It has been very interesting to hear from people using mono bullets, the variances in on game performance. Some have used them exclusively on game with great success, while others have had some very bad experiences with them.
I have only taken a few animals (4) with them in various calibers so cannot say conclusively either way yet. Fortunately, my experiences have been positive to date.
What I can say from personal experience and from what others are saying, is that your rifle will either love 'em or hate 'em. There doesn't seem to be much middle ground with them.
Best for accuracy has been in a 6.5x55 and a 416 Taylor, and had good accuracy in 300 WSM and 358 Win as well. On game performance has only been in the 6.5x55 on 3 deer and moose with the 140 Barnes X Bullet. No DRT, all went 15 to 80 yards. Not that different to a cup and core bullets performance. The moose took a finishing shot (probably did not need it, but did not want it to make it into the creek), the deer were one shot harvests.
What I can say is that the Nosler AccuBond has become my favourite hunting bullet, since first introduced, in all of the calibers that I have tried them in to date (270 Win to 376 Steyr. the 6.5's and 25 cal are looking promising so far, but have not yet been used to harvest game). They are the easiest to work up good loads for, consistently the most accurate bullet in the rifles that I have tried them in (MOA and better), and have given consistent, great on-game performance (double expansion and 90-95% weight retention of recovered bullets on a variety of big game from antelope to bison, from 15 to 354 yards).
I have also had great success with the Nosler Partitions, Sierra Game Kings, Speer Hot Cors, Hornady Interlocks and Winchester Power Points.
At the end of the day, if the hunting bullet it shoots well in your rifle, use it in the field on game. If placed properly, it should harvest your animal just fine.
If it doesn't, try to determine if it was bullet failure or poor placement. Be honest about the bullet placement. Did you have someone else watching and witnessing your shot? What did they see? We have all made shots we thought were good, but our companionshave called otherwise, or video has captured and can verify. We all try to be perfect in our execution everytime, but are not perfect 100% of the time. Pulled shots, mistaken range estimation, animal moves, wind changes, etc. So many variables in the field!
But an isolated incident does not necessarily mean that the particular bullet make and model is going to be the problem. It could be an isolated issue. Manufacturers spend plenty of time and resources on R&D before bringing a product to market, and I think that we have some of the best products available out there today. Repeated failures will be the true test, but who wants to have that on game in the field? (I know I don't!)