Convert 38 cylinder to 9mm

If you’ve got the funds, I’d say there’s nothing to it but to do it. Contact one of em.

In some instances, within Frame size, cylinders, can be interchanged with little problem.

You'll also have to decide about barrel bore. With a .357 barrel, 9mm are a tad under sized. Might not matter to you for plinking. Or if you hand load, there are .357 bullets in 9mm weights and form factor.

Might be better to buy a second cylinder, have it rechambered and fitted, now you have a dual cylinder convertible like a Taurus, etc.

Just a thought..

Stay safe.

Worthy of thought, the 9mm is a 35,000 lb pressure cartridge, the .38 spl. is a 20,000 lb (+/-) cartridge, even in +P.
Just because Ruger sells a 9mm revolver doesn't mean any revolver can be made into a 9mm.

Did they make the 640 in .38spl only? I thought that was the 642.

I had a 640 Centennial in .38 Spl. It was all stainless steel. The 642 is an Airweight alloy gun.

Stay safe.

alfsauve said:

You'll also have to decide about barrel bore. With a .357 barrel, 9mm are a tad under sized. Might not matter to you for plinking. Or if you hand load, there are .357 bullets in 9mm weights and form factor.

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Same thing with a 9mm barrel.

9mm and 38/357 barrels have the exact same specs = .355 +.004". https://saami.org/wp-content/upload...FP-and-R-Approved-2015-12-14-Posting-Copy.pdf

I've found no difference in barrel groove diameter between 9mm and 38/357 barrels.

fxvr5 said:

9mm and 38/357 barrels have the exact same specs = .355 +.004".

I've found no difference in barrel groove diameter between 9mm and 38/357 barrels.

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WOW. I had never noticed that. Always looked at the SAAMI spec on the bullets. For 9mm it's .3555 -.0030 and for .38spl/.357mag for jacketed it's .3580 -.0030.

I’d like to see the finished product If you get it done please!

I have a 640 and 642, both .38 Spcl. only. Also have a 940 and Ruger SP101 9mm, so haven't been tempted to convert my .38 J-Frames to 9mm. Just for the heck of it, I recently had a 686 cylinder converted to 9mm. I've not done much in the way of accuracy testing of 9mm yet, only shooting some targets out to 15 yards. Did get some preliminary 2" 7-shot groups at 15 yds. with the 9mm cylinder installed.

I have noticed that chronographed velocities of most 9mm ammo tested is down from what would be expected when shooting the same ammo in a dedicated 9mm pistol or revolver. Not surprising to me since there is considerable approx. .381" diameter freebore ahead of the 9mm case mouth in the .357 cylinder.
FWIW, Chronographed velocities of 9mm shot from the little 2" 940 do exceed any of the major manufacturer 38+P I've tested in the 2" 640 and 642. This explains the "snappy" recoil often mentioned when discussing these little 9mm revolvers. So anyone thinking of converting a little J-Frame to 9mm might want to consider this before proceeding...... ymmv

Most likely for less than the cost of the conversion you could buy a simple reloading kit and reload 38 Special cases with hot 110gr bullets. You could even reload 9mm bullets in the 38 cases. I have done that before.

ThomasT said:

Most likely for less than the cost of the conversion you could buy a simple reloading kit and reload 38 Special cases with hot 110gr bullets. You could even reload 9mm bullets in the 38 cases. I have done that before.

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I just picked up 50 of the Lehigh 105 gr segmenting copper bullets for just such an experiment.

Stay safe.

I loaded a hundred 110gr Winchester bullets in 38 cases for lower recoil. I have been loading 110gr bullets for many years and the difference in recoil is real. Especially in an airweight gun. It is much more pleasant to shoot. I also load a 9mm Lee 124gr lead tumble lube bullet with a light powder charge of 3.5grs of Bullseye and its about like shooting a 22 mag in the recoil dept. It would be a great load for a recoil sensitive elderly person and the blast isn't too bad either.

S&W Model 986

I’ve had TK Custom modify a couple 38 Special revolver cylinders for use with moon clips. Their service was top notch so I’d feel their service to rechamber 38 Special cylinders to 9x19 would be as good.

I have an SP101 and a couple S&W 986 L-frame revolvers all chambered in 9x19. They are great with moon clips but really do not have any advantage over straight 38 Special for the most part.

But I reload so I do not have to scour the internet for cheap 9mm ammunition.

Didn't Ruger make a Blackhawk that had both .357 and 9mm cylinders?

MI2600 said:

Didn't Ruger make a Blackhawk that had both .357 and 9mm cylinders?

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Yes, still do. I have been hoping to get one. I don’t even care what barrel length at this point.

MI2600 said:

Didn't Ruger make a Blackhawk that had both .357 and 9mm cylinders?

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Yes, I have one. If you like single actions it's good but slow to reload since you can't use speed loaders or moonclips. It is the least used revolver I own due to the single action. I have become a double action only fan.

alfsauve said:

Did they make the 640 in .38spl only? I thought that was the 642.

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Wheelgun Perfection: S&W Model 640 - GunsAmerica Digest

640 J magnum, That has to be a handful.

I must be less than clever. How do you convert a .38 cylinder to a 9 mm cylinder?

Bill M. said:

I must be less than clever. How do you convert a .38 cylinder to a 9 mm cylinder?

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Basically you run a 9mm chamber reamer into the 38/357 chambers in the cylinder. This will enlarge the mouth of the chamber slightly. After that you machine the face of the cylinder face to create the clearance for the moonclip. With this conversion they leave a raised rim around the OD of the cylinder so that 38/357 still has a correct surface to head space against in the absense of a moonclip. The 9mm require the moonclips to head space against.



The black is a nominal 357 Mag Chamber. The blue represents a nominal 9x19mm chamber.



This is what the face of the cylinder would look like. Notice the rim around the OD for the 38/357 to head space against and recess to accommodate the moonclip for any of the three cartrdiges 9mm/38/357/

Pinnacle charges $225 to rechamber. I don't see where they offer or specify what clips to use, but that matters, I have seen clips from $1 to $7.

TK is considerably more expensive.

I thank you sir for your clear and complete explanation. I did Google and found a company that does it. But they did not explain it well like you did. Not for reloads, the conversion shop says. I guess if you start with a .357 cylinder pressure is not an issue.