The UK's Finest Independent Forum for Shooters and Gun Owners. Est 2010.

I would agree, internal volume is going to have an impact. As an example, a #2156 built to 2.900" with a given load of TR140 behind it through a 30" barrel:

Case capacity 55 grains water gives 2966fps
Case capacity 56 grains water (Default) gives 2942fps
Case capacity 5y grains water gives 2919 fps

I have shot both at long range. With the right sorting and prep, PPU is OK. However, Lapua is more consistent and stronger, so it is a much better choice.