Accuracy Is All About Testing And Practice

BY Herschel Smith
2 months, 3 weeks ago

Our friend Andy at Practical Accuracy has given us an awesome video on the use of 55 gr. bullets in a 7:1 twist barrel.


Comments

  1. On September 12, 2022 at 11:04 pm, Ambiguousfrog said:

    Geez. 586 yds.

  2. On September 13, 2022 at 8:03 am, Russell G. said:

    The faster twist (7T vs 8T) was to accommodate tracer rounds that are longer.

    And, yes…spin drift may show up differently at longer distances but overall accuracy always depends on the projectile and barrel and the harmonics of the whole she-bang. (Note also that he has a non-floating barrel) The issue with “Over stabilization” (faster twist) is pure voodoo.

    As an example, the PMC X-TAC boxed x193 shoots about 4 moa in my Colt 16″ floating barrel, no matter what. Forget it past 100. If I pull the bullets and put in a Hornady bulk FMJBT 55 grain at the same closed case volume (meaning I’m equalizing pressure) I’ll pull that down to sub-MOA at 100 and about 1.5 MOA at 230. OTOH, the PMC Bronze consistently shoots dime size prints out of the box at 100 and about 1.5 at 230 (I do 16 round runs ALWAYs at the end of the yard). More: The OEM PMC X-TAC in my 16″ Roscoe Wylde floating upper goes down range sub MOA at 100 and the X-TAC goes long in that barrel. This stuff is all with the same lower and buffer system.

    Now, loaders know that the ball game gets even better if you move to a Hornady Vmax or Nosler or SIE OTM in the 223/556. And, if you take a projectile out of a good over the counter x193 and put it in a 22-250 REM you will see remarkable accuracy in a run of the mill bolt platform with 12T – 14T barrel.

    And, finally, any weight above 55 grains means trial and error in a 223/556. Ask any reloader. You really have to do a lot of tweeking with powders, jump, etc. for your platform. It’s just one of those things.

    I’m not sure he is a reloader, but the AR is exactly the same as a 22lr bolt gun—you MUST try different boxed ammo to get the best out of it.

  3. On September 13, 2022 at 9:01 am, Herschel Smith said:

    @Russel,

    Yes we’ve discussed the issue with tracer rounds before and why the twist was selected based on that.

    Thanks for the perspective on ammo. I’ve heard others talk up the PMC Bronze before. It comes in .223, not 5.56. Doesn’t matter, of course.

  4. On September 13, 2022 at 1:08 pm, RHT447 said:

    Nothing profound to add, just my particular experience.

    One of my rifles is an AR A2 heavy barrel that I built back in the early ’90’s for NRA Highpower. It has a 1/9 twist

    Another is one of these–

    https://www.gunsamerica.com/923195121/Winchester-Model-70-Heavy-Varmint-223-Rem.htm

    –also 1/9 twist. I shot both rifle with this handload–

    Hornady 75 gr. A-max that I moly-coated over 25 gr. of Varget, seated .010 off the lands for each rifle. Also beyond magazine length for each rifle, so single load only.

    The M70 literally shot bug holes–5 rounds 3/8 inch center-to-center @ 250 yards (shot from a cement bench with 20X Nikon scope).

    I had my doubts about the AR’s 20-inch barrel, but wanted to try it. Shot as I would in a match, prone, with shooting jacket and sling. Was not group, was pattern–a bit over 24 inches @ 200 yards. Someone suggested a Reloader powder, but I never got around to trying it.

    A side note on loading those long A-max bullets. I start them into the case with my bench mounted press–RCBS Jr. and RCBS competition seating die. I finish them with the same die in a Lee hand press. I hold the press inverted so that as the bullet seats up into the case, the powder tends to flow down around the base, and you crush less grains.

