What do we really know about the transonic zone?

[Don McDowell]

The bullet on the far right is Brooks "new" postel nose.

[Kurt]

It only takes a couple minutes with an indexable end mill.
Jim might have saved one

[Kurt]

The bullet on the far right is Brooks "new" postel nose.

Take the rumble strips off the third and I think you would have a winner.

[Don McDowell]

That's his Brooks original postel nose.

[J.B.]

I've been looking at Steve Brooks doing a dual diameter 40 base pour for my sons 40/70. An 'original Postel' nose and 1.35" long. Diameters at .395 up to .405/6 at the base for about .22". Staying with ..or 'around' that nose shape has
generally posted the better results for me. Just seems to perform more consistently in all conditions. Now getting the operator to perform consistently 'full stop'. ..is a much greater challenge.

J.B.

[Distant Thunder]

Gavin,

Good to see you chime in! I don't think you can go wrong with that Brooks original Postell nose shape. You just have to remember to keep the overall length in line with the twist rate and the nose length somewhere around 40-45% of the OAL. Then keep the tip radius something close to 30%, or slight more, of the cast diameter.

Following those guide lines should make for a very well stabilized bullet with enough weight in the nose to keep the center of gravity and center of pressure close to as good as it gets. It somewhat depends on the ogive radii because that will also determine how heavy the nose is.

Making the nose too light weight (slender) pushes the center of pressure forward and the center of gravity back and that is some of what can make a bullet easier to knock out of balance as it spins toward the target. More velocity can help prevent that, but we are so limited in gains there with the black powder and lead bullets we use. We are pretty well stuck between 1200 and 1450 fps, with most of us being in the 1300 to 1400 fps area. I think that is the sweet spot velocity wise for us if the bullet design is kept in line.

I hope to move forward with an original Postell design this winter for my .44-77, but first I have to clear this hurtle that has me struggling beyond 300 yards. I will shoot two different bullets at Rapids Saturday and hopefully see some improvement and come away with a sense of direction. My money is on the slightly harder alloy, but only shooting at more than 220 yards is going to tell.

It's hard to make this .44-77 shoot bad at 220 yards. Most everything I've tried here at home will group near 1 moa at that distance and then seems to open up past 400 yards. I'm thinking the bullets are setting back a little too much wit the extra kick they get in the .44-77, but Saturday should tell me for sure.

[Don McDowell]

Jb that dual diameter bullet I had him make has a .400 base, and 395 nose.

[Kurt]

I personally like to keep the ogive radius at one caliber. A 1/2 caliber is a full round nose. I used to swage bullets mostly because I could not get the quality bullet moulds that are available now days as well as HP bullets when I did a lot of CMP matches, I swaged them to get what I wanted to use.
The photo below are a few I used to swage and I made the jackets from copper tubing.
The top row are some .458" and the finished bullet has the 1E (one caliber ogive) and I also have other dies for the .40 and .44

Here is a link to the Corbin swage company and it has a lot of good information for bullets designs of all types. For what we mostly use look at the Round nosed and Ellipticals.

http://corbins.com/bullets.htm#elliptical

[Distant Thunder]

The bullet I designed for my .40-65, 18-twist, follows that original Sharps design that I borrowed from the internet. It shoots very well to at least 600 yards and only weighs 382 grains. The design works very, very well. The OAL and length of the base diameter as well as diameters should be adjusted to fit the intended rifle and paper.

[Don McDowell]

My 40 dual diameter is 1.34 long
I'm of the opinion that the base of a dual diameter bullet should be the same as the bore diameter of the barrel, before patching.