.220 Swift Twist Rates

[2_Grumpy]

hi,

can someone explain why the most common twist rate in a Swift & common in the 22-250 is the slow 1:14"

I am looking at loading a 60-70grn load but these bullets all seem to require a 1:8 - 1:9 twist.

Does the higher speed of the Swift projectile & its 1:14 twist make the bullet perform as if it was coming out of a .223 with the 1:9 twist?

cheers

[IllinoisCoyoteHunter]

I am no "twist-rate" expert, but the I would imagine that because of the velocities the swift is capable of you have to use lighter bullets so they will engage the rifling and begin to spin instead of stripping. A heavier bullet is harder to get spinning.

Hodgdon has data for a 70 grn bullet.

BUT, I'd think you would be able to find one with a 9 twist. Have you contacted any custom bbl manufacturers?

I am sure someone with more knowledge will chime in shortly.

[Scorch]

The 220 Swift was introduces in 1935 with a 36 gr bullet at 4,015 fps. Speed and flat trajectory was the name of the game, and the game is varmint shooting, relatively small targets at verying ranges, so flat trajectory was important. At that time most 22 centerfires fired 35-45 grain bullets at relatively modest velocities. No one was trying to shoot 90 gr 22 cal bullets because they didn't exist, and even if they had no one was trying to shoot 1000 yds with 22 centerfires. Since the 220 Swift used relatively light bullets, there was no need for a harder-to-make fast twist barrel, so a 1:14" twist was adequate. It became the norm for the Swift and other high-velocity 22 centerfires.

[jimbob86]

Longer bullets need more spin to stabilize, hence a faster twist rate.

Shorter bullets do not need as much spin.

Hyper velocities through a fast twist barrel = a hyperfast spin with rotational forces that can cause thin jacketed varmit bullets to fly apart as they exit the muzzle........ bullets go "poof" in flight......

A faster twist also is not conducive to max velocities, which is the intended purpose of the Swift........

Sooooo..... Varmint caliber guns have a twist suited for their intended purpose...... imagine that.

Just curious- why do you want to launch 70 grain bullets out of a Swift?

[mehavey]

I am looking at loading a 60-70gr load [in a Swift] but these bullets all seem to require a 1:8 - 1:9 twist.

Bullets need a specific spin rate to stabilize, and that spin come from two factors: twist rate and velocity

Let's do a little extrapolation from long-established .223 experience with bullets in the 63-69gr regime doing 2,800fps.
Twist rates of 1:9 are deliberately standardized and produce a spin rate of 225,000RPM when all the dust settles.

The Swift will shove those same bullets into an average 3,250fps range.
To produce that same 225,000RPM spin rate, you'll need a twist rate of 1-to-10.4

[603Country]

Back in the 80's, before I was really clear on twist rates and optimum bullet weights, I worked up 220 Swift loads with the 63 grain Sierra flat base bullet and with the 60 grain Nosler Solid Base Boattail bullet. Both shot great (tiny groups) in the rifle, though I never shot them over about 200 yards. The 63 grain Sierra was really deadly on small to medium sized pigs. But, I finally decided that a 55 grain bullet was really best in that rifle if I was going to shoot coyotes, which is why I bought it, so I went back to the 55 grain Nosler Ballistic Tip. The 55 Grain Vmax shot great too. My powder was and is IMR 4064. If I wanted slightly larger fast moving bullets, I'd probably get a 243AI or a 6mmAI.

[Unclenick]

That's an important point. Flat base bullets will generally be shorter than same-weight boattails, so they need less spin to stabilize.

I think Jimbob86 hit on the main problem. As you go to higher velocity the air pressure on the nose of the bullet is higher, so you need more RPM's to remain stable. So velocity and corresponding spin rate increase tend to cancel each other out, though not exactly. Taking a typical 69 grain bullet from 2800 fps to 3200 fps will let you relax the twist rate from 9.0 to 9.3 to maintain the same stability factor. Not much. The JBM site has a stability calculator you can use here.

So, bottom line, if you spin the heavy bullets fast enough to be stable at the velocities the 220 swift can given them, they will have to be spinning so fast to remain stable that they will tend to fly apart. That means you will likely be limited to using solids.

[Jim Watson]

Scorch, I think the standard Swift bullet was 48 grains.

It was only after the military went smallbore than anybody took much interest in heavy bullet .22s. Prior to the M16, a 14 twist for a 50-55 grain target or varmint bullet was all that was wanted.

Ken Waters had a 10 twist .22-250 that shot well with the 69 gr SMK.

