Prommy M90 soft?

[bop]

Evening,

Just looking opinions on something which I am in two minds about please.

Recently rebuilt my M4 as I am planning on selling and wanted to check everything was ok. Was on the chrono shooting around 350/360fps on a SHS M100 spring. So swapped out the spring for a Prommy M90 and back on the chrono and it's only coming in at 286fps and is pretty consistent at this reading.

Does 286fps sound about right for a Prommy M90 spring? I was expecting a little more.. I have done some air leak tests and the compression in the cylinder is great and when I done the paper on the feed chamber of the hop up it never moved. Also wrapped the arm of the hop up with ptfe tape.

Current air seal parts:

Lonex chamber
Lonex bucking
ZCI 275mm 6.02 barrel