I have been trying to work up a load for my HS Precision 375 RUM. Loading 300gr Barnes TSX. My test loads shot well, but were hard to chamber, not good for hunting ammo. Thinking I overcrimped the test loads, I reset the die, and even with no crimp, could barely chamber/extract the unfired round. Factory shells chamber fine. Between bad words, I tried loading a squib, and it chambered fine. With powder charged rounds the case diameter was about .005 larger at a point about 3/4 inch below the shoulder, and rub marks on the case suggested that is where the hangup is.
The Barnes is quite long for caliber, and even though the 98gr of IMR 4831 is just up to the base of the neck, it seems that seating the bullet is creating enough internal pressure to deform the case?!?! The condition persists with both once fired and virgin brass, all trimmed and run through the sizer before loading.
I have never seen this condition, any thoughts would be appreciated.

try champfering the case mouth before you seat the bullett. i have seen new sizer dies made out of speck. the crimping may of caused this problem too,from the case being harder to crimp and once the case wall is deformed,theres not much to change that. the other possibility is in the chamber of the rifel,i have a rifel that shoots factory rounds and extracts fine,but my reloads are tight. you might just have a tighter chamber.
i personnally would try new brass and not crimping, then talk to the manufacturer about defective resizer die and see if they will warrenty it. if you still have a problem,id say its a tighter chamber

Guy I used to work with reported a similar problem with a 300 RUM. I don't know the details or how he resolved it. Sounds like excessive annealing, but that's just a guess.

Update-
I talked to Barnes today- Ty was most helpful. He has seen this but not in this cartridge. Since the squib loads chambered fine, and the cases expanded .005 in 1/2-3/4 in below the shoulder when charged with powder, that's pretty good proof. Even non crimped loads wouldn't fit. Must load another powder with less required. H4350 looks like a good prospect- maxes out 6-8gr less than IMR4831. At least I'm not crazy, at least in this case. I guess if you live long enough, sooner or later you see everything.

quote:

Originally posted by Marty:
Factory shells chamber fine. Between bad words, I tried loading a squib, and it chambered fine. With powder charged rounds the case diameter was about .005 larger at a point about 3/4 inch below the shoulder, and rub marks on the case suggested that is where the hangup is.

You are crushing the shoulder with your sizing and/or seating dies , turn it UP 1/8 of a turn and remeasure.. I bet you fired cases don't have the same symptom, until resized.


if you have a FLAT surface handy (like a machining parallel) lay a reloaded case and a fired case on it. you will see a ridge RIGHT on the shoulder, and a gap in contact just behind the shoulder south towards tbe base.


Ty is a good guy, but unless you are 110% over full and crushing the HECK out of them, and then you are now in a "broken powder" issue, it's not the charge.

jeffe

Update-
I tried H4350. Working from 92-96gr. All chambered with no problem, without readjusting dies. Best accuracy with 93gr, 1 moa from the HS Precision. Groups gradually spread to 2 moa at 96gr. As an aside, that bullet measures 1.49 inches long! IMR 4831 yielded slightly better accuracy, when I could get them chambered.