AR15.Com Archives
 UPDATE with pictures: Forcing cone gap specs on S&W?
SkagSig40  [Member]
3/30/2007 4:19:40 AM
I have several 686's and 629's and I was wondering what the tolerences were on the forcing cones? I have some guages I was going to check them with. Thanks!
Paid Advertisement
--
RogerBall  [Member]
3/30/2007 10:07:14 AM
I am pretty sure S&Ws are between .003 and .008 inches.
dfariswheel  [Member]
3/30/2007 8:15:30 PM
Depends on what you're gaging.
If you mean you want to measure the barrel/cylinder gap, you use a feeler gage set.
The S&W spec is from a Minimum .003" to a Maximum of .010" with the ideal being around .005".

You need to also measure end shake, which is the amount of fore and aft movement of the cylinder in the frame.
You have to do this along with the barrel/cylinder gap, since end shake can give a false barrel/cylinder gap measurement.

To measure end shake:
Gently push the cylinder forward and measure the gap.
Then gently push the cylinder to the rear and measure again.
Subtract one from the other, and that';s the amount of end shake between the cylinder and the frame.
The spec for S&W is a Minimum of .002 with a Maximum of "Around .006".

If the end shake is out of specs, this can cause a false reading of not enough barrel/cylinder gap.
The "fix" is NOT to open up the barrel /cylinder gap, it's to correct end shake.

The forcing cone is the tapered "funnel" in the rear of the barrel.
S&W and all other revolver forcing cones are gaged with a special plug gage, available from Brownell's:

www.brownells.com/aspx/NS/store/productdetail.aspx?p=626&s=2579

This gage is the ONLY way the cone can be gaged.

Remember, the depth or taper of the cone is not what's critical.
What's critical is the outer diameter of the cone's mouth. THAT'S what the plug gage measures.

S&W uses "About" a 9 degree forcing cone cutter as I recall.
SkagSig40  [Member]
3/31/2007 1:12:21 AM

Originally Posted By dfariswheel:
Depends on what you're gaging.
If you mean you want to measure the barrel/cylinder gap, you use a feeler gage set.
The S&W spec is from a Minimum .003" to a Maximum of .010" with the ideal being around .005".

You need to also measure end shake, which is the amount of fore and aft movement of the cylinder in the frame.
You have to do this along with the barrel/cylinder gap, since end shake can give a false barrel/cylinder gap measurement.

To measure end shake:
Gently push the cylinder forward and measure the gap.
Then gently push the cylinder to the rear and measure again.
Subtract one from the other, and that';s the amount of end shake between the cylinder and the frame.
The spec for S&W is a Minimum of .002 with a Maximum of "Around .006".

If the end shake is out of specs, this can cause a false reading of not enough barrel/cylinder gap.
The "fix" is NOT to open up the barrel /cylinder gap, it's to correct end shake.

The forcing cone is the tapered "funnel" in the rear of the barrel.
S&W and all other revolver forcing cones are gaged with a special plug gage, available from Brownell's:

www.brownells.com/aspx/NS/store/productdetail.aspx?p=626&s=2579

This gage is the ONLY way the cone can be gaged.

Remember, the depth or taper of the cone is not what's critical.
What's critical is the outer diameter of the cone's mouth. THAT'S what the plug gage measures.

S&W uses "About" a 9 degree forcing cone cutter as I recall.


A little over my ability I think!
I used a feeler guage and all my revlovers (7 of then are between .005 and .008. All I did was insert the guage till I found one that fit but was tight. Based on this you think mine are in spec ok?

The reason I ask is a couple of them are showing flame cutting on the top strap. This is a picture of one of my 686 and the gap was a .005:



dfariswheel  [Member]
3/31/2007 8:55:54 PM
That type of flame cutting is 100% normal for the S&W.

If your barrel/cylinder gap is .005" it's actually perfect.
SkagSig40  [Member]
4/2/2007 2:33:38 AM

Originally Posted By dfariswheel:
That type of flame cutting is 100% normal for the S&W.

If your barrel/cylinder gap is .005" it's actually perfect.


How far off is 0.8? I have 2 that are at about 0.8 and one a tight 7. Should I send these in to be corrected a bit tighter?
dfariswheel  [Member]
4/2/2007 1:41:05 PM
The S&W factor spec is, anything under .10" is in spec and they will charge to set the barrel back and re-cut the forcing cone if it's under that.

