RSA Blackhawk 9mm Cylinder Excessive Clearance

RSA Blackhawk 9mm cylinder, looks like previous owner did some machine work at front base pin area. In the gun shown, breech to cylinder measures about .006 with the cylinder pushed back. Surprisingly no marks on the cylinder to breech area. Remedy? Would a larger shim be practical?

Just a question of curiosity as this particular cylinder with such a large base pin end clearance escapes my limited experience. Don't plan to use it. It was with a box of parts purchased at auction.

That .006" B/C gap meets most factory specs EXACTLY !!
And so it goes...

That large gap between the cylinder and frame can be corrected with a shim,
Not a good idea to fire it the ay it is. If it ere mine and I wanted to use that cylinder,I would machine it and fit a bushing into the front of the cylinder Ike Colt uses and get proper cylinder/ frame fit. You can live with .006" B/C gap but you don't want the cylinder to rub the back of the barrel like it will as it is now.

WIL TERRY said:

That .006" B/C gap meets most factory specs EXACTLY !!
And so it goes...

Click to expand...

In the pic, look at the gap at the base pin from the cylinder to cylinder frame. The .006 is OK but would expect the chamber face to rattle against breech at rebound from recoil.

Chuck 100 yd said:

That large gap between the cylinder and frame can be corrected with a shim,
Not a good idea to fire it the ay it is. If it ere mine and I wanted to use that cylinder,I would machine it and fit a bushing into the front of the cylinder Ike Colt uses and get proper cylinder/ frame fit. You can live with .006" B/C gap but you don't want the cylinder to rub the back of the barrel like it will as it is now.

Click to expand...

This cylinder was purchased by an acquaintance at auction. He had fired it about 100 rounds. I fired it 6 rounds with no aberrations and upon empty case removal noted the base pin clearance issue. No witness marks were noted on cylinder face or gun. The friend did pull the cylinder from service and donate to my scrap inventory. I have seen the bushings and may attempt as an exercise in futility once I have my vintage lathe operational. I have other 9mm cylinders if I really need to shoot 9mm from a Blackhawk.

The cylinder bushing can also be swaged to lengthen it for proper fit. Brownells sells the swaging tool and Kuhnhausen describes the process in his book on Ruger single actions. I've done the process on a number of cylinders with short bushings.

Fit the bushing and the cylinder gap usually arrives just at factory specs.

I have the book. Interesting. The Brownell's Single Action Gas Ring Stretcher is $86. From the tool instructions looks like the gas ring can be "stretched" quite a bit (over .030). While not cost effective for a single 9mm cylinder, I do have other RSA that might benefit from a good stretch.

May do it just for the fun of saving the cylinder. It did shoot quite accurately for a 9mm Blackhawk for the very limited use before the end shake discrepancy was noted.

From the book, also could install a short gas ring bushing, but probably really overboard cost wise for a 9mm cylinder.

A hardened steel shim washer would work just fine and could be superglued to the cylinder for ease of installation and to prevent loss when removing the cylinder.
I would bore the cylinder part way and make a bushing but I like to do things the hard way.

Looks like the Brownell tool moves the gas ring bushing by pinching the gas ring at the cylinder face. Somewhat turned me off on making up that much of end play by wringing the bushing neck. McMaster has .250 ID, .375 OD 316 stainless or spring steel shim washers in various thicknesses. Also several vendors have the correct sized ID/OD but in smaller, thinner increments. Should be able to superglue something useable.

Later this summer should have my '40's vintage lathe running and will re-visit a short bushing install. Really don't shoot 9mm through an RSA all that often, and have another RSA with a correct 9mm cylinder if I do. This salvage cylinder project is just a "because I can" exercise...unless someone buys it for their project.

Do you still have the 9mm cylinder.
If you wanna sell how much?

looks more like an old model cylinder in a new model gun, too short a gas seal stud.......hhhmmm

or did they take a new model cylinder and cut it down that far to "fit" in an old model???? if only it could talk....... 8) :roll:


we used to put in a brass .250 dowel, weld it up around the dowel and recut it....shims and stuff get loose , fall out, etc........ :wink:

rugerguy said:

looks more like an old model cylinder in a new model gun, too short a gas seal stud.......hhhmmm

or did they take a new model cylinder and cut it down that far to "fit" in an old model???? if only it could talk....... 8) :roll:


we used to put in a brass .250 dowel, weld it up around the dowel and recut it....shims and stuff get loose , fall out, etc........ :wink:

Click to expand...

re: "or did they take a new model cylinder and cut it down that far to "fit" in an old model???? if only it could talk....... 8) :roll:" ......

I guess anything is possible...but even if someone did do enough cutting to get a NM 357 cylinder to fit into the (smaller) OM-357 frame opening it still wouldn't be usable because the centerline of the NM chambers are too far from the base-pin hole for them to align with the centerline of the OM barrel.

DGW

The Ruger NM mid-size frame cylinders are the same as the OM 9 MM cyls and can be fitted.

