686-6 2 SMALLER CYLINDERS

[forestswin]

When testing loads at the range, I consistently get 1 or 2 fliers.
This has been bothering me for awhile and frequently just test shoot out of 4 of the cylinders.
I finally got a high quality vernier micrometer (0.0001") and pushed soft lead through each of the cylinders.

This is a S&W 686-6 SS 6 inch bought new last year.
Cylinders measured: 0.3565", 0.3567", 0.3565", 0.3562", 0.3558" & 0.3548"

I also pushed the soft lead bullet 0.256" deep into the forcing cone and measured 0.3566"
I doubt if this forcing cone measurement is of much value, I need to get a wood dowel and slug the entire bore. But can I assume the barrel is 0.357" (0.3565" to 0.3574") for now?. I tried measuring the bore at the muzzle with the inside edges of a caliper, but the grooves don't seem to oppose each other so the measurement wouldn't be a true diameter, through the center of the barrel.

Am I correct that cylinder diameters shouldn't be less than the bore diameter?

Those last 2 cylinders diameters have me concerned. It could explain those frequent fliers. I've been numbering my cylinders for the last few months and refer to those 2 smaller cylinders as #5 & #6. In looking at some of my saved targets, sometimes they are way outside the group and sometimes in a little closer to the group and I know some fliers are all me, but I can see a pattern.

I'm no gunsmith or machinist or craftsman of any kind that's used to using micrometers or calipers and these measurements could be somewhat inaccurate, but I know "greater than" and "less than".

Any help, thoughts or guidance would be appreciated.

 

[OKFC05]

1. When you slug the bore, you can get an accurate measuremet by wrapping .001 shim stock tightly around the bullet, measure, and then subtract .002 from the measurement.

2. I would need a lot more information to comment on your "fliers." First, are they lead or jacketed. throat measurements are more critical with lead.
Second, what level of accuracy is involved, and what is the firing method? Have you numbered each chamber and recorded each shot from each chamber, or are you guessing? How far out are the fliers?

3. If I seem skeptical, it's because I've seen people shooting with questionable technique and guessing their accuracy must be the gun's fault.

 

[Engineer1911]

Put up 6 targets #1 to #6, fire 5 strings, #1 cylinder to #6 cylinder, at each target. You now have five #1 cylinder shot at #1 target, etc. Do you have 4 groups and 2 patterns? Or, does each target have flyers? Fire the 30 rounds out of the same box of ammo.

I did this exercise 15 years ago. I had 5 groups (acceptable size) and one ragged hole that was ~3/4" with 38 spl ammo. It wasn't just me, but the gun had a part in the results, also.

 

[Moonman]

A vernier is not the tool to measure the inside diameter of the firearm cylinder.

The accuracy of it depends upon a LEARNED FEEL and deflection occurs easily to give you an inaccurate reading.

Steel Plug Gage Pins are what's needed to measure holes with accurately, you can get sets relatively cheaply.

You want the .0002 MINUS SIZE GAGES. The sets are also available in PLUS .0002 sizes.

Google GRIZZLY. com, they have 250 piece sets ( 2" long, the size is laser engraved) from

.251 to .500 at .0002 minus size for $63.25 plus shipping. Other sized kits are available too.

It comes in a plastic 17 x 12 x 3 carrying case.

All serious revolver shooters should have a set of these.

Small Hole Gages and a Micrometer is another method to measure accurately with. (provided you have the experienced feel of a machinist).

You cannot directly read the S&W barrell groove diameter as you found out, the grooves are an odd number and not OPPOSITE each other.

You are also correct that the cylinder bores should not be SMALLER than the Barrel Groove Dimensions.

A gunsmith can ream them out larger if this were to prove to be the case. I think you may possibly have mismeasured with the vernier.

I would not attempt to measure to 4 decimal places with a vernier, even after 40 years in the machinist trade.

Better tools exist to make that measurement.

Good Luck with your choices, and it does look like your records indicate a problem with two cylinder holes, just how much.

 

[forestswin]

1. When you slug the bore, you can get an accurate measuremet by wrapping .001 shim stock tightly around the bullet, measure, and then subtract .002 from the measurement.

what size bullet do I use if I wrap shim stock around it

2. I would need a lot more information to comment on your "fliers." First, are they lead or jacketed. throat measurements are more critical with lead.

all lead

Second, what level of accuracy is involved, and what is the firing method? Have you numbered each chamber and recorded each shot from each chamber, or are you guessing? How far out are the fliers?

see my range reports (with pictures) as to the level of accuracy and shooting technique
in "Range Report W231 & 148 DEWC" last reply dated 8/31 all shots were fired with cylinders #1 through #4 only

in my Range Report with Hornady 158 last reply dated 8/7- in the second picture the #6 cylinder is the one up and to the left - I did not document that - but I vividly remember the last shot messing up the group - again it could have been me!
yes I numbered cylinders with a sharpie and yes I have other targets showing several shots for each cylinder on their own target - #5 & #6 are not consistent with the other four

3. If I seem skeptical, it's because I've seen people shooting with questionable technique and guessing their accuracy must be the gun's fault.

the "fliers" were much more prominent with Laser-Cast 158 LSWC. When I switched to softer bullets - the groups are much better

I can take pictures and attach other targets - but the question remains do the cylinder diameters alone raise any flags???

