Greenhill formula results

[Charlie Sometimes]

Out of curiosity, I just ran some ball numbers through the Greenhill formula calulator that was posted in another thread.

I punched in 440 RB, 445 RB, 530 RB, 535 RB, 570 RB, 575 RB, 45 Maxi, 54 Maxi and my Lyman 54 Shocker and associated appropriate numbers into the blanks using the setting "Under 2800 fps".

Here's what I got-

440 and 445 RB needs a 1:66 twist (no difference because of diameter.)

530 RB needs a 1:79 twist (strange number- I expected 72)
535 RB needs a 1:80 twist (one turn difference because of diameter- weird compared to the above example.)

570 RB needs a 1:85 twist (thought this would be faster, too.)
575 RB needs a 1:86 twist (another off by one because of diameter.)

45 Maxi needs a 1:41 twist (faster than I thought it would be.)

54 Maxi needs a 1:49 twist (Might as well be on the money.)
54 Shocker needs a 1:45 twist (445 gr.)

I was surprised at the great difference in what the formula says they require, and what the Thompson Center factory supplied in the barrels (1:48 in the Hawken and Renegade).

I see why my 54 Renegade shoots the Maxi's so well, too.
I haven't tried the Lyman Shocker boolit yet for comparison.

Comments or thoughts?
What is the twist in your rifles, and how do the above projectiles shoot in what you have, or have you tried any of these?

[rhbrink]

Don't know anything about the maxi's but I use to shoot a Douglass .45 in a 66" twist, matter of fact several and still have one left that I'm going to recycle into a underhammer. Those were the best round ball barrels around for a long time took about 80 grains of 3FFF to make em work. Sure wish they were still made. There also were some guys shooting heavy bench guns (talking about 50#+) maybe still are? Most of these at the time were 54's usually starting with a 90" twist some going up to 120" twist with a god awful about of powder 180 to 225 grains? But they sure did shoot some great targets even out to 200 yards, never-never land for a 45 shooter. I did play with a one time a .58 with a 70" twist and about 135 to 150 grains of 2FF it was starting to group at 200 but rifle wasn't heavy enough for prolonged shooting sessions. Didn't bother me much while shooting it was a hour or so latter would start getting headaches and I never get a headache so I backed off that game.

[jhrosier]

Greenhill's Formula gives good data for rifle bullets, not so good for round balls.
If you use a factor of 111 for round balls instead of 150, you will get better results.

Jack

[northmn]

This all goes back to the belief that faster twists are better with lighter charges and slower twists with heavy charges. There has been a bit of discussion on twist rate on the ALR site. Most of the more experienced shooters do not get too excited about twist rate with round balls. Bench rest shooters have won with a variety of twists, such as 1-48 to 1-72 in both 50 and 54 cal. Some have even had reversed results where a 1-48 was more accurate with a heavy load than a 1-66 for instance. One old barrel maker stated that if he were to use a single twist he would use 1-48 for all calibers. I saw no difference in powder charge loading between a Douglas and Numrich. The factors that really matter are the depth of rifling and patch and ball combinations. TC's rifling has pretty much been critisized for its comprimise rifling, as in shallower rifling with a 1-48 twist. Which for slugs is a little slow and with its shallower rifling a little touchy for RB. Still I have seen some pretty good groups with RB out of TC's. Personally I think that one barrel maker uses too deep of rifling and could care less about the rate of twist. Some use liquid lubes and tight ball combinations that pretty much clean out bore when they shoot and do not have to swab as much. There are a lot of mathematical formulas out there that are developed off of more of an opinion than any hard a fast data or as stated for bullets instead of ball. The Greenhill formulas would work, but so do a variety of other twists. Bullets like the longer 6.5 or 7mm centerfire may be a different story. Its a lot of ado about nothing.

Northmn

[rhbrink]

northmn I pretty much agree with you "Its a lot of ado about nothing" every ball, patch, lube, barrel is different whatever works for you is best. Part of the fun for me is learning what it takes to make each combination shoot. What is the ALR site? it's 4* outside truck is froze solid must have been some freezing rain last night might need some more confusing issues running around in my head.

[10 ga]

Fast twist, slow twist -- high velocity, low velocity: It all relates to optimum RPMs to stabilize the boolit. A boolit stabilized at one velocity may be unstable at a different velocity due to the difference in RPMs, all in the same barrel. I didn't take physics but my son in law is a nuclear engineer and he just shoots an Encore .50 and 2 pellets of 777 behind a 295 Aerotip belted. What the hey, he's happy and kills deer. This is interesting stuff. More info is always welcome. 10 ga

[northmn]

The ALR stands for the American Long Rifle site, which I also interact with. They are a group of rifle builers, traditional shooters and very very traditional in most things, and very experienced. Like this group a pretty good bunch. I would guess that the Greenhill formula refers to the "standard bullet" 3 x as long as the diameter. The 6.5 Swede and the AR15 using 70 grain bullets have very fast twists of about 1-8. The nature of the round ball is such that it is not likely effected as much by the same things as a bullets. Also the nature of black powder may be such that they cannot be driven fast enough to matter much for the differences. I have heard of round ball loads at 2400 fps but that uses a lot of powder and would likely require a lot of cleaning between shots. Most usable loads in big bores liek my 54 are somewhere around 1700-1800 fps and smaller ones like the 45 maybe around 2000. Target loads are often pushing maybe 1400 or better. At these velocities twist may not matter much. Original rifles has faster twists, with some Hawkens at 1-48 and some at 1-60. GGGrandad also was not known to use as much powder as we do today. He never was introduced to super magnums.

Northmn

[mooman76]

I thought I read somewhere that the greenhill formula doesn't apply to RBs.