The Fast Twist 45...

[sabotloader]

This seems like a very popular topic of late. And since I also know that Knight wants to come back with one in 2012.. I have some interest in the subject

I currently have a couple of Elite 1-30 twist rifles and they serve my needs very well. Since I am shooting basically two bullet from these rifles, a Lehigh 40-200 and a Speer .40-180 grain bullet - it does serve my purpose.

The shorter Speer bullet being shot at 22-2300 fps works perfectly into the 1-30 twist - very accurate and very good ballastics. But, the Lehigh is on the long end of the twist as I also imagine is the Barnes 195.

The Lehigh/Bloodline at 22-2300 fps works very well from the twist but for a lot of other is marginal, hence the Lehigh 40-185 which fits into the 1-30 twist, as well as most of the other twist rates available. Even the 40-200 will fit into the 1-28 and under rate and be very accurate.

So now that people are asking for the higher twist - I wondered why the 1-20 was such a failure in the period of time they (different manufactures) tried it.

One thing I would add to to this is that most 40 cal bullets that we shoot were never designed to be shot in a rifle so the velocity that these bullets reach from a muzzle of a pistol is probably very different than what most are trying to push from a ML.

This problem leads to another problem - construction of the bullet... which I think may have created the problem in a 1-20, even more than the ability of the sabot to handle the spin.

The term 'Over Stabilization' is often used as a problem but in theory 'over stabilzation' does not occur but because of rate of spin bullet problems as accentuated... sort of like shooting a PRB with a hot load from a fast twist barrel. I have highlited this discsussion in the article.

I found this basic explanation on the net... This explanation also explains the 'Greenhill' formula that Lee often uses.

http://www.loadammo.com/Topics/July01.htm

Topic of the Month: July 2001

Twist Rate

Bullet stability depends primarily on gyroscopic forces, the spin around the longitudinal axis of the bullet imparted by the twist of the rifling. Once the spinning bullet is pointed in the direction the shooter wants, it tends to travel in a straight line until it is influenced by outside forces such as gravity, wind and impact with the target.

Rifling is the spiral or helix grooves inside the barrel of a rifle or handgun. These grooves were invented a long time ago, perhaps as early as the 14th century. However, the smooth bore, using the round ball, was the choice of weapons for warfare even through the American Revolutionary war. The smooth bore musket could be loaded faster than the rifle and didn?t foul, as bad, with the combustion products of black powder.

The rifling grooves helix is expressed in a twist rate or number of complete revolutions the grooves make in one inch of barrel length. A 1in10 or 1:10 would be one complete turn in 10 inches of barrel length.

How important is twist rate? David Tubb, a winner of several NRA High Power Rifle Championships, was using a .243 rifle with a 1 in 8.5 twist barrel. He wasn?t able to get consistent accuracy until he changed to a rifle barrel with a 1 in 8 twist. The ?" twist change made all the difference between winning or losing the match.

A term we often hear is "overstabilization" of the bullet. This doesn?t happen. Either a bullet is stable or it isn?t. Too little twist will not stabilize the bullet, while too much twist, with a couple of exceptions, does little harm. Faster than optimum twists tend to exaggerate errors in bullet concentricity and may cause wobble. The faster twist also causes the bullet to spin at higher rpm, which can cause bullet blowup or disintegration because of the high centrifugal forces generated. For example, the .220 Swift, at 4,000 fps., spins the 50-grain bullet at 240,000 rpm.

One of the first persons to try to develop a formula for calculating the correct rate of twist for firearms, was George Greenhill, a mathematics lecturer at Emanuel College in Cambridge, England. His formula is based on the rule that the twist required in calibers equals 150 divided by the length of the bullet in calibers. This can be simplified to:

Twist = 150 X D2/L

Where:

D = bullet diameter in inches

L= bullet length in inches

150 = a constant

This formula had limitations, but worked well up to and in the vicinity of about 1,800 f.p.s. For higher velocities most ballistic experts suggest substituting 180 for 150 in the formula. The twist formulas used in the Load From a Disk program, featured at this web site, uses a modified Greenhill formula in which the "150" constant is replaced by a series of equations that allow corrections for muzzle velocity from 1,100 to 4,000 fps.

The Greenhill formula is simple and easy to apply and gives a useful approximation to the desired twist. The Greenhill formula was based on a bullet with a specific gravity of 10.9, which is about right for the jacketed lead core bullet. Notice that bullet weight does not directly enter into the equation. For a given caliber, the heavier the bullet the longer the bullet will be. So bullet weight affects bullet length and bullet length is used in the formula.

To measure the twist of a barrel, use a cleaning rod and a tight patch. Start the patch down the barrel and mark the rod at the muzzle. Push in the rod slowly until it has made one revolution, and then make a second mark on the rod at the muzzle. The distance between marks is the twist of your barrel.

