Korth Revolver 2nd Cylinder Customization Question -

Virtually any Korth can take a second 9mm cylinder (4th picture) for their .357 as long as the imported extra cylinder has been professionally fitted to the frame. I have a somewhat new 3” Korth (1st and 2nd picture) imported by Nighthawk and was told today by Nighthawk that the work for the second cylinder in 9mm would be 5 to 6 weeks; and, that the 9mm would be equally accurate to the impressive .357/38 cylinder.

While the slick cylinder switch is literally a one button drop-and-mount change, and the rimless 9mm doesn’t need moon clips due to some ingenious German engineering, I always believed the downside would be that the 9mm would have to be less accurate (but still outshoot most shooters) and never ordered the work. My belief was based on:

1. Being smaller, the 9mm bullet does not make the same rifling contact of the .357 or .38.

2. The 9mm has to jump quite a bit of empty chamber on its way to the forcing cone. Consequently w/the 9mm, 25 yard groups I thought would open up.

Who’s right, me or the Nighthawk customization shop? THANKS!

dwever said:

Virtually any Korth can take a second 9mm cylinder (4th picture) as long as the imported extra cylinder has been professionally fitted to the frame. I have a new 3” Korth (1st and 2nd picture) imported by Nighthawk and was told today by Nighthawk that the work for the second cylinder in 9mm would be 5 to 6 weeks; and, that the 9mm would be equally accurate to the impressive .357/38 cylinder.

While the cylinder switch is literally a one button drop-and-mount change, and the rimless 9mm doesn’t need moon clips due to some ingenious German engineering, I always believed the downside would be that the 9mm would have to be less accurate (but still outshoot most shooters). My belief was based on:

1. Being smaller, the 9mm bullet does not make the same rifling contact of the .357 or .38.

2. The 9mm has to jump quite a bit of empty chamber on its way to the forcing cone. Consequently w/the 9mm, 25 yard groups I thought would open up.

Who’s right, me or the Nighthawk customization shop? THANKS!

Click to expand...

I'm unfamiliar with the gun or Nighthawk.

However, why not use the same diameter bullet in the 9mm you are using in the .38/.357 (as long as they are within SAAMI spec range)? This is all assuming you are handloading ammo. If you're restricted to factory ammo, that's okay, too. See below-

If you're using jacketed bullets, they are most forgiving of diameter being slightly undersize or oversize. You'll likely see no accuracy difference.

Bullet "jump" usually is of no signifcance in handguns as for as accuracy.

If you're using cast bullets (which will likely shoot better than jacketed bullets, but only if they properly fit and are of the right alloy) they almost always need to be slightly larger than bore diameter for best accuracy. Even a little undersized and they will shoot poorly and probably lead the bore.

Thanks, I use Federal Premium .357 Magnum 140 or 158 Grain Barnes Expander JHP or 154 HST JHP at around 1,350 FPS for EDC; and for practice Federal .357 Magnum 158 Grain JSP at 1,240 FPS.

For 9mm I was planning Federal Premium Personal Defense Ammunition 9mm Luger 124 Grain HST Jacketed Hollow Point (1,150 FPS).

The 9mm is almost half the price and a little less than 3/5 the power of the .357.

dwever said:

Thanks, I use Federal Premium .357 Magnum 140 or 158 Grain Barnes Expander JHP or 154 HST JHP at around 1,350 FPS for EDC; and for practice Federal .357 Magnum 158 Grain JSP at 1,240 FPS.

For 9mm I was planning Federal Premium Personal Defense Ammunition 9mm Luger 124 Grain HST Jacketed Hollow Point (1,150 FPS).

The 9mm is almost half the price and a little less than 3/5 the power of the .357.

Click to expand...

Sounds like you already have a good factory load with known accuracy in .357. As for the 9mm... what you like may work fine, but if you haven't tested that specific factory load for accuracy, I'd also try at least two or three other loads benchrested at 25 yards. All loads may shoot very well, but there is a good chance one or two may really stand out from the others.

I haven't fire many 9mm through the extra cylinder in my Mongoose. Most were shot under 10 yards with acceptable results, just trying to get used to the gun.

The original concept of the switch cylinder Korth revolver, back in the Willi Korth days, was to take advantage of cheap 9mm ammunition available to the German gun owners who were the primary intended market at the time.
A lot of serious Korth owners were active UIT target shooters. Often you had to be to acquire a pistol permit anywhere in Europe.
Guess what? Those guys ALL shot 38 wadcutters, or got the 32 Match version and shot wadcutters in that. I've never heard of a serious target shooter use the 9mm cylinder, except maybe for fun. In a match? Never!

A good friend if mine, dual German-American citizen, used to import about a dozen pistols a year. This included many old Korths. Quite often, if the revolver included the two cylinders, the 9mm cylinder was in practically unused condition.

