GunSmith Bros Aluminum BlowBack Housing - Red
Tried and tested by many of the well known Hi-Capa builders, who have nothing but positive things to say about them - durable, efficient, improved cycling.
Will fit 5.1 and 4.3 variants, includes nozzle return spring and fitting screw to the rear.
Don't forget to pick up some spare Nozzle Springs too, you will need them - trust me!
*colours shown may differ slightly from final product.
* These are exactly the same as the AM BBUs