Rechambering to 9mm Largo

I have a question about this topic and am not sure if this is the right forum for it or not, since this is a gunsmithing question but the gun is not a S&W. Anyway, here goes:
the gun that I am considering doing this to is a Star Super B that is currently chambered in 9mm Luger. I have two of these pistols; one is in really nice shape, the other is sort of a "beater" that is shoot-able, but nothing much to look at. It seems to me that since these pistols were originally chambered for the longer Largo round (both the magazine and the ejection port are bigger than for 9mm para.) that the pistol would feed more reliably with the Largo. Sooo.. I thought I might like to rechamber the beater in 9mm Largo - just because I would like to reload for it and experiment with that cartridge a little.
Am I correct in thinking that lengthening the chamber by 3mm (with the right chambering reamer) is sufficient or is it necessary to rework the breech face of the slide as well? And yes, I know to use only real 9mm Largo brass and NOT 9mm Win Mag brass. Seems like a fun project (and no, I am not thinking of overloading the 9mm Largo rounds). Any input on this idea?
I suppose someone might say; " why don't you just buy another Star in 9mm Largo", and the answer is that I already have two Star pistols and don't want to buy another one. Also, the Stars that are chambered in the 9mm Largo have barrels that are not compatible with this model- so can't be interchanged, or at least not without a lot of (expensive) work done to the barrel.

9mm Largo (9x23mm, 9mm Bergman Bayard) should have the same head diameter as 9x19mm, so that should be no problem. For quite awhile, many have rechambered 9x19 barrels for .38 Super and 9x23 Winchester, and even though .38 Super rims are slightly larger in diameter than 9x19, that doesn't seem to be much of a problem regarding the fit on breech face. The main problem would be the magazine. 9x19 magazines, such as the Colt GM, usually have a spacer at the rear to keep 9x19 cartridges forward. I have no idea about the magazines for the Star Model B, or for that matter, anything about the Star Model B. So I can't say that what you propose is feasible for it. Closest I ever had was an old pre-WWII Llama "Extra" military auto similar to the Colt, and I shot 9x19, .38 Super, 9mm Largo and 9mm Steyr in it with no problems. People say you shouldn't fire 9X19 in a longer chamber, but I never had a problem with it in that Llama - I fired thousands of rounds of 9mm military ammo that way. The latter two cartridges were very cheap 40 years ago when I did it, and I fired just as many of those also. But for the most part, I used .38 Super. I currently have a M1911 (a real one from 1918) with a Colt 9mm slide, a 9x19 barrel, and also a 9x23 Win barrel. I use .38 Super magazines for all sizes, even 9x19, works fine. I have also fired .38 Super, 9mm Largo and 9mm Steyr in the 9x23 Win barrel, no problem, except 9mm Largo has a slightly greater COAL than the 9mm Steyr, and doesn't fit well in the Colt magazine. Regarding brass, Starline did sell both 9x23 Winchester rimless brass and conventional 9x23 brass for Steyr and Largo. Also they have something called the 9mm Super Comp. All are samey-samey dimensionally. Any should work OK for you. You might even be able to use .38 Super brass also. Dimensionally, all are close enough to use in the same chamber. To lengthen a 9x19 chamber to 9x23/.38 Super, I have read that some simply use a 3/8" end mill. Never did that myself, but it probably could work.

i would trade the beater in for an original in largo in much better shape. Not as much fun but I've always seen the largos sell at a pretty steap dicount compared to the 9mm para. You want the star that no one wants but the largo is a neat round if you reload. I don't know enough to weigh in on the conversion but I will say that the super b is a great little pistol for the money. What ever you end up doing good luck

The Super 'B' was originally made in 9mmLuger ,,as was the Model 'B'

The Super 'A' (and Model A) were the same pistol(s) but chambered in 9mm Largo.

The 'A"models were commonly converted to 9mmLuger by 'bushing' the chamber. Press fitting a short bushing into the front of the chamber of the 9mmLargo chamber and effectively shortening the chamber oal to 9mmLuger length.

