The thing about military rifles chambered in .303 is the chambers can be rather generous, after all they were designed to be used in war where a shot was fired and the spent cartridge case discarded. The military certainly were not interested in preserving fired cases and a generous chamber meant the round could be chambered in muddy or dusty conditions which it did admirably. The downside is the cartridge case which head spaces off the rim tended to rattle around inside the chamber when ignited, the shoulders would go forward however the rim would go back and this would lead to stretching/thinning of the brass just forward of the rim, this can be evident on even once fired cases where the stretched area of material is clearly evident.
This leads to case failure in time so if I have a new box of brass to work with I add an O’ring to the rear of the case just in front of the rim. This means when the bolt is closed the O’ring compresses and holds the case head tight to the bolt face and as the internal ballistics take place the case head stays where it is and the shoulder moves forward. Yes the case has stretched but in a far more manageable manner.
Look carefully and you will spot a ring on the bullet just behind the meplat, this is where the seater stem has been cutting into the jacket as it is designed for a 174 SMK as opposed to a 150 grain soft nosed bullet such as the Pro Hunter here. I will machine a new seater stem to suit the profile of the 150 at some stage however as today was a combination of zeroing and blowing the cases neck forward it was not incredibly important.
Regarding fire forming .303 brass (First shot) with an O’Ring seated tight to the cartridge rim, this image shows from top to bottom:
No1 New and unfired .303 brass.
No2 Once fired with O’Ring .303 brass.
No3 Once fired without O’Ring .303 brass.
No4 Shows what can eventually happen as the case is repeatedly stretched and full length re-sized between shots.
No3 is from a P14 with a reasonable chamber however after just one shot you can see indication of stretching as a shiny section just in front of the rim. The actual case length is now +.007.5 thou/0,02mm so shorter than that fired in the Lee Speed.
The difference in shoulder profiles is interesting, No2 being a commercial BSA Lee Speed probably built around 1900 and No3 being a Remington built P14 from around 1917 so it is worth remembering not all rifle chambers are equal and especially not the .303 service rifles from the first quarter of the last century.
No4 is from a 1915 BSA No1 Mk3 (Star) that was well past its sell by date and sadly had to be retired for a number of reasons.
So there you are, fire formed 303 brass that should last for ages with neck sizing only and an occasional annealing. Before you ask, the O’rings I use are actually those used on our .308 Cleaning Rod Guides and I leave the ordering of such things to the Viking and have long since forgotten the details, however if you would really like to know give her a shout and I am sure she will be able to help.
