Why am I stringing some ammo all over creation and shooting sub MOA with other.

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Thread: Why am I stringing some ammo all over creation and shooting sub MOA with other.

  1. #1
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    Why am I stringing some ammo all over creation and shooting sub MOA with other.

    Something is wrong and how do I figure it out.

    I went to the range today and I am having a hard time reconciling the results. I'm shooting my AR15 on a Lead Sled Solo trying to get groups. Using a new Vortex 6-18x44 AO scope. At 16-18 power I have a nice bead and with the Solo the hairs are real real steady.

    I started out shooting some Browning 50 gr varminter and I shoot four, 3 round groups. Largest was about 1.5moa.

    Then I load up some Black Hills 69 gr TMK. The rifle likes Federal GMM 69 gr SMK's; and I previously shot a bunch of 1.0 - 1.5 moa groups with it. So I am expecting even better seeing as I have a much higher power scope now.

    However, this is where everything goes wrong. Those 69 gr TMK's were going all over the place. I shoot four, three round groups, and they are all 3-4 moa. WTH! So I hand five rounds to the pro next to me and he proceeds to shot a 5 round sub moa group with his gun without even trying hard. So it not the ammo.

    He tells me to load up the last of my 50 grainers and to not touch the rifle. Just set it in the stand, Without leaning on it at all look through the scope, using only my thumb and finger, so I am not effecting the rifle, squeeze off a round, rest, reset and do it again. I proceed to make a 3/4" four shot group. Damn! 4th Picture
    So the rifle seems to be very capable of sub moa.

    I move on to M193 NATO using that same technique and holy god I had to aim dead center of the 8.5 x 11 paper just to make sure I could see where they hit. I was stringing them from top to bottom. Literally some going 3-4 inches high and some going low. So again I hand a handful of them to the pro next to me and he proceeds to punch out a 1.25 moa six shot group so its not the ammo.

    The pro hands me a handful of his 52 gr handloads and I make a 1.5 MOA group. I just cant reconcile why those 55 gr M193 are stringing all over the place. Wondering why those NATO rounds are failing so miserably IN MY RIFLE? The Pro shooter has me pull off my handguard and notices that there are witness marks inside the handguard under the gas block. He was speculating the gas bock is hitting the handguard and thinks that the NATO, hotter round, is making it hit harder and causing them to spread all over and the varminter 50 gr was not. *I don't know* I can see that there is about a 1/8" gap between the GB and hand guard. Yes, if I push them I can make the GB touch so it probably is hitting from barrel whip. Again *shrug* I don't know. I don't think its me and its not the ammo so there has to be something with the rifle and THAT ammo.

    I finished the day by making a 20 round group with some 75 gr Gold Dot LE. Made about a 2 moa group. I then did one last 15 round group of NATO and it had to be 8-10 moa.

    If you are still with me thank you. Where do I start? How do I figure this out?

    Targets are 1/2" grid squares.
    1st pic = Browning 50 gr Varminter.
    2nd & 3rd = Black Hills 69 gr TMK
    4th = 50 gr Varminter only touching rifle with thumb and trigger finger to fire. Cheek maybe just barely touching the stock to look.
    5th = 20 rounds of Gold Dot LE 75 gr soft point
    Attached Images Attached Images
    Last edited by little_scrapper; 05-19-2017 at 10:57 PM.
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  2. #2
    Senior Member Kakashi66218's Avatar
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    I wanted to post in the last thread; that barrels get picky with the projectile weight, but figured you'd be more likely to experiment anyways regardless. Lol.

    If I remember correctly you have an custom hand built 223/556 barrel 1:8, which I'm leaning towards more of a 1:8~9-10 twist rate.

    Here twist rates don't matter to the Cycling part of the weapon, or the composition of the barrel. It has more of a determination on what you feed your toy. I meantioned a range for that barrel of 55-62gr before, it's more of a sweet spot for that twist rate.

    Bright side, at least your Blaster likes cheap and lean ammo.

    1-in-10 Inches
    My first centerfire rifle was a Ruger Mini-14 with a 1-in-10 twist. This is a good twist rate for lighter bullets and will also generally stabilize projectiles up to 69 grains, such as Federal Premium’s Sierra MatchKing BTHP load. If you’re happy with 55- and 62-grain FMJ bullets, you don’t need any more twist than this. In my mind, however, the 1-in-10 twist is just a bit too restrictive.

    1-in-9 Inches
    This is the beginning of the road for the shooter wanting to take advantage of the heavy bullet trend. The 1-in-9 is a great compromise twist rate—not too fast to cause problems with the 55-grain Bullets, but fast enough to stabilize all but the heaviest bullets under most circumstances. This twist will stabilize most traditional bullets up to 75-grains, and monolithics up to 70-grains—but they do so right at the edge of the envelope so not all rifles will do it. My personal 16-inch Rock River Arms carbine with a 1-in-9 twist does fine with ASYM’s Tactical Match Grade 77-grain OTM load, but has shown signs of instability with handloads using the 70-grain Barnes TSX—unless the bullet is pushed to maximum velocity. With longer barrels and the commensurate faster velocities, this twist can be more forgiving.

