[L473ncy]

I dunno about the purchase TBH.

They say Guarder/Systema parts but to the best of my knowledge they aren't the same company (ie. SRC/TSD or Aftermath/CYMA or Laylax/Prometheus/9Ball).

Other than that Airsoft Global seems like a reputable company.

You might want to switch out that spring though. An SP150.... yeah is way way way too hot to run on any field in Canada (a little over 500 FPS apparently if they have a linear progression of their spring strength). Apparently the Guarder SP110 fires at 410 FPS. Best to get like an M120 or M110.

Also it sounds like a custom built mechbox, if it is you probably won't have to shim but a tech in the back of a shop probably isn't thinking of making it the best shim possible and will probably settle for "good enough" but if you want a "perfect shim" then you'll probably have to open it up. Just my 2 cents.