The aluminum receiver ws made close to a three-­lug bolt that locks into a barrel extension hooked up to your barrel. The barrel and barrel extension are much like that of an AR-­pattern rifle, i.e., the barrel and barrel extension contain many of the strain from firing. I guess that's https://sigcrossupgrades97444.full-design.com/the-2-minute-rule-for-sig-cross-5-56-69590175