Nice group Ben!
That is a couple times now I've seen a picture of that 31-175BP.... Each time it has taken me back to my youth! This time I went to Accurate and looked at a drawing... I can see why it shoots! Harry Pope himself had such a design when cast plain base was still king!
A couple of years after the war (that's WW2) I remember my father ordering a mould from Lyman in Middlefield CT. I even remember him buying a money order for $6.00 for it which included shipping! It was for 308403.......
Here's the cavity. Note my father's scribe lines for venting in these early blocks.
(What looks like lead by the alignment pin hole is from the box.)
My father told an interested kid (me) that the bullet was tapered... I said "tapered?"
"Well he said.... "Each band gets larger from front to back.... So it can go into the lands a ways." Later I would know what he meant.
It didn't shoot well in the beginning in his double heat-treat '03 Springfield. My Dad thought the base band cast too big. (I think it casts .315"?) So he sized it to .309".
Does this sound familiar Ian??
Dad started with Unique but soon changed to 2400. 12 grains.... This interested young kid asked Dad why..... "Know those bullets you dug out of the backstop?" I nodded. "I saw gas cutting on the base band so I changed powder to a slower one." I nodded like I understood (and did later)
We always shot 200 yards... Even now I can reminisce the .22 rimfire like crack, then the pause, then the 'slap' on the thick military type elevating targets!
Dad won a lot of events at the range using that load usually again other '06 rifles as the club got G.I. ammo from the DCM for military qualification courses. Dad was winning with that soft plain based bullet at 200 yards against full power jacketed .30-06!!
I sent a Winchester Model 94 barrel to a fella named Ward Koozer in Oregon to rebore to .38-55.... About 1959 or '60..... I remember talks later about my Dad's target rifle in the '30's after I showed him a cast round for my 'new' .38-55 ... Dad had a Winchester Hi-Wall .38-55 with a 28" octagon barrel! We talked about the "Hudson bullet".... This was an early Lyman bullet for .38-55 with bands increasing in diameter towards the base like the Pope bullet..... He told me his mould was for the standard Lyman bullet but the Hi-Wall throat allowed him to seat out a "couple lube grooves" from the case.
My Dad sold that .38-55 Hi-Wall and a Colt Single Action Army .44-40 that he bought new in 1935! Money for my Mom when he went into WW2.
My Dad taught me to cast and reload when I was still single digits! Must be why some think me 'old fashioned'!!
Pete