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.
![Image](https://i.imgur.com/80XPdWT.jpg)
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.)
![Image](https://i.imgur.com/s1FvNSP.jpg)
POF .410 case used to make all three calibers.
![Image](https://i.imgur.com/AKSjvas.jpg)
Primers needed.
![Image](https://i.imgur.com/lC19gTx.jpg)
6.5 Dutch made from .410 brass shells.
![Image](https://i.imgur.com/PqNZU6r.jpg)
.303 Britt with shoulder out .020. This worked out great!
![Image](https://i.imgur.com/fXfsb63.jpg)