Shoulder bump problem or no problem?

Tidesloe

Tidesloe

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Joined
May 7, 2012
Messages
326
Location
Western North Dakota
I fired 5 fireforming loads in a new chamber that's a cartridge necked up from .30 to .33 and shoulder from 35 deg to 40 deg. Part of determining if my cases expanded to chamber dimensions after one firing, I removed my firing pin, and I have a fixed blade extractor to see at what point my brass chambers without resistance. I've had to bump the shoulders .008 to get the brass to chamber without resistance. I've done various things to try to determine what may be causing this. It seems to be a problem to me. Anyone run into this, and what was the cause, and final outcome of it?

Thanks!
 
I have sharpied a case up and even at .004 bump, I'm getting marks just above case web, and below shoulder. They aren't big marks but seem to be a problem. The one just above the web appears to be a significant mark. I've measured in this area with a set of calipers and get .552-.553. The point at which the resistance is gone, I've taken this area back down to .551 and bumped the shoulders .008. A body die and a neck die may help as far as sizing goes, but short of having those dies custom made, they aren't available. It also doesn't correct the problem. Is it safe to assume I may have chamber burrs In those spots?
 
I'd definitely polish up the chamber a bit...use enough to clean any debris from it and do a retest...
Wouldn't think you'd be hitting in the throat but it's always a possibility too....
 
I see no sign of neck contact. I'm a little apprehensive about trying to polish a chamber myself. I've read a bit about it today, and most seem to think cleaning it up with the same reamer that cut the chamber it the way to go.
 
A little JB on a papertowel wrapped around a 20ga fiber brush.....you won't remove a huge amount..just hoping to find and take out any irregular areas....
I use a rod in a drill.....30 seconds ought to do more than enough.... it's basically to clean the chamber....afterwards you do need to clean the JB out....
Bore scoping helps too...
 
Did you measure your neck diameter near the shoulder?
I'm doing the same thing, but I'm going from 7mm to 30 cal. I found that using Lapua brass instead of Peterson brass that after resizing a case after fireforming The neck diameter near the shoulder junction is significantly larger and in a lot of cases larger than the neck in my chamber. I sharpied up that area and chambered the case, with resistance, and there were no identifiable marks in that area. That measures larger. I did find that there was a very, very tiny thin ring at the shoulder junction where it seems the shoulder junction in the chamber is hitting the case. This happens even though I've bumped the shoulders back. 0.003. so, its almost like the donut exists in the neck/ shoulder junction area as well and shows up when I size the case.
I'm not sure what to do about it other than neck turning or honing out the rear portion of the neck in my chamber
 
Barehandlineman11 said:
You sure your die is sizing your case web enough? You might be going .008 to get enough die on case web. Id measure before and after sizing bumping it .002 then measure your cases sized to chamber freely

What cartridge is case off of?
Click to expand...
This is what I think as well.
Your case web area is the tight spot and running the die down a couple of times to bump the shoulder back more eventually gets the web down to fit.
It may not need .008 shoulder bump.
It may be the case web size.

I'd first do what 26Reload said and run a scope and/or polish the chamber for possible burrs or ridges if needed.

FYI... It has happened to me in a 284 Win chamber. I ended up switching brass and the web problem went away.

Just my thought!
 
Barehandlineman11 said:
You sure your die is sizing your case web enough? You might be going .008 to get enough die on case web. Id measure before and after sizing bumping it .002 then measure your cases sized to chamber freely

What cartridge is case off of?
Click to expand...
Well, I don't know for sure other than I have measured before and after as I'm bumping shoulders back. I didn't write #'s down but did at the point that all interference went away, and that had my shoulders pushed back .008 from fired. Base to shoulder datum and I've tried two different bump gauges and get pretty much the same result, but after fired I'm at 1.771, and bumped till that interference is gone is 1.763 It's a .338 Sherman Mega. It seems that other than the small marks on my brass that it would be sized enough at the web, just 2 small points of contact. One at the web, one at the shoulder. I'll try to get a pic of the mark well enough to see.
 
Tac-O said:
Did you measure your neck diameter near the shoulder?
I'm doing the same thing, but I'm going from 7mm to 30 cal. I found that using Lapua brass instead of Peterson brass that after resizing a case after fireforming The neck diameter near the shoulder junction is significantly larger and in a lot of cases larger than the neck in my chamber. I sharpied up that area and chambered the case, with resistance, and there were no identifiable marks in that area. That measures larger. I did find that there was a very, very tiny thin ring at the shoulder junction where it seems the shoulder junction in the chamber is hitting the case. This happens even though I've bumped the shoulders back. 0.003. so, its almost like the donut exists in the neck/ shoulder junction area as well and shows up when I size the case.
I'm not sure what to do about it other than neck turning or honing out the rear portion of the neck in my chamber
Click to expand...
I have and sharpied my neck shoulder junction. I see no contact in that area
 
Tidesloe said:
I have and sharpied my neck shoulder junction. I see no contact in that area
Click to expand...
Sounds like case web. Before my custom dies on lapua case id run it through a 33xc die first to size case web then id bump it in a redding lapua ai die to get me by. This is just reference for what's probably going on… also causes clickers
 

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