Miles,
I've have seen evidence of monos not tracking straight as it traverses through a critter. I can only speculate what caused it. I have also seen them fail to open, probably because of lower velocity. Don't get me wrong, I think monos do well, I have used them myself and witnessed their performance on critters quite a bit. If or when I use them in the future it'll be with confidence.
Casey
Well, out of right on 100 deer killed with monos, the majority of which were Barnes and maybe 10 were with both E-Tips and GMXs, I have observed, the worst deflection I have seen is maybe 20 degrees or so on a fawn double lung shot with a Barrnes 130 out of a 30-06. During that period I did see one Hornady Flex tip 160 grain out of a 30-30 deflect off a rib rid up under the hide, pass through part of the chops and exit directly above the spine. I have seen the same pre-mono days with cup and core bullets on several occasions, but in those same days a number of internal deflections, some of which were quite startling.
What gives me so much more confidence in the monos is along with the noticeable absence of deflection, the extraordinary penetration of bone without deflection. One particular doe I high shouldered at closer to 300 yards with a 110 gran .270 TTSX: Fist size hole in the onside shoulder blade, four ribs near the spine edgewise, a fist size chunk of spine removed from the bottom of the spine, two more ribs edgewise and a quarter size hole in the off side blade and then out. Spine and shoulder blade are not particularly hard, but they're still bone. Ribs are very hard and springy. For that bullet to traverse that much bone in a straight line is remarkable. The particular deer also had caliber size in and out holes in the hide which contrasted quite surprisingly with the massive internal damage.