  5. On September 13, 2022 at 3:50 pm, Elon Muskox said:

    From Bryan Litz’s Applied Ballistics for Long Range Shooting, Ch. 10, Bullet Stability (p. 155 in the 1st Edn.):

    “… It’s true that higher stability levels do produce a more rigid spin axis that tends to resist bending as the bullet follows its curved trajectory. However, even bullets with very high stability factors will still trace (sometimes called track) very well with the trajectory, the angle will only lag a little more than a slower spinning bullet. An exception to this statement is for very high angles of fire, near 90 degrees, where the bullet would have to turn on its axis abruptly at the apex of the trajectory. Failing to trace is a consideration for artillery shells fired at very high angles because if the shell doesn’t trace, it won’t hit the ground point first which is required to activate the fuse and detonate the charge. Bear in mind that even for such high angles of fire, failure to trace is still uncommon. For the small angles of even the longest range small arms trajectories, it is very easy for the bullet to trace with the trajectory….”

    So “over-stabilization” of small arms projectiles is a complete myth (at least according to Bryan Litz, but what does he know, right?). Which is not to say the shooting community isn’t errantly attaching the term “over-stabilization” to some other legitimate physical property, but I seriously doubt it. I think it’s just a convenient “boogie man” they keep in the bottom desk drawer for whenever they can’t explain what’s gone wrong. But one fact I know to a certainty: it’s not over-stabilization.

    Litz also mentions in that same chapter that competitive shooters sometimes might opt for a more marginally stabilized bullet-barrel combination (he specifically mentions as low as Sg 1.3, with carefully-selected components) because all bullets have imperfections and the negative effects of those imperfections are reduced when the bullet is spun more slowly. But these are competitors chasing marginal gains you aren’t likely to see the effects of unless you and your rifle already are shooting low tenths of an MOA.

    However, the point is not lost on the less astute shooters that competitors do sometimes opt for a slacker twist — and here’s the crux of the biscuit — they’re doing it in the interest of better precision. And if you don’t understand the “why” of competitors using a slacker twist, it’s only one step from there to the “too fast a twist causes over-stabilization” myth.

    Lastly, suggesting that projectile weight alone is responsible for differences in precision is just silly. Andy is implying that dwell time, charge weight, powder characteristics, seating depth/bullet jump, primer selection, and neck tension (et Al) play no appreciable role in determining precision of flight. Hardly a well-thought-out argument.

  6. On September 13, 2022 at 8:43 pm, Andy said:

    Elon- Not sure what video you watched, but I want to correct some of the assumptions made about my thinking in your comment.

    I never implied or claimed that

    “dwell time, charge weight, powder characteristics, seating depth/bullet jump, primer selection, and neck tension (et Al) play no appreciable role in determining precision of flight.”

    because I would certainly agree they do.

    I also never suggested weight alone of a bullet is responsible for accuracy. I think I pretty much showed weight was not the issue as 2 different 55 gr bullets shot drastically different at 100 yards.

    The whole point of the video was fairly simple. 55 grain bullets can be shot accurately and precisely out of a 1/7 twist barrel, but you will have to test your individual rifle to see what works for you.

    On a side note, I prefer 1/8 or 1/9 twist rifles and I have personally not had a problem shooting accurately and precisely with these twist rates and 77 grain bullets out to 1000 yards. I don’t claim to be a great competition shooter, just an average guy observing my personal experiences on YouTube to show what can be done with an Ar15.

  7. On September 13, 2022 at 9:40 pm, Herschel Smith said:

    @Andy. That’s the way I took your simple points. I appreciate the video.

  8. On September 18, 2022 at 1:48 pm, Elon Muskox said:

    “… 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 1/2 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….”

    https://web.archive.org/web/20050208065618/http://www.loadammo.com/Topics/July01.htm

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You are currently reading "Accuracy Is All About Testing And Practice", entry #31923 on The Captain's Journal.

This article is filed under the category(s) Ammunition,AR-15s and was published September 12th, 2022 by Herschel Smith.

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