Something to consider, does the lighter bullet expand to the same diameter as the heavier bullet ? A heavier bullet will be longer than lighter bullet(calibre and design remaining constant).
from personal use, i have some thoughts.
in my 9.3x64, i am known for not being a great promoter of the 286 nosler partition.
the equivalent swift aframe on the other hand lets this gun realize far more potential on a broad spectrum of agme.
i personally do not rate the nosler as reliable on donkeys to give a guide to my thoughts.
30% of 286 is about 86, so reducing wt by this much brings the bullet to 200 gns.
cannot say what a monometal in this weight can do as have never tried one, and do not know of one.
if it is as good as the partition, in my mind it is still not much of a bullet, and only suited to light game.
this topic has however got me thinking about the 250 barnes for certain applications.
a good calibre to test this in would be 338 of various chamberings, due to a plethora of available different lighter weight monometals.
problem is you need to shoot a lot of animals of different sizes, at different ranges, and different angles, to achieve a valid statistical analysis.
Very interesting post @sgt_zim, Thank You. 100% agreed on the 2,000 fps threshold for the TSX based on various reads, but I really would love to see the results of a controlled experimentation about this. Is this a legend carrying through from past issues, or is this still real? The only thing I can say for sure, is that, actually, the failure to reliably expand was the reason why I quickly abandoned the original X back in the days. Some I tried would not even expand in wet telephone books (when such things existed LOL), but I did not own a chronograph in those days, the Shooter app did not exist, and published figures were pies in the sky, so I have no idea what speed they were flying.At shorter distances (under say 200-250), the lighter, longer bullets probably work at least as well as the heavier bullets.
using .308 cal bullet as an example
it depends on case capacity. a 165 gr tsx will be almost the same length as a 180 partition, and certainly longer than a 165 gr partition. speed advantage to the 165 gr partition over 165 gr tsx, and speed advantage to the tsx 165 over the partition 180.
Partition and Scirocco II 180 gr both have higher BC and SD than 165 tsx. So MV is somewhat higher in tsx, but the lower BC means it decelerates at a greater rate than either of those 180s. There is a point along the energy curve where the path of the 180 crosses (and thus exceed) the 165. At impact beyond that intersection (and for some distance to the left of the intersection), the 180 has probably a fair momentum advantage.
As far as MPBR advantages for the lighter monometals...there just isn't an appreciable difference. In general, non-magnum cartridges will have an MPBR of 250-300 yards, and medium and small magnums will have an MPBR of about 300-350 yards (deer-sized game). Obviously, the bigger the target, the further out MPBR goes, but this is more of an effect of target size and less so about bullet weight.
Last, all bullets do not expand equally at given velocities. Nosler asserts that partitions will expand reliably down to 1800 fps. I expect at the lower end of their performance envelope, the issue of frontal separation is less of a thing than at the higher end. AFAIK, Barnes makes no assertions about minimum impact velocity, but between this and a couple other boards I frequent, it seems to be a widely-held view that 2k fps is the bottom end for Barnes. For me, the take-away of that is that a Nosler 180 is at least marginally better than a tsx 165 as MPBR is approached. And it may even be the case on non-magnum cartridges that MPBR exceeds the distance at which a tsx is thought to reliably expand.
30-06 shooting ttsx 165 gr at 2800 fps.
calculated mpbr for a deer sized animal is a little over 300 yards.
ttsx decelerates to 2000 fps at around 225 yards.
same 30-06 with NP 180 gr at 2750
roughly the same mpbr
NP is north of 1800 fps at 500 yards, and is still north of 2k fps out to 400 yards
30-06 shooting 180 gr Scirocco II at 2700
still north of 2k fps at 400 yards
It's for certain TSX is a slayer inside its performance window. But it unquestionably has a smaller performance window than either NP or Swift Scirocco. If you're certain to never take a long shot, TSX 165 may be preferable to a separating NP 180. But if you have the skill to shoot 300+, and the opportunity arises for a long shot, you'll probably be wishing you'd gone with one of the 180s.
Do you have any insight as to the general wisdom of a 2,000 fps threshold applying to the TTSX (as opposed to the TSX)?