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This is actually more the path of thought I want to follow, all my cases I own are between 3 and 7 reloads. These were 3 when I started reloading again. (This annealing is noticeable in many ways).Come to think of it, I have had this issue with this rifle for since for ever, and seeing it on the .303 now as well. It has however always been a non issue amount of resistance, it has now become a problem amount of force needed I believe it is likely part of my reloading process that is causing it. I neck size, collet size and bump shoulder back only to the minimum. 

Use a Micrometer to measure a factory round ( actually a few of different manufacture ) at different points on the case
Then measure the reloaded cases that are giving problems
See what the difference in the measurements are ?

Try a different FL sizing die
May not help if the problem is in an area the die cannot reach

Try a set of - SMALL BASE DIES

Try a set of shell holders of different dimension - the Redding set

Headspace adjustment with Shellholder??

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This is actually more the path of thought I want to follow, all my cases I own are between 3 and 7 reloads. These were 3 when I started reloading again. (This annealing is noticeable in many ways).Come to think of it, I have had this issue with this rifle for since for ever, and seeing it on the .303 now as well. It has however always been a non issue amount of resistance, it has now become a problem amount of force needed I believe it is likely part of my reloading process that is causing it. I neck size, collet size and bump shoulder back only to the minimum. 

Use a Micrometer to measure a factory round ( actually a few of different manufacture ) at different points on the case
Then measure the reloaded cases that are giving problems
See what the difference in the measurements are ?
Try a different FL sizing dieMay not help if the problem is in an area the die cannot reach
Try a set of - SMALL BASE DIES
Try a set of shell holders of different dimension - the Redding set
Headspace adjustment with Shellholder??

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I will try these methods as well, thank you.