We talked at length about many of the characteristics and qualities of the Korth. The 9mm switch cylinder is mostly just a novelty.

But, there's a lot of "9mm Kool-Aid" drinkers out there....
They'll argue the point, having never handled, let alone shot one.

6string said:

The 9mm switch cylinder is mostly just a novelty.

Click to expand...

So what are the the downsides of using the 9mm cylinder? In spite of all my 9mm ammo, I never considered an S&W 9mm revolver because moon clips were a necessity.

dwever said:

So what are the the downsides of using the 9mm cylinder? In spite of all my 9mm ammo, I never considered an S&W 9mm revolver because moon clips were a necessity.

Click to expand...

There aren't any, except having two cylinders to clean.

As mentioned above, try several different 9 mm loads. You may find one that matches the accuracy of your favorite .357 ammo at a fraction of its cost, theoretical bullet diameter notwithstanding.

And if you can afford two Korths and want an S & W 9 mm revolver that does not require clips, search up "model 547". A pinned barrel 3 and 4" is a good goal.

The Ratzeburg Korth 9mm conversion cylinders have very poor ejection and are little fun to shoot because of that but another reason that the 9mm cylinders are basically unused when preowned guns are imported from Germany is, that the largest German shooting association, the DSB, does not allow 9mm in the practical revolver matches.

Expecting a .356 projectile to perform equally well in a .357 barrel as a .357 projectile would defeat physics and my personal experience.

FWIW, when Willi Korth had toyed with the idea of a .22 WMR/.22 l.r. combo gun, he had been ignorant of the larger bullet diameter of the .22 WMR and the .22WMR/.22 l.r. combos are a good example of giving up accuracy for the convenience of being able to shoot two calibers through one gun.

Andyd said:

The Ratzeburg Korth 9mm conversion cylinders have very poor ejection and are little fun to shoot because of that

Click to expand...

So now that the Ratzeburg factory has been shut down and there have been significant design changes; even the extra cylinder got another updated design a few years back due to simultaneous frame redesign changes, do these ejection frustrations persist?. Recent reviews don’t mention problems where the additional cylinder is present with the .357 9mm combo, has the spare 9mm non-moonclip cylinder tech caught up to the .357 iteration?

While I don’t expect to get the sub-half-inch 5 shot groups Guns & Ammo got from a Korth in a December 2021 review from full-house .357 Magnum rounds, I would like a two inches with 9mm.

dwever said:

My belief was based on:

1. Being smaller, the 9mm bullet does not make the same rifling contact of the .357 or .38.

2. The 9mm has to jump quite a bit of empty chamber on its way to the forcing cone. Consequently w/the 9mm, 25 yard groups I thought would open up.

Click to expand...

I have been shooting 9MM ammunition out of .357 bores for several decades now.

Accuracy is mostly a function of proper bullet spin.

Bullet spin is caused by the rifling engaging the projectile

Most people forget that there is both a land and a groove diameter involved when they talk about bore diameter. What is actually measured when folks slug a barrel is the groove diameter.

The difference between the land and the groove is the depth of the rifling, the part that actually engages the projectile thus causing spin.

This difference is somewhere around .008" - .013" depending on the type of rifling and who did it

Jacketed, plated and coated 9MM projectiles measure anywhere from .355" - "3565" depending on the manufacturer. There is still plenty of projectile for the lands to grab onto and get spin even in a .357" barrel.

I have been shooting jacketed 9MM projectiles through many different .357" barrels for several decades now and accuracy is just fine.

BTW, most 38 Super shooters (.3565" bore) have been loading 9MM (.355) projectiles for more than half a century now, but this discussion never comes up. Heck, most of them do not even realize they are doing it

The accuracy exception/complaints from shooting 9MM ammunition in a .357 bore comes when we are discussing lead projectiles. Cast lead projectiles should be matched to the diameter of the barrel they are being shot in. The accuracy complaint comes from barrel leading


As to bullet jump, 357 Magnum revolvers can be shot with several shorter cartridges as well. Americans routinely shoot 38 Special in those revolvers with no perceptible change in accuracy due to bullet jump. I know you are thinking the 9MM has a greater distance to overcome

357 Magnum revolvers are shot with 38 Long Colt and 38 Short Colt as well. Action shooters often use the 38 Short Colt in moon clips for competition. The 38 Short Colt is only about 1/2 MM longer than a 9MM cartridge case

So NightHawk is correct

BTW, the moon clipped, 38 Short Colt cartridge makes for a very speedy reload

Theoretically can the shorter cartridge be less accurate than the longer one? Yes, however it would take a ransom rest and a distance greater then 25 yards for this to be an issue worth worrying about

colt_saa said:

...
Most people forget that there is both a land and a groove diameter involved when they talk about bore diameter. What is actually measured when folks slug a barrel is the groove diameter.

