GREENHILL, STABILITY, TWIST AND 227-80 IMPROVED

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Last Post 14 June 2016

CBA Member

joeb33050 posted this 23 May 2016

I tried 227-80, a .917” long bullet, in a Striker with measured carefully 12” twist barrel. It didn't stabilize, wouldn't stay on the paper at 100 yards.

OU812 wrote, here, of an improved NOE 227-80, .82” long without gas check, that stabilized in a 12” twist barrel.

I FILED 227-80 BULLETS TO .82” LONG, FIRED THEM IN THE STRIKER, WITH 6/TITEGROUP AND THEY WENT THROUGH THE PAPER AT 50 YARDS, SIDEWAYS.

OU812 SENT me some gas checked and lubed bullets that are .89” long and weigh 76.5 grains.

The Greenhill Formula (my weight est) says: A .224” DIA. BULLET .89” LONG MINIMUM TWIST IS 8.5”, EST. BULLET WEIGHT IS 82.3 GR. A .224” DIA. BULLET AND 12” TWIST BARREL WILL STABILIZE A BULLET .627” LONG, EST BULLET WEIGHT IS 58 GR. Today I shot 5 into .75” at 50 yards, there is no visible tipping.

This bullet shouldn't be anything like stable, based on the constant of 150 and assuming s.g. is something like 10.9. Note that the Greenhill cite, I'll put it up, says that the constant of 150 can be replaced with 200, and the bullet is stable. (bottom of first page.) The Greenhill formula with constant of 195, .224” and .89” as above, has a minimum twist of 11” per revolution. Greenhill remains correct.

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CBA Member

joeb33050 posted this 23 May 2016

The/AS Greenhill cite.

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2.6.2 GREENHILL, TEXTBOOK OF SMALL ARMS.doc

CBA Member

joeb33050 posted this 24 May 2016

We know that wind drift increases as BC = ballistic coefficient, falls; so, wanting less wind drift, we've understood that we want to increase BC.

BC is determined by bullet length, among other things. (Same shaped bullets, regardless of caliber, have the same BC when the length is the same. Same shaped 22 cal 1” long bullets have the same BC as 30 cal 1” long bullets.)

We know that faster twist is required to stabilize longer bullets, from experience and Greenhill, Miller, Dell and Powley. We also have some evidence and opinion suggesting that slower twist, approaching the stability threshold, is more accurate.

We thought that the Greenhill 150 constant described the twist required, but with John's design of the NOE 227-80, things changed. We now know THAT, (not WHY), a 75 grain version of the 227-80 is stable at lower = 7/Titegroup in 22-250, velocities.

This opens up a whole new approach to CB accuracy. Long pointy bullets at slower-than-expected twist with high BCs and less wind drift.

Or maybe a 1.2” long 110 grain 22 bullet in a 9” twist barrel?

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CBA President

John Alexander posted this 24 May 2016

What do the other methods of computing required twist for stability say about a .89” 22 bullet in a 12” twist? John

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CBA Member

joeb33050 posted this 24 May 2016

John Alexander wrote: What do the other methods of computing required twist for stability say about a .89” 22 bullet in a 12” twist? JohnHello John; T he attached excel workbook shows Greenhill, Dell, Miller and Powley twist rates, Miller at 3 values of gyroscopic stability and Powley at 3 values of Stability Factor. Interpolation works pretty well here. This ain't an easy workbook, it's going to take a few minutes to understand. I'm at 352-775-3449. (I have individual workbooks for Miller, Greenhill, Dell and Powley also.)

Since we don't know MV, let's look at a .224” dia bullet .89” long at 1500 fps.

Greenhill says twist = 8.5" Dell says 7.6" With Powley SF = 1.3, twist = 8.2" With S sub g of 1.3, Miller twist = 9.7" If the bullet is marginally stable at 12” twist, the Greenhill constant is .213

If you look at the table at the right, that bullet is not stable at any reasonable velocity.

I'm reloading now to test these and my 227-80 bullets at 100 yards, will shoot tomorrow AM.

joe b.

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2.6.1.5 TWIST WORKBOOK.xls

Standard Member

OU812 posted this 24 May 2016

Joe, I believe closing the gap between gas check and first drive band is what made this bullet shoot lots better. Most all cast bullets can benefit by closing this gap. I remember Veral Smith asking me how long I wanted the gas check shank to be on one of his custom molds...I opted for longer (more lube) but I wish I chose shorter.

Greenhill and other software is mainly for jacketed bullets. Cast bullets are a different animal.

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Standard Member

rmrix posted this 25 May 2016

joeb33050 wrote: This opens up a whole new approach to CB accuracy. Long pointy bullets at slower-than-expected twist with high BCs and less wind drift. Short range indoors, sounds good.

If the game is shot outdoors, under what ever the days conditions are and the range is on the long side..... I would enjoy shooting against those loads.

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CBA Member

joeb33050 posted this 25 May 2016

22-250, 100 yards, 7/Titegroup. "A” is my 227-80, ~.917” long, 77.7 gr, GC, Unsized, LLA "B” is OU812's 227-80Modified, .89” long, 77.5 gr., LBT Blue "C” is gpidaho's 227-80, .917” long, 77.6 gr., Unsized, LLA "D” is my 227-80, filed nose to .885” long, 77.5 gr.

Only OU812's bullet stabilized.

I don't know what's going on, or why. Note that the U812 bullet OAL is 2.655", the others were seate to 2.540” (unfiled) to go in the rifle.

