Using cast bullets at what velocities does lead fouling start to be an issue?

It depends on the lead alloy but by 1800fps, you can expect leading to accelerate with most alloys.

George
P.S. That is based on posts by others, not my own experience.

With the right techniques it is possible to get velocities over 2400 fps without leading. The chief cause of leading is gas blow-by around the bullet. Preventing this blow-by will greatly extend the velocity any cast bullet can reach. The commonly held belief that if leading occurs you need a harder alloy has been proven false - in many cases at least. The bullet has to be soft enough to slug-up in the bore upon firing to seal off any gas. If the alloy is too hard it will not slup-up at the specific chamber pressure, gas will bypass the bullet and leading will result. Going to a softer ally would solve the leading in that instance. Higher pressures require harder alloys.

in the 1990s Cast Bullet Association members achieved 2400+ fps with cast bullets by filling the case with a solid filler like CoW or Grex. This kept the gas away from the bullet while it was in the bore and allowed high velocities without any leading. Accuracy was not stellar at first but further development improved on that.

But all that said, for the average cast bullet shooter 1600-1800 fps is the normal upper limit.



.

Gas checks will help.

Thëre are a number of things that must be taken into account when talking about leading.

The fit of the cast bullet and its design is first in importance along with the alloy, + or - gas check, the lube and the powder choice. A slow powder allows a "softer" start and engagement in the barrel. Then the is the barrel twistto consider.

I run 50/50 ww/Pb at 1900fps without leading because the boolit is sized to fit correctly both on the drive bands and the nose.

I also run a soft nosed boolit in my 7x57(65gn 50/50 soft nose on a 100gn lino rear) at over 2400fps and get good hunting results and no leading.

I have run HT ww to nearly 2500fps in my 404, and there are those on the Cast Boolit forum that runsmaller bores up to 2700fps, and they look at all the aspects from case prep right through the aspects noted above plus there is paper patching where jacketed velocities are obtainable

.........Just the same as any specialised area of the shooting game there are entry level and advanced techniques that can give so much more than is generally excepted.
Have a look at this forum.

http://castboolits.gunloads.com/


Von Gruff.

Cast bullet recipe that WORKS! No leading at 2400fps in 416 Rigby. Use same loads as for jacketed bullets!
1. 410 gr REAL Linotype alloy- water hardened, cast 0.001 over bore size. Not sized! Flat base bullet no gas Check.
2. SPG lube all grease grooves.
3. Tuft of Dacron between powder and bullet.
This combo has worked in EVER shallow groove modern rifle I've ever tried it in including Marlin Microgroove barrels.
Try it it Works!-Rob