Hey John,

When opening out receiver shoulders on a No.1, I have not had to when doing one to the 450 NE, but have always had to when going to the 470 or 500 NE.

Usually remove around 20 thou or so out of each side, but trial and fit, trial and fit is the way to go, as normal. Usually there will have to be a little taken out of the top of the block as well to allow the shell to clear it. Care is necessary here as the firing-pin gallery is under there. I have never broken through into that gallery, but if one was to do so, the block would be ruined.

Some No.1’s are a little “sloppy” compared to others, so one thing that I have occasionally had to do is gently heat and bend the block cam and re-fit as necessary to ensure complete downward travel of the block when the under-lever is fully dropped.

Once you have the shell nicely clearing the block top, the loading trough may need to be slightly lowered to match the block height. The relationship between the block height and the loading trough is fairly critical, if the loading trough is too high in relation to block, the shell won’t extract because the shell rim will catch on the bottom edge of the trough, and if the trough is too low the rim of the case will hang up on the back of the block when the shell is being loaded. All being equal, and with a decent safety catch, the shells should now load smoothly and eject cleanly.

Hope this helps and makes sense.

Best
ALEX