Advice sought after a long journey

[longfellow]

A couple months ago I purchased a new flat top blackhawk in 44 Special, intending to work up a cast load. After two months and spending nearly what the gun costs I am no closer to finding a non-leading, accurate load; the short version of the story with a final request for help;

1.Bought the flat top and subscribed to this forum intending to find advice on getting a lead-free load for tin can and paper punching. The gun would be used to shoot all lead exclusively.

2. I tried many commercial cast bullets (.430-.431) with a medium (800-900 f/s estimated - no chrono) load of 7 gr Unique - barrel leaded badly (Incidentially I have stuck with this load throughout this saga for standardization purposes).

3. Slugged the barrel (.4294) and pin gauged the throats (.433 and all very consistent). Based on recommendations here, ordered some .432 / BHN 12 / 200 gr bullets - barrel leaded badly (forcing cone and about a half inch beyond).
4. Had FC cut to 11 degrees and polished (surface finish is comparable to the bore I would call it.) based on recommendations here. Same .431-.432 bullets leaded barrel (maybe the leading now extended only about .25 inches past FC). By leading, I am always referring to it appearing within ten rounds. This is my benchmark after which I swab out and inspect carefully. Also had timing, alighment, crown, cylinder gap checked as well.

5. purchased a bottom pour pot and a custom mold (based on recommendation... You get the picture) to cast oversized bullets to fit tightly in throats. Loaded and fired .433 to .434 bullets cast of medium hard scrap. Since they no longer slip in throats I seated them to just touch the transition area in the cylinder so they get swaged to fit throats upon firing. The bullet is a custom tumble lube design from Accurate (You can see the design as it is now in their on-line catalog - the 220 gr tumble lube wadcutter), lubbed with Lee liquid Alox. Results? Leading of course.

So after spending far more time and money on this project than I anticipated I am no closer to an accurate (I am not even at the point where I am testing for accuracy), lead-free target load. I realize that I am going back to the same well that led me down this path but I genuinely do believe that the advice given here is honest and well-thought out and comes from much experience and personal success so that's why I am comming back to the source to once again ask for input (but don't you dare tell me that I am in need of a custom cylinder).
Thanks all,
Ed

[mehavey]

FIRST:
Detailed fit to the throat/bore is best described is here, and (even after what you've already done) is considered the primary factor in leading:
http://www.lasc.us/Brennan_2-2_BulletDesignFit.htm
Note that sealing the throat with the base while simply riding the bore with the nose is given as key to performance. That said, and thinking that the pin gauged throat measurement might be a thousandth-or-so off. I'd size to .436+ and try that next. At least "sealing the throat" would be put to the test/eliminated.

Barring such a throat sealing problem, I am at a loss as to why a < 900fps load would lead a barrel as you describe even when using the BN-hardness numbers (~12) you report.
(See http://nhunting.com/forum/topic/5765...-lead-fouling/ for some informed discussion which you may already have looked at. ) As an aside, have you got and/or access to hardness testing equipment or a Lee Hardness Tester? This might at least give you real data as to what you are actually firing:
http://www.midwayusa.com/viewproduct...tnumber=731364

BTW: The BN-12 material is softer than Lyman recommends as their #2 alloy:
Lead is BN 5-7
Lyman#2 (5/5/90) is ~15 (Tin/Antimony/Lead)
Linotype is 22. (Allloy 8/8/84 is also 22)
‘Hardcast’ alloy 2/6/92 BN15-16

Antimony drives the hardness.

Even here there is a bit of black magic involved due to cooling/aging/heat-treating effects involving antimony. As noticed in other forums, plain old wheel weights (my own standard for about 30 years) are about:
- 8 BHN immediately after casting and air-cooling
-12 BHN about 2 weeks after casting with air-cooling
-14-16 BHN in about 2 weeks if tin is added to the mix and air-cooled
-18-30 BHN if water quenched
-25-35 BHN if heat-treated in an oven and water quenched.

The end-all/be-all discussion of cast bullets and hot velocities is probably found here:
http://www.lasc.us/CastBulletAlloy.htm
Note (again) the emphasis on bullet fit to the forcing cone/bore as the primary disriminator for leading.

As far as general cast fit & function, Lyman's Cast Bullet Handbook is a library requirement.

[Unclenick]

Is that one of the Lipsy Bisely's you got? I've been itching to get one for some time.

First, even in a perfect bore I usually get lead traces just ahead of the throat. That's where the bullet is when the pressure is highest, so the most friction with the bore due to bump-up occurs there. The good bore reaches an equilibrium with those traces, though. That is. It stops building up and gets no worse, as it seems to be blown out as fast as it is created.

Detail how you slugged the bore. Did you use truly pure lead so you could feel constrictions? A cast bullet alloy is too springy to let you feel those. Did you feel even the slightest constriction where the barrel screws into the frame? That's a common leading cause in revolvers. If you have that you need to hand lap or firelap the bore to clear it. All barrels with such a constriction will lead.

If you have no constriction, polishing may still help. Wrapping a couple of patches around an undersized (.357) bore brush will usually fit fairly tightly. Load the outer patch with JB Bore compound, and give 50 short strokes back in the area that leads and a few all the way around the tube. Follow that by doing the same thing with Flitz.

Sizing bullets right at or half a thousandth under your throat should be about ideal. You can test this later by testing accuracy with them. The bullet that gives you the best groups are the best fit.

Other measures: The polished bore can be degreased with brake cleaner, then plugged with a Neoprene stopper at the muzzle and filled with Sprinco Plate+ Silver and let sit for three days. This puts a semi-permanent lube in the bore that helps prevent lead sticking.

Another item is the P-wad. NECO sells these, but charges a lot for them (a nickel each). You can buy a wad punch and 0.060" LDPE sheet and make your own for less than a cent. Buy a bag of 100 from NECO (scroll down, here) to try them out, but rolling your own is far cheaper for volume, especially with a press mounted die. NECO's insertion tool works well, but is a luxury and not required. P-wads pretty much stop leading, IME. The act as a gas check and a heat shield and a bore sealer.