Replacement Spring for Umarex HK 416D?

[Pipewrench]

Any of you guys know if there are any carrier springs that would fit the Umarex HK 416D? Maybe a 10/22 spring after little modification? I can't seem to find any spare parts for HK 416D ...

I'm trying find a lighter spring so I can cycle Subsonic CCI Quiet rounds. The stock spring is too heavy unless I remove rear spring bolt and timing screw. I would rather just have a modified / shortened spare spring to swap between loads.

[DaveBC]

I thought the HK 416D was already adjustable for fine tuning bolt speed. Its an allen key. You turn it counter clockwise for slower ammo. You remove the butt stock and you'll see the hole w/hex screw in it.