.223/5.56 twist rate to bullet weight?

I would say ideal is 60-80gr tho all barrels will be different, my 1-8 shoots 40gr Sierra bullets very good from what I've seen, under 1moa and that's with a red dot.

Do you have an AR that will handle the 80 and 90 grain bullets. 5.56 will handle them as will the Wylde chambers (might wanna double check this), but in any case, they're gonna be a single shot proposition. They are too long for the magazine. How far out are you planning on shooting? The 77 grainers will get you to 500 yards and beyond.

If you're planning out going out past say 600, I'd go to a bolt gun. You'll likely get better results, but this is really stretching the .223's legs.

You'll see better results with the heavier stuff mostly because there heavier stuff is a better designed bullet and more likely match grade. Heavy plinking ammo isn't the norm.

Here is my stock Colt 6920 at 50 yards with cheap American Eagle 55 grain.

https://flic.kr/p/2iztYXU

Waterboy3313 said:

Would stepping up to a 80-90 gr bullet make any difference in accuracy?

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Yes, but there are more headaches that come with it. If plinking ammo is what you want, basic 55 gr. Hornady FMJ bullets seated to the cannelure will be sufficiently accurate.
Every once in a while, I treated my 1:9 16" DPMS Sportical to some 60 gr. Black Hills V-max that was accurate, and M855 was OK out of it, too. Now I only have a 10.5" pistol, so I stick to 55 gr. M193-spec fodder.

A lot has to do with the quality of the bullet in addition to the weight. My 1-7 & 1-8 guns seem to prefer the 60+ grain bullets, but within that weight range I see a big difference between FMJ and say a Ballistic Tip or a V-Max. Then with the 69 grn OTMs or TMKs there's another big difference in accuracy.

My 1-9s due better with the 55s and under, but also shine with the 69 grain match bullets. Both of them have 20" barrels with increased MV to stabilize up to the 75 grainers.

I routinely shoot 69 grain OTMs and TMKs out to 550 yds with good results.

The 77 Nosler Custom Competition and Sierra Matchking are excellent for the 1:7 & 8 twist. Also, the Hornady 62 and 75 BTHP work well.

I have shot the 77 NCC to 1030 yards with an 18" AR. It's not easy but if you figure out the wind, it's pretty consistent.

Don't overthink it. I have 4 AR's:
1 in 8" 16"
1 in 7" 18"
1 in 9" 20"
1 in 8" 24" bull barrel
I also have a pair of 1 in 12" bolt guns with 22" and 26" heavy/bull barrels.
The least accurate are the 1 in 7" and 1 in 9" twists, with various bullet from 55 to 77 gr bullets. The more accurate AR's are both 1 in 8" twists, and they are consistently more accurate with ALL bullet weights from 40 gr up through 77 gr. But I think it is more the quality of the barrels, triggers and overall balance that results in their superior performance. Quality bullets shoot better than cheaper ones, no surprise there, but some inexpensive bullets shoot surprisingly well, the Hornady 62 gr BTHP from Mid-South Shooters Supply, in particular. The bolt guns tend to not group with anything over 55 gr, although the 26" barrel seems to be able to stabilize that Hornady 62 gr BTHP if the temperature is over 75 degrees or so. At 30 degrees, it can't keep 5 shots on a notebook paper size target at 100 yards from a rest. Lots of variables, and rate of twist is only one factor.

A lot of this sort of discussion misses a critical factor.

Performance of a bullet in a particular twist rate is not dependent on its weight. It's based on it's Ballistic Coefficient, which largely comes down to it's length. Because the caliber is going to remain the same, a heavier bullet is *usually* going to be longer- but not always.

My most accurate load for my 1:8 rifle uses a 50gr Varmint Grenade from Barnes. Even though it's only 50gr weight, it's almost the same length as a 69gr SMK, because it's an all copper bullet, instead of Copper/lead.

I have had good results with heavy (75 and 77 grain) rounds through 1:7 (standard US mil twist rate) 1:8 , and 1:9. This is with barrels between 10 and 20 inches. Anything other than the 55 grain is about worthless in older "A1" type barrels (1:12).

I have rifles with 7 and 8 twists. I shoot 50-75 gr bullets equally well in all of them. I'm betting I could do fine with heavier, I just haven't tried any. I'd worry more about buying accurate bullets regardless of weight. As long as the bullets are good they shoot great. The most inaccurate loads are the ones with cheaper bullets regardless of weight.

