Hi, I have a CPA 44 1/2 in cal 40/60 Maynard and have encountered a small problem with case extraction owing to case diameter just ahead of the rim.
When I first got the rifle I also ordered 50 cases from BACo which had been formed from 30-40 Krag brass.
Some of these were slightly difficult to seat and difficult to extract as the Stevens extractor is not the strongest out  there.
Anyway after shooting about 2 or three thousand shots using these cases I decided to buy more as I was starting to lose cases because of the primer pockets enlarging somewhat.
I ordered another 50 cases and was surprised they had been formed from 303 British, these were nearly impossible to chamber and considerably more difficult to extract, often requiring the use of the cleaning rod to knock them out.
The Krag cases measure .452" just ahead of the rim, those that are difficult  to extract measure .455", all the 303 brass measures .455".
My question is how do I fix this problem, do I get some sort of case sizing die to make the case smaller at this point, or do I get the chamber enlarged slightly at the tight spot, if so, how.
Mike.

Mick I have a similar problem with .25 Kraig in my CPA. Kraig based brass is not very consistent, some work well other headstamps stick. Add brass from 303 another inconsistency. Your measurements confirm the same issue 

Sizing dies work fine on hollow tubes. Solid brass near the rim they have little effect. I turn a few thousandths off in the lathe. Solves the problem for good. 

Boats

as hepburnman said   art

When base diameters are slightly large after forming from donor cases I simply turn them down using my drill press or lathe. I put a rod inside the case neck to keep the cases from collapsing, and then clamp the necks in my drill press. Simply spin the cases and hold a file to the area just above the rim and take some material off until they chamber easily. 
It might take a couple tries with the first couple cases to get a feel for how much to remove, but after that it goes quickly. I use the same method to remove thickness off rims that need thickness. The area above the rim is thicker brass, so removing metal there wont weaken the cases. 
Simply setting the dies lower often wont work as the shell holder itself stops the die from totally reducing the last 1/8" or so, and turning the case will get that part easier.

30/40 brass is not consistent add the further complication some cases were formed from 303 it’s a case problem not a chamber issue.

Best thing to do is bring all the cases down to the same size.  Micks .452 cases work his 455s don't. 3 thousandth too big OA takes one and a half thousanth reduction one side . That’s not much off the web. Of course you should confirm the problem is at the web not further up the cases body. Several ways to do that. 

Be good if a sizing die would do it but sizing displaces the material. Solid around the rim no place for the material to go. That’s why turning is a better answer. 

I just turned two thousandth just in front of the rim off some brass 10 G shotgun cases for a friend . They would chamber one of his guns not the other. Some had suggested altering his chamber. I can’t see making the gun fit brass. Particularly when the brass is not consistent.

Boats

I'd fit the chamber to the brass, the American processed brass is a problem due to extrusion so I would stay away from that stuff. Try the Privi Partizon 303 British brass supposedly made from tubing as is all the quality European stuff. Buy enough for your purposes and ream/polish the chamber to fit, good luck.

The Web right in front of the rim is really quite thick and why it's always a bit of a challenge to swage down as it also has a tendency to just want to spring back.

JLouis

Mick plenty of good hobby machinists in Australia. Bet you can find somebody.   It’s a easy lathe job. I run a mandrel in a collet turned to suit the case neck which is facing the headstock. Mandrel has a shoulder that ends in a small flash hole sized end that indexes it. Tailstock end I press the case into the mandrel with a revolving center that has interchangeable ends.  Flat one pushed against the cases flat bottom. I should make one with a small rim sized recess but the mandrel runs true without it. 

Its friction that keeps it from slipping  which is enough to take a very light skim cut.  You may be able to hold the rim in a collet too, but you need to work right up to the rim, better to have the rim out.

I have trimmed serveral different head-stamped 30/40 cases that were sized to 25 Kraig however it’s better to use one head stamp same lot of cases if you can.  Make sure you are trimming solid brass not the hollow body. Best calculated by sectioning one case. 

All this without looking at your outfit and confirming thick case body’s are the problem. Based on my 30 Kraig cases and your description sounds like it but I could be wrong.


Boats