My LGS has a lightly used Sig MCX Virtus for sale.  I'm thinking about buying it.  

Can I tell by ser. # if it is Gen 3?  

Is there a list for AR/Sig MCX compatibility parts?

Spare parts that I would need?

I do intend to wade through the big threads on these but I need to figure this out soon so I don't miss out.

Thanks.

Gen 3? I don’t think there was/is such a thing. There’s the original MCX, the updated MCX virtus and then the spear LT. The original rattler was a virtus variation,or precursor,I can never remember. The rattler has a couple parts specific and non interchangeable to it like the handguard and the op rod
People erroneously called the spear LT a gen 3 before it was released.

Like with most sig products there were some rolling changes within each gen but nothing really worth worrying about enough to do serial # checks, not that that would tell you anyway. The handguard is the easiest way to distinguish between the 3 different models, then receiver length, barrel thickness gas block position and a couple others.

Unless it’s dirt cheap I wouldn’t bother with an original MCX but a virtus is great.

G3k...thanks.  I know nothing about these so I was relying on googling and that is where I saw the references to a gen 3.

It is definitely a Virtus.  It's in great shape.  My ffl took it to the gun show this weekend.  I might grab it if it comes back.  I'm still up in the air on it.

It's a fine gun, heavier than the Spear LT but the rail setup is very solid.

I’ve had my Virtus for about a year now and love the thing. There is very little difference between the Virtus and the Spear LT and the VIRTUS will accept almost all Spear LT parts except the hand guard and a maybe a couple other minor parts I believe.
If it’s a good price, I would snag it.
Cp