I recently acquired a complete M1911 45ACP slide assembly. It mates perfectly with my several 45ACP frames. One of the reasons I purchased it was to possibly mount my 400 CorBon barrel in it to make swapping out for that caliber a little easier. I also have several M1911s in 9mm/38Super. I'm considering using one of them instead to mount the new slide assembly. If I decide to do that, do I need to do anything to the 9mm frame or the slide assembly other than swap out the ejector?

You will have problems. The ejector and extractor will need changing and possibly the slide stop. The big issue is the feed ramp...the angle is different for different calibers unless you convert the frame to use a ramped barrel for each caliber.

Basically...not worth the expense of the conversion.

Assuming you're talking about the actual full size 1911 frame, no.

You might try one of these, which claims to work for both calibers. Not sure how it does that as I'm no gunsmith.

Extended Ejector | Colt Government/Commander/Officer's

Thanks for the suggestion! I've done exactly that.

Why does the OP have two threads on this? Impatience when posting? This forum is notorious for hanging for up to 30 seconds after hitting "post".

__________________
Release the Kraken

I can tell you for sure that a 9mm or .38 Super slide works fine on a .45 frame. All you need to do is swap the .45 ejector for a 9mm ejector and use a 9mm or .38 Super magazine. I don't know about the reverse of that, but I would bet that there is no difference in frames, other than the ejector, which is very simple to swap. Just punch the retaining pin, pull out the .38 ejector, drop in the .45 ejector, and push the retaining pin back in. Actually, the retaining pin is not needed, but I use it anyway. My Colt .45 frame is used for .45, 9mm, .38 Super, .400 CorBon, and .22. The .38 Super barrel works fine in a 9mm slide, but .38 Super magazines are unreliable for 9mm cartridges. All the above applies to unramped barrels and standard GI-type frame.

I did have to do a slight bit of fitting to get a 9mm slide to fit the .45 frame smoothly, but it didn’t amount to much, just a few minutes with a rectangular needle file. Also, you may need some different recoil spring weights.

It sticks in my mind, and I could be wrong about this, that a 45 slide and barrel will not work on a 9mm/38 Super frame. Seems like I tried this long ago. The fit is fine but the larger round will not feed on the 9mm frame ramp. The shape is different than the .45. I'll try this again when I get time and will find out for sure.

__________________
Everybody could shoot

FEED RAMP IN FRAMES ARE DIFFERENT

Assuming that is correct, does it cause the use of a .45 slide and barrel to be unworkable?

YEP. RAMP ANGLES ARE DIFFERENT,

As you seem to already have everything needed, just try and see if there are cartridge feeding problems. I am assuming your barrels are all unramped.

I have both ramped and unramped barrels and frames available.

Won't know until the extra 45 ejector I just ordered earlier this week gets here.

Thanks! I have ramped barrels and frames as well as unramped.

Thank you, now I know. I noticed the mistake, but couldn't figure out a way to delete the second post. Was hoping a moderator would come along and delete it. They are usually on me in about 30 seconds when I screw up. I have trouble with computer stuff all the time. I am more used to mechanical devices where it either works or doesn't right away, and where you can try double-clutching or stop and climb out and try to fix it.

When you try it, please provide results. I like the idea of multiple caliber conversion capability. I have never owned a factory .38 Super GM so I have never tried adding a .45 upper to a .38 frame to see if there are any feeding reliability issues. I would expect no feeding problems in using .400 CB in any event. The main concern is that you must reload for it. But that is not really much of a problem, I have been loading .400 CB for many years. Simple to re-form .45 ACP brass, and there is a wide variety of .40 bullets. It is not difficult to emulate 10mm ballistics, but I don't do that. My .400 loads are kept more in the .40 S&W range. In fact, I use .40 S&W reloading recipes, usually with cast bullets. It's not a match-grade gun, but the .400 CB shoots the best groups of any of the calibers.

My first experience with the .45 ACP to 9mm/.38 conversion was via Elmer Ballance, the founder of Springfield Armory, the initial location of which is about four blocks from my house in San Antonio. He rechambered a 9mm barrel to .38 Super/9x23 for me, gave me a new 9mm ejector, and found me a new 9mm slide. We put it together and it worked fine. I have put a ton of 9x23 Win loads through that Colt. I also have a 9mm barrel for it. I have had no contact with Elmer for about 15 years, and I do not know if he is still alive, but if so he would be in his early 90s at present. Springfield Armory | Criminal Minds Wiki | Fandom

If you want to get real tricky. Mill the .45 slide out to accept a 9mm ejector, then you have the best of both worlds and all you have to do is swap out the slides when you want. The 9mm ejector will work on all calibers.

Once you modify the frame for a ramped barrel there's no going back to original. I'm not saying don't do it...just think it through.

Personally...I'd rather have a gun originally chambered for a particular round than modify an otherwise good gun. You can never have too many guns.

I hadn't thought of that, will have to look at slide to see how it could be done. But I have no particular interest in actually doing it as it takes less than a minute to swap out ejectors so it doesn't seem worthwhile to expend the effort (I have a milling machine).

Bingo! 9mm, 38 Super, 40/10mm slides are milled for a wider ejector. To put a 45 ACP slide on a receiver that was originally made for one of the smaller diameter calibers, you either mill the 45 slide or change the ejector. As to receiver feed ramps, my experience was with a Colt Delta Elite, the receiver feed ramp is cut differently than any my 45 ACP M1911's. Barrels with integral feed ramps negate this potential issue.

__________________
VCDL, GOA, NRA

Over a good many years, I've experimented with so many combinations, I can't remember them all now. I do remember changing ejectors between .45 and 9mm, and recall that .45 slide/barrel worked on 9mm frames, but 9mm slide/barrel on .45 frames did not get along well. The .45 frame ramp being cut further forward caused feeding issues with the shorter 9mm cartridge. That little gap between frame feed ramp and bottom of barrel throat goes away when the 9mm barrel is used on the .45 frame, and 9mm barrel may actually hang out over the .45 frame ramp a few thousandths. Not my photo, but the attached picture does show the difference in the frame feed ramp machining between 9mm,top, and .45 ACP, bottom. Of course, using ramped barrels in each caliber, the feeding issues are cleared up..

Attached Images

45 and 9 frame ramps.jpg (51.3 KB, 11 views)

__________________
NRA Life, COTEP 640

After many years of use, I have yet to experience my first feeding reliability problem when firing 9mm and .38 Super ammunition with any bullet using a .45 ACP frame. And that is using standard unsupported chamber barrels.

DWalt, I am envious. Even the Colts I've had that were originally chambered in 9mm, to include my recently purchased 9mm Gold Cup NM, were reliable only with RN ball ammo. Same with the Colt 9MM conversion kit I had years ago. My last Colt SCG in Super 38 had trouble feeding ammo with wider hollow points. For example, the factory SIG V-Crown, or handloads with the Speer Gold Dot bullets could not be relied upon to feed reliably in my SCG Super 38. My 9s and Supers by other manufacturers, with the integrally ramped barrels, are reliable pistols with all types of bullet shapes, weights, pressure levels, etc.

I'd read such good reports by Colt 9mm owners in recent years about the reliability of their 9mm Colts, I bought the new GC in hopes it would exhibit the reported reliability. No such luck. Maybe next time...

__________________
NRA Life, COTEP 640