I'm using them in my long barreled (29") .260 AI with good performance, 2920 fps well under max, which was about 3000ish fps. I loaded the 147's to 3040 fps, but that was pretty close to max. I would say I loose about 50-60 fps at the same pressure to the 147, probably around 100 fps or or a little less to the 140 vld, which I was loading at 3070 fps at a near max load.
As far as ballistics compared to the 140, you will gain a little wind drift, but not much, only a few inches at 1000 yds. You will have more drop. Where you will gain is in terminal performance, more penetration and more energy over the 140. From what I have seen in the 4 pronghorn that it has taken, on game performance is just like the 140 VLD, only it delivers more energy. I have not tested it on elk or mule deer yet, but I will. If your hunting bigger mule deer or elk type game, I would absolutely switch to the 156. If medium or small deer are the biggest game you take, it's likely not worth the load development.
Another consideration will be your mag length. In my .260 AI that has the same standard SAAMI length throat a .260 rem has, with around 1500 rounds through it, I was at the lands somewhere right around 3.010" OAL, and I am running them at 2.950" to run in my ARC AICS mags, and they happen to shoot very well. If you have a standard BDL mag box, your max length is around 2.830", that is quite a jump, and a lot of powder space taken up. Just something to think about.
