Difficult to pull charging handle back

[JoeP83]

I bought the buffer, buffer tube, spring, and T91 rear stock from T91 Tactical, and now its harder than normal to pull the charging handle back to charge it.
I installed a ‘normal’ buffer and spring and everything works fine.
Any suggestions would be appreciated

[Tunnellord1337]

I'm pretty sure the spring T91 tactical sells is a stronger spring.