Discussed this with a moderator as to where to put this thread and putting it here would be best.
I'll start off by stating the project was attempted just to see if it can be done, not to improve the loading/unloading of the cylinder. Moon clips are excellent and fast for that purpose.
The project was started about 5 years ago.
The first step was using 41 Remington Magnum brass. Ran one thru the 10mm sizing die. The solid part above the rim in the area of the primer flash hole was too 'solid' to size down. That area was 'machined' (using a file) down to match the sized down diameter of what was attained with the 10mm sizing die. Trimmed the length down to 10mm case length spec. That modified 41 Magnum case chambered well in the 610. The concern was having to machine multiple cases for actual load testing.
The next step was with a 30-30 case. The diameter above the rim was perfect for a 610. Used a tubing cutter at the area where the powder would normally be to rough length of a 10mm case. Trimmed it to length to 10mm case length spec. That modified 30-30 case chambered well in the 610. The concern was the thicker wall dimension of rifle brass and once a bullet was pressed into it, would it become too large in diameter to be chambered.
The project was put on hold for further investigation looking for something better.
I've got other posts to put in here, I just want to keep the pictures (many) relative to the text of the post.

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Eventually 401 powermag ammo/brass was found to be a perfect candidate. 401 Powermag was a short-lived production for revolvers with the ammo distributed by Herters and manufactured in Sweden. Needless to say the ammo was extremely rare and the search was on. Being that I go to a lot of gun shows, always looked for that obscure ammo. Most/all never heard if it. I've seen it on auction sites but wasn't about to go that route. Two Akron shows ago I asked a table/vendor of misc stuff and he heard of it and he believed he had some. The last Akron show he brought it in for me. A full 50rd box of ammunition.
Project back on.

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Disassembled 10 cartridges for evaluation. 8 of the 10 were sized thru the 10mm die, no 'sizing' was performed by the die, they were perfect as is. Put 6 new Winchester 10mm cases into a moon clip and measured how much/length was actually in the 610 chambers. Used that dimension plus the rim thickness to trim the length. The modified 401 mag cases chambered well in the 610.

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I thought this was done with the .41 Magnum case when they made the 10mm Auto Rim RMS. But my memory is always suspect these days. There's some info and load data for that on AmmoGuide I think.

Made 3 more pieces each of the 41 Mag and 30-30 for dummy round visuals and sectioned/cutaway visuals.

Eventually I'll make up 6 loaded rounds with the modified 401 Powermag brass for load/pressure/chronograph testing.

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Forgive me, sir, if I have missed something here – but Starline sells 10mm Magnum brass. Everything they have that I have checked is marked “backordered“ but I have received two orders from them in the last few months. Understand this is probably just a project to keep you out of the bars but the Starline brass might be easier. Great photos and write up, either way.

Edited to add: Yeppers, I’m a dork - I missed the “rimmed” part ...

Evidently you missed the 'rimmed' aspect.
10mm and 10mm Magnum are rimless cartridges/brass for using with moonclips.
The project was for a 'rimmed' brass for using without the necessity of a moonclip and conventional cylinder loading as in a regular revolver.

..only problem with your thought is that 10mm Magnum brass is nothing more than a long 10mm...it has no rim which is what the OP is tying to achieve... Shooting 10mm without having clips...

I have written Starline several times requesting both a 10mm round with a rim and .401 brass...maybe one day they will....

The .401 would be a GREAT round in a GP100....

Bob

I, too, have contacted Starline. 401 Powermag brass would be ideal for making rimmed 10mm Magnum as not much shortening would be needed.

Have you tried inside neck reaming the 30-30 brass to get a proper bullet fit ?
30-30 is easy to find and except for the thicker wall where the 10 mm bullet needs to go , a good candidate for the Rimmed -Ten .
The last time I saw 401 Powermag ammo / brass for sale was at a gunshow ...in 1968 !

I do like your idea of a "Rimmed-Ten" ... ( RM-10 ? )
Keep On Keeping On and keep us updated on project .
Gary

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NRA Member

Yes, considered but didn't try as didn't want to do an extra 'machining' step as also avoiding the extra 'machining' step with the 41 Magnum brass in that the thick base by the rim needs to be reduced.

Aligning the cutaways of 10mm and the 401 case and matching where they would sit (10mm in the moonclip and 401 case against the cylinder), the powder capacity appears to be less with the 401 case.
I'll use my 10mm reloading data (backed off of course) for when I eventually start testing for pressure and velocity with the chronograph. I don't expect better ballistics over a standard 10mm, actually should be less with reduced powder capacity.

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I've asked Starline several times if they had any plans to make 10AR brass & they repeatedly say No.

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Not sure what the issue was when you used the 41 Mag brass but I made some 10AR brass almost two years ago & posted here that they worked fine but weren't worth the extra effort to me to make more.

They still headspace on the case mouth (not the rim) & use a taper crimp, but the extractor easily grabs the rim for ejection.

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Before I did my 10mm Auto to 10mm MAG conversion I made some 10AR brass from 41 Magnum brass & test fired them with full handloads without any issues.

I trimmed the sized down brass (using a 10mm Auto sizer die) to be just under the maximum length for the 10 Auto, .992" long. This length means they are headspacing on the case mouth, just like if you were shooting 10 Auto's without moonclips.

