cylinder throat diameter, too tight?

[ripvanwinkle]

I purchased a new 686+ and I have been working up new loads searching for what works best for it. Its going slower than expected. I am looking now at the cylinder diameter. I have used the search function and suggested topics, but it doesn't get exactly what I need. I do not have gauge pins, but I do have an assortment of bullets. Bullets measuring .3570 (plated) are hard to push thru, but I can with thumb pressure. Bullets measuring slightly larger .3575 are a no go. All the information I have found reference lead bullets. I am interested in plated/jacketed. Am I correct in assuming .3570 and .3575 should give me more consistent accurate results.

 

[AtomHeartMother]

You didn't mention why your load work ups were taking time....accuracy I assume..
Sounds to me like the cylinder mouths are small, swaging your bullets down. I'd slug the barrel as well to see where it measures. Measure, measure and re-measure before you decide on anything though....then it may be time to see a gunsmith to ream the cylinder mouths. How does factory ammo shoot? Could pull a factory bullet, measure it and see if it presses through the cylinder too. Just by what you're saying, if any of the chambers are under .357, that's a problem.

 

[4barrel]

Your cylinder throats are perfect. Use a .357 jacketed or plated or powder coated bullet. I use a hard cast .357 lead but a .358 will work also. Dont go over 850 fps on soft lead. Hard lead @ .357 will go 1100 or so. Get a Lyman reload manual & you are in business. Get some Unique powder for 38s & 2400 or 4227 for mag loads to be on the safe side & stick to minimum loads with each starting out. Ask a question--lots of reloaders willing to help. Go to the bottom of the page for more info.

 

[ripvanwinkle]

Thanks for the responses. No panic button here. I am an accuracy nut. I compared the cylinder throat of this pistol to my very accurate Python. I can drop a .358 dia. bullet thru it and it rattles but falls thru. I have slugged a 9mm before and will do that as a last resort. My thoughts were if the throats swaged a large diameter plated bullet too much it could make the bullet unstable. But a small diameter bullet must be large enough to properly engage the rifling. I like reloading. I must shoot more so I can reload more!

 

[SMSgt]

Cylinder throat diameters should be equal to or greater than bore diameter. In general, they are slightly larger. Unless your cylinder throats are truly undersized, find the measurement of the largest and size your lead bullets to that.

 

[ripvanwinkle]

I changed up my searches and went to people that make their living working on revolvers to be more accurate. What I came away with was the cylinder throat needs to be .001 to .002 larger than the bullet. And the bullet needs to be the same size and the groove diameter.

 

[BLUEDOT37]

Ideally the throats should be .001" larger than the groove & the bullet .001" larger than the throats. That way everything is slightly squeezed down to seal.

.

 

[forestswin]

I agree with 4barrel
My 686 has .3572 cylinder throats and .3565 groove diameter


I shoot .357 lead mostly and get 1.5" or better groups at 25 yards on a bench

 

[Rule3]

I am interested in plated/jacketed. Am I correct in assuming .3570 and .3575 should give me more consistent accurate results.

If you are planning on "plated" bullets it is not going to matter. Plated are not very consistent as to any dimension or weight compared to lead of quality FMJ.

Have you even shot the gun yet? I would not dwell on the bullet(.0005) so much. There are so many other factors involved in accuracy.

Perhaps try some Coated lead bullets over the plated. Quality FMJ bullets are good also but expensive if you do not want regular hard cast lead bullets,

 

[cowboy4evr]

I have found over the years there is another " culprit " in shooting cast that needs to be addressed ? It's the " barrel to frame " fit . When they tightened down the barrel to index the front sight , over torquing the barrel will result in a " choke " right at that junction point . Tapping a lead slug all the way through the barrel is the only way to ck that .
Measuring the slug after it has just entered the muzzle and engaged the rifling to get the bore diameter and then again after it comes out of the barrel at the forcing cone , that difference will tell the results.

 

[series guy]

L frame Smiths are noted for their accuracy. You are talking about modifying a $600 - $800 gun but haven't invested $20 in a few pin gauges to get a true measurement of your cylinder throats. Not sure who you are putting your faitih in as far as needing the throats to be larger than the projectile but through much experimentation I've found throats one to one and a half thousandths smaller than the projectile to deliver the best accuracy when shooting cast Bullets. John Taffin wrote an excellent article on this a few years back. A goggle search should turn it up. Don't ruin a fine gun.

 

[noylj]

>Bullets measuring .3570 (plated) are hard to push thru, but I can with thumb pressure. Bullets measuring slightly larger .3575 are a no go

1) All the data is about lead bullets, because lead bullets must be sized correctly to the gun. Plated and jacketed are not that critical.
2) Personally, if you can push the bullet through and it is snug, that sounds perfect to me. A little bit larger bullet wouldn't hurt any.
3) The TARGET shows what the gun wants. Try doing some shooting (personally, I would say with real jacketed or cast lead bullets with cannelures and crimp grooves).

 

[fredj338]

In a couple rev with tight throats, I found leading & so-so accuracy. Opening the cyl throats to at least groove dia helped with both. Better slightly larger than slightly smaller. An undersized throat means an undersized bullet, never ideal for best accuracy IMO.

 

[Virginia John]

You may want to find a smith or machinist to lap your cylinder and make sure that each chamber is round and equal. That makes a big difference when it comes to accuracy no matter what bullets you use.

 

[fredj338]

You may want to find a smith or machinist to lap your cylinder and make sure that each chamber is round and equal. That makes a big difference when it comes to accuracy no matter what bullets you use.

Fortunately I have a friend with a machining business, specializing in ID & OD polishing.