Correct Forcing Cone for Mod. 66-8?

Good afternoon. I have a current production 66-8. It was in the first run and, apparently, the forcing cone is not correct. There is some debris coming back. It fact, it looks like there is no cone at all. Want to have that cleaned up by a competent gunsmith in Charlotte. Don't care to screw around sending it back to Smith & Wesson.

Just so I know going into it...what is the correct forcing cone angle? What is factory spec (7 degree, 11 degree, etc.)? Is there any good reason to deviate from factory spec? If so, what would you recommend? Thanks.

** If it helps answer the question...this would be an occasional CCW, hiking, and range gun. No competition.

I would send it back to the factory, for two reasons. If it is a warranty issue you should not have to pay for it, and if the gunsmith decides it needs a new barrel he will have to get it from the factory anyhow (and make you pay for the work). S & W will usually even pay shipping in both directions for an authorized repair. Good luck in your decision.

There is no "magic angle" for a forcing cone or muzzle crown. The main thing is that they are concentric to the bore and fairly smooth. In addition, the forcing cone opening needs to be large enough to funnel the bullet in even if the cylinder is off location by a tiny bit.

I use an 11 degree cutter because that is what came in the set from Brownell's. I cut mine about 1/8" in from the end. A 10 or 15 degree cutter would work equally well as long as it was centered with a smooth surface. It doesn't need to be a mirror finish, just no big circular grooves or chatter marks.

murphydog said:

I would send it back to the factory, for two reasons. If it is a warranty issue you should not have to pay for it, and if the gunsmith decides it needs a new barrel he will have to get it from the factory anyhow (and make you pay for the work). S & W will usually even pay shipping in both directions for an authorized repair. Good luck in your decision.

Click to expand...

I understand. S&W would cover all of the costs, etc. Quite frankly, I am too lazy and not inclined to screw around with the shipping and receiving aspect of it. Also, don't want the process to drag on for weeks or months. I visit a place weekly that can do the work for a reasonable price. Probably just going to sell the gun when all is squared away. Don't want to sell the gun with the forcing cone issue after becoming aware of the concern. May decide to keep it. Not sure at this point.

66-8 forcing cut & muzzle rechamfered

My 66-8 had an improperly cut forcing cone too. I fixed it myself.

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66 Combat Magnum - forcing cone, before

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66 Combat Magnum - forcing cone, after

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66 Combat Magnum - forcing cone, rechamfering

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66 Combat Magnum - forcing cone, rechamfered

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Chamfered the muzzle too.

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66 Combat Magnum - muzzle recrowned

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Shoots great now!

Sometimes you just have to take matters into your own hands.

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66 Combat Magnum (Zero-Power Pistol target)

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BLUEDOT37 said:

My 66-8 had an improperly cut forcing cone too. I fixed it myself.



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66 Combat Magnum - forcing cone, before

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66 Combat Magnum - forcing cone, after

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66 Combat Magnum - forcing cone, rechamfering

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66 Combat Magnum - forcing cone, rechamfered

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Chamfered the muzzle too.



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66 Combat Magnum - muzzle recrowned

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Shoots great now!



Sometimes you just have to take matters into your own hands.



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66 Combat Magnum (Zero-Power Pistol target)

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Click to expand...

Great post. Why 5 degree? Is that spec? Personal preference?


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OK, the 5 degree cutter is a Ruger spec. The old original industry standard forcing cone angle is 18 degrees. The 11 degree angle came about from shooting lead wadcutters.

Brownells notes the 18 degree cutter is best for jacketed and LSWC bullet shapes, the 11 degree for general lead use. I've cut (on a lathe) the 11 degree cone in custom barrels (and some of my own) and it seems to work well as an all purpose choice. Depending upon the maximum diameter of the stock cone (see below), it may be the best way to clean up a stock cone without going oversize.

With a K frame, the big concern is the maximum diameter of the forcing cone. The barrel is really thin at the bottom, as evidenced by the cracking issues. I've heard a rumor that S&W slightly changed some dimensions to eliminate the flat on the bottom of a K frame barrel shank on new production. Looking at the pictures above, it would seem there's substantially more meat in the shank, but I'd like to see actual measurements on barrel shank outside diameter at the forcing cone.

