This is one thing I was curious about. Many people gravitate to the heaviest option for the higher BC; but for middle ranges lighter offerings can sometimes have better drift #s. I hadn't bothered to run any #s through my calculator though, as I hadn't heard how effective the 129/130gr offerings were on large whitetail, particularly with high speed impacts.
Have you put many 6.5 129LRABs on target and seen the effectiveness yourself, particularly on shots that weren't broadsides through the ribs?
No, but if you'll hold a deer for me, I'll shoot it at whatever angle you want, point blank range from my 260AI loaded with 129gr. ABLR at 2800fps and I'll lay even money every time it dies a sudden death. Is there a possibility of failure? Sure, everything is a possibility. More velocity will probably make the bullets more explosive on impact, but this should be enough gun to cleanly kill regardless(on deer sized game).
But seriously, I've always used BT's and AB's. Hoping to use 129 ABLR with my 6.5 Grendel. What's the benefit of ABLR's over say AB's? BC and extended range, primarily from the bullet opening down all the way to 1300fps due to a thin jacket, right? So if you need to kill something at a range between 1800 and 1300fps theoretically the ABLR should be a benefit, provided your shooting something within the capability of the 6.5 with a 129 or 142gr bullet(meaning you shouldn't be hunting Cape Buffalo with this caliber/bullet combination generally speaking, right?).
Drift and high speed impact don't go together. If your shooting so far as to have a drift issue, your probably not dealing with high speed at that point, generally speaking, right?
For me, my 300wsm(Elk size game) shoots farther and with more energy for the game I'm after with 180 AB's than I can, so I haven't found a need for 190gr ABLR's yet(believe you me, I rely wanted to shot these, but the ballistics tell me I don't need them, plus my off the shelf Winchester twist rate may not like them, I know it likes 180AB's) Plus I believe it will hold up better at close range. Win/win. I like the performance I've been getting with berger 130vld's in my 260AI(deer sized game), but planning to change to 135 classics when I have enough casings. The 135's have a higher BC than the 129 ABLR and reach far enough for me, so again I don't need the 142 ABLR. Others needs may require the ABLR.
I said I was thinking about 129 ABLR's for my 6.5 grendel. Why? Here's my theory and it's only a theory. The 6.5 grendel needs all the help it can get to be effective at longer ranges. Because the ABLR's bullets will open down to 1300fps, I believe I increase the distance I can harvest a deer/coyote. At 2400fps it only carries 1,000 ft lbs out to around 375yds or so at my elevation, where it's traveling a little over 1800fps. This would normally be velocity limit for most bullets. Because the ABLR will open at slower speeds, I think I can get another 100 to 200 yards of effective performance. At mountain elevations this might be all a guy needs for mule deer. The other reason I'm thinking about the 129 ABLR for the 6.5 Grendel is because with only a 2400fps muzzle velocity, I shouldn't have a issue with the bullet blowing up at close range. It's traveling to slow. This is also my theory for BT's, they might work better in rifles that are velocity challenged, were they wont blow up at close range, and open easier at longer ranges.
Please note, this is generally speaking and theory based on my experience. There are always outliers, always. I know this probably doesn't help much with your question, but there are lots of guys on here with real world experience with the ABLR's that can give you their experience.
Food for thought, if nothing else.