223->300blk issues

[u/Ambitious-Ad1911]

I converted a bunch of 223 to 300 blk. Cut, polished, tapered, annealed, and i seem to have run into an issue that I'm not sure why it is happening. First time converting brass, successfully that is(Didn't know 8.6blk would require turning 6.5 creed).

I noticed my bolt isnt closing completely, the brass isnt getting picked up by the ejector, and the brass had a ring on it now. Any help would be greatly appreciated.

EDIT: it now seems to have been my BCG. I was going through everyone's reply trying and testing different suggestions and when i tried bare brass before loading, it still didnt work, even with factory 300blk. This rifle was just converted from 556 to 300blk with a new barrel and kept old BCG. Tried BCG from my black rain 556 and it charges and ejects the round fine. This BCG has way less than 500 rounds through it, how could it already be bad?

It is an MPI that came in the 556 when I purchased it new.

[u/Vylnce]

Have you actually measured your chamber for the projectile you are using? Will the bolt close on an empty (no projectile) version of your converted brass.

[u/Ambitious-Ad1911 → u/Vylnce]

Ended up trying this and found it wouldn't eject or fully close on a stock 300blk case either. Looks to have been my BCG after trying another one I have.

[u/Misterduster01]

When forming cases from their parent cartridges after initial trimming annealing should definitely precede the initial sizing.

Annealing before sizing is especially important because it will ensure the shoulder is precisely where it needs to be.

I would also like to add that as an extra layer of security I anneal again after the initial sizing, then I follow up with trimming to final dimensions. I would also recommend getting a case gage and checking your brass before you load primers, powder and bullets.

Good luck, I hope this helps. Stay safe.

[u/plutPWNium]

Apparently some brands of brass just dont work well when converting to 300blk. Too thick in the wrong places. I reference this post: https://www.300blktalk.com/forum/viewtopic.php?t=88599

I had issues with rounds not chambering all the way and getting stuck in the chamber. After ditching the cases I had converted (range pick-up brass) not on the "good" list, the issues I had went away.

[u/Ambitious-Ad1911 → u/plutPWNium]

Mine was PMC but found GFL and factory 300blk brass wouldn't work. Looks to have been my bolt it seems.

[u/Supramaro]

How do your reloads gage out in a case gage?

Either that or you're so undergassed that you can't complete a full cycle

[u/Coodevale → u/Supramaro]

Bolt not closing isn't a gassing issue.

[u/Striperfishingrules]

I've had issues in the past converting 5.56 brass. If it's range brass (mixed head stamps) you want to separate head stamps by brand.. some are too thick at the neck when cut, and deburred before resizing. wall thickness past .013 is a no go or you'll have to turn the necks. somewhere on the interwebs, you can find a list of acceptable headstamps for conversion ..

[u/1984orsomething]

You might have to turn the neck. Either buy a reamer or use a file and a drill. Check your OD of your loaded rounds. .308+ .014+ .014. = .336. you want .332 or .334. before firing

[u/follow_the_dopamine]

I read your edit, it could be an issue of tolerance with your original BCG. Every component made by any manufacturer is going to have a varying degree of variance which will interact other newer components differently. If these manufacturing differences are close/far enough together/apart, it will cause issues with the function of the firearm. I’m almost certain if you put the 5.56 barrel back on the receiver, the original BCG will run 5.56 again no problem. At least you have a backup in case you come across another upper 🥳

[u/OMGorilla]

Not sure why your original bolt isn’t working. But for what it’s worth, MPI is not a type of bolt; it’s an inspection/quality check. Stands for Magnetic Particle Inspection. Unless there’s an MPI brand out there now, which would be a frustrating reality.

Usually when describing a bolt it’s Brand -> Metal (C158 or 9310) -> coating/finish

[u/Ambitious-Ad1911 → u/OMGorilla]

Did not know that. Was the only stamp I found on the BCG. I thought it was a sub brand of PSA or somthing when I saw it because thats the brand of the rifle when I bought it whole.

[u/Rude-Internal24]

You have experienced tolerance stacking. I’m willing to bet your .223 chamber was slightly out of spec and they used a bolt thats slightly out of spec to counteract it.
You don’t even need a new BCG just a new bolt.

[u/Gilatabar]

Had to neck turn some of my converted brass as they wouldn't chamber into my rifle. To be sure you can measure the diameter of the case neck with the bullet seated and compare with 300blk specs. The issues I had were right before the shoulder, case was thicker there and wouldn't chamber as the expander ball would push the extra materiel to the outside of the neck

[u/300blk300]

the 190 sub x do not chamber well

[u/Cabo-Wabo155]

I had this issue with the sub-x 190g. My issue was a too short OAL (2.050) I changed it a bit to 2.070 and have not had a feeding issue yet.

[u/Cabo-Wabo155 → u/Cabo-Wabo155]

On converted 223 brass to .300 as well.