This also means the larger (unsized/partially sized) diameter of the case near the rim is above the chamber opening & I had no problems inserting/removing them, before or after firing.

And even though the rim of the case is not touching the face of the cylinder they still easily extract using the ejector, just like a regular rimmed cartridge does.

http://smith-wessonforum.com/140603811-post12.html

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Waiting for the break of day

Cool project!

Inside neck reaming isn't all that difficult if you get the right reaming die setup.
The price might be a consideration though.

In the early days of the 44 supermag (an even earlier version was the 44 Rhino, a 1.7" case)
there was no brass so cutting down rifle rounds was mandatory.
My neck reamer is from RCBS and worked well for several hundred cases.
I don't remember using any lube but in retrospect a little might help a lot.
I have even neck reamed a box of the Starline .445 brass for the purpose
of loading oversized cast bullets in a tight chambered Encore barrel.
That was easy as there was not much to remove .. .001" max.

Occurs to me that someone who has a 401 is gonna regret your trashing those cases.
I got a small amount of friendly flak for doing in 30USA cases.
I paid no real mind as 30-40 was available at the time from W-W.
The only difference is 30USA has less capacity due to thicker brass.
Also used 303 Brit. which I am convinced the USA simply modified
to shoot .308" bullets when they went to design a smokeless rifle round.
God Forbid our military should have ammo compatible with anyone else!

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NEMO
"Everything 44"

The only revolvers that chamber them were distributed by Herters 1969-1971, that's all. They've had 50 years to find ammo/brass for their guns. There's a 45 cartridge box of ammo on GB with a buy now price of $255. The stuff occasionally shows up on GB.

Thanks for the information.
I never really "looked into" the 401 and didn't realize they were that rare.
Good reason Starline would hesitate to make them.
They sure saved us supermag fans' bacon by making several of those.

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NEMO
"Everything 44"

What about 30-30 cases? Wasn't some of the early history of the 10mm is that it was made from cut off 30 Remington cases? The 30 Remington is a rimless version of the 30-30.

This is one of those solutions to a nonexistent problem. 10mm cases are easily loaded and unloaded into moonclips with your fingers. No tool needed! What purpose would rimmed cases serve in a 610? I would shoot clipped 40 S&W in my 610 before trying to cobble up some rimmed cases.

Lord knows where it is amid the mountain of junk I kept from a house I sold after living in it for 20 years, but I vaguely recall from long ago an article about making rimmed 10mm from the .401 Powermag brass. May have been in Reloader Magazine.

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Pisgah

Nobody said it's a problem that exists.

oldman10mm;
Years ago, I had a similar problem, but with a rifle cartridge. This was a LONG time ago. I had some friends who were competing in Black Powder Cartridge Rifle Silhouette Matches. I decided to join them. It was suggested that a .40/65 had some advantages over the .45/70. Mostly because of less recoil. Prone shooting over sticks could be really hard on the shooter. Because of body position, the recoil was not absorbed by movement of the upper body, so it could be serious over a lot of shooting during a match.

There were a lot more 45/70 cases available, then, than 40/65 cases. The .45/70 was the parent case of the .40/65.

There was an issue though, similar to the issue you are having with the making of 10mm rimmed brass. When we ran the 45/70 cases through the 40/65 die, the area near the case head was not sized because the shell holder would not allow the case to be fully sized. Just like the 10mm, to chamber properly, that area HAD to be sized. My buddy had already "been there and done that". It was really quite simple. Using a strong single stage press (the RCBS Rockchucker), a steel washer of the proper size was laid on top of the shell holder and the case carefully set on the washer and pushed into the die until the rim of the case seated against the base of the die. Of course, beforehand, the decapping rod was completely removed from the sizing die. After the case was fully into the die, a dowel rod was inserted in the die from the top inside the case, then you would gently tap the case out of die. It was easy/peasy and only had to be done once.

Note: our 40/65 die was, of course, steel. Further, the cases were lubed carefully with case lube before being sized. The effort to remove the brass was not terribly heavy. Now, your 10mm sizing die is probably a carbide die and that would worry me a bit. I would feel better, if a 10mm steel sizing die was obtained to use. Carbide is brittle and won't stand much pounding. You could fracture the ring or actually drive the ring out of the die. I would just get a steel die and proceed. You won't believe how easy it should work and production of the processed cases would be MUCH better than any other way I could imagine.

Understand, I have not done this on 10mm but if I wanted some rimmed 10mm cases, I would be all over trying this. Maybe one of your friends already has a steel die you could borrow to try.

Let us know how it works for you - there may be others out there who will become interested, too. I have shot my 625's a LOT with both .45 Auto, with moonclips, and .45 Auto Rim cases, also. Having the ability to choose either, depending on circumstances IS a worthwhile thing.

FWIW
Dale53

For 10mm mag rimmed brass….in a SingleSix…..I use 30-30 brass wire h the rim trimmed….reliable headspace

I’ve run 30 carbine all the way into a die and tapped them back out building brass for a neat 7.65 Mannlicher pistol. Enjoying your thread. Sometimes it’s just about seeing if you can do something. I’ve put a Mini30 into a M1a stock and my current Ruger build is putting a rebarreled Mini14 into a garand stock.