Click to expand...

Korth is not using a conventional barrel design anymore but polygonal rifling. With lead bullets that is opening Pandorra's box. I have some recommendations that H&K gave to German reloaders for the P9S in .45 ACP and it was interesting to see a firearms manufacturer giving out reloading data, especially since the keyboard jockeys on Glocktalk always had said that lead in polygonal rifling was a no-no.

On top of that, the OP clearly stated that he wanted to use factory ammo. The lead in the Korth cylinders would need to be individually checked on all chambers.

After Andyd’s post #12, I did a Google search on “Korth Polygonal” and got the answer from none other than Massad Ayoob in On Target Magazine attributing the outstanding 9mm/.357 swappable accuracy to the, yup, polygonal rifling. With the 9mm hand-held bench, Massad got a three-shot 9mm group of 0.65 inches. See below. Wow. [of course the article is for a Korth Super Sport, but the polygonal rifling and cylinder swap engineering is identical to the Korth Mongoose].

From Page 1, “It’s expensive as hell . . . but OMG does it shoot!”

From Page 3: “Bench Rest Testing: I didn’t expect a 9mm cylinder to do as well as the .38/.357 through a bore that allowed for the latter’s very slightly larger diameter. I turned out to be wrong.

With the .38/.357 cylinder, the first load up was Federal’s famously accurate Gold Medal Match 148-gr .38 Special target wadcutter. All five shots went into 1.05”, with the best three at 1/2-inch apart center to center. Winchester’s inexpensive “white box” generic .38 Special comprises the old USAF 130-gr. full metal jacket bullet at modest velocity, and is a hugely popular practice load. From the Nighthawk Korth Super Sport it put all five shots in 1.70”. The best three measured one-inch even, and hand-held from the bench rest, that’s a good predictor of what all five rounds would have done from a machine rest. For a .357 Magnum I chose that highly regarded man-stopper of yesteryear, the 125-gr. semi-jacketed hollow point. The scallop-jacketed Remington UMC bullets slammed in a group measuring 1.50” for all five hits, and 1.15” for the best three.

Picture caption Page 3: “With the 9mm cylinder affixed, Federal 115-gr. JHP “Classic” printed this incredible 0.65-inch five-shot group at 25-yards.”

Main text Page 3: Next up was the 9mm cylinder. Three loads of known high accuracy were used, in three different brands and the three most popular bullet weights for the caliber. One shot strayed with Rem. UMC 147-gr. jacketed truncated cone, bringing the group to 1.95”; it would have been a 1.15” group if I’d kept it with the other four shots. The best three shots, however, were just half an inch: 0.55” center to center. For a 124-gr., I used SIG’s V-crown jacketed hollow point, resulting in a 5-shot group of 1.25 inches. Once again a single shot had ruined an outstanding group—the other four were in 0.75” and the best three, in 0.50”, which would have been linked by a single .45 caliber bullet hole. Finally, Federal’s great old 115-gr. JHP from their Classic series, product code 9BP, delivered the triumph of the day. All five shots were in a very uniform 0.65 inch.

Any gun that can let an old man with bad eyes shoot a group like that might just be worth all those thousands of dollars, after all.

Why was the Super Sport so accurate with both .38s and .357 Mags, with nominal bullet diameters of .357”, and slightly smaller 9mm bullets only .355” in diameter? Korth sizes the bore for the 9mm and, with polygonal rifling, expects the larger bullets to tighten into the rifling. The folks at Nighthawk tell me it does not increase pressure inside the gun to use the larger diameter .38/.357 bullets. Our testing showed that, conventional wisdom and expectation to the contrary, both the revolver cartridges and the auto pistol cartridges gave us excellent accuracy out of the same barrel.

Screen ShotPicture Caption Page 1: Without moonclips, “Extraction was equally positive with both .38/.357 revolver rounds and rimless 9mm.”

This thread has been very interesting ,learning about Korth revolvers.

You can get the same accuracy results by putting a .355 rifled barrel on a .357 Smith and making an extra 9mm cylinder for it. The .357 bullets go right through the .355 barrel just fine.

Protocall_Design said:

You can get the same accuracy results by putting a .355 rifled barrel on a .357 Smith and making an extra 9mm cylinder for it. The .357 bullets go right through the .355 barrel just fine.

Click to expand...

If that is true, Korth doesn't offer that, and as I understand it, they have already solved the issue with polygonal rifling.

Anyway, I had an e-mail saying they finally tracked down a 9mm cylinder they can hand-fit to my .357, and I'll have the weapon back in 5 to 6 weeks. Thanks! Peace. (picture of Korth Mongoose with 9mm extra cylinder is not mine).