From their FAQ's.
My Desert Eagle pistol will not chamber or my bolt does not close fully, why is this?
The first thing is being sure your pistol is unloaded. The main reason this may happen is your pistol is dirty and needs to be cleaned; a dirty pistol will affect the chambering, extraction and the overall performance of the gun. Inspect the chamber, clean it with a bore brush (we use a bronze brush) and solvent, and lightly oil it with a patch. Next the recoil spring assembly gets lead and carbon-fouled that it may not let the bolt shut. All you need to do with the recoil spring assembly is fieldstrip it and clean it, oil it, and be sure to properly assemble it. Use your 5-in-1 tool to remove the firing pin, remove the bolt assembly and inspect the bolt - basically just clean your bolt assembly, clean your firing pin, review your manual and reassemble the pistol.
Another problem is a lot of people that shoot wheel guns and different types of pistols have a tendency to limp-wrist. They have to in order to take up recoil of the gun itself. With the Desert Eagle pistol, you can't. You have to take a good two-handed grip to assure a clean, crisp snapping action of the slide forward and back. If you are limp-wristing, it takes ups the inertia of the slide, it won't come all the way back, and the action doesn't cycle properly.
What ammunition is recommended for use in my Desert Eagle pistol?
Remember that ammunition is very important with the Desert Eagle pistol. Defective ammunition will keep you from chambering. Check the type of ammunition you are using. If ammunition is underpowered it will not reliably cycle the action of your Desert Eagle. Shooting lead or full-metal jacket with an open lead base will not only foul the recoil spring assembly crosspiece and the rods, but it will also carbon and lead-foul the piston and solder it to the barrel. You should stay with good, semi-jacketed ammunition. We do suggest trying as many commercial, manufactured, semi-jacketed Magnum cartridges as possible and see which one works the best for you and your pistol.
http://www.magnumresearch.com/docs/DEP_Ammo_List.xls