Basic upper question

[xwray]

Are there any unique differences between an upper one would purchase to build either a DI or a Piston SBR or are they completely interchangeable?

Thanks for any feedback

[fallenromeo]

Are you asking if all parts are interchangable between a DI upper or a piston upper? Or just the actual upper receiver itself?

[xwray]

I mean the upper receiver itself. Let's say I decide to build a piston SBR...do I start looking for a "piston upper" or will any upper I settle on work with the appropriate parts to become a piston upper.

[Leaveammoforme]

Normally a piston upper will have a round hole for the op rod to pass through. The round hole works as a guide for the op rod.

A gas upper tends to have the X shaped hole. A X shaped holed upper will require a bushing should a person go piston.

[xwray]

That makes sense...thanks

[Leaveammoforme]

I should have stated that the round hole applies to short stroke systems like Adams Arms/Huldra.

Don't know for a fact but I'd imagine a long stroke system like a PWS wouldn't require an op rod guide in receiver.

Your best bet is to buy a complete piston upper assembly in the flavor you desire.

ETA: Just looked at PWS stripped upper pics. They have very large (comparably) round hole for the piston to clear during install/removal.