What are you having trouble figuring out? The locking block goes inside the bolt in such a way that it locks into the top of the receiver. The firing pin goes under/through the groove in the locking block. The firing pin retractor spring goes on the front of the firing pin and pushes the firing pin rearward. Observe that one side of the rear of the firing pin has a cut-out (flat spot) in it. The firing pin is retained at the rear of the bolt by the firing pin retaining pin. The breech bolt buffer goes in the rear of the bolt. Assemble the parts in the approximate above sequence. Sorry I can't tell you the exact orientation or sequence of assembling the parts. You just have to look at them and position them in such a way that they fit. BTW, you don't insert the operating handle into the bolt until you have the bolt inside the receiver.
I just want to make a technical correction to what I said in my post above. The locking block locks into the barrel extension, not the top of the receiver as I incorrectly said. Of course, the barrel extension is positioned such that its locking recess is at the top of the receiver, but technically, the locking block locks into the barrel extension.
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