BCG differences 9mm vs 5.56

[Arson]

I noticed the differences in the bolt carries keys between the 9mm and the 5.56. Does the 9mm operate like a DGI like the 5.56, is a gas tube required?

[spdrcr]

9mm is blow-back and no gas tube is required. My 9mm (and .22LR) MRP barrels do not have gas tubes.

[ar15barrels]

Gas impingement bolts lock into the barrel when the bolt carrier rotates the bolt during its last 5/8" of travel while closing.
Blowback bolts such as the 9mm do not have a locking bolt.
The bolt and the carrier are all one piece.
There are no locking lugs.
The 9mm cartridge hangs out the back of the 9mm barrel by about 1/8" and the bolt captures it when it closes.
It is only the weight of the bolt and the spring tension locking the chamber closed on a blowback gun.
There is no gas tube on a blowback.
The pressure in the barrel blows the case back out of the chamber.

LMT MRP direct impingement barrels do indeed have gas tubes that work with standard bolt carrier groups.
There are also gas piston MRP barrels which use a gas piston specific bolt carrier group.
Who made your MRP blowback barrels?

[spdrcr]

Spike's Tactical made the 9mm and 22LR barrels for my MRP.

[ar15barrels]

Spike's Tactical made the 9mm and 22LR barrels for my MRP.

Were they adapted standard barrels, or made from scratch as MRP barrels?

[spdrcr]

Were they adapted standard barrels, or made from scratch as MRP barrels?

They are custom made in small batches by Spike's.

http://www.spikestactical.com/new/z/barrels-9mm-barrels-c-210_192.html?zenid=85bf1300741896a870538d0b4d07f6e3