Daryl and mauserand9mm, thankyou for your discusion, very informative.

Well fella's you have exposed just how little I know about reloading and wildcats. I have experience reloading .357 and .44 mag in my Lever Rifles, thats it. I'm doing something right there as I'm up to 16 reloads with the .357 cases and they are showing zero signs of wear and tear.

I am aware of the case life issue's with the .303 British and only a basic knowledge of the stresses around forming cases. As for headspacing,chamber dimentions etc I am on a learning curve and continually cross referencing any info I read.

On thursday after work I am taking some fired cases and a dummy round back to the Gunsmith who put my Rifle together to talk further with him about my Rifle. He did tell me he headspaced the Rifle with a No Go Guage. The bolt is also tighter to close than your average SMLE and needs to be worked quite smartly to chamber a round that last 1/2" I feel this is due to the chamber being tighter back towards the Rim and not all to the cock on closing of the bolt if you get my meaning.

Trim too length of 2.188 remains unchanged on the once fired brass.

Unfired case measure .379/.380 case neck dia and .454 immediately in front of the rim and .399 / 400 immediately behind the shoulder

Fired cases measure .384 case neck dia and .449 immediately in front of the rim. I guess this explains the tight closing of the bolt. They measure .401 immediately behind the shoulder.

It's hard to be precise but mid case the taper appears to have expanded about .003 over unfired

These measurements are not as pronounced as I expected as the by the naked eye things appear to have changed more.

Daryl or anyone else considering the above, some questions -

I have been informed that when necking the .303 case up to .375 the shoulder disappears on the .303 Brit and on some cases causes a larger than chamber bulge where the shoulder used to be due to the brass changing thickness in this area. Case reaming or turning sometimes being necessary.

Unrelated to the question but the 375.303 suffers poor feeding from the SMLE magazine. These 2 reasons are why I did not go with this calibre conversion - to keep things simpler and cheaper.

If I choose to follow the necking up advice that Daryl has suggested am I in danger of causing the brass thickening and the larger than chamber bulge even after I have resized back to .358 ?????

I am most definetly keen to achieve excellent case life and enjoying my introduction to Wildcats.

regards Jacko