rate of twist and .224 bullets

Status
Not open for further replies.
Actually many varmint hunting oriented .223 rifles have a 1:12 twist.

It's a matter of application.

If you want to hunt big game or perhaps stretch the range of the .223 (as you might if you were shooting one in a long-range competition) then you would probably do that by shooting heavier bullets. Heavier (longer) bullets require a faster twist for stabilization.
 
still doesn't make sense. why would you want to use a less accurate, lighter bullet, which looses energy quicker while varmint hunting? cause the early trajectory is flatter?
 
why do .223 guns tend to have 1 in 7-9 rate of twist, which allows for heavy bullets, while 22-250s seem to all be 1 in 14, which limits it to 55gr?
Click to expand...

Many long range guys like to shoot the heavy for caliber bullets and the heavier bullets require a faster twist.

A 1 in 14" in the 22-250 does not limit you to 55 gr bullets. I have many that I use bullets up to 70 gr in with superb accuracy.

still doesn't make sense. why would you want to use a less accurate, lighter bullet, which looses energy quicker while varmint hunting? cause the early trajectory is flatter?
Click to expand...

Who says a lighter bullet is less accurate? Who says they have only a flatter early trajectory? A 55 gr Nosler BT at 3200 fps out of a 223 REM has a flatter trajectory the whole way out to 1000 yards than a 69 gr Sierra MatchKing fired at 2900 fps. Where the difference is in your long range shooting is wind drift (from 300 yards on out) and a slight edge in velocity (from 700 yards on out).

Why would you want a lighter, faster, and flatter bullet for varmint hunting, why because most varmint hunting is done well under 350 yards and that is where the lighter bullet shines, that’s why.

J.
 
A larger, heavier bullet isn't necessary for varmint hunting and in many cases a larger bullet is undesirable if the hunter collects or sells the furs. Smaller bullets do less damage to coats and can often inflict more damage internally on small game than their heavier counterparts, which may simply pass through the animal, instead of "exploding".

As for accuracy there really isn't any difference. If anything smaller bullets tend to be flatter shooting, however they are more susceptible to wind drift.


Edit: looks like Chappel beat me to it. ^^^ :D
 
Also, just to add to what has already been said..

A long barreled .22-250 is going to easily be able to push the same bullet 400fps faster than a short barreled .223/5.56 ( most 1 in 7 and 1 in 8 twist barrels are on ARs ), so i can get the same muzzle RPM out of a bullet than a faster twisted but slower velocity rifle.
 
The above posters pretty much covered it, Heavier bullets require faster twist.

But I'll add: Varment bullts tend to have thinner jackets, they are light and are fast, the reason being in varment shooting you want the bullet to break up on impact with the gound or target. You dont want the bullet to bound off the ground and hit some ranchers cow. They get cranky. The thinner varment bullets are safer in that respect.

Now if you were to shoot those thin jacked bullets in a faster twist, there is the posibilty they will come apart in fight. That tends to screw up your scores in high power matches.
 
agree with what has been posted so far... the faster velocity can stabilize a heavier bullet than a slower velocity twist for twist, but the fater twist barrel can also actually add significantly to the chamber pressure of the cartridge...

... I'm just a regular guy, so I don't have engineering data to back this up, but I'll insert my foot anyway...:o

the 22-250 with a 1 in 14" twist barrel will likely have to lose alot of powder to safely fire the same bullet with a 1 in 7 twist because of the increased resistance added to the bullet, as it is forced through the twice the twist rate barrel, the rifling imparts much more resistance to the bullet... the result is a much slower projectile

also agreeing with the O.P. that the twist rates seem antiquated, & in reality, they are... there were not the heavy bullets that alot of us use today, when these cartidges were developed, & the chosen twist rates were based on available bullets at the time, & velocities the designers were trying to achive...

I just traded in my old 223 Contender carbine barrel ( a 1 in 12 twist ), & built a custom 1 in 8 twist, because the old barrel would not stabilize anything over 55 grain bullets, & I've been wanting to shoot 68-70 grain bullets... the old barrel was very accurate with 45 & 50 grain bullets, & started to get marginal with 55's... I find I shoot mostly at 300 yards, & often in windy conditions, so I was wanting something more wind stabil
 
still doesn't make sense. why would you want to use a less accurate, lighter bullet, which looses energy quicker while varmint hunting? cause the early trajectory is flatter?
Click to expand...