So if you want to load heavier bullets in a Swift, you will have to have one rebarrelled for the purpose. Pac Nor would probably make you a user installed Savage barrel.

The 63 gr Sierra semipointed and the 70 gr Speer semispitzer (looks like a roundnose to me) were made blunt to get the weight up and keep the length down for standard 14 twist barrels. My 14 twist .22-250 shoots the Speer pretty well out to 200 metres but I don't see much point in it.

I know a target shooter with a fast twist Swift (I don't know the exact rate.) that does well clear out to 1000 yards but he is paying for it with short barrel life. I have a fast twist .223 for Long Range but prefer the .308 for anything over 600.

[edward5759]

Unclenick

You got me thinking so I went to the safe, I have several swifts. I do have one that has a 1:11 inch twist.
I think I bought it around the late 50s.
its a re-barrel Remington. Paul Marquart in Prescott Az
I know about this time there were a lot of arguments from people about the 220 on deer so a lot of states like here in Arizona banned anything less than 23 caliber for use on big game. This was in the 50s and with the development of now bullet technology it should be re-looked at!

I also have one in 1:18 inch twist. It was from Rock Island and I was doing a study on hypersonics.
on that we were shooting a solid 16 grain bullet of Titanium Isotopes at some different types of plates
other than that all the other 4 are 1:14

edward5759

[FrankenMauser]

Bullet stabilization can be boiled down to a single concept: RPM.

Low velocity requires a fast rate of twist to achieve a bullet RPM that provides stability.
High velocity can use a slower rate of twist to achieve a bullet RPM that provides stability.

What the .220 Swift (and similar) lacks with the slow rate of twist, it makes up for with increased velocity.

And, you can reverse that:
If you put a fast rate of twist on a .220 Swift, you can cause such high RPM, that the centrifugal force will actually tear the bullet apart. In that case, the Swift needs the slower rate of twist, to keep it from causing bullet self-destruction.


Some of my previous posts on the subject of bullet RPM, twist rates, and .22 centerfires:
http://thefiringline.com/forums/show...0&postcount=16
http://thefiringline.com/forums/show...9&postcount=14
http://thefiringline.com/forums/show...1&postcount=11

[jdillon]

My #1V has a 1:14 twist and shoots best with 55gr or less bullets. Both the 50 gr. Sierra BK and Berger Varmit work well behind 39.4 gr of IMR 4320.

[2_Grumpy]

Thanks to you all, for your input.

I can see I was thinking along the right track re twistrate x velocity = something but a couple of 100fps doesn't mean much in the equation.

I'll stick with my favorite 40grn Nosler BTip + H380 load.

edward5759: Out of curiosity only, the Swift you mention shooting those titanium isotopes were pointed at a armoured truck would it go through that kind of "plate"

jimbob86: To answer your question, I was looking at what was possible to widen the Swift's range of possibilities.

cheers

[edward5759]

2_Grumpy
I would have no idea if they would. Most tests were done with high speed cameras and were testing the air flow and drag. back then it was 60s technology but it was still state of the art. I do remember that in some rare cases over 5k was reached.
most were of the #48 isotope
Now days I here of some projectiles reaching over 10k.

Edward5759

[DWFan]

A custom barrel is called for. Luckily, thanks to the .223, twist rates from 1:7 to 1:10 are easily had. I believe PacNor even has pre-fitted barrels. My buddy has a 1:9 on his Remington and it is deadly with the 70-80gr bullets. I don't know what kind of velocity he's getting. He hasn't tried a 90gr yet that I know of.

[hootey]

Have you thought about Savage? They will custom build for a nominal fee. Several years back I ordered a 22-250 FV-12 with a 1 in 10" twist rate. The price was very nice. It will shoot .850" groups all day with 55 gr bullets. 69gr & 70gr are about half that if I do my part. Still playing with it when I can. Want to try some heavier bullets when I get time. Something to think about. Offering my opinion for what it is worth.

[Ralph Allen]

Just a bit of food for thought. My Swift has a 10 twist barrel. A buddy of mine gave me 5 boxes of Hornady SXSP 55 grain bullets years ago. Has a velocity restriction either somewhere on or in the box. Loaded up a box of 20 at my standard 3700+ fps for 55's. What a hoot! Could watch the vapor trail almost all the way to a 100 yard paper target. Yeah, I said almost. Not a speck on the paper. Disentigrated in 75-80 yards! I use the rest of those SXSP's in 223 loads. Great on prarie dogs at the lower velocities. Would have hated to take those hi speed loads to the dog town. Hate to give a prarie dog a heart attack laughing!
Ralph