Howa 1500 1-12 twist .223

[pmer]

I had some fun shooting cast in the Howa the other day. Sevaral years ago, I bought it with a slower twist for varmints and lighter bullets. Compared to ARs with 1-8 twist and faster I wanted to stay on the lighter side for barn yard pests etc.

I have a NOE 60 grain FP mold that I only used once for a couple hundred castings and made up some lighter loads and forgot about them. They didn't really cycle an AR. The Howa came along after I assembled these rounds. They're powder coated but no gas checks.

But anyways the combo was really good. It shoots close to MOA at a hundred 100 yards and it took out two water jugs with 2 shots at 140 yards. It will sneak in a flyer I suppose because they shouldve been checked and would have nicer bases.

It had me wondering about the comparison of twist rates between the 30-30 and the 32 Win Special and how one seems more cast friendly than the other. Or the 35 rifle calibers that seem cast friendly too.

[Tracy]

Nice. I built an AR with a Green Mountain 1:12 barrel a few years ago, specifically for cast. Would have went for 1:14 if they had been in stock.
1:14 is a great twist for .223, .222, .22-250 etc. for those who aren't interested in shooting heavy-for-diameter bullets. Also great for cast bullets.

[Larry Gibson]

My shooter AR has a milspec M16A1 barrel [20" with a 12" twist]. It is by far more accurate with cast than is my 9" twist Colt Competition. Especially when the velocity is pushed above 1900 fps.

I also have a Winchester sporter with a 12" twist which is excellent up through 2300+ fps for use on small vermin/game with cast bullets. My M700V which was purchased new in '72 also had a 12" twist and was always accurate with cast bullets up through the same 2300+ fps. With my 14" twist 223 Rem [Savage M24] and a M788 Rem the same cast bullets could be pushed to 2500+ fps with excellent accuracy as was anothe M788 but in 222 Rem. My Ruger #3 in 22 Hornet having a 16" twist was excellent up through 2600 fps with 45 gr cast bullets.

I also found years ago shooting 311291s and 311041s that Marlin 30-30s with 10" twist would lose accuracy above 1950 fps but the Winchester M94 30-30s with 12" twist would hold accuracy upwards of 2300 fps. Interestingly the Winchester 32 SPL with the 16" twist would hold accuracy upwards of 2400 fps [max velocity achieved pre LeveRevolution powder] with the RCBS 170 gr cast bullet.

Understanding what was the reason for slower twist to increase the accuracy potential took some time and education in external ballistics but I figured it out and the RPM Threshold theory was developed over time and well proven. Also, with my 14" twist 308W I am able to push 311291s and 311041 upwards of 2400 - 2500+fps and maintain excellent hunting accuracy [consistent 2 moa accuracy] through 300 yards. Using the NOE 30 XCB bullet velocity can be pushed up to 2600 fps and still maintain excellent accuracy through 500+ yards.
with

[405grain]

Just an FYI: the barrel blanks that Green Mountain sells for the 22 magnum are .224" bore diameter and 1-14 twist rate. I'm using one to make a 22 K-Hornet single shot. The 1" diameter x 21" long dimension might be a deal breaker for some actions (wish they made it in 1.2" dia.) Here's a link: https://www.gmriflebarrel.com/GMRBIt...Item=22M-BLANK

[charlie b]

...It had me wondering about the comparison of twist rates between the 30-30 and the 32 Win Special and how one seems more cast friendly than the other. Or the 35 rifle calibers that seem cast friendly too.

Yes. As Larry noted the spin rate makes a huge difference. I've not figured out why the bullets become unstable at some point, but they do. For one of my bullets I even had a video showing the vel at which it happened (.308Win, 210gn bullet, 2400fps). FWIW, the critical vel is dependent on a lot of things, including bullet design and diameter.

[Larry Gibson]

The bullets don't really become "unstable". This is well proven by targets as the bullets still make round holes, thus they are still stable in flight being point forward.

When the bullet goes beyond the RPM threshold it does not lose "stability”. It still is flying point forward. Its flight path simply becomes a larger expanding helical flight path. The larger helical flight path, as the range increases, is the result of an outward or radial acceleration caused by the centrafugal force from the intended flight path (line of departure) and will try to get the bullet to rotate around the intended flight path in a constantly growing helical arc. The higher the RPM [caused by velocity and rate of spin (barrel twist)] the greater the adverse effect on the bullet, thus the larger the helical arc will deviate from the intended flight path. This is why when the RPM threshold is exceeded the expansion of the groups as range increases is non linear.

Linear group expansion with bullets not exceeding the RPM Threshold would be something on the order of 2" groups at 100 yards, 4" groups at 200 yards and 6" groups at 300 yards. With the same bullet boosted above the RPM Threshold the groups may be something like, 3" groups at 100 yards, 12 - 16" groups at 200 yards and not even holding on the target paper at 300 yards. All bullet holes, even at 300 yards, will still be round indicating the bullets are still "stable" in flight.

Bullet stability and exceeding the RPM Threshold are apples and oranges.......

[charlie b]

Yep, I used the wrong term there. Thanks for the correction.

[pmer]

With exceeding the RPM threshold is there a term for the bullet getting settled in the bore for the first part of internal ballistics? I'm wondering from the point of view or comparison of jacketed and cast. Like maybe a jacketed bullet with its "tougher skin" gets setup in the bore more centered and in line with the axis of the bore? Where maybe a cast boolit has harder time of getting acquainted with the stress of a faster twist and is getting squished slightly off center as it begins to pick up rotation. With a slower twist maybe life is easier for a cast boolit as it starts move and begin rotation.

Would slightly off center to the axis of the bore be the main cause for linear group expansion? The boolit could have some wobble that couldn't be detected visually by a hole in the paper.

[charlie b]

Linear expansion is usually due to other things. Can also be related to your shooting position, especially horizontal spread. Vertical spread is typically velocity related. Off center bullets lead to more random groups.

Do you weight sort your bullets? That will give a vertical spread to groups.

I did some long range testing a while back to test my upper vel limits. It shows the effect of too fast a rotation rate quite dramatically. There is a lot of slow motion stuff so you can fast forward to the second half. FWIW, the best accuracy I get with that bullet is still around 2000fps.

https://www.youtube.com/watch?v=cHZxFLsDLlE

You comment on bullet jump is appropriate. The bullets in the video are long bore riders. They are sized to be a jam fit in the bore, which centers them up prior to firing. My favorite bullet these days is the XCB. It is not a bore rider but I still set the OAL so the rifling engages the bullet. I seem to get the best accuracy that way. If I am not shooting near MOA I am doing something wrong. FWIW, best accuracy for the XCB in my 1-10 twist .308 is around 1900fps.

As an aside, my most accurate 6BR bullet is the Berger 105VLD. It is loaded to a jam fit as well. The 103ELD match from Hornady likes a .020 or more jump to the lands. All depends on bullet and barrel.