(This was previously post on another forum, which might share some members, but not all, so I am re-posting it here as well.)

Here we go... I will periodically update the progress of my first attempt at chambering a Desert Eagle in 10mm auto.

So the .357 magnum barrels needed for this project finally came back into stock a few weeks ago, and I have acquired a couple of them for this project. This attempt will be based on the six inch barrel.

The story so far...
I was looking at a ballistics chart a while back and realized that a 10mm Auto round overlaps into the .357 magnum range pretty far, relative to pressure and energy. (higher SAAMI pressures actually) This established potential usage, in theory at least.

First I got my .357 barrel running well with .357 mag, as performance out of the box for this barrel, was poor. This was a two part issue I believe... rough chamber, and sharp bolt. I polished in specific places on both... I used a lot of Dremel time in small amounts, and a lot of Dykem to achieve very good results with most any .357 magnum rounds above 1200fps. Also, extraction was excellent, so I was confident the headspacing was very good also.

I don't own a 10mm auto, so I bought some of the higher loadings, which were Federal 180gr "Trophy Bonded" JSP's... a hunting round for 10mm Auto basically. These are 1275fps 180gr, for 650ft-lbs energy... that should be plenty to cycle a Desert Eagle slide... on or off paper. We shall see... "real world" often includes variable which we don't consider. Worst case, if the rounds have any issue cycling the slide, I can remove the inner springs, as these small short rounds won't need as much spring pressure as other rounds do, to close the slide. Also, I can make a custom gas piston with smaller vents, no vents at all, and/or a tighter fit, for less blow-by of gas. As I said... I believe I can make this work. It won't be simple, easy, or inexpensive, but that is the price for having something you want sometimes.

Extraction: of great importance, because of the Desert Eagle not being blowback, was extraction... I just looked this up at first, and the rim diameter is so close to .357, only TINY modification to the extractor claw allows it to fully engage the rim... I am going to try it without this first, as I think it will still work. The rims are only around 14 thousandths (0.014) different in diameter.

Feeding: So I modified a .41 magnum magazine a little and added a space filler to the back of the magazine (temporary for testing, as with almost everything at this point) and got the 10mm rounds to where I could feed them out of the magazine... I sketched up a simple filler that will pass through a hole/slot in a modified follower to keep the rounds forward to the correct position in the magazine for the bolt to get them. Then, by hand operation of the slide, with a sleeve I made to fit a 50ae chamber (which I headspaced with a dowel through the barrel) I was able to feed and extract 10mm rounds with the .357 extractor. I stopped here as there isn't much more I can do without making the barrel. I believe the probability is high that I can work out feeding bugs later... I just need a 10mm barrel to do much more relative to feeding.

Barrel making methods: I looked into bore and rifle, and sleeving. Both have their advantages and disadvantages. Both are expensive. I have never done either. I am not a gunsmith, nor a great machinist... what I make, I make well, but I just don't have that much knowledge and experience. I am a general machinist. Most of my experience being at a factory, I know only specific procedures, and we do nothing of complexity, and with very specific tooling. I am buying all tooling for this project.
So... I decided to get enough to try both methods. I got enough barrel sleeve to get two tries in case of issues Then I got a "gun drill" (bit) which is kind of a hybrid reamer/drill for precision which will be used to drill the barrel out to near 10mm for reaming, pre-rifling. I then obtained a rifling button for rifling after drill/ream polish process.
OR, I can also drill the barrel out dramatically, to fit the Barrel Sleeve.

Keeping the gas port clear during this is going to take effort... I am thinking I might make an adapter that forces oil through the gas port backwards during drilling to keep it clear and add lubrication... can't hurt.

If I drill/ream/rifle, all I have to do is keep the debris from the gas port. (might wax plug it also)
If I bore/sleeve, all I have to do is drill the gas port in the sleeve at exactly the right spot... pretty challenging, but I can do it.

So that is where I am as of today... in the next few weeks, maybe months, I will come back and state progress and success with each stage. Even if I am not successful, this documentation might be something someone else can reference and work off of to make it successful.

One of the main reasons I think this round was never considered for a Desert Eagle is reliable cycling of the slide... if you look at the weakest native Desert Eagle round, the .357 Magnum, 90% of factory loadings on the shelf will work. If you look at 10mm Auto, it is probably almost inverse of that... 90% of factory loadings simply would not cycle the slide of a Desert Eagle in my opinion. Most 10mm factory ammo is loaded WAY below SAAMI pressure maximum for some reason.

I just want a 10mm Desert Eagle, so I am going to try this. If I hit a wall I didn't see, I will get some stitches and report back here.