You can keep on patching that bore with JB, and it will always come out black - that's the nature of the stuff.  And no, it isn't barrel steel....

Chris wonder if JB ever published a grit rating That would tell a lot. My guess is its 1200 or higher.  How would you tell, microscope comparing to a known rated compound ?

Boats

I've never used JB without it coming out back.  I think you could push 1000 patches through and the last one would still have black on it

Chris  I have used JB on(in) 100+ yr old rifle barrels with those softer steels: 1 Ballard, 2 Hepburns, 1 trapdoor, several military and also got seemingly disheartening results at first --  with more patches they came out lighter and grayer but never came out pure white. The bores were a lot more shiny afterword

My 32-40 has over 144,000 lead and tin bullets down the bore and fairly recently set a new ASSRA record in 2013. It as well as my fairly new 28-35SS barrel have always been cleaned using JB Bore Paste not the JB Polish and my patches have always came out clean. If there has been a loss in accuracy I have not seen it over the past sixteen years. I also feel it has maintained it or possibly even improved it by its use. Carbon if not kept on top of destroys accuracy and if let to go for to long is damn near impossible to remove as it gets as hard as glass and will eventually start building up in the bottom of the grooves and also quite typically it will develop a carbon ring that can clearly been seen by the naked eye just in front of the chamber. I also typically clean some where around having shot thirty shots depending on where I am at in the middle of match. Sometimes more sometimes less but I won't go beyond having shot fifty. I have also seen the accuracy start to drop off after only having shot around twenty depending on how hot the day 
is and I will then stop and clean before going to the next target and if not points will indeed be lost based on long term personal competitive experience. A close friend once stopped by his 25 quit shooting up to par from one day to the next. A carbon ring was clearly present and it took me over an hour of constant cleaning with JB before I got it out and the next day his accuracy returned to what it should be and a good lesson learned by him as not being one to clean very often.

JLouis

Well if John Louis says it worked for him then I'll have to get me some and try it. Thats proof for me.

So if the jb bore patch comes out black it is due to carbon present in the grooves?  I.E. it will come out clean/grey eventually?   I've never had one not come out black...hmmmm....