The Laser Cast bullets are .358 and if your throats are larger than that you could see some leading. Harder bullets don't obdurate as well as softer ones to fill larger throats. Ruger GP-100's generally have throats right around .357 to .358 so you should be okay.
A really quick way to clean leading is to just shoot a few jacketed bulles through the revolver and is my favorite way to clean out leading.
A less favorite way (much less favorite) is to get a brass scrubbing pad, cut several long strands off of it and wrap the strands around a standard .357 bore brush so it's a fairly tight fit in the bore. The brass strands won't hurt the bore but will cut the lead out efficiently - but not as efficiently as three or four jacketed bullets.
