I have been having a leading problem in my Contender 357 rifle and someone suggested that I try a soft check. They specifically suggested CF Ventures soft checks but CF seemed be out of stock and anyway we bullet casters enjoy making stuff ourselves.
The CF Ventures check began life as dental wax but was "improved" over the years. Dental wax is nothing special.
The logical thing would have been to make the soft check out of my bullet lube, Rooster HVR. Only problem is that HVR is out of production and my supply is dwindling. However, I did have a partial stick of Rooster Zambini, a cousin to HVR that was formulated for commercial casters. HVR is tacky while Zambini is waxy because commercial casters don't like sticky bullets. I had tested Zambini previously and found that it was a better than average lube but not as good as HVR, hence I had the partial stick of Zambini laying around.
My first thought was to use a tortilla press to squeeze Zambini into a thin sheet. A tortilla press would probably work with some lubes but it was no match for Zambini. So I switched to a rolling pin and that got the job done though it was very hard. If I had to do it over again I would use my 20 ton shop press and 2 wires to control the thickness. As it turned out my hand-rolled soft check was about 0.050" thick.
To use, press the sheet of soft check over the case mouth, then load the bullet on top of the check.
One question I had was "how will the soft check affect velocity?" On the one hand, it reduces powder space which should increase velocity. On the other hand some powder energy is probably consumed in melting & vaporizing the lube, tending to reduce velocity. So it could go either way. In my test the two opposing tendencies seemed to balance out because velocity with the check (1982 fps) was about the same as without the check (1984 fps).
Did the soft check reduce leading? Yes, it completely eliminated the leading problem I was having with the test load!
Unfortunately, accuracy deteriorated and velocity variation doubled. The doubling of the velocity variation by itself was enough to make me lose interest in the soft check, so I will not pursue it further at this time. Perhaps if I tried 50 different soft check recipes & thicknesses I could eventually find one that fixes the leading problem without hurting accuracy or velocity variation, but right now I have more interesting projects to work on.
Have you had any positive experiences with soft checks?