In practical terms, how much more powerful is a 44 Magnum Semi Auto such as the Desert Eagle than a 10 mm such as the Glock 20 or XDm 10 mm?
I have both those 10mm and am Seriously considering getting a DE 44, since I already have several 44 Magnum revolvers.
My primary purpose is Hunting and Defense.
So what is Gained by adding the DE?
Accuracy, Range, Lethality, Impact?
The Glock 20 and the Desert Eagle can both use full power ammo. So from their respective barrel lengths;
10 mm Auto:
200 gr JHP @ ~1200 fps
220 gr hardcast @ ~1100 fps
.44 Rem Mag:
240 gr JHP @ 1200 fps
The Desert Eagle is gas operated and per the manufactures recommendations, cast bullets should not be used. Cast bullets are not recommended for the Glock's polygonal rifling either, but aftermarket barrels with conventional rifling are readily available and common among those of us who handload for the cartridge. If you get the 10 inch barrel for the Desert Eagle, you can get another two or three hundred fps from that bullet. You may also be able to find jacketed projectiles for the .44 that are heavier, but I don't have any experience with them. My dad has used a 240 gr Sierra JHP for years in his Desert Eagle Mk VII and has taken deer and several black bear with it, so that is what I am familiar with. Getting more than 1200 fps with a 240 gr bullet will be difficult with the factory 6 inch barrel, because that is essentially a 4 inch revolver barrel. Autos measure barrel length from rear of chamber, so you have to subtract cartridge length to get usable barrel length. So by the numbers using these figures, we derive that the 10mm Auto gets between 590 and 640 foot pounds at the muzzle, and the .44 Mag from the Desert Eagle gets around 768 foot pounds. If you give it an optimistic 1400 fps, the .44 can boast 1045 foot pounds at the muzzle. The 10mm starts out with a frontal area of .126 sq inch while the .44 mag has an unexpanded frontal area of .145 sq in. So the 10mm Auto will have 87% of the .44's frontal area, 56 to 83% of its energy, and 83 to 92% of its mass. Meanwhile it has almost twice its capacity (which admittedly shouldn't matter hunting) and under half the weight (about 31 oz for unloaded G20 vs 64 oz and some change for aluminum framed Mk XIX Desert Eagle).
Of course, these are just the numbers. Deer don't read ballistics charts, so you have to keep perspective with these things.
The 10mm Auto should get the job done. If you need more power than the 10mm, the .44 Mag Desert Eagle isn't going to do it, unless maybe, you stick the 10 inch barrel on it. The .44 Mag has more capacity, the 10mm Auto operates at higher pressure. Pick your poison. Personally, the Glock 10mm is easier to pack and to shoot well, and is plenty lethal or deer, black bear, and hogs. If you're going after bigger game with a handgun, the .44 Magnum can do it better, but the Desert Eagle with the stock length barrel is not the platform I would choose. To really get an advantage over the 10mm from the .44, you're going to want a revolver with a longer barrel that will allow you to shoot heavy hard casts, like a 300 gr LBT WNFP at 1100+ fps.