In target shooting, the targets are always exactly 100, 200, 300, 600 or 1000 yards away. They never give you a surprise 489.3 yard target to shoot at, so a flat trajectory is relatively unimportant.

When hunting varmints, the opposite is true so a flat trajectory becomes relatively important.
 
When hunting varmints, the opposite is true so a flat trajectory becomes relatively important.
Click to expand...

True, and that's the crux of the matter. I've read criticism of Remington's 700s in 223 because of the 1:12 twist, but that's exactly what I wanted and why I got it. I can drive tacks with the little 40 grain Hornady varmint rounds. Zeroed at 200, I'm less than an inch high at 100 and at 300 I'm only 5 inches low. And the light weight rounds with fragmenting bullets are perfect for coyote size game and do the least amount of damage to the hide while being utterly devastating - quick and humane.

Perfect example: This week I took a coyote in the pasture behind my house. I barked at it to get it to stop for the shot but it didn't - and then it did, after I decided to shoot it on the trot. I pulled the shot and foul hit it just forward of the hip. It didn't matter. It flopped and bled out in seconds, all internally - a tiny entry, no exit, and DRT despite my embarrassingly crappy placement.

I love these light varmint rounds out of a slow twist in both 223 and 220 Swift. And I have other 223s in 1:9 and 1:8, perhaps better with larger bullets in wind, but it's so nominal I'm finding I don't take those out much and have recurrent thoughts of selling them. My recent thinking is that if I want to shoot a heavier bullet, why not just take out my 243?

(Naw. I probably won't sell those faster twist 223s. Just making a point. :))
 
Always think "purpose". Most ARs are used for punching paper at various distances and heavier bullets have become commonplace in that use. When considered as defense weapons, the heavier bullets are seen as having better penetration. It's not common, overall, for them to be used in hunting.

The bolt-action .22 centerfires are more commonly used for varminting, so it makes sense to use bullets in the lighter weights.

As example, I found that the Sierra 52-grain HPBT provided 3/8 MOA from my .220 Swift. It was devastating on feral cats at 300 yards. I get half-MOA from my Ruger 77 in .223. 50- to 55-grain bullets do bad things to prairie dogs to 300 yards.
 
B.L.E gets the prize. I think that is answer. The rest of the replies, it seems to me, mis-state, re-state, or mis-understand the question. It comes down to application, hunting versus target shooting. Hunting rifles and their appropriate ammo are very different than target rifles and their ammo. Lots of variables to consider in the art of the rifle!
 
Gee, doc, and there I thought I was explaining the application! While I in no way disagree with BLE's comment, I note that out to around 300 yards there's not a nickel's worth of difference in trajectory.

:D:D:D

And, FWIW, my lil Rugilator does 1/2-MOA with 70-grain bullets. Go figure.
 
It's a matter of bullet RPM.

The average bullet requires a certain amount of RPM to stabilize.

With the .223 Remington's lower velocities, that requires a faster rate of twist to achieve stability.

With the .22-250, .220 Swift, etc.. You can achieve the same stabilizing RPM by pushing the bullet faster through a slower rate of twist barrel. As an added bonus, the slower rate of twist helps mitigate copper fouling.

I have found the average RPM to be between 175,000 and 275,000 for most centerfire .22s. It seems 160,000 rpm is sufficient for most .224" projectiles, but some require more; and a few stabilize far below that mark.


Some may see it as rocket science, but it's a simple equation.

Muzzle Velocity * 720/rate of twist = RPM

Example, (I'm not trying to prove anything with these equations; just providing examples.)
.223 Remington: 1 in 8" and 1 in 10" rate of twist
.22-250: 1 in 14"
.220 Swift: 1 in 14"
------
.223 Rem, 40 grain Ballistic Tip, 3,700 fps
3,700*720/8 = 333,000 rpm (This bullet is likely over-stabilized and close to centrifugal-destruction.)
3,700*720/10 = 266,400 rpm

.22-250, 43 grain TNT HP, 4,000 fps
4,000*720/14 = 205,714 rpm

.220 Swift, 40 grain Ballistic Tip, 4,250 fps
4,250*720/14 = 218,571 rpm
-----

.223 Rem, 62 grain JHP, 3,025 fps
3,025*720/8 = 272,250 rpm
3,025*720/10 = 217,800 rpm

