Montero who used to post here had failures through overexpansion with 120gr 6.5mm speers.

Bullets have a very hard job to do. We want controlled expansion across a broad range of velocities and that is extremely hard to acheive.

The impact velocity on sierra prohunters is quite important from my field testing.

I find fallow tend to stay on their feet longer when I shoot them at longer ranges with my 7-08 and 140gr pro hunter (MV 2,800fps) and expansion is reduced. No problems even on reds at 30-50yards but it is quite a bit more substantial than a 120gr 6.5.

With the 150gr 30cal pro hunter I found the results good but slightly soft out of my 30-06 (2,850fps MV) and excellent out of my 308 at 2,630fps MV until I passed 175yards at which point fallow stay on their feet a lot longer. By 220yards it's initialy as if they haven't been hit and expansion is nearly zero. If it's a roe at 200yards the bullet acts like a FMJ. I had one doe walk away, look at me, walk off and expire 10minutes later - absolutely zero expansion.

I generally think that the 'industry standard' for calibre bullet weights is a place that you depart from at some risk. You can do things to reduce the risk (bullet construction, shot placement, species etc) but the risk is there never the less. Even sticking to the industry standard is no guarentee.....

One of the reasons the ballistic tip is so good is even if they fail (and they don't nearly as often as people say) the remaining jacked has enough mass with it's solid base to go quite a way.

Bet a 140gr sierra doesn't drop much trajectory given it's great BC!

I have shot six large whitetails with a 6.5 swede and 120 grain bt and sierras from 20 to 160 yards none of them exited, but they all fell within a few feet. I too am thinking of going to a tougher bullet