In my experience, the terminal performance of [J4] jacketed bullets is more affected by core alloy than by the jackets. My bullets have always featured somewhat harder cores than most BR bullet makers use: including .243, .257 and .308 calibers, BIB BR bullets have performed not only predictably, but extremely well on deer - almost as admirably as in competition. By extremely well, I mean complete pass-thoughs AND either instant or near instant kills are the norm.
To my knowledge, with about four dozen mule deer, white-tail deer, and pronghorn to their credit, only three BIB bullets have failed to exit - all were of "soft" core alloy (1/2% or less antimony): one was a head-on, 168 Yd shot (132 Gr.,300WSM, @ 3400+FPS .), which entered just left of center and was recovered between the last two ribs on the "off side", having wrecked havoc on the respiratory goodies - the mature mule deer ran about 20 Yd and expired - the recovered bullet had shed about 55% of its weight; the second was a .257, 1/2% antimony cored, 110 Gr. bullet , fired at 3500+FPS (.257 IdiotMag) - again about a 160 Yd. shot, with the bedded mule deer angled toward my position - that bullet just missed the lead edge of the on-side shoulder, broke a couple of entry side "short-ribs", destroyed the lungs and liver , after which only traces of jacket remained; the deer ran about 15 Yd. and expired; the third was a mature white-tail doe (another "soft-cored" 110 Gr. 257) fired at a MV of about 3170 FPS, via a .257 Ackley Imp., at about 25 Yd. - a steeply quartering away affair - the deer dropped in its tracks. All three of these examples were with cores of 1/2% [or less] antimony - too soft for good hunting bullets . . and harder cores make better BR bullets too! ;)
Over the last two years, BIB ("hard-core") bullets (6MM -95 GR. and .257 - 110 Gr.) have been used for extensive culling operations on a couple of Southern IA farms which are managed for BIG white-tail bucks: terminal performance has been better than expected. During these operations, the shooters are extremely slective, making certain that "button" bucks are not killed, while a variety of shot angles are tested, whith an emphsis on GOOD shot placement, at ranges from 25 to 350 Yd. The goal is removing antlerless deer: during the Late season, where for practical purposes, tags are unlimited - as of last Friday, I could have still purchased in excess of 600 tags for Lucas County alone - and rifles are legal. Last year, one "tester" griped about the .25 Cal BIBs exiting - he perferred the more explosive performance of the Nosler Ballistic Tips (NO EXITS - even on broad-side, rib-cage hits) - I'll take an exit-hole EVERY time - on a deer sized critter, I consider a failure to exit as marginal performance ! ;) Therefore, especially when they are likely to go huntin', I no longer make "soft" cored bullets. RG