.40 to .38 Frame Compatability


April 6, 2004, 01:56 PM
I've read a few posts about various caliber conversions, 38 Super to 9mm, 10mm to 40S&W, or vice versa, as well as some others. I didn't see a 40S&W to 38 Super (or 9mm (x19 or x23)) conversion. The breachface is different, so a new slide & barrel setup would be needed. However, would the frame assembly be compatible? If anything, what would you have to change (other than the obvious - mags, slide & barrel)?

I've also read the expense of buying a slide & barrel combo, plus having it installed, could almost get you a new gun. However, I don't really want a whole new gun (or guns). It seems to me that having one frame that could accommodate several calibers might be a reasonable solution.

For example: One frame capable of handling two slides. One slide with 10mm/40S&W/357Sig barrels, and the other slide with 38 Super/9x19/9x23 barrels.

That would offer a lot of versatility without having to own multiple complete guns or frames.

Anyone have experience on this topic? I was thinking about trying something like this with my Delta Elite, but wanted to hear about any good/bad experiences first.


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Old Fuff
April 6, 2004, 06:40 PM
To a degree it depends on what manufacturer and basic model you're looking at. Besides the obvious slide & barrel assemblies there are sometimes different ejectors or the location of same. The shape, angle and size of the frame's feed ramp may be slightly different.

These things can sometimes be worked out, and on a Colt a .38Super/9mm combination isn't hard too do, although you usally need to go to an extended ejector. While I haven't tried it you could probably build a .45 on a 10mm frame, but I not sure about going the other way around.

There's no law against looking into it.

April 6, 2004, 07:22 PM
You can build a 45 on a 10mm frame, I have done it and it works pretty well. The only thing that has been somewhat problematic has been the frame feed ramp. The 10mm ramp is very similar to the 38 Super's, so if a 45 round comes out horizontal it can hit the very bottom edge of the frame ramp and hang up. I did very slightly extend the frame feed ramp and made it just a little more like a 45 ACP ramp, but when the mag springs begin to weaken, first round jams become far more common. It is still 100% reliable with the 10mm top end and will even feed empties, but only with the 10mm top end.

Converting a 45 to one of the smaller diameter calibers doesn't always work well.

April 7, 2004, 02:03 AM
A 38 super barrel and maybe a magazine should be all you need to shoot 38 Super in a 10mm.


Dave Sample
April 7, 2004, 02:19 AM
Wrong! You need a 38/9mm slide or a 10mm/40S&W slide. They are not the same. Feed ramps vary also in the lower ends.

April 7, 2004, 02:44 AM

Have you tried it? I've shot one that seemed to work well enough.
I know the slides are not the same, but they will work. Kimber, for example, uses exactly the same slide for their 40S&W and 38 Supers. The feed ramps may be different, but that seemed not to matter either.

I'd be willing to make a small wager if you can think of acceptable and affordable manner of me proving it to you.


Note: I only said 38 Super in 10mm pistol and I assumed that the reader would have the sense to change recoil springs. A 10mm breechface is a bit big for 9mm size case heads and the 38 super breechface too small for 10mm as a general rule.

April 7, 2004, 08:08 AM
I recently called Kimber to ask about installing a 10mm barrel in my Kimber Custom 40S&W, and whoever I talked to (John?) said something about installing a 38 Super or 9mm on the 40S&W slide. I remember being surprised by that comment, but I didn't follow up on it at the time. I need to call Kimber today about a couple other things, so I'll try to ask about it then.

April 7, 2004, 11:17 AM
I just got off the phone with the Kimber Custom Shop (Susan?), and she told me they use the same slide for 40S&W, 10mm, 38 Super, and 9mm. I didn't ask for a detailed explanation of just how they do that, but she said that my 40S&W slide will accept any of the other mentioned calibers. I expected there would be breachface issues, but since I don't know any better, that's why I asked. So, my 40S&W is soon going off to Kimber for new barrels (9mm, 10mm, and 38 Super). Now I'll just have to come up with a way to keep track of all the respective barrels and associated parts (springs, magazines, etc.)

Old Fuff
April 7, 2004, 11:47 AM
In an ideal world they would use a different slide between the .38 and .40 caliber cartridges, and some makers do. The 10mm/.40 S&W cases have a .424-.425 head diameter. The .38 Super is .406, and the 9mm is .394 (all in inches). Obviously the smaller cases will fit in a slide made for the largest cartridge, but extractor tension, which is critical in a 1911 style design, is going to be different between the larger vs. smaller rounds.

