Educate me on single shot sleds

[Diabolus]

I want to purchase a M&P 9mm long slide. I was told it's possible, but you need to bring it in as a single shot.

Does anyone know if this is possible, and if so, where do I start?

[Olav]

I think the barrel has to be at or over 6.5 inches to qualify for single shot amongst other things.

[mikaarce]

Call Valkyrie arms