.22-250, 60 grain Partition, 3,500 fps (Higher velocity is achievable, but I couldn't find a factory load.)
3,500*720/14 = 180,000 rpm

.220 Swift, 60 grain Partition, 3,400 fps (Higher velocity is achievable, but I couldn't find a factory load.)
3,400*720/14 = 174,857 rpm

----

As a note here - The .220 Swift is gaining popularity as a long-range match cartridge. However, you may notice its velocity is below that of the .22-250 with the 60 grain partition. The .220 Swift does not scale very well with heavy-for-caliber bullets. Once you surpass 55 grains, velocity drops very quickly. So, the limitation based upon rate of twist doesn't matter much if the cartridge can't handle those heavier bullets well.
(I think it is a matter of the 'ideal' powders for heavier bullets not burning well within the case shape of the Swift, but can't prove it. Just my theory.)
 
art, you were on it too, sorry. But now, I am really interested in franken's post.

Hey franken, how heavy a bullet do you think a 1 in 14 22-250 can stabilize?

Why do bullet manufacturers sometimes recommend a twist when they don't know what cartrige and charge might load?
 
Why do bullet manufacturers sometimes recommend a twist when they don't know what cartrige and charge might load?
Click to expand...

Because the required twist is not relative to velocity or cartrige, its bullet lenght and diameter. Sir Alfred Greenhill developed a fomular in 1879 to determine the twist of a given bullet (be it small arms or artillary). It dosn't, nor does it need to take into account velocity or cartrige type.

Basicily its to divide the lenght of the bullet by the diameters in caliber. Then divide specificgravity by the results. Take that results and multiply it by the caliber of the bullet.

The specific gravity of a lead core jacketed bullet is 150.

Let take a .30 cal bullet with a length of 1.35 inches.

1.35/.30 = 4.5

150/4.5 = 33.33 1/3

33 1/3 X .30 = 9.999

Round it off to 1 in 10 twist.

The internet experts are gonna tell you thats an old usless fomular. I'm not an engineer or math wizzard, but I do know math dosnt change.

If you use a given bullet in the above fomular, and compair it to the recomendations listed by bullet manufactors you'll see they match. Maybe a little differance in rounding up or down, but they match.

When I was heavy into building target rifles, I would first choose the bullet I wanted, and based on the Greenhill Fomular, I would build the gun around the bullet, not the other way around. It always worked for me.
 
Because the required twist is not relative to velocity...
Click to expand...
Actually since the spin rate (rpm or revolutions per minute) is what is actually doing the stabilization, muzzle velocity does play a part.

If a bullet is travelling 2000fps when it exits a 1:9 twist barrel it will be spinning at 160,000 rpm.

If the same bullet is travelling 3000fps when it exits the same barrel it will be spinning much faster--at 256,000 rpm.

Greenhill's formula is more a rule of thumb than it is a true formula, and was really developed for pure lead bullets and relatively low muzzle velocities. The '150' number in the formula does not relate to the specific gravity of the bullet, it is rather a "fudge factor" that is plugged in to provide a reasonable result. Many sources recommend using a fudge factor of '180' or even higher when muzzle velocities exceed 2800fps.

Here's a good discussion of Greenhill's equation and also rifling twist. It includes some improved formulas for calculating rifling twist with more modern bullets and muzzle velocities.
http://kwk.us/twist.html

When a manufacturer tells you what twist rate is good for a particular bullet they're guessing a little, but it's an educated guess. If you buy a .224" diameter jacketed bullet that weighs 55gr, it's likely that you'll be shooting it in a velocity range that is reasonably easy to guess. But if you took one of their bullets and fired it in a gun with unusually low muzzle velocity you might find that it wouldn't stabilize even with their recommended twist.
 
1:14? I'll guess "light". :) I know that a 1:12 .223 will stabilize bullets of 50 to blunt-nosed 70 grains. (I've not loaded 40-grain bullets.) A slower twist with .223 velocities would probably limit out at around 55 grains, maybe.

I'm not sure about 1:14 at .220 Swift velocities, but I'm dubious that you'd get stability for bullets which are longer than is common for 55-grain.

Just speculating...
 
Status
Not open for further replies.
Back
Top