Forcing cones and spitting

[ezb57]

Hello: How bad do forcing cones have to be before they cause or contribute to spitting? This old Model 49 of mine has always been a bit dirty shooting. The B/C gap is at .002. Not many rounds through it overall, less than 1000 for sure. Concentric machining lines are very clear on the cone. Should I clean this up? I realize if its way out of time it doesn’t matter how good the cone is. My inexpert inspection makes me think the timing is pretty good.
I don’t have a range rod or cone cutter; they aren’t easy to find for sale either. I don’t know of any sources other than Brownells. May rent them, but it doesn’t look like 4D rents range rods.
Also, what forcing cone angle does Smith use on their revolvers?
Are there advantages to the other angles used out there?
Thanks in advance.

 

[rockquarry]

Before messing with it, I'd benchrest it with good equipment from a solid rest and shoot some groups with the ammo that's proven to be most accurate. Shoot at 25 yards; up close will only tell you that even poor ammo and a poor gun are accurate. Dirty is a relative term. If you're gun shoots well you can put up with whatever degree of dirty you're dealing with. It all cleans up easily. Good luck-

 

[ezb57]

Thanks. I don't mind cleaning, but the spitting is really more the problem than accuracy.

 

[pantannojack]

Those fording cone marks look like my 586. But further inside the bbl looks very good.

 

[rockquarry]

Thanks. I don't mind cleaning, but the spitting is really more the problem than accuracy.

I suppose if the "spitting" is really consistent, there's likely a problem. After fifty+ years of shooting many revolvers, I've dealt with this on a few occasions but never on a regular basis. As for the cause with my guns, I don't know, but I've seen no reason to be concerned since they were isolated instances.

 

[Protocall_Design]

From the 1/4 of it we can see, it looks a bit small and pretty rough. I think the factory angle is 11 degree, but don't know for sure. Anyway, that's the one I've always used with good results.

 

[WR Moore]

Way back in the day the forcing cone angle was 18 degrees. An 11 degree reamer cleans those up really well. However, there's not a lot of meat in a J frame barrel to work with. You might not get all those marks out.

That said, before you start cutting-or pay someone else to do so-I'd check yoke alignment and carryup with the proper tools & gauges. Wouldn't be the first time that the assembler installed a minimum thickness hand and called it good enough.

 

[chief38]

You said the BC Gap was .002" but did you check it in the proper position and for end shake?

I would get a Range Rod and make SURE the cylinder charge holes are lined up properly with the barrel/chamber. I'd also check the BC Gap from both sides of the gun to see if the forcing cone is cockeyed or favors one side by being angled.

The roughly cut forcing cone is unfortunately more common that I'd like to see, but rarely have I experienced spitting because of it. YMMV.

BEFORE removing any metal (which can't be put back), make sure you check everything else out first.

 

[54Bill]

“You said the BC Gap was .002" but did you check it in the proper position and for end shake?”
What is the proper position and acceptable tolerance?

 

[stansdds]

Measure the gap with the cylinder pushed forward, then again with the cylinder pushed backward. The difference between the two measurements is the end shake. You have to have some end shake and 0.001-0.002" is ideal. I forget where S&W draws the limit, but I would say that 0.004" would be excessive.
Spitting does not likely come from the machining marks in the forcing cone, but can be the result of excessive barrel-cylinder clearance, and unevenly cut forcing cone, and certainly will occur if the chambers are not properly lined up with the forcing cone.

 

[BLUEDOT37]

Assuming your .002" B-C gaps is correct, & you do not have excessive endshake or alignment issues, I'll agree that the little we can see of your forcing cone doesn't seem to indicate a problem.

A problem that does come to mind that can cause spitting is a forcing cone that's too small in diameter.

I, & others, encountered this on a batch of M66-8s a few years back. I found mine amiss before I ever shot it but excessive spitting was their main complaint. I fixed it by re-chamfering the forcing cone myself.

Your can see in the before & after pictures how little the bullet could enter the forcing cone and then after chamfering.

Just another item you could look at.

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- shoots good & no spitting afterwards-
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[Protocall_Design]

I'm with Bluedot. I have found a lot of undersized forcing cones on revolvers over the years. He illustrates the point very well.

 

[ezb57]

I'm with Bluedot. I have found a lot of undersized forcing cones on revolvers over the years. He illustrates the point very well.

Undersize in respect to depth, diameter or both?

 

[Protocall_Design]

Mainly diameter, but the 2 are connected. Larger diameter = more depth. How much of each is dependent on which cutter is used: 5, 11, or 18 degrees.

 

[ezb57]

A smaller angle would reach further into the barrel at a given diameter though, correct?

 

[WR Moore]

Correct. I looked up the spec for .38/.357 forcing cone maximum diameter and it's 0.370 in +/- 0.005 in. Be very gentle on J frames!

As noted by several above, unless the forcing cone is really undersize-or doesn't exist, barrel/cylinder alignment is the usual cause for spitting. I once rebarreled an H&R .22 for a friend and was horrified by the over size factory forcing cone. I cut a typical .22 rf forcing cone on the new barrel. Then we discovered the factory funnel was necessary due to the rather casual carryup of the cylinder and resulting barrel/chamber alignment variation. Ended up duplicating the factory version to eliminate spitting.

 

[ezb57]

Did some measuring today and forcing cone is already at .360" so I don't think I'll be doing anything with it.
Still would like to get a range rod if anyone knows a source other than Brownell's who are out of stock.
Thanks for all the great comments and shared knowledge.

 

[.45mtngun]

All my revolvers use bullets that I cast from .38 to .45. I always cut the forcing cone to 11 degrees. As I have told people most of the time it improves accuracy, but never degrades it. It's just a good step for setting up a revolver for cast bullets.

Jim

 

[NCBeagle]

I had the same Model 66-8 forcing cone problem as BLUEDOT37. First range trip left my face and neck bleeding from the spitting lead. Had a local shop ream the forcing cone. All good after.

 

[BLUEDOT37]

Did some measuring today and forcing cone is already at .360" so I don't think I'll be doing anything with it.

As WR Moore mentioned forcing cones can have a larger diameter (.377") than that.

I don't know how you measured your F-C opening but if you didn't use a cylindrical gage it may not be accurate?

Since typical pin gages are 2" long they can't be used because they're too long to fit in the cylinder's window.

I did not buy any of Brownell's barrel chamfering plug gages but rather used a fired case from the revolver as a gage in the F-C mouth. Some flaring/bell-mouthing of the case may be necessary to reach the desired case mouth diameter. It's cheaper & gets you in the ballpark.

This is from Brownell's instruction pamphlet on their Revolver Chamfering Tool Kit:

When cutting a chamfer, you normally do not want to have the internal diameter of the rear-most portion of the chamfered area to be over .020" larger than the diameter of the bullet of the cartridge that is being used. In other words, in a .38 Special revolver, which utilizes a bullet that is normally .356" to .358" in diameter, the maximum diameter of the chamfer should be .376" to .378". A very simple and easy way to check this, and to ensure you do not cut more than you should, is to utilize the Brownells Chamfer Plug Gauges. By using these Gauges, you can tell at a glance exactly how deep a cut should be. Above all, be extremely careful when cutting with this tool. It is very easy to cut too much. Go slow! Be careful!

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As for your question about a range rod again it's an item I've never bought. Since I have several sets of pin gages I just use a slightly smaller pin gage then largest gage that can freely fit down the barrel's (clean) muzzle/barrel & tip the muzzle slightly up to allow the gage to slide down the barrel & into the cylinder noticing if it passes the B-C gaps without interference or hanging up there.

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