An update from my post 6 years ago!
It turns out the rifles original bolt had seen a better life. The locking lug was peened a little and it did not help the excessive chambers length. ( .0250 ). I bought a new bolt body from Grampa's Parts and the bolt is now a nice tight fit.
Over the decades I've tried the Dental floss and the O-ring trick but all they do is blow the shoulder out thinning the brass at the web. Never got more than two shots out of a case. Now with the new bolt I decided to try something a little different. If I can't blow the shoulder out, why not form the shoulder further out? It can be done in several ways. Here is what I just did and it worked so well I could not be happier.
I have on hand hundreds of once fired POF .410 brass shotgun shells. These are .303 Britt that have never had the shoulders and mouth formed into the brass. ( that is how the CORDITE was loaded originally for the .303 ball ammo.)
I annealed the mouth of the brass cases and started to form the neck and shoulder in my sizing die. Once I could close the bolt on the newly sized case with resistance at the 2:00 position, I knew I was golden. The .410 cases formed into .30-40 do not need to be trimmed. I loaded up five 220 grain rounds and fired them into my bullet trap. BINGO! perfectly formed .30-40 cases that fit my rifle like a glove. Neck size only from now on.
I fired the rifle 25 times in my clubs match this past Saturday and Won the Off-Hand 200 meter match! Target was NRA steel silhouette chickens. This rifle will shoot.
The match in March will be firing 20 rounds at a man size AR550 steel torso with electronic flash to score hits set to 500 meters. I'm hoping the rifle will hold it's own.
This rifle has been a safe queen since I bought it in 1975. First there was the mercury primer destroyed bore. Then the problem of the OEM barrel replacement having a long chamber and a loose bolt locking lug of the rifles bolt.
You can do the same resizing of a .303 Britt casing as well. It will be a little short for .30-40 but should not hurt your rifles throat.
By re-sizing the brass .410 shotgun shells I have been able to make:
6.5 Dutch
.30-40 Krag
and of course .303 Britt.
All needed the shoulder to be further out to save the brass from case head separation. Yes, the brass is Berdan primed.
I just threw the fired cases into the wet tumbler and not one case shows any signs of stretching or cracking.
Here are the shells:
L to R- .410 POF annealed, formed case by die set back and fired in chamber with full load, original Winchester new casing.
Arrow pointing to where case head separation would happen if round fired again.
Formed and fired case on left, new Winchester on right. ( fired case to have mouth trimmed up.)
POF .410 case used to make all three calibers.
Primers needed.
6.5 Dutch made from .410 brass shells.
.303 Britt with shoulder out .020. This worked out great!