases - 243 LBC

[labattred]

Hey, so I've just installed a new BHW .243 LBC barrel, and I'm running into issues with the cases getting stuck in the chamber.

I'm using new Lapua brass loading 90gr Sierra TGK game changer bullets to 2.200 COAL. I'm resizing the brass using a .269 bushing in a Redding type S die. There's a slight bulge at the base of the case neck after resizing, but I've read elsewhere on here that that isn't uncommon on the first sizing (note: this isn't an issue on once-fired brass).

My first ladder test, I ran into this issue. However, I assumed it was a gas problem. I struggled through the first 10 rounds by manhandling the charging handle to get the case to clear, sometimes more effort than others. These 10 rounds gave great results on the chrono, and even though the powder charge was increasing, still printed a respectably tight group at 100 yards.

I've since resized these cases, and adjusted my gas block all the way out for another trial. Unfortunately, I got the same results. This time, I realized that these cases are sticking once chambered into the barrel, prior to actually being fired. I sprayed out the chamber with some CLP and ran a bore snake through just to make sure there was some lube and it was clean(ish), but the next cartridge I chambered was stuck again.

I can't see any visible defects in the chamber (burrs, roughness, porosity, etc.)

Thoughts?

[GLSHOOTER]

There is nothing wrong with your chamber. It is your ammo. Just bump the shoulders back further. You should have 0.003 to 0.004 shoulder set back from a fired case. On yours just screw the die in about 1/8th turn and try a sized, not loaded, round in the case with the upper off the lower. The BCG should close by hand and then you use the charge handle to extract. You should encounter NO RESISTANCE in pulling the case out. Once you reach that point lock it down and measure your shoulder for repeatability. Do five cases and check for verification.

Greg

[labattred]

Thanks for the quick response! I agree that the issue is very likely to be my ammo. The info about the barrel/chamber was just adding context in case those questions arose. I'll definitely try bumping the shoulder back a bit using your method, and see if that resolves the issue. I wouldn't have expected the rounds to have fully chambered, if I wasn't getting enough setback

[GLSHOOTER]

Aug 29, 2020 14:39:43 GMT -8 labattred said:

Thanks for the quick response! I agree that the issue is very likely to be my ammo. The info about the barrel/chamber was just adding context in case those questions arose. I'll definitely try bumping the shoulder back a bit using your method, and see if that resolves the issue. I wouldn't have expected the rounds to have fully chambered, if I wasn't getting enough setback

When that BCG slams home propelled by that buffer spring you can definitely move the shoulder just enough to chamber. That also means you have virtually zero room for the case to expand and contract so you have induced your "stuck case" condition by merely dropping that BCG. Guys that think they are going to neck size only learn this on their first trip to the range.

Greg

[maxbc]

I'm designing a custom reamer for 243LBC bolt gun and want to keep the chamber as close as possible to fired Lapua brass (+.001) resized in Redding TypeS F/L die.

Can you tell me what your resized Lapua Grendel brass measures at the web and shoulder?

Thanks,

Bob

[GLSHOOTER]

The chamber is the same as a standard Grendel. Take 0.001 off that and you should be good. Redding sizes mine about 0.002 smaller.

Greg

[GLSHOOTER]

I dug out some sized/loaded LBC. I got 428 and 440. Different dies will size a different amount in my experience.

Greg

[labattred]

Alright, so I've revisited this project a few times since I had made the original post. However, somehow it always ends up further down the list of priorities.

I ended up procuring a set of 6PPC dies to run, rather than the Redding Type S Bushing dies, and have had better luck regulating the shoulder bump. My comparator measurement for once-fired brass is 1.214, and I've tried bumping from .003 to .010 back to see if that abated the issue.

While I am able to get the rounds to chamber more easily, I'm still getting resistance when I release the bolt. They do chamber and fire, but don't eject and need to be mortared to clear the chamber.