While it is entirely possible that one slide can be made to work for all, my personal conclusion would be that they are doing what they are doing for cost-saving reasons. I would also say that while they are using one slide, the extractor tension is being adjusted for the cartridge chambered in each gun. If your slide has an external rather then internal extractor it may (or may not) be more forgiving so far as extractor tension is concerned, but I would suspect that something that was set up for a 9mm would have too much tension for a 10mm cartridge.

Anyway, if this set-up is going to be a play-toy it may be acceptable. If not I would re-think what I was doing. Unfortunately too many makers are building guns that may be used as personal weapons without any concerns about what their drive for cost savings may have.

April 7, 2004, 03:08 PM
Thanks! Those are helpful comments. I knew there must be some sort of compromise being made, but couldn't put my finger on exactly what. Will the difference is head diameter create any potential hazards (like an exploding gun for example)?

The gun in question is merely one I'd use for pleasure, practice, or maybe some type of shooting sport (nothing serious though), and not a gun I have to stake my life on (I have others prepared for that purpose). So, it's probably a worthwhile trade-off to have it in multiple, though perhaps not completely reliable (?), calibers.

Old Fuff
April 7, 2004, 04:33 PM
So long as the cartridge(s) are fully chambered and the slide is locked into battery there is little likelyhood of a "ka-boom!" and zip chance of blowing up the gun. Problems, if there are any, will be with reliable function. For the purposes you have in mind functional reliability doesn't seem to be a serious issue. Now that you are aware of the full situation I'm sure you can make you're own call.

April 8, 2004, 01:36 AM
While the rim specs may appear to be very different, if you measure random 40 S&W you will find that .412" rims are almost as common as .422" rims with .416" being about average. I don't have a huge selection of 38 Super to measure but all mine are .403-.405".
Since the round is almost centered by the chamber the difference is only .006-.007". I'd be willing to trust a reliable 38 Super with a 40/10 slide. I'd have concerns about a 9mm on a 40/10 slide.


Old Fuff
April 8, 2004, 12:05 PM
My concerns had more to do with extractor tension - which can be a major factor in feeding reliability and case ejection in a 1911 design pistol. While the case is (hopefully) centered in the breechface when the slide is in battery it isn't necessarily so during much of the feed/extraction cycle.

Handguns of all kinds are used for many purposes. In a game/target shooting context absolute reliability (or as close to that as we can get) is not of critical importance. However in a personal weapon it is, and at the beginning of this thread it was unclear what purpose "bradvanhorn" had in mind. When he explained the circumstances I ceased to worry.

On the other hand his report That Kimber is using one size of slide on pistols chambered from 10 mm on the high side to 9mm on the other does concern me because the manufacturer cannot know in advance what a buyer will be using the gun for. I am sure the "one size will do for all" attitude is based on cost savings, but if the product was going to be used as a personal weapon this would represent a compromise I wouldn't accept. Others may do as they wish.

Dave Sample
April 10, 2004, 02:41 PM
Good Luck! I only built very high end guns so I do not know what Kimber would do. I like the breechface to be the right size for the caliber. I do not like sloppy guns. I am not required to prove anything so I will pass on the bet.

April 11, 2004, 09:45 PM
This is my multi-caliber philosophy. For serious social purposes, a frame should be dedicated to a single caliber. For play, there are a few swaps which can be made to work.

My Delta Elite, before I replaced the extractor, was actually more reliable with a 9mm barrel:fire:

I bet it doesn't work that way most of the time, though. I haven't fired it as a 9 or a .38 Super since I have changed the extractor. I have fitted a 357 SIG barrel, and am having great fun with it. Looking for a cheap .40 S&W barrel to use up all the thousands of pcs of .40 brass I have accumulated.

My .38 Super Gov't & Commander models both have standby 9mm barrels for cheap practice. Both work well with hardball, and the Commander doesn't seem to mind JHP's, but I still consider both of them to be a "not quite ready for prime time" item.

I had a SIG p229 with both 357 and .40 barrels. Now this one was reliable, and I would trust it with either barrel.

April 13, 2004, 01:48 AM
Mr. Sample,

I never asked you to prove anything. If you remember, it was you that told me I was wrong. Regardless, I shouldn't have thrown out a challenge like that. I apologize.

I continue to believe our friend will have no problems with a 38 Super barrel on his Delta. It may be a minor compromise but it seems to be one he is willing to accept.


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