Home Forums Hunting & Shooting AR and Tactical Rifles AR nube question

I am dipping my toes in the AR pool this weekend, a friend needs some $$$ and I'm buying his Spikes AR with a Shilen match 204 Ruger barrel.
I was reading about the 300 blackout round and an article mentioned all that is needed to convert a current 556 AR to 300 blackout is a new barrel. would this also apply to my 204 or is the bolt or BCG different? the 204 uses standard AK mags and visually the 204 and 223 look a lot alike (without a micro) until you get to the shoulder.
The "Fire" has always been a reliable source of good information in the past so I thought I would check here first.
It would be nice to know for the cost of a couple of barrels I could have the diversity. or would I be better off just getting additional uppers?

Yes, all three can use the same bolt. The .204 and the .223 both were developed from the .222 Rem or it's brother by a different mother, the .222 Rem Mag, and the SAAMI-spec rim diameter for all three is 0.378".

Lips of the mags are different but a lot of guys are running .204 through USGI mags with no apparent problems.

Be advised that some folks will tell you it's bad ju-ju to switch a bolt to another AR barrel once the lugs have "married" to the original partner. Others say that's horse hockey. I wouldn't know, I've always changed calibers by swapping entire uppers. In any case, you need to get cozy with checking headspace if you're going to be swapping barrels.

yep, you do have to check headspace, which is no big deal. Otherwise go for it.

The AR I'm getting comes with a headspace gauge, Another member sent a PM suggesting I get 223 and 300 blk uppers and save the time of having to change the barrel.
The more I read the better I understand why my neighbor said, "AR's are Barbie dolls for big boys".
And I thought the "Encore" platform was busy, mere tinker-toys by comparison. Still think I'll have fun with it...they go bang!

Thanks for all the help