Forcing Cone Problem

[teamgeek]

I have a new 686-6 with a defective forcing cone. Referring to the digital bore scope image, significant burrs have been pulled off the side of each rifling land and laid over into the adjacent groove. This image is of the replacement barrel following return from Smith & Wesson. The first barrel showed equivalent defects. I also owned a recent model 986 with very similar forcing cone defects. Apparently, this is becoming a common quality defect in Smith & Wesson revolvers.

Burrs at these locations are certain to cut grooves down the full length of the bullet bearing surface creating significant leak paths for high pressure gas. These leaks will reduce velocity and result in gas cutting of bullets. Greatly increased barrel leading will result if lead bullets are used. None of this can be good for accuracy.

I have many earlier Smith & Wesson revolvers. None have this problem. I have chambered many firearm barrels and have never damaged a forcing cone like this. There can be no good excuse for putting out revolvers with this type of defect. I am hoping others on this Forum will examine their new revolvers and express concern to Smith & Wesson if they find forcing cone defects.

I have Brownell’s forcing cone tools and could use them to attempt my own repair. Jacketed bullets were fired at the Smith & Wesson repair center indicating the burrs are obviously very sturdy and hard to remove. I don’t have confidence the Brownell’s tools will work because of the significant amount of material that would need to be removed. Can Forum members suggest other approaches to repair?

 

[BrBa]

Send it to S&W and have them fix it.

 

[Yendor357]

First of all, a new gun shouldn’t need repair. Ever. There are too many owners of S&Ws that own reamers. What does that tell you?

What would I do? I’d shoot it. If it groups well, hold your nose and look the other way. The proof is in the pudding, as they say. Put it on paper.

I’ve had good luck with fire lapping. That’d be my first course of action. The one or 2 rounds that the factory fires isn’t going to do a whole lot when it comes to smoothening out a rough barrel. The more you shoot something, generally speaking, the better it shoots.

You want to ream it? Ream away, it’s your gun, your money. But if you do, there’s more of a chance that if things go sideways, you’re on your own if smith’s customer no service spots that.

Posts, and photos like this is why I buy old smiths and new Colts.

 

[WR Moore]

Looks like a tooling problem. (ETA: might also be tooling feed being a "bit abrupt".) That said, most of us don't have borescopes, so it's unknow just what one would show in barrels from "the good old days". I just had a flashback to a old (tan box) but pristine M&P that turned out not to have a forcing cone at all.

I'd go with the "run a box of jacketed bullets and then look again" thought and then re-evaluate. I've got an old military rifle whose barrel looks horrid to the naked eye, but it shoots MOA all day.

I'm not sure what angle S&W currently uses for their forcing cones, but if it really nags you, a super cautious application of an 11 degree reamer might be worth a try. But re-read paragraph 4 in the above post.

 

[WR Moore]

Having been both a production and prototype machinist, QC wouldn't be using a bore score. Unless it was required under some special contract-that the taxpayers would probably be financing. Heck, I toured a barrel plant who's products were considered premium 50 years back and don't recall seeing a bore scope. Air gauge for uniformity, yes.

ETA & bearing on problem: a long time back, there was a brief thing in the American Rifleman. One of the army ammunition plants suddenly realized their test rifle for accuracy of ammo lots (M1 Garand) had fired 80,000 rounds. They replaced it with a new rifle. Some curious soul sectioned the barrel. Despite erosion having removed the rifling for 8-9 inches in front of the chamber, it still shot acceptable groups. A picture was included.

 

[H Richard]

I'm not sure if available in pistol caliber, but rifle calibers can be bought with a abrasive coating which is touted for breaking in a barrel. I've never used it but thought might be a possible fix.

 

[308 Scout]

Not an S&W, but my Ruger Blackhawk .44 Special. Notice the chunks out of the left sides of the lands-

I cut the forcing cone with a Brownell's 11° cutter then fire-lapped the barrel. This did not eliminate the areas in question, but made them better-

Even with the flaws, the revolver is still very accurate-

So I would suggest cutting the forcing cone and fire-lapping the barrel (I used a Wheeler kit)

Good luck.

 

[Yendor357]

WOW Scout! That is some fine shooting!

As stated earlier, the proof is in the shooting.

I have a 4 5/8 inch stainless Bisley in 44 Special. Before I bought it, I read a couple of articles stating how accurate this guns were. Mine shoots really good. But I’ve never gotten a group as good as Scout’s.

The 44 caliber Ruger barrels that I have all started out a bit rough. Ive fire lapped all 4 of them with good results. I’ve never felt the need to fire lap any of my old Smiths, nor new Colts.

I’ve also read the fire lapping helps the barrel shank, that some manufacturers make too tight and thus reduces the bore diameter in the shank area, is made better by fire lapping. I can’t prove that. It’s just what I’ve read.

