[Cheese Man]

The polar star pistons are much better than just about anything on the market. And, you really don't need to replace the stock cylinder, or the cylinder head. Just taper it yourself. There is a guide on it.

I would suggest:
Laylax Spring guide (7 and 9 mm - that way you can use any spring you want)
Zero Trigger - amazing trigger pull, it can go off if it is set down too hard.
Polar star piston
PDI hop chamber (arms of choice, the regular ones worked for me)
Prommy/PDI 6.03
Guarder clear bucking, or a KWA 2GX bucking - those are incredible, they just wear out if you don't maintain them in a BASR.
Any spring on the market with the Z-trigger. I was thinking about a PDI SS 2000, and then cutting it to about 550 fps, around half the length

 

[Cheese Man]

Yes, it was. Mine worked for about 4-5 years with nary an issue.

I was just posting my experience, and I have never had a w-hold bucking. Maybe in my next X-fire order...

I have no idea. I like them, personally, but my laylax spring worked just fine too.

But you don't need one. I use about 10-15 mL of white lithium grease on my cylinder every week, and it is quieter than the Teflon or palsonite cylinders, and a smoother bolt pull too. You save more money, and can put it towards a z-trig or a better barrel/hopup parts.

If the trigger box works, fine. I just like the trigger pull of the z-trig.

 

[Cheese Man]

Yeah, kinda. But, you really don't need it.