Honestly, I've killed three deer with handguns in my life.... and all of them have been with a 10mm in one form or another... (two with my Dan Wesson Razorback and one with my Fusion custom longslide. The first two with the RZ were both with Doubletap 200gr XTP's (~1150fps literal vel.) and the third with the Fusion was with a much hotter handloaded 200gr XTP (1325fps literal vel.). The first deer was a 10-15 yard shot that led to a very quick death (deer ran for about 5-10 yards after the bullet punched through the shoulder on one side and out the other side after breaking the opposite front leg), the second deer was a 25y shot from my climber stand and was a single shot to the boiler room, bang-flop. The third deer was a 5-10y shot and the deer went about 5y. In the future, I'll be using a heavy WFN hardcast at high speed for my 10mm hunting endeavers as I feel that, while the heavy 180-200gr XTP's are good, even THEY won't guarantee a full pass-thru on a deer depending on what's hit.
As for the .44 mag.... I've been on a .44 mag kick for the last several months and will probably be using my Ruger Super Blackhawk Bisley Hunter in .44 most of this coming season. I have a Fastfire 3 mounted to it which is AWESOME, making those intermediate-range shots (20-60y) MUCH easier to make, although I took the FF3 off a week or two ago to play with open sights for a while. (It takes about 3 minutes to put the FF3 back onto the Ruger and minimal shots to ensure the sight is still sighted in, so I just keep the FF3 and its wrench in my .44 case so I have options). I'll be using a warm handloaded 250-255gr WFN or Keith hardcast at 1250-1300fps which, after my recent firelapping project, allow me to get sub-1" 25y groups with OPEN SIGHTS.... Can't wait to get a deer with ol' Blackie!
The bottom line is that either caliber will do the job as long as you put the shot where it counts. If you don't do your part, you could lose a deer, yes. This is the case with ANY handgun, and even any rifle. Place your shot correctly or don't take it
Make sure that if you use the 10mm, choose a platform that you can shoot accurately and practice practice practice! The 10mm, if loaded properly, can take deer at ranges much farther than most can shoot accurately at... and we all know that the .44 is effective to at least 100y on deer.
Pick your poison, or do like I do: pick both and switch it up daily during season! (Just remember, practice with both!)
Good luck,
Nick
(pics below)
G20SF w/Barsto and Heinies
http://imageshack.us/a/img43/723/img4503w.jpg
Fusion Longslide
http://imageshack.us/a/img852/399/ni...adionxl8xx.jpg
Ruger SBH Bisley Hunter
DW Razorback
http://imageshack.us/a/img514/6765/img0808s.jpg