I have AR uppers in 9 different cartridges. I am running out of fingers. 
I don't have time to be making all those dummy rounds since I would need about 10 of each to test full magazine conditions.
I am sure many here have cycled live ammo through firearms to test fit.
This just makes it safer.
HuntTXhogs, I had a slam fire at the range as well with a 458 SOCOM under the same conditions you described; full slam on chambered cartridge.
I stopped doing that at home, figuring that magazine feeding would slow down the bolt to avoid slam fire.
But I was still a little worried because of the dimpled primers.
I wish there was a way of blocking the firing pin without disassembly but if there is I don't know it.
Anyway, I can only suggest ideas and others are free to use them or not as they see fit.
Sticks,
Did I really put the washer on the firing pin?
Did I really remove the washer from the firing pin?
With the BCG out of the upper, push the bolt into the carrier and push the firing pin forward, simultaneously.
If the pin is sticking out, there is no washer. If not, there is a washer. Simple.
I don't have time to be making all those dummy rounds since I would need about 10 of each to test full magazine conditions.
I am sure many here have cycled live ammo through firearms to test fit.
This just makes it safer.
HuntTXhogs, I had a slam fire at the range as well with a 458 SOCOM under the same conditions you described; full slam on chambered cartridge.
I stopped doing that at home, figuring that magazine feeding would slow down the bolt to avoid slam fire.
But I was still a little worried because of the dimpled primers.
I wish there was a way of blocking the firing pin without disassembly but if there is I don't know it.
Anyway, I can only suggest ideas and others are free to use them or not as they see fit.
Sticks,
Did I really put the washer on the firing pin?
Did I really remove the washer from the firing pin?
With the BCG out of the upper, push the bolt into the carrier and push the firing pin forward, simultaneously.
If the pin is sticking out, there is no washer. If not, there is a washer. Simple.