    1-in-8 Inches
    For a 16-inch general-use carbine, the 1-in-8 twist is about as versatile as it gets. This twist rate will comfortably stabilize bullets up to 80-grains, and the excellent 75- and 77-grain bullets also work great at a wider spectrum of velocities—which means barrel length isn’t critical. My 3-gun rifle, built by my friend Iain Harrison, wears an 18-inch, 1-in-8 twist White Oak Armament barrel and shoots just about anything well.

    1-in-7 Inches
    This is the twist chosen by the military since the switch was made to the M16A2—and the 62gr. M855 cartridge—in the 1980s. This twist is found on the M4 carbine, the M16A4, the Mk12 Special Purpose Rifle and even the HK416. Its ability to stabilize tracer rounds in-flight is one of the reasons that the military chose this twist rate.
    How to Pair Barrel Twist Rates with Bullets - Guns & Ammo

    ***New edit sorry re-read your post. I can't speculate why the impacts are all over the place tho without shooting it... GL bro.
    Last edited by Kakashi66218; 05-19-2017 at 09:38 PM.
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  3. #3
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    You are correct K. It is a home built 18" 416R SS 1:8 Rifle Length Gas system 223 Wylde. I measured the twist one day while cleaning it by marking the rod and then measuring one rotation of the rob when drawing the brush out. Not exactly precise but measured 8 inches for one rotation with a tape measure.

    Now to the point. I understand some ammo shoots better than others. That being said, How is my rifle shooting 1 MAO with Fed. GMM 69 gr SMK but shoots 4+ MOA with black hills 69 gr Tipped Match King?? I would think the TMK would actually be MORE consistent then the rough hollow point of the SMK.

    From my reading there seems to be some credence to the GB hitting handguard causing poor accuracy. Y/N? Wondering if that guy was right. Is it possible the Federal 69 gr SMK was not causing the GB to hit and the Black Hills 69 gr TMK was? The 50 gr Varmintor was not and the 55 gr NATO was?

    I could understand a couple MOA but 8+?? Hard to believe at 100yds don't you think?

    Top left = pro shooting some of my Black Hills 69 gr TMK out of his rifle
    Top Right = Me shooting the last three rounds of that box of BH TMK after his shots.
    Lower Left = me shooting his hand made 53 gr, as he drscribed it, low power rounds. The flier may have been there previously.
    Attached Images Attached Images
    Last edited by little_scrapper; 05-19-2017 at 11:21 PM.
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  5. #4
    Senior Member Kakashi66218's Avatar
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    When I reread it, I was thinking antinodes with the GB and that may be it, or possibly too tight in the sled. Either way, yes, He might be right. In my experience the ARs (for that matter, all rifles) like bone and muscle support.
    It's not the things I did that keep me up at night.. it's the things I didn't do, but could have done, that's what has me losing sleep. - Me

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  6. #5
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    Quote Originally Posted by Kakashi66218 View Post
    When I reread it, I was thinking antinodes with the GB and that may be it, or possibly too tight in the sled. Either way, yes, He might be right. In my experience the ARs (for that matter, all rifles) like bone and muscle support.
    What is, are antinodes? What does too tight in the sled mean? Im ignorant and dont possess the vocabulary yet.
    "I saw some girl texting and driving the other day and it really pissed me off, so I rolled down my window and threw my beer at her!" LOLz

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  7. #6
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    Lol, no prob scrapper. I'm hoping to make a mess of this and someone else swings by and cleans it up for all of us.

    Off the top of my head: Nodes, ?false nodes?, and antinodes, it's technical verbiage for barrel harmonics. Easier put kinda like a guitar sting vibrating and frets, where it means the samething. I was indoctrinated that anything that interferes with the barrel will cause significant poi shift ?false node?. Inadvertently the GB (as the pro pointed out) may be creating problem with the barrel harmonics, torque on the handguard and the upper as a whole may be what's influencing it.

    If you didn't know already, getting better at shooting usually is the result of becoming brutally honest with yourself.
    It's not the things I did that keep me up at night.. it's the things I didn't do, but could have done, that's what has me losing sleep. - Me

    I support veteran owned businesses. They supported America. Thank you for your service.
    Joshua 24:15


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    *Updated previous posts with pictures*

    Honesty is not an issue for me. Mostly its me. The pro and I figured that out, as he already suspected, when he had me feather the rifle. I mean damn! minus the first shot upper left, the rifle put out a 3 shot half MOA group. That being said, with the NATO ammo, even he was scratching his head. It would literally throw one shot 3 inches high, then the next would go 3 inches low then one would go left.... There was just no rhyme or reason. I will look into the GBclearance issue. However, I can see a visible 1/8" of clearance. Thought taht should be enough. Originally it was SUPER tight so i hit the GB with an angle grinder and ground off a few mm.

