Tight cylinder throats

[Rex]

My S&W 686 is a barrel leader! Not being very smart I imagined a dozen things that could cause it. I'd like to shoot a light load with cast bullets and Unique but that is a real bugger on the barrel, even the 358156 GC bullet will leave slight lead streaks that follow the top edge of the rifling.
So yesterday I loaded some with 12.5 grains of 2400 and after a dozen rounds the barrel was clean (yes a dozen shots would lead it). Now that load isn't hot but enough more poop to swell the bullet and seal the bore. I'm cheap and hate to burn 12.5 grains powder when 6-7 will do it.
The down side of opening the throats is that I'm not sure how many moulds I have that drops a bullet big enough to size .358. May have to ask Santa for a custom mould next year. Mr. Keith told me once that 2400 burned cooler than Unique and that would stop barrel leading by not burning the bullet base, I'm not sure if it burns cooler or just gives the bullet enough more whack to bump it up to size. That was before he or I figured out that Ruger cylinder throats were bored to no particular relationship to the bore diameter in their .45LC revolvers.
THE FUN GOES ON!

 

[Brad]

If you ever make it to the Bellevue area stop by and we can ream those throats. My wife’s 686 was a leader too. Reamed the throats and lapped the forcing cone and no more leading.
We actually should meet up in Lincoln with 358156 as I believe he has the Brownells forcing cone reaming setup. We could fix that revolver in a single stop.

 

[462]

Super cool!

 

[Rick]

Yep, throats should be reamed it sounds like even though you didn't mention any sizes. That the bullet base will melt or burn or whatever you choose to call it is simply an old wives tale. Not enough heat for a long enough time to melt any lead on the base of the bullet. If the heat from the burning powder could melt the lead ask yourself this . . . Why doesn't paper shotgun wads burn?

From the drift of your post with no throat measurements given it's like the throats are too small. When they are it doesn't matter in slightest what you size your bullets to in an attempt to "fill the bore" THEY WILL BE THROAT SIZE when they exit the throat. Revolver throats are the best bullet sizers ever made.

 

[Rex]

My Chinese micrometer says a lead slug driven through them are .357. I don't have equipment to measure the bore. Many years ago, when I was starting, the popular rumor on the net was cut a Styrofoam plug out of the bottom of a grocery meat tray and make a "soft check". I tried that and It never helped but it also never scorched during firing. I learned a bit there.

 

[Brad]

.357 is a bit tight I would bet.
Can you get a photo of the forcing cone?

Look at the photos I posted in this thread. That rough as hell forcing cone scraped lead off the bullets and lead to leading issues. The tight throats didn’t help matters.

Revolver leading

Here are photos of the muzzle and a couple different areas on the forcing cone. Holy crap is that sucker rough! Anyone know what angle S&W uses on forcing cones? I need to turn a brass lap and smooth it a bit. I also looked and have 200 358 Hornady XTP on hand.

www.artfulbullet.com

 

[Brad]

Look at post 82 in that thread and you can see what a couple minutes of work with lapping setup, some silicon carbide in grease, and a drill can do.

That revolver doesn’t lead at all now.

 

[fiver]

357 isn't all that bad if the barrel is too.
I'd be using 358 bullets [shrug] that's the only 35 cal size die I have anyway,,, so that really narrows things down for me.

 

[Rick]

.357" throats are good as long as they are uniform .357" in all throats AND if the groove diameter is .357" or a tad smaller. Should the groove diameter be any larger at any point along it's length it doesn't matter in the slightest if you size .358" - .359" or whatever, the bullets will be .357" when they exit the throat. Then 357" bullets in a larger groove diameter bore will have blow by causing the leading.

 

[fiver]

exactly.
you have to look at the whole funnel, funnel, pipe system to see where or if your having the problem.
it could be as simple as one chamber...