I've now opted to transition from Lapua brass to Hornady. When loading these, I drop a single round directly into the chamber and send the bolt home with the release. They bolt locks in easily, with no signs of resistance. These also do not eject after firing, but will eject with a reasonably normal amount of effort applied to the charging handle.

Should I look at neck turning the brass? What are the nominal dimensions that I should be expecting at the case mouth? I just checked a loaded Lapua (0.271) and Hornady (0.269). The Lapua may have been loaded with the old Redding bushing die, but I'm not certain as it's been around a year since I loaded that batch.

Any other thoughts that I should look into? I'm honestly reaching the point of moving back to 6.5 Grendel or just grabbing a 6ARC, as I've never encountered any challenges loading the other 8 bottlenecked rifle rounds that I run.

[GLSHOOTER]

Does it fail to extract after firing or extracts but doesn't eject m

Greg

[labattred]

The bolt doesn't even slide back. There's too much tension applied in the chamber for it to reciprocate. I'm not ruling out the need to replace my gas block, but I'm not seeing any direct evidence of misalignment there.

I don't get nearly as much time to tinker with this, given my work schedule, toddler, and newborn scenario. I just try to fit it in when I can steal an opportunity.

[GLSHOOTER]

So it has never ejected or moved the bcg?
Does it extract a loaded unfired round with no trouble?
Greg

[labattred]

Correct.

Loaded,unfired,and dropped directly into the chamber.

The Lapua brass would feel as though it was force seating into the chamber. After a more aggressive shoulder bump, it would seat more easily, but certainly not without just letting the bolt release rip.

The Hornady brass that I just tried would seat smoothly and there was no audible difference from what you would expect when releasing the bolt. If unfired, there was no noticeable resistance when clearing the loaded unfired round. It was only after firing that the bolt didn't come back and there was noticeable resistance when trying to pull the charging handle. Not egregious, but definitely prevented cycling.

No pressure signs and I've reduced the charges to ensure that wasn't a component.

[GLSHOOTER]

Have you made sure the port is clear? Have you measured the fired brass compared to sized? Do those numbers line up with the specs on a Grendel case?

[labattred]

Alright, I'm back in town and had a chance to measure everything. I don't have a 6.5 Grendel Case gage, which would come in handy, but I'll likely be picking one up soon anyway.

So, the base to neck and base to shoulder datum lines may not be perfect, as it's tough to precisely define that delineation point visually. However, I think the data below seems to be pretty consistent between both the Lapua and Hornady brass when unsized and sized. Both pieces of brass were sized using a 6PPC die, and provided the desired amount of shoulder bump. I didn't notice a discernible difference in resistance with brass that I've previously sized with a more pronounced bump (back to 1.204), so I've left this at the desired amount to minimize the amount that brass is worked.

The one thing to note is that the Lapua brass grew a surprising amount after sizing. I'm not sure if that's indicative of anything important, but I did find the change surprising. However, I've not regularly measured the change between sizing on any brass, just that it was beneath max trim length, which the Lapua is not.

As for the gas port, I don't really feel that's an issue, as I still have to manually overcome the resistance with the charging handle. If I was receiving insufficient gas to the carrier but the brass/chamber interface was fine, one would think that the charging handle would slide back smoothly or with minimal resistance.

I'm running short on ideas here, but am certainly welcome to any other thoughts/considerations. 

1x Fired Unsized Brass	Lapua	Hornady	Variance
OAL	1.512	1.512	-
BASE TO NECK	1.290	1.290	-
B350 COMPARATOR	1.214	1.214	-
BASE TO SHOULDER	1.156	1.156	-
SHOULDER DIAMETER	0.432	0.432	-
BASE DIAMETER	.440	0.438	-0.002
2x Fired SIZED Brass	Lapua	Hornady	Variance
OAL	1.522	1.516	-0.006
BASE TO NECK	1.290	1.297	0.007
B350 COMPARATOR	1.210	1.210	-
BASE TO SHOULDER	1.155	1.155	-
SHOULDER DIAMETER	0.428	0.429	0.001
BASE DIAMETER	0.440	0.439	-0.001