    P.S. My Aero Lower has that tensioning screw in it to keep the upper/lower from wiggleing. But I dont use it. Should I be? Do I need to screw that in so the upper lower are solid?
    Last edited by little_scrapper; 05-19-2017 at 11:17 PM.
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  9. #8
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    There are 3 different components to rifle accuracy to think about here:

    1. Twist rate. This is a go/no go type of thing: are you twisting fast enough for the projectile? Twisting too fast is not a big deal, up to a limit, but twisting too slow will put you all over the place. Sounds like you have a 1:7.7 twist. I think it should be stamped on the barrel somewhere, but maybe not everyone does it. I do not think twist is your issue - 7.7 should stabilize things up beyond 70gr, and yours are all below that.

    2. Load consistency. Black Hills ought to be more consistent, but I don't think 1MOA to 4MOA is load consistency.

    3. Muzzle velocity, aka barrel timing. I think this is the issue. When you shoot, and the bullet is accelerating down the barrel, all sorts of harmonics are happening. The big one is recoil. The rifle is accelerating backwards as the bullet is accelerating forwards. Since the center of mass of the rifle is below the bore centerline, and since the center of mass of the gas block sits above the bore centerline, as the barrel accelerates back, it will also twist and whip. THis will induce a vibration in the tip of the barrel. The tip of a barrel is by definition an anti-node in vibration, so it will whip back/forth. As it is whipping, it will obviously stop at the end of a swing, and reverse direction. Right at the end of the swing, when the barrel tip velocity is zero, is when you want the bullet to exit, because that is when your aim is the most consistent. If the bullet arrives 1/4 cycle sooner or later, the barrel will be passing through the midpoint of its swing, exactly when the barrel velocity is at its highest, and you will scatter your shots.

    This is why competitive shooters will work up a custom load for a rifle, where you start with a low load, and make 5-10 rounds, then increase your powder by a tenth of a grain and make 5-10 more, and so on. When they shoot the different rounds, they will see their group size tighten up, then get big again as they go through the sweet spot of the harmonics. So the barrel has a defined harmonic and you load your ammo so the barrel residence time coincides with its frequency.

    THe other option is to add weights to the tip of the barrel, changing the barrel frequency slightly, to try to tune the barrel to the ammo. Those used to be in vogue in hunting rifles in the olden days - you don't see them much anymore.

    So to sum it up, its not that one ammo is better or worse in the absolute, its just that one happens to coincide with the harmonics of that barrel better. If you go to a different rifle, a different ammo might work best.
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  10. #9
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    Quote Originally Posted by ShootingSight View Post
    There are 3 different components to rifle accuracy to think about here:

    1. Twist rate. This is a go/no go type of thing: are you twisting fast enough for the projectile? Twisting too fast is not a big deal, up to a limit, but twisting too slow will put you all over the place. Sounds like you have a 1:7.7 twist. I think it should be stamped on the barrel somewhere, but maybe not everyone does it. I do not think twist is your issue - 7.7 should stabilize things up beyond 70gr, and yours are all below that.

    2. Load consistency. Black Hills ought to be more consistent, but I don't think 1MOA to 4MOA is load consistency.

    3. Muzzle velocity, aka barrel timing. I think this is the issue. When you shoot, and the bullet is accelerating down the barrel, all sorts of harmonics are happening. The big one is recoil. The rifle is accelerating backwards as the bullet is accelerating forwards. Since the center of mass of the rifle is below the bore centerline, and since the center of mass of the gas block sits above the bore centerline, as the barrel accelerates back, it will also twist and whip. THis will induce a vibration in the tip of the barrel. The tip of a barrel is by definition an anti-node in vibration, so it will whip back/forth. As it is whipping, it will obviously stop at the end of a swing, and reverse direction. Right at the end of the swing, when the barrel tip velocity is zero, is when you want the bullet to exit, because that is when your aim is the most consistent. If the bullet arrives 1/4 cycle sooner or later, the barrel will be passing through the midpoint of its swing, exactly when the barrel velocity is at its highest, and you will scatter your shots.

    This is why competitive shooters will work up a custom load for a rifle, where you start with a low load, and make 5-10 rounds, then increase your powder by a tenth of a grain and make 5-10 more, and so on. When they shoot the different rounds, they will see their group size tighten up, then get big again as they go through the sweet spot of the harmonics. So the barrel has a defined harmonic and you load your ammo so the barrel residence time coincides with its frequency.

    THe other option is to add weights to the tip of the barrel, changing the barrel frequency slightly, to try to tune the barrel to the ammo. Those used to be in vogue in hunting rifles in the olden days - you don't see them much anymore.

    So to sum it up, its not that one ammo is better or worse in the absolute, its just that one happens to coincide with the harmonics of that barrel better. If you go to a different rifle, a different ammo might work best.
    That actually makes a lot of sense. