Just remember that 70mm shells are typically loaded up to the old 2 3/4" British standard service pressure of 3 1/4 tons per square inch rather than the 2 1/2" standard 3 tons.
Do not confuse the idea that a home-loaded shell with the same pressure in a 65mm case as loaded into a 70mm case is the same thing as putting a factory loaded 70mm shell into a gun chambered and proofed for 2 /12". You will be over-stressing your gun.
If you see the ends of your plastic cases 'ragging' or splitting after use - your case is too long for your chamber and/or your forcing cone is too tight.
This is quite common. The solution is to ease the forcing cone or use shorter cases. If you lengthen your chambers,the gun will be rendered out of proof.
All kinds of things are possible. not all of them are agood idea. My advice is to use ammo of the correct length for the chambers in your gun.