 

[308 Scout]

WOW Scout! That is some fine shooting!

As stated earlier, the proof is in the shooting.

I have a 4 5/8 inch stainless Bisley in 44 Special. Before I bought it, I read a couple of articles stating how accurate this guns were. Mine shoots really good. But I’ve never gotten a group as good as Scout’s.

The 44 caliber Ruger barrels that I have all started out a bit rough. Ive fire lapped all 4 of them with good results. I’ve never felt the need to fire lap any of my old Smiths, nor new Colts.

I’ve also read the fire lapping helps the barrel shank, that some manufacturers make too tight and thus reduces the bore diameter in the shank area, is made better by fire lapping. I can’t prove that. It’s just what I’ve read.

Thanks!

I once owned a New Vaquero 45 Colt that had the tight spot to which you refer. 60+ fire-lapping rounds helped, but only somewhat.

 

[.455_Hunter]

Why do forcing cones always look like they were cut as somebody's first lathe project in junior high metal shop class?

 

[stansdds]

Why do forcing cones always look like they were cut as somebody's first lathe project in junior high metal shop class?

Cost cutting; by using a cutter that is worn out and should have been replaced long ago and by using less skilled labor that does not care about quality, but cares about meeting production quota.

 

[chief38]

I'd actually be afraid to send a gun back to the current S&W repair center in fear they might actually make a bad situation worse! You might try sending a few hundred jacketed rounds through it - it might smooth out. I know it looks nasty, however the rear of the barrel (forcing cone area) is usually nowhere's near as critical for accuracy as the muzzle end. It might shoot fine. Eventually it should smooth out by just shooting it.

That said, it's a shame things are this way from S&W!

If you have a very small delicate needle file and are handy, you could try smoothing it out a but. Just don't hit the sides. I know you should not have to do this on a brand new gun, but it is what it is......

 

[pistolpete10]

but it passed smith and wesson quality inspection..

T
What don't pass?? They don't have a quality inspection.

 

[SWFan27]

Send it to S&W and have them fix it.

That is the correct answer.

 

[308 Scout]

My 29-10's forcing cone pre-lapping-

I need to get better post-lapping pics, but this gives an idea-

 

[308 Scout]

why does it look like you have extra lands between the actual lands.. made me wanna hurl trying to figure it out

I have no idea. Maybe it has something to do with the EDM rifling method...?

 

[WR Moore]

Why do forcing cones always look like they were cut as somebody's first lathe project in junior high metal shop class?

I kind of suspect they do the forcing cones in what amounts to a fixture on a drill press. And, they don't change tooling as often as they should. Apparently the surface finish spec is either really generous or doesn't exist.

That said, the forcing cone is pretty much a funnel to allow for minor misalignment between bore and chamber. Surface finish-within limits- doesn't have much effect on practical accuracy for most of us. Heck, my first new revolver (Herter's single action) only had a chamfer where the forcing cone was supposed to be and was/is very accurate. I cut a forcing cone maybe 20 years later.

That rifling form-and apparent surface finish-doesn't make me a fan of EDM rifling.

 

[steelslaver]

I doubt the factory uses a brass lap with abrasive compound, but just a cutter. The lap's angle must match the cutter's

 

[teamgeek]

Thanks for all the feedback. I failed to report that I sent this 686 revolver back a second time to S&W. They returned it three months later with the comment “No Repair Required”

You have made many good suggestions. I am considering firing full power 357 loads with jacketed bullets, and/or using my 11 degree forcing cone reamer. I will, however, test the accuracy of this 686 using my Ransom Rest before attempting to correct the defects in the forcing cone.

I did fire some carefully prepared lead target loads in 357 cases in the 686. For comparison, I also fired some of the same loads in my 1970’s vintage M66. I was able to recover projectiles by shooting into snow. Images are included below with the rougher looking bullets coming from the 686.

Hopefully the images are clear enough for you to see the differences. On the bullets from the 686, the rifling marks are tapered with the raised portions narrower at the front of each bullet. There are also areas on the raised portion of the rifling marks at the back of the bullets that are ablated by high pressure gas. The burrs on the sides of the 686 rifling at the forcing cone are on the driving side and appear to have left a very rough edge on the bullets in some areas. Also, much of the bullet lube has been blown out of the rolled lube grooves. Surprisingly, for twelve rounds fired, there was hardly any leading in the throats or barrel.

The bullets from the M66 look much better with parallel sides on the rifle marks. There were no ablated areas and the lube remains in the lube grooves.

 

[38magnum]

Why do forcing cones always look like they were cut as somebody's first lathe project in junior high metal shop class?

no real tool set up is happening? most of the forcing cone burrs i have seen on smith revolvers, could probably be solved with a few twists of a forcing cone cutter. even a good shaped insert with lapping compound..