The J and older K frame factory forcing cones I've measured have run about 0.010 inches over groove diameter or about 0.367-give or take a couple thousandths-maximum diameter at the cylinder end. I've never measured one of the new ones. I'd be hesitant to go much, if any, beyond this on an older model gun, due to the flat, depending upon caliber. Where either diameter of the barrel or magnum loads/thin barrel shank aren't issues, the general model is that maximum diameter can be about 0.020 in over groove diameter. That doesn't mean it has to be, but it can be on the N frame and probably on the L frame. The old design K frame is generally limited to wadcutter .38's at this diameter.

Before blaming the forcing cone, make double darn sure the cylinder is carrying up properly and ranging (aligning with the barrel) acceptably. While I understand your reluctance to do a return to the factory, it's a darn good way to get if in factory spec and maintain your warranty.

WR Moore said:

OK, the 5 degree cutter is a Ruger spec. The old original industry standard forcing cone angle is 18 degrees. The 11 degree angle came about from shooting lead wadcutters.

Brownells notes the 18 degree cutter is best for jacketed and LSWC bullet shapes, the 11 degree for general lead use. I've cut (on a lathe) the 11 degree cone in custom barrels and it seems to work well as an all purpose choice. Depending upon the maximum diameter of the stock cone (see below), it may be the best way to clean up a stock cone without going oversize.

With a K frame, the big concern is the maximum diameter of the forcing cone. The barrel is really thin at the bottom, as evidenced by the cracking issues. I've heard a rumor that S&W slightly changed some dimensions to eliminate the flat on the bottom of a K frame barrel shank on new production.

The J and older K frame forcing cones I've measured have run about 0.010 inches over groove diameter or about 0.367-give or take a couple thousandths-maximum diameter at the cylinder end. I've never measured one of the new ones. I'd be hesitant to go much, if any beyond this on an older model gun, due to the flat. Where either diameter of the barrel of magnum load aren't issues, the general model is that maximum diameter should be about 0.020 in over groove diameter.

Click to expand...

Great post. Thanks. This is the current production 66-8, so jo flat spot at bottom or forcing cone.

I will most often shoot jacketed or LSWCHP if I keep the revolver. Few of my revolvers see more than a few hundred rounds because of rotation. Gunsmith took for granted that he was going to cut it to 11 degrees. May just go with that if it's a good overall choice.


Sent from my iPhone using Tapatalk

On my 66-8 I found the FC issues before I fired one round thru it. Having gotten a few poor FC's it's something I check, along with other dimensions, on my initial inspection before going to the range. Some are too rough & some too large.

Upon trying to see how deep the base of a jacketed bullet would go in I found it wouldn't even enter the FC (which is why the before pic has the nose of the bullet in it, not the base.)

Brownell's says the FC shouldn't be over .020" of the nominal bullet/bore diameter. I've bought new revolvers that have been over that from the factory.

The reason I go with the 5 degree cutter is because when I did my 686-6's rough/short FC I tried the 11 degree first. Because it already had the factory cut, which was just under the max. diameter (.377"), I found that using the 11 degree cutter would have given it too large of a diameter opening if I removed enough to take a full cut (because of the wider angle).

Stopping the cut at .377" would leave a compound cut, the old & the new angles, not preferred, & would not have fully removed what needed removing. Going with the 5 degree cutter, & it's narrower/longer cut, allowed me to remove the factory cut without materially going over .377". (see cutters in pic below)

The Brownell's kit only gives you (1) bore pilot (in upper left corner) for each caliber. I ordered a second set (in lower center) for each caliber so I can have one close to the breach end/FC & another about a 1/4 away from the muzzle.

Using both, in conjunction with the rod's center (end) guide, I felt it keep things better aligned while cutting & was glad I got them.

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Revolver Chamfering Tools Kit instruction:
-Instructions- (pdf)

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Brownells Chamfering Tool Kit

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The muzzle can be chamfered with their 45 degree cutter & pilots.

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Brownells Chamfering Tools

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Brownells Chamfering Tools

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Toolguy said:

There is no "magic angle" for a forcing cone or muzzle crown. The main thing is that they are concentric to the bore and fairly smooth. In addition, the forcing cone opening needs to be large enough to funnel the bullet in even if the cylinder is off location by a tiny bit.

I use an 11 degree cutter because that is what came in the set from Brownell's. I cut mine about 1/8" in from the end. A 10 or 15 degree cutter would work equally well as long as it was centered with a smooth surface. It doesn't need to be a mirror finish, just no big circular grooves or chatter marks.

Click to expand...

I too have cut 11º FC's on two of my revolvers and have truly not noticed any difference what so ever. It did not hurt anything but I don't think it changed anything either. Would I do it again as long as said Revolver was shooting perfectly? Probably not.