To see how this works out, assume you bought a .222 Remington rifle and you measured the twist rate as described above. The twist was 1 in 14. You have two .224 bullets you want to use, the 70-grain Speer SPS and the 50-grain Hornady SX. The Speer bullet measures .812 inches in length and the Hornady measures .520 inches. Using the formula above we calculate the following twist rate:

Speer 70-grain: 1 in 9

Hornady 50-grain: 1 in 14

These calculations show that the 50-grain bullet will be stabilized, but the 70-grain won?t. Sure enough, when you try these bullets out, the 50-grain shoots ? MOA while the 70-grain won?t group on the paper at 50 yards. Twist is important!

Watch our web site for the next topic of interest "What is Recoil and how is it Calculated." Until then, shoot safely and know where you bullets are going.

Sincerely,
The Ballistician

But as always.. this is just my thinking...

 

[james 14]

Makes sense to me. Is there a 40 cal rifle bullet that could be substituted for the pistol bullet? I'd rather a soft point than a hollow point anyways and it would seem a rifle bullet would be made to fly at higher velocities.
I know I've tried 35 cal bullets in my 1:28 and they keyholed pretty badly.

 

[sabotloader]

Makes sense to me. Is there a 40 cal rifle bullet that could be substituted for the pistol bullet? I'd rather a soft point than a hollow point anyways and it would seem a rifle bullet would be made to fly at higher velocities.
I know I've tried 35 cal bullets in my 1:28 and they keyholed pretty badly.

While I really like my two 45's I really do not know a lot about the bullet options available out there. My first thought is know there are not any 40 cal rifle bullets, but then again PR bullets might make some all lead 40 cal bullets.

I actually prefer the HP to the soft lead point because it increases the frontal area of the bullet and at contact offers better expansion, as long as it does not over expand (pan cake). The Lehigh, Speer Gold Dot, and the Barnes insure that over expansion does not occur.

 

[bp45cal]

you ever see that commercial about cheese :?: :?: a lady was talking about her kids not leaving home when they were fully grown.the WISE older lady says if you want your kids to leave home STOP FEEDING THEM CHEESE.
the moral of the story is stop feeding your 1 in 20 twist a SHORT LIGHT bullets feed it a nice looong piece of PURE LEAD :wink: AND LEARN TO READ THE RAINBOW.
docs guns been doing it for awile now rayer: rayer:
if anyone wants to get rid of thier 1 in 20 PM me :wink: :wink:
i might be a little byest because i have afew 45's of doc's and i cast and size um two fit the gun.seems too work for me got afew 5 and 10 shot groups at 200yds in the 3 to 5 inch range.no cleaning till the end of the string and i'm not that good of a shooter
just may 2 cents

 

[Underclocked]

A barrel is more than just twist rate, obviously. I think the problem with some of the earlier efforts was a lack of QC along with a lack of better design. It's amazing that Doc's .451 barrels will shoot both the heavy conicals and shorter sabot'd rounds with nearly equal performance. Doc prescribed a more tightly controlled rifling job so far as dimensional consistency as well as the more shallow grooves.

So, IMHO, the key to a good, fast-twist .45 barrel lies in the quality of the barrel. Eliminating the QLA type loading feed at the end of the bore also helps achieve accuracy - it can do NOTHING to enhance it and plenty to destroy it. I think the smaller the bore, the greater the impact of barrel imperfections.

I wish CVA would make a fast twist Bergara barrel to fit the Apex, might have to try one out.

 

[sabotloader]

UC

When I asked Doc about sabots and pistol bullets in his 451 - he would not give a definitive answer... He said the gun was built to shoot moderate to long conicals. Of course he said the same thing when asked about buying the U-Mag with a 1-24 twist and shooting sabots in it.

I am still not sure that you will get a 1-20 to shoot a wide variety of 40 or 357 cal bullets.

I think the 1-22 might be right at the edge and a 1-24 would be great... but, i am not smart enough to know for sure. I wish somebody would send me a 1-24 45 to try!!

 

[sqezer]

:huh?: I wouldn't give up my 1-20 for anything, It shoots the SST's , & ShockWaves very well. Next week I'll be working with the 40-200 Leigh's. A few weeks ago I sent my other 1-20 SS out to Grouse45 to do testing for Knight & Dave Leigh. Who knows, maybe there will be a NEW Leigh coming down the pipe for us all. :yeah:

 

[GM54-120]

Sabotloader i really want to see how a 1-24 compares too. Im sure some of the bullets that need more fps to stabilize will benefit from a faster than 1-28 twist.

 

[sabotloader]

Sabotloader i really want to see how a 1-24 compares too. Im sure some of the bullets that need more fps to stabilize will benefit from a faster than 1-28 twist.

I agree with that totally. i shoot a lot of 40 cal bullets in my 1-28 50's and they are very accurate. That little 40-200 Nosler you sent me are a perfect example. They are really well made - roll them across a sheet of glass... they roll perfect no bumping or chatter and the shoot lights out from my 50's - of course they shoot just as well from the 1-30.

