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Bullet Length? (Read 377 times)

JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Bullet Length? Feb 20^th, 2026 at 3:23pm	Print Post
	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?


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oneatatime Frequent Elocutionist Offline Posts: 4331 Location: Rocky Mountains Joined: Oct 30^th, 2011	Re: Bullet Length? Reply #1 - Feb 20^th, 2026 at 3:59pm	Print Post
	What bullet is this? What does it weigh?


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #2 - Feb 20^th, 2026 at 4:43pm	Print Post
	BACO mould. Not sure which one. Weight is 536 grains. Major diameter is .215” long. Minor diameter is .505 long.


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curdog Full Member Offline Posts: 108 Joined: Feb 26^th, 2022	Re: Bullet Length? Reply #3 - Feb 20^th, 2026 at 5:06pm	Print Post
	Do any of these formulas take into account, or should we take into account, the foreshortening of the lead alloy bullet upon obturation (especially with black powder)?


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gunlaker Frequent Elocutionist Offline Posts: 2554 Location: lower mainland, B.C. Joined: Dec 13^th, 2010	Re: Bullet Length? Reply #4 - Feb 20^th, 2026 at 5:42pm	Print Post
	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.


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #5 - Feb 20^th, 2026 at 5:53pm	Print Post
	That’s good to hear Chris. This one seems to shoot well too but because of the deep snow I haven’t shot it past 100 yards yet. I’m wondering if 1.456” is pushing it for an 18 twist.


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #6 - Feb 20^th, 2026 at 6:30pm	Print Post
	oneatatime wrote on Feb 20^th, 2026 at 3:59pm: What bullet is this? What does it weigh? Most likely JIM453545E I don’t have the mould yet. Just lots of bullets.


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gunlaker Frequent Elocutionist Offline Posts: 2554 Location: lower mainland, B.C. Joined: Dec 13^th, 2010	Re: Bullet Length? Reply #7 - Feb 20^th, 2026 at 6:36pm	Print Post
	I suspect it'll probably work well. I have shot the 443530E to 800m in an 1:18 twist rifle, but only in testing, haven't shot any matches with that one. It's 1.46" long and seems to work well, although not as well as a .446" diameter Money bullet. I have yet to mess with any of the dual diameter PP bullets. Chris.


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #8 - Feb 20^th, 2026 at 6:47pm	Print Post
	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


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RJ-35-40 Senior Forum Member Offline Posts: 257 Joined: Dec 7^th, 2016	Re: Bullet Length? Reply #9 - Feb 20^th, 2026 at 7:35pm	Print Post
	IIRC correctly, I understood 125 is a better constant to use when calculating twist rates at Black Powder velocities. <1200 FPS ish Also It's also my understanding that as the bullet transitions to the subsonic velocities some instability is encountered... So when shooting at targets beyond a certain distance (transonic range) a slower than optimum twist rate has a greater effect on accuracy. My perspective is based on what I have read and not based on personal experience. A good book on the subject is 'Rifle Accuracy Facts' by Harold Vaughn and other books by Paul A. Matthews I am a member of the 'Faster Twist is better Club' This presumes there are no off center air bubbles voids in your cast bullets. Just for fun, take a couple of your big 45 cal bullets and melt them down with a torch, nose first, you might be surprised. JKR wrote on Feb 20^th, 2026 at 3:23pm: 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?
	« Last Edit: Feb 20^th, 2026 at 7:41pm by RJ-35-40 »

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Schuetzendave Frequent Elocutionist Offline Retired Ex-Shooter Posts: 4210 Location: St. Albert, Alberta Joined: Jan 28^th, 2005	Re: Bullet Length? Reply #10 - Feb 20^th, 2026 at 9:56pm	Print Post
	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.


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #11 - Feb 21^st, 2026 at 7:30am	Print Post
	RJ-35-40 wrote on Feb 20^th, 2026 at 7:35pm: IIRC correctly, I understood 125 is a better constant to use when calculating twist rates at Black Powder velocities. <1200 FPS ish Also It's also my understanding that as the bullet transitions to the subsonic velocities some instability is encountered... So when shooting at targets beyond a certain distance (transonic range) a slower than optimum twist rate has a greater effect on accuracy. My perspective is based on what I have read and not based on personal experience. A good book on the subject is 'Rifle Accuracy Facts' by Harold Vaughn and other books by Paul A. Matthews I am a member of the 'Faster Twist is better Club' This presumes there are no off center air bubbles voids in your cast bullets. Just for fun, take a couple of your big 45 cal bullets and melt them down with a torch, nose first, you might be surprised. JKR wrote on Feb 20^th, 2026 at 3:23pm: 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? Using 125 gives a twist of 17.6. This sounds reasonable.


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Ranch13 Oldtimer Offline Posts: 620 Location: East Central Wy. Joined: Jan 20^th, 2018	Re: Bullet Length? Reply #12 - Feb 21^st, 2026 at 8:31am	Print Post
	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.


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JKR Full Member Offline Posts: 123 Joined: Nov 2^nd, 2021	Re: Bullet Length? Reply #13 - Feb 21^st, 2026 at 9:17am	Print Post
	Don, You’re preaching to the choir here! I don’t know why I keep messing around with DD bullets when straight sided ones work well for me. Curiosity I guess. Last year I thought I had it figured out. I was shooting some tall mid range scores with one. I decided to take it to Lodi for the LR match. It was an embarrassing disaster! Winter boredom has me playing with this one. We’ll see what happens. Keep an eye on the for sale section! Jim


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silver Full Member Offline Posts: 234 Location: Central wi, Joined: Sep 20^th, 2016	Re: Bullet Length? Reply #14 - Feb 21^st, 2026 at 9:18am	Print Post
	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.


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