Blackened Cells On Outside Of MM Cob Bowls

Starting with my experience in smoking cigars, I began my pipe smoking journey a bit on the fast side. I had only two useful pipes (briars) at the time, and I wanted to add a few more to my rotation as I experimented with different 'baccys without spending much, so I got myself a few MM cobs. From smoking the stogies I was used to vast clouds of smoke, and when smoking my pipes for that I got the heat and the gurgle in my cobs and briars which goes with it. The same mistake had been made for about as much time and intensity in my briars - they did get uncomfortably hot in the hand, but without noticeable damage either inside or outside of the bowl. The cobs all have blackened cells which show on the outside, although the inside of their bowls still appear to be even, with healthy cake. So, I'm not really sure if I was smoking either at the heat levels which would cause a briar to burn out - they, as much as my cobs got uncomfortably hot, and perhaps the fact that they did not "fissure" (as a newbie here recently put it), or burn a hole right into my hand was on accoun of my having smoked tobacco in much cooler cigar, therefore I understood this sort of heat could not be normal. I find it somewhat incomprehensible that one can smoke a briar past it's limit without the motivation of killing himself in one of the most painful ways possible, but here I am wondering if the beginnings of burnout on my cobs is evidence that I was close to doing that to my cobs. Or does cob have a lower heat tolerance than briar, thereby they are easier to burn out?
Also, I sort of wonder whether a few blackened cob cells isn't fairly normal, when the pipe still remains smokable. Does anyone who knows cobs find that to be inevitable for certain types of cob? By that, I refer to the difference between the highly porous and lighter weight white cobs, as opposed to the more dense dense stuff (so it feels apparent to me) of the MM Country Gentleman (which I later aquired, the other cobs in my collection are white). I'm more inclined to guess that different texture is a different cob variety as opposed to a different finishing style.

Thanks, you guys, for the insight and good advice.

Jonnyreb, Nope. My cobs are all MM. I actually went and combed the net for alternatives (I found the apparent lack of competition suspicious), and found few if any available at all. May have seen one which wasn't MM, and it looked like shit.
As noted before, the white cobs which MM makes their less expensive pipes with appears to be not a difference in finish. I see a difference in grain texture between my Country Gentleman and the stuff my Diplomat and Mark Twain are made of, plus the tighter grain of CG feels more dense, and perhaps by a lot. Not problematically so for weight, just noticable, and it's definitely more resilient to abuse than lower priced MM material. Does anyone have names for referring to these different cob materials?

Thank you, Huntertrw, that description sounds like the Country Gentleman cob material "large, dense, woody..", which is different than most of the MM product line. Most MM cobs such as the Washington and Diplomat are ordinary cob stuff, although still better than the Chinese crap.