The 'A ' series magazines are a bit different than the 'B' models in the feed lip length. (The A&B magazines will not interchange with the A&B SUPER magazines. There are also early & late style A & B model magazines.)
The 'A' 9mmLargo feed lips being slightly shorter than the 'B' models sometimes give faulty feeding (smokestack live round) when used w/9mmLuger ammo in the conversions.
But not always and the conversions generally went well.Nothing needed be done to the breech face.
No filler block in the mag or crimp to take up room for the shorter 9mmLuger case.

Sometimes you have to peen the area of the 'step' on the follower slightly so it'll catch and operate the hold-open. But that's something very common on any extra magazine fit-up on these STARs.

If you are going the other way,,Model B 9mmLuger converted to 9MMlargo,,,,,you will need to rechamber the bbl to 9mmLargo. A 9x23Winchester reamer will do to task.
It is a rimless tapered case, so a straight feed on a lathe with an end mill would do a shade-tree job of a chamber. The .375d end mill would knock out the very end of the Largo chamber from the existing Luger chamber. Problem being the Largo chamber is supposed to be tapered and ending at .379/.380d. So it'd be tight for sure.
Do it right or leave it alone.

It's possible to do a st taper chamber with a tiny boring bar on a lathe if you really know your stuff. The commercial reamer is the way to go IMO.

The magazine may need the feed lips adj slightly but other than that nothing need be done.
The recoil spring is the same on both the A Super and the B Super.

If you really want a 9mmLargo STAR (Model A, or Model A Super),,I'd sell the 9mmLuger B Super or trade it for a Largo caliber pistol.
The 9mmLargo Stars are the lesser valued of the two.
AIM surplus just sold some very nice Model B Super pistols for around $250. They have (had) some lesser condition B Super for $200.

Anyway you look at it,putting money into one isn't a very good investment. Unless you have the tools and can do the work yourself it's not really worth it.,,but I admit that hasn't stopped me from some projects in the past.


JMHO.

"It's possible to do a st taper chamber with a tiny boring bar on a lathe if you really know your stuff. The commercial reamer is the way to go IMO."

Although I have two lathes and the required tools, I still would not attempt the boring bar trick; I am simply not that good. I agree that the commercial reamer is the way to go. Thanks for the heads up on using the 9 X 23 reamer- that makes sense. You include a lot of good information to chew on, and I will give all of it more cogitation. The magazines that I have for these guns look like they would do for the Largo rounds since they are dimensionally longer than needed for 9mm Luger. One reason that I do not want to sell the beater is that it serves as "parts gun" for the other Star in case a part fails, and the usual parts sellers have very few parts in stock for these pistols. Besides that, the rechambering idea seems like fun to me. Yes, I do want the Star that no one else wants - it can be fun to work up loads for an oddball cartridge.

2152HQ:

"If you really want a 9mmLargo STAR (Model A, or Model A Super),,I'd sell the 9mmLuger B Super or trade it for a Largo caliber pistol."

Well yes, that would be the easy road to take, but the older Stars like the Model A were built during an era when weaker steels were the norm. I prefer to rechamber one of the Super B's because they were both made in 1972 and of more modern steel, thus they should (I hope) be up to snuff for reloads that might be a little stiffer than the old factory loads. I know, I know; " don't try to make a .38 super out of the 9mm Largo", and I will not try to hot rod the Largo. But that said, I still feel like the more recent made pistol is a better choice for reloading.

I also wanted to say "thank you" to you guys for responding to my questions about this idea. I appreciate the information you have given me.

Find someone that will cut the chamber to the proper dimensions -


Shouldn't take much from where you're at now -


The cartridge base is the same diameter so the breech face should be okay. Also, the 9mm Largo runs about 30k psi, that's less than regular 9mm so pressure shouldn't be an issue either.

If you can locate a 'smith with a .38 ACP/Super reamer, that should do the job. Also, it seems to me that Bar-Sto was at one time offering stainless barrels for the Star in both 9 Para. and 9 B-B. Might be worth giving them a call.

