Forcing cone leading

[levernut]

Veral,
I have a custom Ruger flattop converted to 44 special.  The gun consistently shoots 1.00 inch groups at 25 yrds but leads badly at the forcing cone.  In only 10 shots with plain base or gas checked cast bullets, I have to remove the lead in the forcing cone area or accuracy falls off.  I shoot bullets from my LBT molds sized .002 over the throat diameter.  If I size them to slip in the cylinder throat, accuracy opens up to over 2.00 at 25 yards.  I have tried BHN 10 to 22, both plain base and gas checked, sized from .430 to .432, mostly with Hodgdon's Universal but also 2400 and H-110.  The leading is the same.  I slugged the barrel and the groove diameter measures .428 which seems a bit small for .430 throats.  I shot 80 lap loads thru this gun and the barrel is choke bored and very smooth.  Any ideas on why the leading?

[Veral]

What kind of bullet lube?
 
What type of powder and  what velocity range are you trying for?

  Your questions bug me, because I promise no leading with my bullets if LBT bullet lube is used, even with magnum loads.  I run my little Charter arms 44 special 3 inch barrel with 1150 fps loads, using my 280 gr WFN plainbase bullets and no trace of leading.  You should be able to duplicate that easily with your stouter gun. 
  With a LOT less painful recoil!

[levernut]

I use LBT blue soft exclusively and Hogdon Universal powder.  Velocity is 1080 fps and accuracy is great until the leading gets too bad.
The lead builds up on the corner at the start of the forcing cone, which looks like sprayed lead, not smeared.  It also builds up on the forcing cone surface and into the barrel.

[gcf]

The lead builds up on the corner at the start of the forcing cone, which looks like sprayed lead, not smeared.  It also builds up on the forcing cone surface and into the barrel.

Cylinder / bore alignment issue maybe? W/ throat diameter .002" over groove diameter, I'd bet that alignment could be off quite a bit, & still pass the range rod test.

[Veral]

  The standard way to check cylinder alignment is with range rods, but I find that pointing the gun at the sun, with my back to the sun, and barrel pointing at my best eye, hammer cocked,  CHAMBERS DOUBLE CHECKED FOR EMPTY, that the face of the cylinder is clearly visable on one side if alignment is bad enough to cause accuracy problems.  It will be very visable if bad enough to cause leading problems with the loads you are using.

  Your pressures with Universal are considerably higher than I was speaking of, as I was using H110, a far slower burning powder.  If you bullets are soft, like air cooled ww or even softer, the bases may be spreading out into the forcing cone after leaving the cylinder throats, causing an extreme drag, which could easily cause the leading problem.

  Tell me how hard your bullets are, or what alloy your using, and whether you water drop, heat treat or what, so I have an idea of what hardness you are using.   Perhaps going to H110 or 296 will be your solution, but don't do it yet.  I consider Universal the optimum revolver powder for a packing gun, as it gives less smoke and muzzle blast than any powder I've ever used.  You should be able to get your speed without leading if your bullets are hard enough.  20 bhn is plenty.

[levernut]

Veral,
This cylinder was line bored when converted to 44 spl. so I doubt there is misalignment.  I have shot a 4 shot group less than 1/2 inch c-c at 25 yards and lots of 5 shot groups at 1" at 25 yards which verifies the alignment.
 
I failed to think about too soft of a bullet for this load.  Most bullets are 50-50 WW-lead, air cooled which results in a measured hardness of 10-12 BHN. 

The buildup at the mouth of the forcing cone looks like lead is being sprayed.  Your explanation of the plain base being spread out too far makes sense.  I will shoot some hardened bullets to see if that helps.  Thanks.

[Veral]

  Please post your results.

  Perhaps unknown to most shooters, this spreading of soft bullets in revolvers with large forcing cones, as most if not all revolvers are made today, can split the barrel at the forcing cone if the lubricant isn't strong enough to let the bullet slide freely.  Hard bullets don't upset or upset very little, and creat far less forcing cone pressure.            Because they upset less or not at all, accuracy is almost always better than with soft bullets, IF the gun is set up right and bullets of the proper diameter to start with.