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mehavey · December 21, 2010, 11:53 AM

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.

December 21, 2010, 11:53 AM	#2
mehavey Senior Member Join Date: June 17, 2010 Location: Virginia Posts: 7,207	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. Last edited by mehavey; December 21, 2010 at 12:32 PM.