For rifles that need to be cleaned fairly often, including at matches, long soaking is not an option.
I would not use a particulate cleaner with a bronze brush or for that matter a stiff nylon brush.
I learned to use IOSSO back in the day from published accounts of how Tony Boyer did it between every match , probably because the T powder that was using back then while very good in most respects, was bad about making hard carbon. (This it how the manufacturer suggests using their product, and I am sure that their way works just fine.)
Back then there were not stiff nylon bore brushes and the ones that were available were quite a bit softer. Dewey sells brushes that work for me for this application. They can be reversed in the bore pretty easily.
After my full normal cleaning, including brushing, I put on a nylon brush and fill it to the ends of the bristles for its entire length with IOSSO, and using a bore guide that has a separate bushing on the rod that plugs into the back of the guide, I work carefully being particularly careful to keep the rod straight and in line withe the bore throughout its entire stroke. I work over the throat with about 20 very short strokes, about 3" and then continue that stroking as I slowly move the rod farther into the bore with the same short strokes, to the point that I am half way down its length. Then I pull back and do it one more time from the beginning, and remove it and clean the bore, chamber, lug recesses, rod guide, bushing, and rod as many times as required to remove all of the IOSSO.
I find that a very light oil works better for this than a solvent. Then I finish with a couple of wet patches of my regular solvent, dry the bore and chamber, and lube the lugs and cocking cam.
Different powders will build carbon at different rates, as will different case volume to bore size ratios. The trick it to only do this as often as it takes to maintain accuracy, without overdoing it. More is not better.
This is where a bore scope can really come in handy. You can clean a bit, clean out the IOSSO and take a look. Once you know how much to clean during a session, and how often you need to with that powder and caliber, you will be all set.
The extreme other end of things is VV133. In my 6PPC I have been able to keep my barres clean with cotton patches, regular solvent, and bronze brushes without accumulating hard carbon. No IOSSO or JB is required.
A friend of mine who shoots LT32 in his 6PPC match rifle has settled on using IOSSO every hundred rounds or so, carefully. He has a bore scope. He is on his second barrel and has experienced no problems as far as throat wear or barrel life. The first time that he used the IOSSO, at my suggestion, he saw a small increase in accuracy, probably because he was well beyond his first hundred rounds with LT32 on that barrel.
LT32 is a fine powder, and having to do this every so often should not be taken as a criticism, nor should it deter anyone from its use. For less critical applications the frequency of these sorts of cleanings could undoubtedly be extended.