Larry

Huh. Apparently it took me a long time to type my post last night and there was a lot going on here while I was doing it. There was only the OP's original post when I started!

As I earlier said, a .38 Super chamber will handle 9x23 Winchester or 9mm Largo or Steyr just fine. If you want to use a chamber reamer, either .38 Super or 9x23 Win reamers will be OK. I load 9x23 Win in .38 Super dies, although 9x23 Win reloading dies are available. I have both die sets, but I use only the .38 Super dies.

DWalt, I think I will go with a 9mm X 23mm Winchester Mag reamer instead of the 38 Super because chamber dimensions that I have been checking on at several websites show the Super to be slightly smaller than the Largo in a couple of areas. Seems the 9mm Win Mag is closest, although I am also seeing discrepancies here and there as to what the original chamber dimensions of the Largo actually were. One source lists an OAL of .905", another lists .910" for the OAL and yet another says it is to be no longer than 0.900" (this last one was from the "Load Data" website). Three different websites list three different dimensions for the case mouth: .375", .377" and another lists .379" for the case mouth. I can't find an "official" cartridge specification drawing from a manufacturer's standardization organization (like SAAMI) anywhere.

The rechambering is straightforward....

I'd be concerned about the mag, feeding and ejection.

Woodsman22 said:

DWalt, I think I will go with a 9mm X 23mm Winchester Mag reamer instead of the 38 Super because chamber dimensions that I have been checking on at several websites show the Super to be slightly smaller than the Largo in a couple of areas. Seems the 9mm Win Mag is closest, although I am also seeing discrepancies here and there as to what the original chamber dimensions of the Largo actually were. One source lists an OAL of .905", another lists .910" for the OAL and yet another says it is to be no longer than 0.900" (this last one was from the "Load Data" website). Three different websites list three different dimensions for the case mouth: .375", .377" and another lists .379" for the case mouth. I can't find an "official" cartridge specification drawing from a manufacturer's standardization organization (like SAAMI) anywhere.

Click to expand...

Keep in mind that actual SAAMI diametric dimensional specifications are usually +/- 0.004". Essentially, there is no practical difference between 0.375" and 0.379". Cartridge OAL is relatively meaningless so long as the cartridge fits into the magazine without jamming. Either 9x23 Win or .38 Super reamers will do the job equally well. Your choice. On SAAMI's website you will find complete toleranced and dimensioned chamber and cartridge drawings. There is no SAAMI spec for 9mm Largo, but they do have .38 Super and 9x23 Winchester. While not SAAMI dimensions, Donnelly's book on cartridge conversions gives the following nominal dimensions for the 9mm Bergman-Bayard cartridge:

Case length - 0.91"
Head diameter - 0.390" (above extractor groove)
Rim diameter - 0.392"
Neck diameter - 0.375"
OAL - 1.32"
Chamber dimensions are not provided.

For the 9x23 Win, SAAMI chamber length is given as 0.900" +0.022"
For .38 Super, SAAMI chamber length is given as 0.918" +0.015"
Essentially identical, as you can adjust the chambering depth to 0.91" with either if you choose.

Several years ago, I resized some fired 9x23 Win brass in both .38 Super and 9x23 Win FL sizing dies, and measured them. As near as I can remember, the critical measurements were extremely close for each die (within a couple of thousndths), nothing close to significant. That's why I use .38 Super dies for both.

rwsmith said:

I'd be concerned about the mag, feeding and ejection.

Click to expand...

OP:
It seems to me that since these pistols were originally chambered for the longer Largo round (both the magazine and the ejection port are bigger than for 9mm para.) that the pistol would feed more reliably with the Largo.

Click to expand...

Like rwsmith, I'm still trying to grasp why rechambering a misfeeding pistol to a LONGER cartridge would make it feed better.... What am I missing?