Out to 250 you’re fine with the lighter bullets. 55ish grainers or 69s if you feel like spending the money. Those should be good out to about 300 or so for the 55s. Much beyond that and I go to 77s. Honestly, I never messed with the 69s much.

I have an old 1in12 that enjoys 52gr bullets but my 1in8 and 1in7 seam to like 62gr. The 1in7 struggles to stay on a 3in target at 100yrds with 55gr bullets, I haven't tried the 69gr or above but would like to.

Waterboy3313 said:

I mostly shoot at 50-100 yards. I'm more or less limited to 250 or slightly closer. The AR I shoot most is a 5.56 chamber 16in barrel. I do have another with a 24" heavy stainless in .223 Wylde 1:8. I haven't shot it too much as it's pretty heavy. Planning on buying or building a shooting table and maybe working out to my 200-250 yard limited area with it eventually.

The 55gr Hornady bullets I have been using as well as the 5.56 American eagle m855 all seem to work great for me. I actually never thought of a heavier bullet being longer than mag length. I was just curious on the thought of of twist rate vs bullet weight. I figured if I'm going to start reloading I have a few more options to explore. I'm not trying to reinvent the wheel. What I have been using is working and I really don't see any need to change it.

I think the whole thing that got me thinking about it was a chart I saw that listed twist rate with list of "ideal" bullet weights. It made me wonder if I was possibly leaving something on the table. For the distance and reasons I shoot I'm not trying to get more out of it or hot rod anything. It's all just for plinking fun.

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My advice is to ignore those ideal twist rate tables so long as you have a 1:7 or 1:8 twist barrel. Either should be able to spin any bullets that are not too long to fit in your magazine adequately to stabilize them.

Here are a few points, some of which are not generally well understood. First, it is not bullet weight, it is bullet length. All modern rifle projectiles require spin stabilization to keep them flying point forward because they are inherently statically unstable. The center of pressure that aerodynamic drag exerts on the projectile flying through the air is well forward of the center of gravity. Having no fins to stabilize them aerodynamic drag will want to flip the bullet 180 degrees or cause it to tumble if it is not spun sufficiently fast to give rigidity to its axis of flight.

If you had two bullets exactly equal in size and shape but of different weight, the heavier bullet would actually have greater static stability and would require less spin. This does not ordinarily happen because most bullets are made of materials with the same or nearly the same density (lead alloy and a copper jacket) so a longer bullet is also heavier unless made out of less dense material. But a longer bullet will have its center of pressure farther forward of its center of gravity than a shorter one, so it will have more static instability and require faster spin for stabilization.

Some slower twist barrels may not spin long projectiles fast enough to stabilize them adequately. The 1:12 twist rate of the original M16A1 often won't even stabilize the M855 62 grain projectile adequately. A 1:9 twist barrel might not adequately stabilize some longer projectiles of greater than 70 grains. But sometimes it depends on air density. If you are mostly shooting in warmer temperatures at significant altitude the air will be considerably less dense than at sea level and cold conditions. The denser the air, the greater the aerodynamic drag which could mean that a certain slower twist barrel might stabilize a longer bullet adequately under some atmospheric conditions but not others.

Under-stabilization is a real thing in that if the spin rate is inadequate for the length of the projectile, accuracy and range will definitely suffer. As to whether over-stabilization is a real contributor to reduced accuracy or range there is controversy. Some ballistic gurus suggest that projectiles that are spun too fast will have such flight axis rigidity that they will not be able to track well along the latter portion of the bullet path when the projectile is arcing downward more rapidly, and that this lack of tractability will result in a larger angle of attack and a deterioration of ballistic coefficient due to the angle of the bullet axis to the flight path. Bryan Litz pretty much debunks this in his book "Applied Ballistics for Long Range Shooting". But some have observed a slight increase in dispersion (slightly larger groups) shooting 55 grain FMJ with 1:7 twist barrels compared to 1:8 or 1:9 twist barrels. But this seems to vary with the particular barrels so there is really no way to know if that would be the case with your rifle or not unless you experimented with different projectiles. I would agree with TonyAngel that for shooting at 250 yards the 55 grain projectiles will probably do just fine. In fact, I have had reasonable accuracy with 55 grain FMJ with my Colt LE6920 16" 1:7 twist barrel all the way out to 500 yards.

The 55 grain bullets have a significantly poorer ballistic coefficient than longer .224 caliber projectiles. They start out with greater muzzle velocity but lose velocity faster because they have more aerodynamic drag. They will therefore run out of energy sooner and have a shorter effective range because they will slow to transonic speed more quickly. The maximum supersonic range of 55 grain FMJ will vary with air density but is typically limited to about 600 meters or so.

