Barrel Cylinder gap problem?

[saxguy]

I have just checked the cylinder/barrel gap on a recently acquired 586. I find that one one side it is approx 6thou, which is within the norm according to Jerry Kuhnhausens book. Unfortunately, the other side is around double that gap at about 12thou. I have checked the yolk and it is dead centre, so it seems that the barrel has not been cut square. If I hold the gun so its pointing downwards (into the bench) and place a steel edge rule balanced across the rear of the barrel (through the frame), I can actually see a slight out of squareness (I have great eyes for levels), which somewhat goes to prove this.

My question is, how far out is okay? I mean, a 6thou difference seems a lot to me. Can anyone with more experience of this tell me if I'm right?

I haven't shot the gun much, just the once. So the not so great accuracy may be either me, the gun, the ammo or a combination of all of the above.

Next time at the range, I will check for shaving/spitting. I have bore scoped the gun, for barrel/cylinder alignment, which showed a slight out of true, but which flexes enough to line up with a little force (when firing).

That'll teach me not to read books technical books!

 

[H Richard]

How does the gun shoot? Is there a problem? Current specs S&W mentions is up to .010-.012 BC gap is satisfactory. You can call them and see if they will take it back and reset the barrel (since it is out of square) I'm guessing it may be spitting with lead loads.

 

[Big Cholla]

The gun is obviously shoot-able. If there is major side spitting the 'best' correction is to have a pistolsmith set the barrel back one turn and to re-fit the barrel to cylinder gap to your preferred measurement. The much less desirable fix is to square up the rear of the barrel to a uniform gap which according to your measurement will be right at 0.012". As stated that is S&W's maximum b/c gap. I can guarantee that you would not like shooting that pistol with maximum loads with that large of a gap. I'm sure that you can find a pistolsmith in NZ that can set the barrel back properly. Or just continue using it the way it is. ............. Big Cholla

 

[saxguy]

Sending it back to S&W is too complicated and much too expensive (the red tape and import/export fees etc). I have my own home machine shop, and am capable enough to undertake the necessary work myself. Obviously any such work always carries some risks, and I would like to leave the gun in one piece if possible. As far as shooting it, well I will try a few different rounds through it before I comment on its capability (I haven't long had it). It is a no dash, an early model and in near mint condition. The gun cost me an arm and a leg, as it was bought on GB at top price, then had to be sent abroad, which cost me $*** on top again. I am actually more than satisfied with the overall condition, it's a beauty, but the only thing is the gap (and a small tool pitting in the barrel).

I have shot handguns for years, and owned one of the very first of the production line I believe. I never even looked at technical aspects of the thing back then. Just loaded loaded it up and blazed away. These days I have the good fortune of a nice workshop and quite a bit more knowledge. Instead of just blazing away, I would like to know that my guns are pretty much all they can be. I even bought myself a Hawkeye borescope to closely inspect the barrels. In fact I have taken to doing some simple repair works for fellow shooters. Ill be setting up blueing tanks soon. I already have anodizing, gold and silver plating etc.

Bottom line however, not having "worried" about such things as cylinder gaps before, I don't have old experience when it comes to the symptoms of such a problem as a 6tho cant between left/right side. It may be that it makes too marginal difference to bother me. However, if the gun is shooting less than accurate, it would bother me not knowing if this could be part of the problem, but my limited knowledge of such matters keeps me from knowing if this could be significant enough to show on the target.

 

[BigBill]

You could square it off to make it even then reset the cylinder gap. I believe it's done by shimming it.

Being a machinist and a class A machine builder my thoughts are if you had a spare cylinder like from eBay along with some lapping compound you could lap the barrel square by turning the cylinder by hand right then left.
The gun needs to be disassembled. Could you possibly make a cylinder from a piece of bar stock in a lathe? As long as the bore is the correct size for the yoke and the flat surface is 90 degrees from the bore you could make a lapping tool.

Another thought is putting a .006" shim on one half of the low side of the barrel and using a small flat file to lower the high side .006" very slowly and carefully. You need to clamp the frame vertical in a vise with the barrel facing down.

 

[saxguy]

I am thinking I may make a squared off plug to slip into the barrel, and then I can accurately assess the run out, that is I will know if the barrel is on the cant, or if it truly is the face cut. If it is the face cut, I can use a through barrel chamfering tool, and wont need to disassemble the gun. This will of course leave me with a 12tho gap.

However, I will try the gun for a few hundred rounds first, just to see if I can live with it as is.

 

[Fkimble]

Does the cylinder have any end play? If so, an end play shim or two may help reduce the BC gap as well has reduce the end play. .001 - .002 of endplay is required to prevent it from binding when fouled or hot.

 

[tomcatt51]

However, I will try the gun for a few hundred rounds first, just to see if I can live with it as is.

Sounds like a good plan. With target loads it's probably fine. With magnum loads you may not like how much it "spits" out the wide side of the gap. Most likely will not affect accuracy.

Some guns have uneven gaps because when the gun is built the gap is set by a person using a file. Quick and dirty... The only thing surprising is how many are as good as they are.

Brownell's has a nice cutter that will square the barrel face with the barrel in the frame (or you can use a file) but then you'll have a big gap all the way around. I'm not sure that's really "better".

 

[BigBill]

Once you square the barrel in the frame you can shim the cylinder more forward to adjust the gap. I think you will end up with a .012" gap and I would shim it down to .004" if possible.

 

[saxguy]

… but surely that would just be shifting the problem? It would be increasing the headspace by the thickness of the shim, and if we are talking about taking the C/B down to a 4thou c/b gap (from 12thou), then that would be adding 8thou to the headspace by shifting the cylinder forward. Also the cylinder is rock solid in lockup, no "shake" at the moment, the timing is spot on etc, and I would just be messing with this, am I not correct?

 

[BigBill]

Then leave it or change out the barrel.

Is this a manufacturing assembly problem?

 

[bgrafsr]

Head space specs for the 586 is .060" to .068". I have a 586 that had a head space of .075" or so. I removed the extractor, chucked it up in a collet on my lathe and removed .015" from the back of it. I then had to cut the rear of the barrel and set my B/C gap at .004", and re-cut the forcing cone. If I remember correctly, I removed the barrel from the frame, chucked it up in my lathe, and cut the end of the barrel to the proper length. This also assured that the end of the barrel was square around its entire circumference.

The gun shoots very well and is one of my favorites.

 

[tomcatt51]

Then leave it or change out the barrel.

Is this a manufacturing assembly problem?

You don't "change out the barrel", you set it back a thread and then set the barrel/cylinder gap.

Yes this is a "a manufacturing assembly problem". During assembly the barrel/cylinder gap is "adjusted" with a file. On this gun it seems it wasn't done too well.