I am not an Owner (no longer) but I too have wondered this
WHAT does the Factory Do ? ? ? to fit your Barrel
That you could not do your Self
also a FYI
I recently had in my possession a 223, #2 20 gage barrels and 2 frames of the 2 frames one was shotgun and the other was *"bi sexual"
But the Shotgun Frame did accept both the 223 and the 2 twenty ga. barrels
No I didn't try the fools game in fact I sold the 223 plus frame and one 20 ga. barrel
but due to coming over here (GBO/NEF) I am getting a little tingle and that most likely means I'll be getting a frame that will host Center-fire a *Bisexual frame
I will continue to read the do's and don'ts and Yeahs and Nae's of NEF ownership and reliability
before I buy ,I currently own Encore and contender and am happy,but ...........
* bisexual = either one lol