380 auto in 357 mag using moonclips

[Metroxfi]

I've been playing around with an idea of making my 6 shot GP100 in 357 mag a bit more versatile. One thing I wanted to do in particular was to get the cylinder rebated for moonclips. Pinnacle performance recently had a sale in cylinder work so I sent in a couple cylinders to get cut. I got the cylinders back the other day and decided to play around.

So, using moonclips allows me to shoot 45 auto out of my super Redhawk just fine... why couldn't I shoot a small rimless cartridge out of my 357? I looked up cartridge dimensions, 9mm is out of the question because of the case taper and wide base, there were a few that *might* work but 380 auto is, well, perfect for the job. Dimensions matched almost perfectly, the only problem is how to headspace them and hold them for firing.

A few years ago I had thought about this so I called major manufacturer of moonclips and inquired about clips for 380 and I was told that they could be made but there would be a custom setup fee plus $8 per clip made. I thought it sounded fair for what it would allow me to do but I wasn't financially in a place where I could do it so I waited. I called them a few months ago and asked the same question and was bluntly to "no." So I called a different place... "no". One place said they'd have to make the stamping dies and the minimum order would be 10,000 moonclips and that's a small order... crap! Yet another place said I'm better off just loading light 38 specials, I get it but thats not the point. I decided to figured something out by myself, here's what I came up with.

The gun used is a Ruger Gp100, 6 shot, 357mag, stainless, 4" barrel. The objective is to reliably shoot 380 auto through it.

Step one was to find the closest moonclip possible, being 9mm conversions are semi popular for this gun I looked for proper moonclips. I didn't want to spend $70 on 8 clips from some of the suppliers when I wasn't sure if this would work so I kept digging. I found a forum where someone referenced a S&W 686 having the same cylinder pattern as a chiappa rhino... hmm, they make those in odd (for revolver) rimless cartridges. Behold!
Found them on midwayusa.com, $28.99 for 10 plus shipping. I figured they're cheap enough to play around with, if they don't work I'm out a total of $34. They say 9mm/40sw and they're used for both cartridges. I know. I had to measure for myself, the rim diameters are obviously different but the extractor groove is the same.

So I got the moonclips and just as expected, they're a touch too open to hold 380 auto. I can set them in and put all 6 in the cylinder and I could shoot them that way but it's a pain to gently coax them into the cylinder. I needed to 'close the gap' by only a few thousandths to get them to hold.

My first thought was to flare or upset the fingers on the moonclips by using a good center punch. If I flared them too far I can file them back, no big deal. Got a couple center punches out and promptly rounded them off. Those clips are frickin hard! I even borrowed a center punch from my dad that he had forged and heat treated, he's never had to sharpen it... but I did... not even his crazy center punch did much to the moonclips. Alright, what's next?

My next idea was to cut a narrow slit down the fingers and use a wedge to bend them apart, closing the gap and providing more tension on the cases. I found I had a pack of diamond cutoff wheels for my dremel that are super thin and, well, coated with diamond.. that should hold up right?


I'll try to simplify what I ended up doing. I started by clamping a clip in a vice using an old primer box to keep from marring it and giving myself a good backdrop so I could see what I was doing. Measure the widest spot with a caliper, divide in half, lock caliper and use it to gently scribe a mark on the middle of the clip's finger. I then kissed the mark with the cutoff wheel and took a second to make sure it was where I wanted it.


I then began to cut downwards, slowly and as steady as I could, leaving enough meat at the bottom.


So we have a cut, now to flare. Unflared they're about .280" and I had figured I needed to close the gap by .015-.020" to get a bite on the 380's. Using a $0.50 garage sale chisel (we all have one right?) And a very small hammer I began to wedge the chisel between the two.



Tap carefully. Very gently and very carefully. Then repeat.



They clipped in and stay there, some hold better than others but they stay there! Wooo! They fit in the chamber but... the cylinder doesn't close. Crap! Wait a minute, let's measure something quick...

The rebated section is 1.225" and the moonclips... are a bit big. Not by much but enough to make them sit high.
Let's see what we can do. They don't have to be perfectly 1.225", they can be a bit on the small side, as long as they don't hang over the edge of that circle. I found that a good mill file moved the metal just fine so I developed a rhythm.

Clamp up a new one. File five good strokes on one side then:

Five strokes on the other, getting the peak to meet in the middle.

Lastly, three or four good sweeping strokes to round off the peak and smooth it out.


Got it! It fits just fine and the cylinder closes!
I decided to run out and try it but it's a horrible day for it, bitter cold and 20+mph wind, I still rattled off three clips worth. Function was flawless, everything fired and ejected without a problem, none of the clips broke. Time will tell if they hold up, I'm not planning on using them for competitions or concealed carry or anything, just plinking, trigger training, and last ditch. I'm just glad they work!