Lehighs shoot very well with a 1-28 out to 200 - so the 1-28 works and I feel works better than the 1-30 at the longer ranges.

Even as Sqezer says the SW or SST shoot very for him from a 1-20 but then they are longer than the normal 40 cal or .357 cal bullets that a lot of people shoot, mostly because of cost per bullet and availablity.

I just have a feeling the 1-24 might be just right for a majority of the available bullets. Then as you get faster from that you start narrowing the field.

 

[GM54-120]

I really like those Noslers too. The price is right. They are supposed to have a pure lead core and the copper jacket seems very consistent.

They are becoming popular with the paper punchers.

I will try to run some BH209 through the 1-22 sometime. I dont see any issues with it and i can push the limits a bit more to see what happens with current common 40cal options.

I planned to try some sabotless BH209 anyway when i get some Parkers sized. You would really be amazed at the advantages if you can get sabotless working for you.

 

[Lee 9]

If you really wanted maximized performance out of a 45 you would use a gain twist that started out at 1-50 and went up to 1-20. The advantage of this is that it takes the strain of starting the spin all at once off the sabot. Sabots are not as tough as gilding metal and they slip a lot easier once you have one slipping you have lost your tight group right there, that's why some bench rest shooters still pay to have special made barrels with gain twists.

 

[sabotloader]

If you really wanted maximized performance out of a 45 you would use a gain twist that started out at 1-50 and went up to 1-20. The advantage of this is that it takes the strain of starting the spin all at once off the sabot. Sabots are not as tough as gilding metal and they slip a lot easier once you have one slipping you have lost your tight group right there, that's why some bench rest shooters still pay to have special made barrels with gain twists.

Excellent point!

 

[sabotloader]

I really like those Noslers too. The price is right. They are supposed to have a pure lead core and the copper jacket seems very consistent.

They are becoming popular with the paper punchers.

I will try to run some BH209 through the 1-22 sometime. I dont see any issues with it and i can push the limits a bit more to see what happens with current common 40cal options.

That would be interesting to see the results of that with some regular 40 cal pistol bullets.

I planned to try some sabotless BH209 anyway when i get some Parkers sized. You would really be amazed at the advantages if you can get sabotless working for you.

Dave made up good batch of sabotless 270 grain 50 that I can shoot from my 50 cal Knights. They work very well in my MK - I really like shooting them. they are very consistent.

 

[Nimrodder]

SL, is Dave still making those bullets?

 

[Busta]

A barrel is more than just twist rate, obviously. I think the problem with some of the earlier efforts was a lack of QC along with a lack of better design. It's amazing that Doc's .451 barrels will shoot both the heavy conicals and shorter sabot'd rounds with nearly equal performance. Doc prescribed a more tightly controlled rifling job so far as dimensional consistency as well as the more shallow grooves.

So, IMHO, the key to a good, fast-twist .45 barrel lies in the quality of the barrel. Eliminating the QLA type loading feed at the end of the bore also helps achieve accuracy - it can do NOTHING to enhance it and plenty to destroy it. I think the smaller the bore, the greater the impact of barrel imperfections.

I wish CVA would make a fast twist Bergara barrel to fit the Apex, might have to try one out.

Oh, but they do. You just need to install a breech plug in their .45-70 barrel. I put one in a SS H&R .45-70 Ultra barrel and married it to my Huntsman frame. If CVA ever comes out with a brown laminate stock and forend for the Apex, I think I would go off the deep end! :lol:

Custom SS .45 cal Huntsman (1:20 twist 24" barrel)

I drank some CVA Kool-Aid the other day, of the pistola variety. :wink:
Should have a report in a week or so.

 

[Underclocked]

I've contacted them about the stock. :lol:

The .45-70 barrel twist rate 1:32. Think I would rather go with the 1:28 twist .45 muzzy barrel.

 

[sabotloader]

SL, is Dave still making those bullets?

No not at the moment as Knight has taken over his world...

Dis is it...

I am shooting it in my MK and it is just a tad loose in the U-Mag but shoots lights out.

 

[Underclocked]

Busta, from Mark at CVA -

"We have had laminated stocks made for other models in the past by American Walnut Co (who also does work for Winchester, Remington and CZ-USA). They looked at the Apex frame and said it was a poor candidate for wood. An Italian maker gave the same opinion. We have, however, made some for the European market with a wood grain dip (same process as the camo) that look pretty amazing."

He included a small picture of the stock which I enlarged a bit

 

[cooperM22]

SL, is Dave still making those bullets?

No not at the moment as Knight has taken over his world...

Dis is it...

I am shooting it in my MK and it is just a tad loose in the U-Mag but shoots lights out.

I hope he starts making those again!

 

[sabotloader]

cooperM22

i think it is still in the works but delayed + the limited testing we have done so far has fostered some other improvement ideals from Lehigh Dave.