It appears that OU812's shortening of the base end by ~.027” makes the bullet stabilize. ?????????????

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Standard Member

OU812 posted this 25 May 2016

Joe, More experimenting will improve grouping. Have you tried a bipod to test with...it will take away a lot of the human error.

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CBA Member

joeb33050 posted this 25 May 2016

OU812 wrote: Joe, More experimenting will improve grouping. Have you tried a bipod to test with...it will take away a lot of the human error.It isn't about accuracy, it's about stability right now. I've never shot from a bipod, too late for me now. Thanks; joe b.

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Standard Member

OU812 posted this 25 May 2016

joeb33050 wrote: it isn't about accuracy, it's about stability right now. I've never shot from a bipod, too late for me now. Thanks; joe b.

Who cares about stability if the bullet will not shoot. I promised the bullet will shoot under 1 inch...even using sloppy loading techniques.

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CBA Member

joeb33050 posted this 25 May 2016

OU812 wrote: joeb33050 wrote: it isn't about accuracy, it's about stability right now. I've never shot from a bipod, too late for me now. Thanks; joe b.

Who cares about stability if the bullet will not shoot. I promised the bullet will shoot under 1 inch...even using sloppy loading techniques. I do. You should. The wizards are strangely silent. They care too.

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CBA Member

gpidaho posted this 26 May 2016

So Joe, only two of mine even hit paper? Guess no need to offer to send ya more. lol Hope it was just that long bullet in the slow twist and not a total reflection on my casting ability. Thanks for the report. Gp

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CBA Member

joeb33050 posted this 26 May 2016

gpidaho wrote: So Joe, only two of mine even hit paper? Guess no need to offer to send ya more. lol Hope it was just that long bullet in the slow twist and not a total reflection on my casting ability. Thanks for the report. GpAgain, it's about stability. Mine and yours are going through the paper sideways. Also, I've shot almost 500 22 shots with aluminum gas checks, and accuracy is very poor. Others say aluminum checks shoot fine.

Everything we know tells us that a .89” long 77.5 gr .224 bullet won't stabilize, other bullets very close DON'T stabilize, OU812's DO stabilize. Is it the LBT blue?

Was gebst?

Do you have any chronographed velocities with the 227-80 and Titegroup, IMR4227, or Blue Dot?

Thanks; joe b.

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CBA Member

gpidaho posted this 26 May 2016

Joe: I'd be happy to put a couple of chronograph strings together for you using the 227-80s. I have Titegroup and Blue Dot on hand and the IMR 4227 is available at local shops. (shot mine up in my 41mag) Send me a range of charges you'll be using and I'll send them over the screens for you. This will get me away from toying with the Blackout and back to the 22s again. Enjoy the day. Gp

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Standard Member

OU812 posted this 26 May 2016

Joe,

I plan on chronographing this bullet using a few different powders (bullseye, titegroup, bluedot, AO, 5744). Been holding off until I receive my new Leupold 45 power target scope. I received scope today along with new Burris 30mm Signature rings. This scope was a big investment and would not have been possible without large 2015 tax return.

I will send you more bullets to test soon (next Monday)

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Standard Member

OU812 posted this 26 May 2016

joeb33050 wrote: Everything we know tells us that a .89” long 77.5 gr .224 bullet won't stabilize, other bullets very close DON'T stabilize, OU812's DO stabilize. Is it the LBT blue?

I tried the longer original 80 grain bullet using LBT lube and it “would not stabilize", so it is not the lube. I also tried this longer bullet using HI-TEK coating and bullet would not stabilize in the same 1-12 twist barrel.

Again...bullet shot well after I trimmed .035 off gas check shank

...

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CBA Member

joeb33050 posted this 27 May 2016

gpidaho wrote: Joe: I'd be happy to put a couple of chronograph strings together for you using the 227-80s. I have Titegroup and Blue Dot on hand and the IMR 4227 is available at local shops. (shot mine up in my 41mag) Send me a range of charges you'll be using and I'll send them over the screens for you. This will get me away from toying with the Blackout and back to the 22s again. Enjoy the day. Gp GP; I'm interested in 22-250, 227-80,

Blue Dot 5.5, 6.5, 7.5 gr. Titegroup 5.5, 6.5, 7.5 gr. IMR4227 9, 10, 11, 12 gr.

Thanks; joe b.

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CBA Member

joeb33050 posted this 27 May 2016

joe b.

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CBA Member

gpidaho posted this 27 May 2016

Joe: It would be my pleasure to help out in anyway I can in your 22cal. quest. I measured (three times) my Savage 112 (26” heavy barrel) this morning and sadly it seems to have a 14” twist. While this might be a good thing with the 55gr or smaller bullets it will be of no help with the long 80s. I'll put together some loads to chronograph anyway as this will give you another reference point. I'm going to keep working on the 227-80s in my 223s. I have 8", 9” and 12 inch twists to work with there. I've enjoyed watching this thread and what you and OUB12 are doing with this extra long bullet. Gp

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CBA Member

Ken Campbell Iowa posted this 27 May 2016

although it would still be of interest if the modified 80 gr bullets would stabilize in a 12 ( or 14 !!! ) twist ....even in a lowly 223 ....

besides ....it still appears that john a. has the only accurate cast bullet 223 rig in the world ....;. let us lower the bar to 2 moa groups ... anyone... ??

ken

speaking of 223 cartridges, has anyine achieved 1.5 moa ... or 2 moa.... from a 300 blackout cast rifle ?? this is getting kinda spooky ...