Thanks to some friends at AR, I have a couple of boxes of 380 grain North Fork CPS bullets in .423 for my .404 Jeffery. I am intrigued by what Mike said about 2200 fps being the worst velocity for penetration, penetration being better either above or below that speed at impact. If that is the case, what is the optimum muzzle velocity for my reloads?

The North Fork Cup Points are a fantasic bullet. I have used them in 416Rigby, 458Lott, and 470NE.

Being a mono-metal bullet, I lean towards pushing towards the high end of the velocity range for your 404 Jeffery....but not exceeding published reliable load data...find what velocity/loading meets your accuracy expectations and you are set...

Unless I an mistaken, I think Mike's sense of humor got you about "2200fps being the worst velocity...better either above or below that speed at impact"....as noted, I would push them faster rather than slower...

I don't think it is a joke, but I'm not sure the info is true for the 404 Jeff bullet. I think that is the number for the 416.

The 416 NF softs open up to maximum diameter at impact velocities of 2200 fps and higher. The relationship between momentum and frontal area is such that minimum penetration is reached at 2200 fps.

The added penetration below that velocity is simply due to the smaller frontal diameter. It travels like a solid at low velocity.

There is some disagreement about what the top effective velocity is, but Mike says it is at least 2800 fps. Some say that bullets in general tend to start to veer erratically in the carcase at very high velocities limiting the maximum effective velocity.

For the 404 Jeff Mike says "This bullet was designed for the 404 Jeffery and the 404 Dakota. The rifle it was tested in was a Jeffery with a 26†barrel and there was no problem in reaching 2500fps at very reasonable pressures. Even 2600fps would be possible but you would be loading to modern, high intensity, pressures (60,000psi+). That sort of defeats the purpose of the stately old 404. Muzzle velocities in the 2300 to 2400 range are far more comfortable and controllable. Because there are no upper end, super magnums in this caliber, this bullet is constructed for more sedate velocities than the 416-370 bullet. It is suitable for big bear, moose, and any African plains game, including Cape buffalo."

I would therefore expect that minimum penetration is at around 1800 fps for this bullet. Hopefully Mike will come along and set us all straight!

I forgot to point out that Mike lists the PIV or Preferred Impact Velocity range as 2000 to 2800 fps for the 404 Jeff bullet.

For the 416-370 SS it is 2200-2800 fps.

With a NF cup point, the velocity is what will limit the expansion. The bullets will expand somewhat with an impact velocity over 2000fps, but under that they will act just like the flat pointed solid. For close range shots they'll act a bit like a TSX, but at greater ranges the TSX is the better bullet if you want some expansion.
The softs are a totally different bullet and need all the velocity you can give them, if maximum penetration/tissue disruption is the goal. They expand readily at low velocites but their large frontal area limits how far they'll go. This is why Mike has suggested to me that running them as fast as possible helps them along in this area.
I can tell you that a 450gr 458diameter bullet driven to 2565fps did not exit the buffalo's chest on a broadside shot. Tried it on two buffalo in Tanzania, with a third getting his bullet from straight on... that one penetrated the paunch and was found in the rear hip area. They all hit the deck in a most spectacular fashion after receiving the first bullet! Anyone who doesn't believe extra velocity is a big help needed to have seen this. Thier eyes practically bulged out of their sockets and they literally fell straight down. Using the 200gr in 30cal, driven to 2900fps gave mostly pass throughs on plains game up to kudu size. On eland, roan and one zebra they stayed inside the animal.Insides were totally wrecked and most of the animals died on the spot. Very good bullets! Similar results on deer and elk stateside.

John,

You correctly point out that I forgot the topic was Cup points rather than softs!

In either case, the answer to Wink's question is: "as fast as you can push it leaving good pressure margin."

Thanks for the polite correction!

On your broadside 450 gr 458 that did not exit, I take it that was a soft? I hear the softs are invariably found under the hide on the far side unless a shard of rib starts a hole in the hide.

Yep, it was the soft point. And it is precisely this type of result that prompted the making of the cup points.
Many of us prefer two holes in buffalo, especially for broadside shots. The soft points, when expanded, do not have the sharp leading edges necessary to penetrate the tough hide on the off side. The cup points, with a high enough impact velocity, will expand somewhat and have those sharp edges so they will make it through.
It's a balancing act with those...and I'm not sure if they really are the best choice overall. Penetration is a must, but I also want expansion to disrupt as much tissue as possible. I believe the TSX is the better bullet of this type if you are not worried about keeping the shots to under 75yds or so...and I fall into this category because where I've hunted the shots can definitely be past 100yds in many situations.