Is a length of 1.456 to long in my 18 twist 45 caliber barrel? 
When using the Greenhill formula with 150 constant I get a minimum of 21. 
Also, when calculating for a DDPP bullet would I use the major diameter (.453”) or the minor(.445”) which is the majority of the length? 
A minimum of 21 doesn’t seem right. Should I be using a lesser constant?

BACO mould. Not sure which one. Weight is 536 grains. Major diameter is .215” long. Minor diameter is .505 long.

Although it's a grease groove, not a PP bullet, my 1:18 twist Borchardt shot very well in all kinds of weather conditions with a 1.455" long Buffalo Arms Money bullet.  That's the JIM458535M1.   

Chris.

oneatatime wrote on Feb 20^th, 2026 at 3:59pm:

Most likely JIM453545E I don’t have the mould yet. Just lots of bullets.

Chris,
I’ve played around with three or four different DDPP bullets. Frankly, I haven’t been satisfied with one so far. I got a pretty good deal on this mould and a bunch of bullets so I’ll give it a try. I’ll know more when I can get out on my 300 yard range. Can’t resist a new mould you know. It’s what my friend calls a January idea!
Jim

The Don Miller formula is a refinement of the Greenhill's formula.

Caliber      0.453      Inches            
Bullet Weight      545      Grains            
Bullet Length      1.456      Inches            
Barrel Twist      18      Inches/turn            
muzzle velocity      1250      fps            
Temperature      50      degrees Fahrenheit (59 is standard)            
Pressure      29.92      inches of mercury (29.92 is standard)            
                       
Sg =      2.30                  
                       
Sg (gyroscopic stability) shouldn't be less than 1.4 (not enough spin).  If Sg is greater than about 2.0, you may gain some accuracy by going to a slower twist barrel but some people like to overspin their bullets for long range shooting (1,000 yards) to compensate for drag.                        

JKR from my actual shooting experience 1.45 is on the limits of what will work well in an 18 twist 45-90, and longer, In the 45.70 it will do ok to 600 yards in decent conditions.
1.4  works in the 70 and 90
Dual diameter bullets cab and do work very well in some rifles other rifles don’t like them one bit. I’ve been telling people that ever since I first started experimenting with them before the craze got started. 
The one thing that I have found that with them is to keep the base diameter at no more than bore diameter before patching and the length of the base to 1 caliber. They also don’t generally like a whole bunch of wad stack the way that straight sided bore diameter bullets do.

Jim the 459535m3 is 1.456 in length and is what I’m shooting
In my 45-90 Shiloh with an 18 twist. I have not had a lot of long range experience with it yet but it’s what I shot a 128 with 
At 900 at Lodi last year. ( my first time shooting that distance)
Conditions were not perfect either.

That’s a great box of cartridges

According to the math, that bullet is 1.406" in length. It has a 550 grain weight so the Sharps nose profile got a lot of weight in a shorter length bullet compared to the Metford shape that Dan Theodore copied.

I think some were. My original long-range Borchardt has a 1-18" though. They were the last of the Creedmoor rifles built so it could have transitioned from1-20"  to 1-18" in that short period of time.

Yeah it seems a little heavy for the length.  BACO lists their .459" 555gr Creedmoor bullet as being 1.440" long.  I think they use 20:1 for their weight numbers.

Chris.

When a bullet is heavy for it's length, it will usually mean that the nose is shaped different and when you transfer weight forward on a bullet, it will need more twist to stay stabilized, because the center of gravity (CG) has moved forward.

That's one of the problems using the Don Miller formula. It will give the same answer for a wad cutter or a 8 caliber ogive.

You will have a lot better twist results, if you use the Geoffrey-Kolbe program. It solves for CG because you input the nose shape and for what happens at subsonic velocity's.

Regarding the Greenhill formula, it was derived for a 3 cal ogive artillery round, as I remember and although I haven't found at what velocity, I think it was ~1000. Before I had a computor, I used 135 as a constant, for a 4 cal ogive at 1400 fps and proved it out in 32 cal, at 200 yards.

Here is a example of the G-K output. Note the sub and transonic curve.

Don’t pull one down to find out!😁
It would be interesting to know how they were loaded. Being cartridges for the 45-110 which wasn’t really a target gun, it would be interesting to know the wad, lube wad structure.
I’ve read accounts of commercial hunters buying enormous amounts of lead and powder. I wonder if any of them bought loaded cartridges like this.