During the feeding cycle, the shorter ctg. has less of its body engaged w/the feed lips of the magazine when the bullet contacts the feed ramp. Thus, the ctg. is held less securely and is more likely to tip or cock before entering the chamber. The feeding cycle is designed around the longer ctg.
Hope this helps. JMHO

Larry

"For the 9x23 Win, SAAMI chamber length is given as 0.900" +0.022"
For .38 Super, SAAMI chamber length is given as 0.918" +0.015"
Essentially identical, as you can adjust the chambering depth to 0.91" with either if you choose."

Yes, I see - thanks DWalt.

0KFCO5:

"Like rwsmith, I'm still trying to grasp why rechambering a misfeeding pistol to a LONGER cartridge would make it feed better.... What am I missing?"

It doesn't happen often, but it does now and then. As to the explanation for that phenomenon - see Larry's comment above. His explanation is on the money.
My main reason for rechambering one of these pistols (I have two) is that I would like to experiment with reloading and shooting the cartridge that this pistol was originally chambered to shoot. It is an interesting cartridge (to me, anyway) and somewhere down the road I would like to find and buy a Destroyer carbine to shoot Largo as well.
While I am thinking of it, I noticed that RCBS will make a set of dies for reloading this round on special order. Since others have said that the Largo can be reloaded with 38 Super dies and I think, regular 9mm dies as well, why does RCBS bother to offer a set of dedicated dies for this cartridge - I have no intention of plopping down $145.00 for a set of these, I am just curious as to why they are even offered?

Woodsman22,

After all the superfluous information that has been provided let's get to the basics of your original question. First, you are correct that the magazines for both the Model B and Model Super B are sized for 9mm Largo/Bergman-Bayard, or several other names it has gone by! Maybe the photos of the magazines loaded with a 9mm and a largo will answer OKFC05's question about how using the longer cartridge will help feeding!

I have seriously contemplated re-chambering my Model B to Largo for exactly the same reasons. From the pictures of it I think you will see why I am hesitant. The gun is in better condition than the cell home pictures would indicate.

There has been quite a bit of speculation comparing the Largo and .38 ACP. While the Star Model 400 is specifically chambered to allow use of both the 9mm Largo and .38 ACP interchangeably, this is the only firearm which can do so! While .38 ACP that is to be fired in a Largo pistol may be re-loaded in Largo dies, 9mm Largo CANNOT be loaded in .38 ACP/Super dies. I am sure you already know this. One comparison that is correct is that 9mm Largo and 9x23 Winchester are externally identical and 9x23 dies can be used.

DIES: Just for the record I have been loading and shooting the Largo in a Star 600 for quite a few years. When I first began I bought a set of RCBS Largo dies. While they are marked for the Largo, internally they are nothing more than 9mm Parabellum dies! Needless to say I was unhappy and bought a set of Lyman 9x23 dies. Guess what, they are nothing more nor less than 9mm Parabellum dies with a spacer in the sizer to raise the carbide ring about 1/8"! So I bought a Lee Largo set. You guessed it, just 9mm Parabellum dies dimensionally. So, with my original 9mm Parabellum dies set I have a total of 4 die sets for 9mm Parabellum!!!!! Forget RCBS and their Largo dies, I would bet all you get are 9mm Parabellum dies marked for Largo, but pay nearly 3 times as much for them just for the marking! Better to just buy a 9x23 set and save money.

In all fairness, since my dies were purchased several years ago the situation described may no longer be accurate.

There is no real reason to not convert your Model Super B. There is nothing negative about the change and several positives. From a practical standpoint the two cartridges are ballistically identical, so there is no advantage from this perspective. The only real difference I see is that standard bullet weights for 9mm Parabellum are 115 and 124 gr, while the 9mm Largo is ca. 135 gr. "X-Treme Bullets" sells a 135 gr. RNFP if you are interested.


Here are the photos

" 9mm Largo CANNOT be loaded in .38 ACP/Super dies"

Gee - wonder why I have been able to load 9x23 Win in .38 Super dies for the last 15 years? And also the Starline 9mm SuperComp cases which are supposedly about the same as the Largo? Maybe you can explain that to me.