Perfect is .005" so a .007" and .008" are a "little" open, but the real test is, how do they shoot?
If they shoot OK, there's no problem, and they ARE in factory spec.
SkagSig40  [Member]
4/3/2007 3:01:20 AM

Originally Posted By dfariswheel:
The S&W factor spec is, anything under .10" is in spec and they will charge to set the barrel back and re-cut the forcing cone if it's under that.

Perfect is .005" so a .007" and .008" are a "little" open, but the real test is, how do they shoot?
If they shoot OK, there's no problem, and they ARE in factory spec.


When you say how do they shoot, they seem to shoot well. Accuracy is good. I don't really notice a lot of gas blowing out the gap sides but then I never really looked for that.
Andyd  [Member]
4/3/2007 5:54:58 AM
Flame cutting is not so much the result of an odd forcing cone gap but more the result of hot loads with light weight bullets from what I remember.
SkagSig40  [Member]
4/3/2007 1:27:38 PM

Originally Posted By Andyd:
Flame cutting is not so much the result of an odd forcing cone gap but more the result of hot loads with light weight bullets from what I remember.


I have heard that too. I heard that light grain bullets are harder on the gun ten heavier bullets. I have never been able to confirm this. Can anyone here confirm or deny this?
hsvhobbit  [Member]
4/4/2007 9:38:48 AM

Originally Posted By dfariswheel:
The S&W factor spec is, anything under .10" is in spec and they will charge to set the barrel back and re-cut the forcing cone if it's under that.

Perfect is .005" so a .007" and .008" are a "little" open, but the real test is, how do they shoot?
If they shoot OK, there's no problem, and they ARE in factory spec.



Ummm, actually I bet if your barrel/cyl gap is a tenth of an inch, S&W will make it right for ya.

However, the flame cutting you see is (as others have said) 100% normal and expected. All my magnums have displayed this and it's a non-issue.
dfariswheel  [Member]
4/4/2007 10:51:35 PM
Oops, forgot that Zero. It should be 0.010".

" heard that light grain bullets are harder on the gun ten heavier bullets. I have never been able to confirm this. Can anyone here confirm or deny this?"

Yes, lighter bullet loads can be harder on a revolver.

The most effective load for the .357 was the .125 grain, jacketed hollow point. This load, especially the Remington load, got an unequaled reputation in police shootings.

The problem is, the light bullet with the heavy powder charge tends to erode the forcing cone.
The impact of the fast moving bullet, along with the erosive blast of the hot burning powder causes the rear of the barrel in the forcing cone to actually develop metal fatigue, and cracks can form.

The super-heated gas and burning powder particles act like a white-hot sand blaster, and this causes erosion of the cone.
In the S&W Model 19 and 66, the bottom of the barrel has a clearance cut to clear the cylinder yoke, and this flat spot on the bottom of the barrel is subject to cracking or even broken barrel shanks.

For this reason, S&W introduced the beefed-up "L" frame to permit police to shoot large quantities of the 125 grain loads without reducing the service life of the gun.
While the 125 grain is still King, the newer "short barrel" revolver loads in the 135 grain range are less wearing on the guns.


A serious question is, how much 125 grain loads is "too much"?
The answer is, no one knows. Some shooters have shot a LOT of lighter .357 loads in "K" frame S&W revolvers with no apparent damage.

So, some one wanting to make a .357 last longer, will shoot the heavier bullet loads, and use the 125 grain loads for serious business.
Andyd  [Member]
4/5/2007 5:42:24 AM
As to the question, how many 125gr loads are too many. One of my S&W M19 shows flame cutting after just a few cylinders full. It's not too bad but all to visible.
dfariswheel  [Member]
4/5/2007 5:44:03 PM
There's a BIG difference between flame cutting of the top strap, and forcing cone damage.

Flame cutting is a self-limiting non-problem.
It'll get just so deep and no deeper.
In other words, no matter how much you shoot it, the top strap cutting isn't going to get deep enough to cause any problems or weakening.

