Forcing cones and spitting

[ezb57]

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!

.

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.

.

Thanks for your great reply. I used clay to get an impression of the FC and then carefully measured that. I feel that this was quite accurate.
Until I can rule out cylinder misalignment, I will hold off on any attempt to alter the FC profile and finish.

Thanks again

 

[WR Moore]

If your measurement was accurate, that cone is actually too small. I measured a couple of J frames available. A 36-1 measured about 0.367 or a tad larger, a model 60 that I reamed because the original cone was uneven, is right at 0.367 in.

Why don't you use the top tips on your caliphers to do a direct measurement of the ID of the cone?

 

[Protocall_Design]

It actually wouldn't hurt anything if it was .380. I usually try to get in the .370 to .375 range.

 

[ezb57]

If your measurement was accurate, that cone is actually too small. I measured a couple of J frames available. A 36-1 measured about 0.367 or a tad larger, a model 60 that I reamed because the original cone was uneven, is right at 0.367 in.

Why don't you use the top tips on your caliphers to do a direct measurement of the ID of the cone?

I did first measure directly, but it was a weird angle and keeping the tips at the very edge was tricky. This seemed much easier.
I called Brownell's and was told that range rods will back in stock at the end of this month if anyone else is interested.
If there is no alignment issue, I may try a 5-degree cutter to clean this up. Thanks again.

 

[WR Moore]

It actually wouldn't hurt anything if it was .380. I usually try to get in the .370 to .375 range.

There's really not a heck of a lot of metal in the barrel shank/tenon. I tend to be a wee bit chicken on J frames. N frame, no problem.

 

[Protocall_Design]

Just making the forcing cone longer won't really help. If it's spitting, it's getting shaved off on the back edge/corner. Maybe in this case fine tuning the cylinder alignment would be the most beneficial. It looks like that is what the OP is working towards.

 

[minconrevo]

Just making the forcing cone longer won't really help. If it's spitting, it's getting shaved off on the back edge/corner. Maybe in this case fine tuning the cylinder alignment would be the most beneficial. It looks like that is what the OP is working towards.

Over vigorous use of a forcing cone cutter can lead to cracking/splitting of the cone. How thin is too thin will vary with frame, barrel, and ammo used. Checking cylinder alignment first is a must.

 

[Sgt. Buzzard]

WR Moore, above mentioned in his first post checking the yoke. Old J frames are sometimes subjected to Hollywood pistol action. Snapping the cylinder open and closed is unhealthy for timing and cylinder/cone alignment.

 

[ezb57]

WR Moore, above mentioned in his first post checking the yoke. Old J frames are sometimes subjected to Hollywood pistol action. Snapping the cylinder open and closed is unhealthy for timing and cylinder/cone alignment.

I've had the gun since new in 1984 and I can assure you that none of that type of handling has taken place.

 

[BLUEDOT37]

Last try

It actually wouldn't hurt anything if it was .380. I usually try to get in the .370 to .375 range.

I'm of the opinion that a tad too large is better than a tad too small ("that's what she said" , The Office).

I'd also think that the wider F-C would be less stressful on the barrel than one smaller seeing it would allow the bullet to enter more easily at a glancing angle.

And as the cylinder gets more play in it as it wears that wider (within reason) F-C will still allow bullet entry better than a smaller one & with less shock.

I think .360" is too small of an opening considering bullet diameters of .357-.358" & the rotation play the cylinder naturally has.

With the hammer cocked notice how much the cylinder play allows misalignment between the cylinder's throats & the F-C & ask yourself if .002" difference seems good?

Again, if a fired 38 Special case (.357+.020+expansion) from that revolver can't enter into the F-C I'd say it's too small regardless of any other issues the revolver might have.

.

 

[ezb57]

Just making the forcing cone longer won't really help. If it's spitting, it's getting shaved off on the back edge/corner. Maybe in this case fine tuning the cylinder alignment would be the most beneficial. It looks like that is what the OP is working towards.

So, in this case a wider angle, such as 18 degrees would be better to increase diameter, and don't worry as much about the area just before the threads?

 

[Protocall_Design]

Yep, you need a bigger mouth to funnel it in. If most of it cleans up, that will help a lot. You can also do a double angle if you want, like 18 degrees to make it wider at the mouth and 11 degrees if that doesn't reach in far enough to finish it off.

 

[ezb57]

I suppose you could use all 3 cutters if you had enough material.
Reminds me of using different angle stones to move valve seats up or down when doing a valve job on an engine.

 

[Matt_X]

If you want to see if its ballpark in line, I basically just did this with my Victory using a precision 11/32" rod from McMaster.*
Its a .0005 to .001 under what seems to be typically recommended for 'service' but showed me what I needed to know.
I basically followed the information posted here http://smith-wessonforum.com/redire...tch-vs-service-range-rods.131321/post-1782295
and in Kuhnhausen.


*Tight-Tolerance Air-Hardening A2 Tool Steel Rod
11/32" Diameter which has good specs for how straight it is, which with a 4" barrel may be more important than a 2"

 

[steelslaver]

Cheap way to check cylinder to barrel line up. Get some of the heaviest bullet with a square base that will slide though you cylinder throats. You may have to get 9mm bullets for a 38 to have them move freely. Lay one in each chamber base forward. Close cylinder and with muzzle up slowly cock it and then slowly tilt the muzzle down. Does bullet base enter into forcing cone? How far? you could use a feeling gauge to make a light scratch to compare the dept it enters to the rest but if it enters freely cylinder alignment is good. Repeat on all chambers. I use a pin gauge instead of bullets..

Range rods are ok, but remember they can only be land dia, not groove diameter. A .346 rod or pin that will go down the barrel has a .01 tolerance all the way around before it will hang on the cylinder face

If I absolutely wanted to make sure a cylinder lined up perfectly, I would remove the barrel, install a threaded piece in the frame with a 357 hole in the center and use a .357 pin gauge to check each chambers alignment and then adjust it by slowly peening the stop notch for that chamber. No actual need for that. Maybe if I was making a 200yard silhouette gun. LOL