Can a .357mag BH convertible owner help me out with some #s?

I am trying to figure something out- headspace measurements on 9mm cylinder when installed in Blackhawk.

If any of you have feeler gauges, a .357mag Blackhawk convertible model and some time, could you makes some measurements for me?

Specifically, can you use the empty 9mm cylinder, installed in frame, pulled to rear of frame [hammer end?] and measure the gap between the cylinder and the recoil shield under the hammer? No ammo/snap caps installed at time of measurement, please.

I would appreciate measurements in SAE, instead of metric.

I know that Ruger has said a Super BlackHawk was supposed to have a measurement of between .060" and .066" in this area.

I know that the 9mm cylinder headspaces on the case mouth, and not the actual cylinder.

I am just trying to get this measurement from, hopefully, 3 different 9mm cylinders [that were factory fit] to see what to do with my 9mm cylinder.

I am trying to set up my bh as a convertible, but am not sure what is going on with headspacing.

Thank you in advance.

I took measurements from a flat top mid frame but in this area it shouldn't make a difference.

.062" w/ cyl. pulled back
.067" letting cyl. move forward to overcome a .005" end shake, which will happen when the hammer hits anyway.

Now, not what you asked but I'm gonna throw it in anyway. The depth from the rear of the cyl. to the step in the chamber for the case mouth on mine is .690" Add the .690 & .065 avg. for a .755" head space, (about perfect?) Wiki calls for a .754" case length.

Does the space between the rear of the cyl. & the blast shield even matter for a rimless cartridge ? Maybe I'm misunderstanding you.

Hope this was what you're after.

On both my 9mm and .357 cylinders the gap is a bit over .063 at the bottom of the cylinder and a bit under .063 at the top. Had to put 3 leaves of the gauge together. The .063 moves the cylinder about .001 or .002 when inserted at the top and seems about that loose at the bottom. A factory convertible but with a replacement convertible cylinder.

thanks Gunzo and woodperson,

That is exactly what I am looking for.

I bought a 9mm cylinder to make my .357mag into a convertible.

However, my headspace measurement is .057"- or too close.

I honestly don't know if this cylinder/frame measurement is what Ruger uses- but it is all I could do at the time.

It could be that my cylinder is bored a bit deeper to allow for less space between the cylinder and rear of frame, but I don't have any info that would support that.

I'm just wondering how to make my 9mm cylinder work safely for my frame- or if it is better to just bite the bullet [so to speak] and get a convertible- then sell mine.

ahh- decisions.

First, I need to make some chamber measurements and see where I am at.

Thanks all- your measurements lead me to believe Ruger bored these 9mm cylinders to have the same headspace as the .357 cylinder- between .060 and .066"

If loading for that gun only, trim your brass to fit. Otherwise the chambers are too shallow when installed in that revolver.

Chuck 100 yd said:

If loading for that gun only, trim your brass to fit. Otherwise the chambers are too shallow when installed in that revolver.

Click to expand...

Hmm,

This leads me to another option- as I don't reload [yet].

Let's assume I get the gun fine-tuned and the .357mag cylinder is fit correctly for timing, cylinder gap, endshake and headspace.

Let's THEN Assume I can get the 9mm cylinder fit to this gun for timing, cylinder gap and endshake, but the headspace is off by .004".

You are saying to trim my brass .004 to fit [and download accordingly, obviously].

WHAT about having someone re-chamber the cylinder to increase the depth before the case mouth is stopped, to make the total headspace appropriate?

This would mean the cylinder could NEVER, EVER be used safely with another gun [I am ok with that], but I would then be able to throw $10 boxes of 9mm into the cylinder safely.

Other than the machining cost [which I admit I have no idea of- but estimate around $100-120 to just bore each chamber another .004"], is there any OTHER disadvantage to doing this?

THERE IS ONE CURRENT CRITERIA : Have you put the cylinder into the pistol and fired it with 9MM PARABELLUM ammunition ?? DO not make mountains out of molehills until you stub your toe on the first one. CARRY on from there.
AND so it goes...

I agree with Wil, have you even put some cases (unloaded but with primers in them OR loaded, I do, and "try"??? does the cylnder rotate?? NOT "hang up"? then you gotta try firing ,see what actually happens...yep, do not try and overthink this, it is NOT rocket science.......if the cylinder "fits" , locks up on ALL six chambers, rotates, spins, whatever.NO drag on the rear of the barrel, then it should be OK.........
as for "reloading" you must make sure you do NOT overly rollcrimp as the cases headspace on the mouth of the case, too much roll crimp, and the shell can move forward and cause misfires.......

Ok, I can make a mountain out of it.

I got home, swapped the cylinder, threw some snap caps into the chambers, and attempted to cycle the cylinder.

It stuck on the frame.


So, I am in a definite 'no go' position.

I am leaning toward sending the gun back to Ruger to fix the .357Mag cylinder endshake [.006, which is .003 more than Ruger seems to deem acceptable- even if they can handle a cylinder gap of .010].

I will hold off on any plans until I get the gun back from them, or they call me to tell me something bad- like time for something new.

IF I get it back without the barrel being set back [just the cylinder fitted], do you think my idea of having the 9mm cylinder re-chambered to allow for the proper clearance would work safely? I am thinking it would drop the headspace line in the chamber by about .005-010", which doesn't seem like it would be that big of a deal.

Any thoughts?

thanks all.

WHY THE SNAP-CAPS !!! Are they the problem ? Try it without 'em and see how it works. THEY are NOT made to the highest specs you know. Matter of fact most snap caps are an answer to an un-needed question.
And so it goes...

WIL TERRY said:

WHY THE SNAP-CAPS !!! Are they the problem ? Try it without 'em and see how it works. THEY are NOT made to the highest specs you know. Matter of fact most snap caps are an answer to an un-needed question.
And so it goes...

Click to expand...

I'll get live ammo next to try it, but very carefully.

I use the A-Zoom snap caps- they seem to be better than average quality. But, still not live ammo.

Was loading some 9 mm tonight for my convertible so I was thinking about this. Have you tried the cylinder with ammo yet?

The 9mm cylinders have the same external dimensions as the .357mag cylinders, or any other current production cylinder of the same frame size. They are not recessed for the 9mms, it's just cut shallow, leaving the cases to protrude as far as a rimmed cartridge would.

Since it's a 9mm cylinder, just have a smith finish chamber the cylinder the 4 thou deeper for you and be done with it. Better to have them measure the appropriate dimensions for headspace and chamber depth, but the answer in this case is to just run the finish chamber reamer the little extra, then your revolver will be happy and singing.