The deformation is not actually wrong, it's just incomplete...

In MANY barrels, 40FP will not result in an AA Field grouping at all well - Theoben barels are an example. OTOH, BSA barrels do seem to shott thme very well at high power.

Bear in mind though that whilst you lose some trajectory advantage with Bisley Magnums, the long range effectiveness may be better due to a greater resistance to wind drift....

They also will typically have an extra 1 - 2 FP at the muzzle...

30FP is about the point I would GENERALLY move to Bisley Magnums...

HTH - JB