I guess this is a known issue but wasn't known to me

Apparently you run the risk of creating a thick case mouth by wet tumbling brass for longer than necessary. I usually just do 2hrs. I probably accellerated it as I anneal each firing.

I don't have a neck turning tool. Heavy chamfer/deburr sorta works but they are still hard to chamber. Aside from trimming alot, is there anything I can do? Will normal trim/chamfer/debur then firing and resizing likely work it out?

If the case mouth is significantly peened, you'll need to cut about 0.005" off the mouth, and you'll need to chamfer inside-and-out to get rid of the thick part.

Get busy trimming.

Trim trim trim.


And stay under 45 mins in the future.

Case OAL is important. I have a mixture of RCBS, Dillon and Lee reloading equipment. My go to trimmer is Lyman, and I resize first then trim to Spec. OAL. My trimmer is manual, I guess the old tool makers that taught me emphasizing feel is why I use a manual trimmer.

Yep, especially with thinned case mouths.
I went with a ultrasonic cleaner  for my br's

In my experience, the likelihood of peening the case mouths depends on a few factors:

1. Time - the longer you tumble, the more likely you are to damage the mouths
2. Fill - the more full the tumbler is, the less the cases 'fall' as they get carried up the side of the drum as it rotates.  The less they fall, the less impact damage to the mouths.
3. Size - the bigger the cases, the more mass they have as they fall, and the more damage they do to surrounding cases when they hit.

As an example... a Thumler's Tumbler with a couple hundred .223 Rem or 5.56 cases can go for hours or even overnight without needing anything more than a routine trim/chamfer/debur like you'd normally do.  The same tumbler with about fifty .338LM cases might ruin them all beyond salvation if you tumble them for a couple hours.

In my experience, they're about as clean as they're going to realistically get after about 45 minutes.  Tumbling longer to get that last little bit out of the primer pocket ain't worth the potential problems.

FWIW... I - and most of the better long-range shooters I know - have stopped doing wet tumbling (or ultrasonic) for match brass.  If you strip the insides of the necks back down to bare metal, you end up with excessive and/or inconsistent seating force.  It is possible to put some sort of lube back inside the case necks, either using ceramic beads or a soft bore mop loaded with dry graphite or moly powder, but why bother?  I'm largely back to tumbling with dry media, and brushing the insides of the necks on the 'good' brass to make sure they are clean/clear/consistent.

YMMV.

I got peened case mouths when I didn't completely fill the FART drum with water. I was trying to increase agitation and it worked so well the case mouths got peened.

Now I fill to the very top with no air pocket and have no problem with peened case mouths. 2hr run time with 223 cases works out fine.

I had my first incident last week with over-clean case necks.

I could feel the bullet (Hornady 75) "gripping" the necks more than usual when seating. I didn't examine the rounds closely after seating. Evidently collapsed quite a few shoulders to the point where the rounds would not chamber. The rounds that failed to chamber had to be "mortared" out of the rifle. I noticed deformation in the shoulders of the rounds when I was fighting them out of the gun at the range. Brass was once-fired Creedmoor.

This is from the cases being too clean. Not from the mouth being peened over

Are you seating with a factory crimp die?  That will happen with a case that is too long, or a die set too deep with that style die.  Been there done that.  Not had one stick like that due to having a case too clean, but then again I typically hit mine with a chamfer / debur tool before I load anyway.

I do not crimp 5.56 ammo.

Not intentionally.

Not by accident.

I’ve been reloading 5.56 since 1988.

The suggestion that the brass is too clean is most plausible. Although, I also suspect THAT LOT of brass ALSO HAS a soft shoulder. Other brands run in the same cleaning-and-trimming cycle are not showing collapsed shoulder issues.

The burr on the outside of the neck may further have contributed to the collapse on chambering. By my measurement, the outside diameter of the cartridge, at the burr, was same diameter as the chamber neck.

I rue the prospect of ever handling moly again. It gets EVERYWHERE. Last time I played with moly, it got on all the basement furniture. It was on the VCR, and my wife’s book collection. It was even on THE BABY. Moly got banned after that debacle. Find some other way!

My brass is trimmed/sized in a Dillon trim die with the RT-1500 trimmer. Leaves a nice, clean edge.

Tumbling with stainless afterwards makes the case mouth look like a cauliflower when examined with a 15x magnifier.

So I now decap and swage (Dillon 1050), Ultrasonic clean for 100% carbon removal, then final process to size, trim and expand the case mouth with a Lyman M-die. Final polish with Corn Cob which helps with the neck insides and prevents tarnishing.

I have found if you fill your tumbler completely up with water, it won't beat up the necks..

I also question the too clean of neck causing issues as well, if that was the case, nobody would ever be able to load brand new brass without some form of prep to dirty the necks first..the few times I had issues with necks, it always traced back to not enough chamfer/deburring..The RCBS 3way cutters solved that issue for good, producing very uniform finishing from case to case..