Ramone said:

Performance of a bullet in a particular twist rate is not dependent on its weight. It's based on it's Ballistic Coefficient, which largely comes down to it's length.

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Absolutely false.

Noting here: Ballistic Coefficient = Sectional Density / Form Factor, which, of course, Sectional density = bullet mass / diameter^2, where the Form Factor is a ratio of the coefficient of drag for the actual bullet versus a standardized projectile profile.

So it’s false to say ballistic coefficient is not directly dependent upon bullet mass. The form factor - the relative drag coefficient ratio - is influenced by length, but length is not defined variable within that calculus, it’s a ratio of measured drag coefficients.

I'm wondering how much improvement is possible or visible with a 16" iron sighted AR that is satisfactory with 55 gr full patch.

Varminterror said:

Absolutely false.

Noting here: Ballistic Coefficient = Sectional Density / Form Factor, which, of course, Sectional density = bullet mass / diameter^2, where the Form Factor is a ratio of the coefficient of drag for the actual bullet versus a standardized projectile profile.

So it’s false to say ballistic coefficient is not directly dependent upon bullet mass. The form factor - the relative drag coefficient ratio - is influenced by length, but length is not defined variable within that calculus, it’s a ratio of measured drag coefficients.

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What you are saying is true, of course in that ballistic coefficient depends upon the bullets mass, its diameter, and its shape (form factor). But it is also true that for any given caliber the longer, and therefore heavier projectiles, do have better ballistic coefficients and therefore better long range performance and less susceptibility to wind drift. But being longer, they require faster spin to stabilize.

For those who are interested in how twist rate relates to bullet length, bullet diameter, and bullet mass, take a look at Don Miller's stability factor and twist rule:
https://bisonballistics.com/Miller-...ist-An-Aid-to-Choosing-Bullets-and-Rifles.pdf

If you know your bullet's actual caliber (diameter in inches) which is .224" for 223 Remington/5.56x45, the overall length of the bullet (easy if you hand load, but available for many bullets on JBM ballistics), and its mass in grains which is printed on the box, you can calculate a "stability factor" for any given rifle twist rate with the following formula:

s = 30m/{(t^2)(d^3)(l [1+l^2])} which is formula B in the pdf article

where: s is the Miller stability factor, m is the bullet mass in grains, t is the twist rate given in calibers/twist, d is the caliber, and l is the bullet length in calibers. Note that the twist rate and bullet length are in terms of calibers. If you want to use the more common twist rate in inches/turn and bullet length in inches then you need to use the following conversions:

T = t*d and L = l*d where T is twist rate in inches/turn and L is bullet length in inches.

What is clear from the formula is that bullets of greater mass have a higher stability factor and those of longer length have a lower stability factor. What is not immediately apparent because of the way that twist rate (t) and bullet length (l) are expressed in terms of calibers is that bullets of greater diameter also have a greater stability factor. If you do the conversions T=t*d and L=l*d and do some algebraic rearrangement, the bullet caliber "d" winds up in the numerator.

The stability factor also assumes a muzzle velocity of 2800 fps and "standard" ICAO atmospheric conditions at mean sea level. It is easily adjusted for different muzzle velocities and different air densities as described in the article. The adjusted stability factor must be 1.0 or greater for the bullet to be stable gyroscopically and fly point first. A minimum stability factor of 1.5 is recommended and if shooting in very cold, dry, dense air at low elevation is possible, a minimum stability factor of 2.0 is recommended.

You can use the stability factor to compute a minimum twist rate by using equations C where T is the barrel twist rate in inches/turn:

T = {30m/[sdl(1+l^2)]} ^ 1/2

So if you want a minimal stability factor of 2.0 you can set s = 2, plug in "m" in grams, "d" in inches, and "l" bullet length in calibers and find your slowest acceptable twist rate.

Berger has a calculator to compute the Miller stability factor pretty painlessly but to use it for other than Berger projectiles you will need to find the bullet length elsewhere or measure it yourself.

https://bergerbullets.com/twist-rate-calculator/

I just read thought this thread again and I think you’re over thinking it. We’re taking about a 16” battle rifle with open sights, right? If you’re worried about MOA groups, unless you are very talented, and some are, you aren’t going to shoot that rifle to its fullest potential without some glass, and I’m not taking about a red dot, and a better trigger.

If shooting flies is what you want to do, there’s a thread here about a Savage .223 with a drop in Shillen barrel shooting way under MOA. That would be a better tool than an M4ish AR.