On older revolvers, the manufacturers sometimes made an oval-shaped clearance on the top strap right in that area to totally prevent flame cutting.
After they had a lot more experience with hot rounds like the .357, they learned that the cutting simply stops after the groove gets to a certain point, and little or no further cutting occurs.
SkagSig40  [Member]
4/6/2007 4:51:55 AM
So if I do a lot of plinking I don't want to use 125 grain ball or HP ammo? Stick with heavier grain rounds? Thanks!
Andyd  [Member]
4/6/2007 8:15:43 AM
If you want to do a lot, a lot of plinking it will be a whole lot cheaper to use lead bullets. In the end the price of a gun, or it's repair, will be nowhere close to the cost to feed it.
If I would not reload, I probably would not not shoot 1/4 of what I do.

On the 629 heavy bullets over 240gr can be a bit hard, too.
SkagSig40  [Member]
4/6/2007 3:35:24 PM
So what would be the ideal weight for a 686 and 629 to practice shooting with? I don't want to shoot lead for several reasons. Thank you!
dfariswheel  [Member]
4/6/2007 10:24:24 PM
Probably the easiest in the 686 is 158 grain loads.
In the 629, heavier bullet loads.

In both cases, the very easiest is to shoot lighter loads.
In the 686, shoot standard .38 Special or +P .38 Special.

In the 629, shoot .44 Special.
SkagSig40  [Member]
4/7/2007 12:59:39 AM

Originally Posted By dfariswheel:
Probably the easiest in the 686 is 158 grain loads.
In the 629, heavier bullet loads.

In both cases, the very easiest is to shoot lighter loads.
In the 686, shoot standard .38 Special or +P .38 Special.

In the 629, shoot .44 Special.


I'm sorry, you got me a little confused.

In the 1st sentense you mention the easiest is the heavier loads(158gr and heavier loads for the 629)
In the 2nd sentense you say the easiest is to shoot lighter loads.

So which is it? What I'm looking for is the bullet/load that will put the least ammount of stress on the guns. I want them to last as long as I can and still shoot them a lot. Many thanks!!!
SkagSig40  [Member]
4/10/2007 11:48:48 PM
Bump
tradrick  [Member]
4/11/2007 10:18:37 AM
I think what he means(and correct me if I'm wrong)is that if you want to shoot 357 mag loads and don't want the risk of added stress to your revolver use the 158gr. loads.Or you can shoot standard 38 special or 38 spl.+P and it won't stress your guns to bad either.I have a 686 357 4''bbl.And I shoot 158gr.loads in it pretty regular.When I'm just plinking and fooling around I'll shoot 38 sp.There also cheaper to shoot.
dfariswheel  [Member]
4/11/2007 10:13:48 PM
Right.

The heavier 158 grain bullet loads in .357 are actually easier on the gun.
It's the light 125 grain hot loads that erode the forcing cone, and have been reported to cause forcing cone cracks.

Shoot 158 grain .357 loads for fun, and .38 Special for cheap, easy fun.

For "business" you can shoot .38 Special +P loads if the blast of a full Magnum is too much, and for really serious business, use the hot .357 with the 125 grain bullets.

Today, there's a nice "in between" with the newer 135 grain range loads from Federal and others.
These are often sold as "Short barrel" loads. They were developed for better results and less ear destroying blast than the hot 125 loads.
SkagSig40  [Member]
4/13/2007 3:35:54 AM
Thank you very much!
One last question:
How well would a high quality 158gr load like a Speer Gold Dot 158gr work as a selfdefence load compaired to a 125gr? Thanks!
dfariswheel  [Member]
4/13/2007 10:52:37 PM
The honest truth of modern premium American defense ammo is this:

There IS no "magic" load, and one load will perform "about" as good as any other.
American defense ammo has undergone a HUGE sea change in bullet design in the last 20 years or so, and today's ammo is so effective it might as well be 100%.
Searching for "the best" ammo, when one is "about" 97% effective and the other is "about" 98% in one test and the exact opposite in another test is an exercise in futility and wasted time.

The key is bullet placement.
In other words......... being able to put the bullet right where it hurts.

The difference between the 125 grain and 158 grain, or any other modern premium defense ammo is negligible and totally a non-issue.
While the ammo buffs can argue endlessly about which load is better, the difference is so small that in the "real world" the person getting shot won't notice any difference at all.

Bottom line: Pick a premium American made defense ammo that shoots reliably in THAT particular gun and use it.

That way, you can get on with MUCH more critical arguments, like which is the best lubricant to use.
SkagSig40  [Member]
4/15/2007 2:47:27 AM
I think I will just stick with the 158gr to keep wear down. Probibly carry 158gr Gold Dots too.
Paid Advertisement
--