Primer batches.

[The Cast Bullet Kid]

Hi all.
I am experiencing difficulties with my .38-303 (.303 British blown out to .375).
It had been grouping well at 100m with WLR primers but I have just purchased a new batch of such and now it is stringing vertically.
Is it possible that such a change of batch could be responsible?

[Ray Newman]

If you change a component, you run the risk of changing the load's performance.

When you say you have a "new batch" of primers, do you mean that the new primers are from a different "lot " or have the same lot number, but were just recently purchased?

How large is the vertical stringing when compared to your previous
group(s)?

[The Cast Bullet Kid]

Hi all.
I stripped the rear sights and forend off the rifle and refitted them both.  The gunsmith may have not tightened the sight properly as one of the screws seemed a bit loose.  The rifle is shooting fine again though I have been using large pistol primers however they used to shoot the same as the rifle.
May have been a case of me 'having a screw loose'!!