Joe, to sing the same song again, antimony in the lead mixture usually means a much harder bullet that takes higher pressures to cause it to obturate.  You are mixing apples and kumquats, since you mentioned in the past as well as on your original post today that you are primarily using gas check bullets in fixed ammo, and almost everyone else on this site shoots plain base bullets, most of them breech seated.  If you are running hard bullets at low pressures, the gas check helps keep the bases free from gas cutting, one of the primary causes of leading.  Plain base antimonial bullets at low pressure can lead because the bullet can't expand to seal the bore and the gas blowing by the base will cut it like a cutting torch, depositing lead alloy in the bore.   

I'm sure that others will expand on what I've said...

David

What about in .22's (higher velocity, usually harder bullets)?

Eley .22s (and probably all the others) contain antimony.
leading comes from undersized bullets that do not set up to fill the bore. There is a limit to how hard you can get a bullet with only a lead / tin mix, beyond this you must use something else, usually antinomy. Hence, leading has become associated with antimony---the real problem is undersized bullets. 
For many years, all my full bore bullets were cast from scrap salvaged from our .22 indoor range. I never had leading problems if I got the bullet dia right.
Fred

Our experience with plain base Lead/Tin bullets in 32 38 & 45 calibers is a different animal than small bullets at high velocity. 

Small has a set of problems all it's own starting with the difficulty in casting a good bullet. Anatomy may well help the mold fill out. As long as bullet fit is good and the base is covered by a gas check the hardness may not be a negative. I can't say as I go for Jackets when looking for high velocity in small caliber center fires . Cast 22's can do well have seen some with very good results. However it's not a easy thing to get shooting well.

.22 rimfires another completely different set of problems.  Factory loaded rimfires have to go through a mechanical process to seat bullets and no doubt need hard to run through the machinery.  .22 rimfires use heel bullets so bore fit is not the same as the bullets we use in Schuetzen.

Best advice for Schuetzen cartridges is avoid antimony

Boats

Joe, please re-read my earlier post.  I am not saying that ww or linotype or any antimony-tin-lead alloy can't perform well.  What I did say is that at the velocities and pressures used in our type of shooting, the harder bullets don't work as well as simple lead-tin alloys that obturate well at lower pressures.  Hard bullets either have to be oversize (raising pressures) or driven at high enough velocity and pressure to cause them to obturate and fill the bore properly.  I had this same discussion years ago with Roger Johnston, and he had a formula that would predict the pressure needed vs. alloy hardness to prevent gas cutting/leading.  Unfortunately, I no longer have that information...not all of my "stuff" was sent to me after Brownells let me go.    

David

Regarding the hardest vs pressure ration that David speaks of, Lee's Modern Reloading, second edition has a chart on page 134 that is suppose to tell you the hardness it takes for accuracy at a given pressure range. He sites evidence of that with groups but, the guys that shoot the small cases with heavy bullet don't fit his chart. It may work at the higher pressures with lino type alloys but not the lower pressure that we use. But then it may not account for breach seating.

Frank

Guys,

I agree with a lot that has been posted here, but have to add the following:

If you know your chamber and bore dimensions very well and cast/shoot WW bullets or antimony content bullets that are around .001 or .002" greater than the groove diameter, obturation is not required and leading should not be a problem at moderate velocities.  Therefore, I agree with Joe B's comment in his opening post "If I do it right, there's no lead fouling at all".  Remember, he said his velocities have not exceeded 1500fps

Now, based on my shooting experiments, when you start approaching 1600fps or there about, it's a different story.  I have found that around 1600fps and above gas checks are required to eliminate leading and reduce group size even if the bullet diameter is optimized for the bore.  Most of my experimenting with hard lead bullets was done with .45-70 bullets in either a Browning M1885 BPCR and/or a Marlin 1895.  In doing so I’ve pushed the velocities of a 405gr hard cast bullets up to around 1900fps.

At 100yds and velocities as low as 1600fps I had groups as large as 12”.  Approaching 1900fps the group opened up further to 14”.  Adding only a .030” wad reduced the groups to around 5” to 7”.  When I switched to gas check bullets (405gr also), using Hornady checks, the groups dropped down to 1.5” to 2”.  By the way, I was firing as much as 56grs of IMR4895 in some of the loads.  Both rifles handled the hot loads just fine although the Marlin recoil was teeth rattling.

Wayne