Trouble chambering first 2 rounds of my AR Build:

[VariableRecall]

You can, but it won't eliminate all possibility of the gun going off if for example you have a high primer. You'd just need to remove the tip so the pin no longer fits through the face of the bolt and is recessed a little bit.

The factory LC cartridges I mentioned are generally on the smaller side for case body diameter just like factory R-P with good quality control. Often surplus or steel cased ammo isn't as small of a dia and doesn't have as good of quality control. Since you have reloading equipment, make up a powder and primerless cartridge for the sharpie test. It's a good diagnostic tool to show you where the cartridge is tight in the chamber causing forcefull chambering or extraction. When I make a wildcat barrel and the dummy or unfired cartridges require more effort than normal to extract (if it's not visible on the cartridge) the sharpie test is the first thing I try.

I do have a large variety of headstamps of .223 brass to try out. After a rather scary batch of badly loaded .223 rounds, I now have an LE Wilson Case Gauge and that has made a huge difference in keeping my loaded ammo consistent. I can also cross-reference the case gauge with my own barrel as well when I get the chance.
I can try the sharpie test with a snap cap, so that there's no chance of a primer going pop in my presence.

[Moleman-]

The factory new LC or RP ammo being on the smaller side for case body diameters can be used to see if it chambers fine and extracts without effort. That'll help point towards a chamber diameter issue. Once fired they are no longer on the smaller side as they've been fireformed to a chamber. If that chamber is generous they might even need run through a small base die to cycle smoothly in a standard chamber. So as a diognostic tool they're only useful if factory new. Commercial snap caps are even more undersized and sharpieing one up will tell you little or nothing. A dummy round with the components you're using and sized by your sizing die would be more useful.

[VariableRecall]

The factory new LC or RP ammo being on the smaller side for case body diameters can be used to see if it chambers fine and extracts without effort. That'll help point towards a chamber diameter issue. Once fired they are no longer on the smaller side as they've been fireformed to a chamber. If that chamber is generous they might even need run through a small base die to cycle smoothly in a standard chamber. So as a diognostic tool they're only useful if factory new. Commercial snap caps are even more undersized and sharpieing one up will tell you little or nothing. A dummy round with the components you're using and sized by your sizing die would be more useful.

I do happen to have a decent amount of brass left over from my previous range trip. I could compare that between the Golden Tiger that I have remaining and the reloaded ammo that I have lying around. I am not exactly spoiled for choice but I think that it would be worth something to try out.

[kerplode]

Were you able to get it working?