If it were my cyl, I'd face of the gas seal hub and ream the pin hole for a Colt removable cyl pin bushing. Less work and that way the cyl can be used in any gun just by having a removable bushing fitting each gun. Bushings are cheap.
The cyl/bar gap will almost always be within Ruger specs.

Work around quickie fix...

Bought a .250 ID, .375 OD .030 thick stainless shim from McMaster. On a fine flat file, lightly oiled, and using a calibrated thumb to push in a figure 8 pattern, thinned the shim to .029. Using feeler gauges, now have a tight .001 at the front, something between .005 and .006 at the business end of the cylinder. For as little as I shoot 9mm RSA and for plinking, will let this go until more pressing tasks are finished.

While not a field installation technique, the shim can be installed at the bench in a handful of seconds if a scribe or toothpick is available.

When I first saw this,, my thoughts were along the lines of what rugerguy mentioned. It is very possible it may be an OM cylinder. If so,,,, it's more valuable unaltered. And if it works with the shim,, have fun!

Oops forgot that part...

When rugerguy assessed possibly might be an OM cylinder, dragged my OM from the safe. From this comparison do not think the shimmed cylinder is OM.

The top BH is an older NM .357 for which the cyl in question is shimmed. The lower is an OM .357 (purchased new in 1969) which does have both .357 and 9mm cylinders.

Yes both guns are not clean...was plinking today. At some point would like to try one of the remedies from above just to further skills.

contender said:

When I first saw this,, my thoughts were along the lines of what rugerguy mentioned. It is very possible it may be an OM cylinder. If so,,,, it's more valuable unaltered. And if it works with the shim,, have fun!

Click to expand...

Please note that regardless of how the excessive end-shake is addressed, an OM-357 cylinder will still not work in a "big framed" NM gun. Reason is...the chambers will not align with the barrel close enough to allow the gun to be safely fired.
In other words, the distance from the base pin hole to the chamber is different on the two (differently-sized) guns, as-is the distance from the pin hole to the centerline of the barrel. PLUS the chambers are closer together in the OM cylinder.

None of that has anything to do with how long the cylinder is, or end shake, or B-C gap. On the other hand though, it has everything to do with aligning the cartridge to the barrel.

DGW

With respects to DGW in the previous post.

Was unaware of the differences between the OM and NM cylinders, so as an exercise in cylinder edification...

First pic, simple attempt to swap cylinders, top gun is OM 357, lower, NM 357. The OM cyl will physically fit into the NM and will mechanically function, though excessive looseness. NM cyl will not fit into OM.

Second pic, quick measurement base pin bore to a convenient chamber on the OM cyl.

Moving the measurement to the NM, quite a bit of difference. Good reason to be careful when mixing and matching parts!

well going back to your first picture at the start, those gaps are wrong , the center pin gas ring ( stud) has the gap, NOT the barrel to cylinder clearance, looks like its is touching...., the cylinder rides on the face of the cylinder at the center, NOT rub against the barrel...…...that picture is just "wrong" and why I made my comment as the center stud ( gas seal) is TOO short for that guns frame....yes , I know and have seen folks do that and it just may work, BUT , its wrong...…..put two cylinders side by side , old model , new model and one can easily "see" the difference in the gas seal ( stud)…………..

don't know what you are trying to measure in the last pictures???

Kind of went off on a tangent. In the very first post of the thread, I had a 9mm NM cylinder that for some reason had been messed with at the gas ring clearance. After taking note of the more correct remedies, I chose short term to insert a .029 shim to gain .001 cylinder shake with .005 to .006 at the barrel.

There was some discussion about OM and NM cylinders.

DGW pointed out that OM cylinders have a different chamber circle than NM and that if one could get the end shake, barrel to chamber clearances correct with an OM cyl in a NM, the chambers would still be misaligned with the barrel.

Now the tangent:

Since I have both an OM and NM .357, thought I would see for myself. The last series of three pics were to compare an OM and NM cylinder swap. The attempt to measure was to discover for myself that OM and NM cylinders have different chamber spacing circles, radii. OM chambers appear to be on a tighter circle, shorter radius.

Not pictured but also noted that an OM cyl has an overall diameter that is significantly less than a NM cylinder. And finally, if both cylinders are removed from the respective guns and slipped on to a common base pin, the difference in chamber spacing is readily apparent as is overall diameter.

So the warning, that even though one might be able to fit an OM-357 (or 9mm) cyl into a NM gun, the chambers would never be on centerline with the barrel at the firing position.

Apology to DGW from me for snipping his quote.

Just a NM guy venturing into the OM world...

DGW1949 said:

Please note that regardless of how the excessive end-shake is addressed, an OM-357 cylinder will still not work in a "big framed" NM gun. Reason is...the chambers will not align with the barrel close enough to allow the gun to be safely fired.
In other words, the distance from the base pin hole to the chamber is different on the two (differently-sized) guns, as-is the distance from the pin hole to the centerline of the barrel. PLUS the chambers are closer together in the OM cylinder.

None of that has anything to do with how long the cylinder is, or end shake, or B-C gap. On the other hand though, it has everything to do with aligning the cartridge to the barrel.

DGW

Click to expand...