Tossing around the idea of either a 10mm or 50AE AR (Carbine) built for me.  The ballistics almost are the same from what I can tell.  Other than ammo costs,  what are the pro/con's of the two rounds?

Thx for your help!

10mm Ammo is easier to find here than 50AE so I vote 10mm

(ballistics almost are the same)
I'm not sure where you are getting your info from, but a 200 gr 10mm at 1300fps has 750 ft/lbs of muzzle energy and a 325gr 50AE at 1450fps has 1517 ft/lbs on muzzle energy.
That's not very close at all.

Are they going to be similar to your 45ACP magazines, but with the appropriate feed lips and followers?

Give us a hint?

The 10mm and 50AE are very different rounds especially when setup in the AR. I have both that are DI uppers and have 10.5" barrels and while you can run  135gr- 230gr in the 10mm the recoil is nothing compared to the 50AE that runs 275gr- 500gr bullets. (Handloads) I hunt with the 50AE and run 300gr gold dots @ 1900 fps in the 10.5"barrel. As far as mags I use Glock and Grease gun mags for the 10mm (you can mod the gg mags to work in a standard 223 lower and use a mag block if you do not get a dedicated Glock or gg mag lower for the 10mm) for the 50AE I run standard 223 mags and it runs great. One thing to remember is if you go with a 16" barrel in either you will not get a huge jump up in velocity with the 10mm or 50AE (the 50AE will not become a 50 Beowulf or 500 S&W with a longer barrel.) Both are fun guns and are great in the AR platform. I think which ever you go with you will like them, so my vote is either  or both...

Olympic sells (or did before they went out of business) a 10mm upper. I have one and it runs 100 %
I loaded up some cast loads with unique and its a hoot. Only drawback their mags are expensive and
long. hold 18 rounds. Glad I bought extra before their exit.

Thx!!!

I have 3 or 4 of those Oly 10mm magazines if you want to purchase them at list price, free shipping.

Ok, Let's start with energy.

A 10mm shooting a 135gr Underwood ammo exits a 16 inch barrel at over 2000fps for around 1225ftlbs.

Think of that as your SHTF or midnight prowler bullet. Violent expansion, low recoil, low flash, highly lethal light bullet matched to your carry gun.

A 10mm in180gr or 200gr or 220 cast is a perfect hunting bullet and here in the Northwest will pass clean through a black bear.

35 of these lethal pellets load into one grease gun mag. Ammo is $0.37  per round according to Gunbot, and that is full house Remington 180gr FMJ fun and break in ammo. 184.00 for 500 case.

15 of these will fit in your Rock River HC 1911 or Elite Limited Witness. making your carry gun and you sub gun compatible.

Get a RWS DI setup and you will never regret it, while a 50 will sit on the shelf because the expensive ammo will keep you away from the range.

Ammo proof:

https://www.youtube.com/watch?v=GUyQ-E9aEnI