One of the guys I spoke with about having them made said I wouldn't be gaining anything by doing it. Well, I have half a 5 gallon bucket of 380 brass that is not being used so that's, what, a few thousand extra rounds that I can now use. I already have a mold and dies for 380. The guy had suggested loading 38 specials with wadcutter and a light load, well my 95 grain hollow point mold uses 60% less lead than a standard wadcutter and I believe I had settled on using 2.5gr of red dot which is less than a starting load for a wadcutter. Basically, it's efficient. It's no magnum and that's not what I wanted it to be. I wanted to make my gun use another type of ammunition that is abundant and efficient, I knew it could be done, i just had to be the one to make it happen.


Also, out of my S&W bodyguard, these hollow points open flat to the size of a dime, who wouldn't want to use them whenever you could?

[Metroxfi]

These are two that I botched. The first one I had tried using an actual metal chisel but the angle was too abrupt and broke a finger. The second one I had cut too far down, when I was flaring the fingers there was a *tink* and it fell apart. Not a huge deal, I now have a half moon, third moon and a.. uhh... 80% moonclip. They're usable, just not perfect.

[Bazoo]

Thanks for sharing. Interesting to see how others approach an idea. Seems like a waste of effort for someone that handloads, but I do see the allure of making a smaller, efficient plinking cartridge. And I can respect the idea of doing it cause you wanted to.

Had you considered just loading 38 short colt? I've never loaded it but I'm considering it just to play with.

I like the idea of a 357 blackhawk with 9mm conversion cylinder, then I remember, well I do handload.

[WillyO]

Too cool!

Sent from my SM-N960U using Tapatalk

[dverna]

You are a resourceful person. I admire that!

But I bet you could sell those .380 cases and get just as many .38’s...maybe a few more?

There is a 105 gr bullet some of the CAS gamers use if saving lead is the goal. But you can likely shoot those 95 gr bullets unsized in the .357.

[hwilliam01]

These are two that I botched. The first one I had tried using an actual metal chisel but the angle was too abrupt and broke a finger. The second one I had cut too far down, when I was flaring the fingers there was a *tink* and it fell apart. Not a huge deal, I now have a half moon, third moon and a.. uhh... 80% moonclip. They're usable, just not perfect.

Would you consider making one for others? I have the exact same gun and would love to shoot 380's in it. What would be your price?

[Metroxfi]

Thanks for the support everyone! I had considered other loads using light bullets and lighter charges, I could sure do that but this allows me to utilize a separate, unaltered cartridge. Having a big stock of 380 that I can use out of the couple small semi autos and also use in this revolver feels nice. I could sell or trade 380 brass for 38spl but this is the only gun I have that would use it.

Another thing I've played with is using garbage/cracked 223 cases. I only did a few handfuls a while back but I cut them at the shoulder and kept trimming them so they would headspace on the mouth of the case, basically making a rimless 357 case that I loaded with a light 38spl load. I had to flare the mouths quite a bit, they worked best with OOO buck and a light load to 'fireform' or straighten the cases out. They were a novelty at best, if I had no other option it'd be fine but ejecting was a pain. I could do that now and clip them in these clips and have medium 357 loads made with brass that is easier to find and costs half as much. Just a thought, I don't really have a need to do that anymore.

Hwilliam01, is your revolver machined to accept moonclips? If it's not the cylinder won't close.

[rancher1913]

do you worry about fit, seems to me the 380's would be undersized and either lead like heck or key hole.

[hwilliam01]

Thanks for the support everyone! I had considered other loads using light bullets and lighter charges, I could sure do that but this allows me to utilize a separate, unaltered cartridge. Having a big stock of 380 that I can use out of the couple small semi autos and also use in this revolver feels nice. I could sell or trade 380 brass for 38spl but this is the only gun I have that would use it.

Another thing I've played with is using garbage/cracked 223 cases. I only did a few handfuls a while back but I cut them at the shoulder and kept trimming them so they would headspace on the mouth of the case, basically making a rimless 357 case that I loaded with a light 38spl load. I had to flare the mouths quite a bit, they worked best with OOO buck and a light load to 'fireform' or straighten the cases out. They were a novelty at best, if I had no other option it'd be fine but ejecting was a pain. I could do that now and clip them in these clips and have medium 357 loads made with brass that is easier to find and costs half as much. Just a thought, I don't really have a need to do that anymore.

Hwilliam01, is your revolver machined to accept moonclips? If it's not the cylinder won't close.

No, but I could have it done.

[Metroxfi]

do you worry about fit, seems to me the 380's would be undersized and either lead like heck or key hole.

Not for my reloads, .358" diameter bullets chamber and shoot in my semi autos so that's all I've ever loaded them with. I only ran 18 rounds through it yesterday, there was some lube haze at the first 2 inches of the barrel but no leading. I'm sure if I spent an afternoon shooting only 380 through it I would have a pile of lead on the forcing cone. Powder coat and/or some soda can gas check might curb that though.

When I was looking up shops to do the machine work I kept seeing the 9mm conversions. It uses the same barrel and same cylinder, they just run a 9mm chamber reamer in the cylinder and rebate it for moon clips. That would also use a .355" bullet in a .357" bore and I didn't really see any negative reviews about it accuracy wise. I'll load some 380 with some Lee 105gr SWCs sized to .356" and shoot them at paper, that should be a good indicator.

[elmacgyver0]

Neat project.
It is nice when a project comes together.