Vagabond:Unfortunatley they aren't made anymore.I'm an older guy(59) and only mention them because I laid in a substantial stash of them during the 80's and continue to use them.In truth their performance is kinda on a par with the Aframes and the Northforks today.
IIRC Bill Steigers started to make them in the late 60's or early 70's.There were few real premiums back then other than a Partition,and guys like John Wooters and Bob Hagel thought very highly of BBC's, wrote them up.They were the first bonded bullet to make a splash,but were handmade, expensive, and hard to get.You could only order 200 max at a time.
If you have access to Handloader and Rifle magazines from the 70's,there is a great article by John Wooters when he and Jack Carter used them in Africa.
They were the inspiration for Jack Carter's TBBC,and the Swift Aframe by Lee Reid..
They have very heavy pure copper jackets and pure lead cores; no partition. Steiger was very fussy about the materials he used because he felt it was essential to the bullet's performance.
As to the velocity thresholds,the faster you push them, the better they work.Steigers always emphasized this velocity thing and said you can push them very fast without concern.IME he was right.Bill always told me to use the 250 in the 375H&H, as it could be pushed faster and would work better than the 275 due to higher velocity. I have an aquaintance that has used the 250 gr in the 375AI at 3100 fps in Africa on Cape buffalo with good results. The 165 gr 30 caliber driven over 3200 in a 300 Win Mag is a great elk load.
As you can see they lose very little weight,and the copper jackets and cores are so well bonded they support each other;you very rarely see a petal torn off from high impact velocity,regardless of impact speed or nature of animal anatomy they hit.They are very rugged and reliable under all conditions,particularly well suited to high velocity..
They may not penetrate like an X type bullet,but IME always as far as you need,and are noted for early expansion and wide frontal area,especially at high impact speed.At long range(say 400 yards,as far as I have used them)they still expand and do a great job,but not as fully and will generally punch through due to smaller frontal area,unless started very fast at the muzzle.
They were a great bullet,even by todays standards,but no longer made,and in truth we have very good bullets today that more or less duplicate their performance.But they started a trend that continues today.
Hope this helps and gives some historical perspective FWIW.