 

[forestswin]

Put up 6 targets #1 to #6, fire 5 strings, #1 cylinder to #6 cylinder, at each target. You now have five #1 cylinder shot at #1 target, etc. Do you have 4 groups and 2 patterns? Or, does each target have flyers? Fire the 30 rounds out of the same box of ammo.

I did this exercise 15 years ago. I had 5 groups (acceptable size) and one ragged hole that was ~3/4" with 38 spl ammo. It wasn't just me, but the gun had a part in the results, also.

Engineer1911 - I've done that, but that was before I improved my bench technique - so if I have to go to the range and shoot my gun some more for a few hours. I'll do it! But I'm not shooting factory ammo - I have a good load. I'll report back in a few days with pictures.

 

[forestswin]

vernier?

Moonman

I'm a little confused, I used a Swiss made Brown & Sharpe Convertible Thimble Micrometer to measure the slug- that was pushed through cylinder. I thought that was how it was to be done. it has a friction thimble - I think it stops at 1.4 pounds and when I checked into it I thought I read about a vernier micrometer is the recommended way to measure to 0.0001" I got this one because it was a good deal at a gunshow, not necessarily because it was that accurate.

Either way, I'll take your advise and get the Gage Pins - I am not a craftsman and realize that I can not just learn something like that by reading about it. I will however need to learn how to use them for measuring the amount of crimp. I'll deal with that later.

Might it be a good idea for me to call Smith & Wesson? I do not know any revolver gunsmiths. I haven't found any yet that do more than install scopes, stock work, bluing, etc.

 

[OKFC05]

Based on your added information, here's more comments:
1. When you slug the bore, use soft lead to make it easier to push. Take the piece of lead you just pushed through the bore, wrap the shim stock around it, measure it, and deduct twice the shim stock. That gives you the actual bore diameter for a barrel with odd number of grooves/lands. Until you get your actual bore diameter, you're just guessing.

2. The cylinder has 6 chambers, and what you measure are the chamber throats. Ideally they should be all the same and a touch over bore size for shooting lead bullets. A little variation between throats is often not significant.

3. We have not addressed the problem of hard lead bullets that are undersized or have inconsistent sizes which is near the top for poor results shooting lead. If you have some bullets that shoot consistently out of the revolver, and some don't, that raises the flag that you have a bullet problem more than a throat size problem.

4. Finally, it is pointless to guess what the problem is, when the answer is to measure everything-bullets, throats, bore- and see what you really have.

5. I cast Lee TL148gr WC and shoot them unsized over 3 gr of HP38 in .38 Spl cases, which gives groups at or near one inch in my various S&W revolvers.
I have bought commercial nominal .358 bullets that actually varied down to .356 and produced erratic groups no matter what revolver they were shot in.
Like I said, undersized bullets are a common problem.

 

[Titegroups]

Try the gauge pins, you can also buy them individually from most industrial suppliers, the throats must be very clean before checking. It takes a lot of feel to get good measurements down to tenths. Check out cylindersmiths website if you decide to ream the throats.

 

[Moonman]

forestwin,

Misunderstanding on my part.

Vernier jumps out and means a vernier CALIPER not micrometer to me.

Reading a micrometer down to .0001 measurements is a gamble at best due to feel, ambient air tempreture etc.

Plug Gage pins are nice.

The big 250 piece set is nice, and a steal at $63.25 (Grizzly.com) as individual pins from a tool dealer may be $6 or so EACH.

Measuring everything and keeping records helps you to arrive at an answer.

 

[forestswin]

0.355" bore diameter?

OKFC05, Engineer1911, Moonman, & Titegroups
Thanks for all your help so far!

Cleaned the gun real, real good and slugged my bore. Beating a lead weight, thats bulbed out the end of my barrel is not fun. Its like watching your kid in the dentist chair.

Anyway, I didn't have shim stock. I was thinking about using the thinnest gauge from my spark plug feeler gauge but it was 0.005. So I took a piece of aluminum foil and scraped it flat with a razor - it measures 0.0009" and wrapped the slug. Measured 0.3564" with many trials - thats the maximum. Locking in a setting of 0.3563", the slug would not turn completely around within the micrometer opening. For a setting of 0.3564", it would. Subtracting out 0.0018" gives the bore diameter of 0.3546" - say 0.355".

You all are correct, this will take learning some skills. I won't make any decisions on these measurements. But I will keep working with it.

I checked Grizzly for the plug gage pins - they are currently out of stock. I will keep checking on them. To check the CHAMBER THROATS for now, I dropped the bore slug through each chamber. 1 through 4 dropped right through. Chamber 5 barely got held up- but came through with a little touch. Chamber 6 however had to be pulled through - but with very little resistance. My guess is when I get the plug gauge pins (-.0002), the 0.356 plug will not fit chamber 6.

