The MPN's should now have the caliber and gas system length listed.
The pistol length tube is at 4.5", carbine is 7", mid is 9", intermediate 11 and rifle at 13".
Pistol Length .223/5.56: SKU 00861 - Carbine Length .223/5.56: SKU 00837 - Mid Length .223/5.56: SKU 00838 - Mid Length .308/7.62: SKU 00855 - Rifle Length .223/5.56: SKU 00839.
I just popped over to POF USA's website for that, but I hope it helps future buyers