71 rd. mag. $40.

I understand the "universality" and what a great thing concept of a carbine that shoots with pistol mags, in a standard round.
That is a manufacturers issue. I, IMHO, would love to see a carbine utilize a high cap .40 or .45 caliber mag, that would work in a pistol, that would work for both platforms.
But I only see "a glimpse", from gun makers. EMF makes awesome "cowboy" pistols. I look forward to other gun makers, expanding this concept.
Glock Model 21 Carbine? Uses same mag as pistol? Expanded to 20/ 30rd mags? Sounds all good to me.