I am thinking about getting the Starret Small Hole Gage set, instead of the pins as I continue to look for a gunsmith that can do this again to make sure its done correctly. Also, when I find one, I won't watch.

I will still document several rounds through each chamber /per target with pictures and start a new post. That's the fun part. Please check back.

I didn't expect the bore to be that small.
Is this bore diameter (0.355) good? okay? Will it affect accuracy for 0.358" hard cast and jacketed bullets?? And if so, how?

Titegroups - cylindersmiths website say he doesn't do 38/357 anymore! only 45's

 

[rkrcpa]

It sounds like the problem could very well be small throats. Rather than buy a whole set of pins (shipping is expensive) when I only need a handful, I ordered individual gages from McMaster Carr for about $3 each. Shipping was about $5.

If you do indeed have a small throat you will need to address that problem no matter what so I would start there. If that fixes the problem the actual bore size becomes irrelevant.

I didn't buy sub-caliber pins because I don't need to know how small the throat is, I just need to know it is small. Big however is another story. I need to know the size of the throat to select the proper cast bullet size hence the larger than bore size gages.

I made up a little box to store them in also.

 

[forestswin]

Rkrcpa
Thanks for the info – I've got myself into this measuring approach kick – to get weights and dimensions – and I want to see it through – I'll check into these individual gauges

I will end up buying more guns – and I'll want to get to know each of them - so I'll end up needing the right tools anyway.

For right now, I am measuring the variances in weight and diameter of a box of 500 DEWC's . This is going to take awhile!
I am also waiting for a guy to send me some 0.001 shim stock to correctly measure the groove diameter slug.

OKFC05 said to measure everything – so there is no guessing. I agree with that – it makes sense. I take it when a moderator takes his time and jumps in and gives out advice that I asked for – I should follow it.

I see you are in SE PA – I'm just over the MD line in Harford County - do you know any good revolver gunsmiths in the area?

 

[rkrcpa]

I bought gages for the calibers I own working under the assumption that I won't be adding any new calibers. If I do add a caliber I'll buy additional gages then. I just didn't see the sense in buying 250 gages when I need 12. It would be different if shipping wasn't an issue.

Measuring all those bullets doesn't sound like much fun. If those wadcutters are fairly soft they should bump up to fill the throat and not present a problem (except in the throats that are sizing them down).

As far as gunsmiths, I've used Randy at The Handgunner up in Topton (Allentown area) a few times with good results. He did a DAO trigger job on a 696 that is an absolute delight.

Good Luck!

 

[mikld]

A lot of posts about the way/tools to measure throat slugs (I think your verniers should be accurate to within +- .001"). But from what I read in the OP, all the throats seem small; .356_". I like the cylinder throats to be about .002"-.003" over groove diameter, and on my .357 Mag. the throats measure .358 to .3585" and the groove dia. is .356" to .357" and I can shoot .358" lead w/o leading...

 

[Moonman]

My 250 pc set with the case was $73.25 and $11.70 shipping to Northeast Ohio from Grizzly.

Measuring closeness is close, +/- .001 is like throwing a cat through a basketball hoop,

we're not carpenters measuring 2x4's, we want real what's what dimensions to deal with problem solving.

This is not really the place for kinda close estimates.

Good Luck With Your Choices.

 

[GCF]

...To check the CHAMBER THROATS for now, I dropped the bore slug through each chamber. 1 through 4 dropped right through. Chamber 5 barely got held up- but came through with a little touch. Chamber 6 however had to be pulled through - but with very little resistance...

Good thinking! Sounds to me like what ever the absolute true size of your bore is, the diameter of your cylinder throats, are at least as large (Chamber #6?), or a bit larger. As they should be for CB.

Would it be more ideal, to have them all perfectly concentric at say 0.358"? Probably. Question is, assuming that you can find a qualified gunsmith who won't botch the job, is it worth the expense - if you can
modify your load, to eliminate the fliers?

For the record, Brownell's sells Manson .357 cylinder throat reamers, for around $80.00. Think this is the same tools most smiths would use for the job.

http://www.brownells.com/.aspx/pid=...ON/Product/REVOLVER-CYLINDER-THROATING-REAMER

 

[Walkalong]

It has been proven over the years that one chamber can be more accurate than the rest, or one inaccurate compared to the others. Me? I can't shoot well enough to prove it. A ransom rest will tell you.

 

[gunman1960]

i would shoot several targets, and get the ones that best show what your problem is. mail them along with your gun,back to smith,and tell them to fix it.
its best to keep your life simple.

 

[ArchAngelCD]

It has been proven over the years that one chamber can be more accurate than the rest, or one inaccurate compared to the others. Me? I can't shoot well enough to prove it. A ransom rest will tell you.

My thoughts exactly. Before you go buying hundreds of dollars worth of testing and machinists tools that you will use only for measuring and not repairing I also suggest you take the human factor out of the groups.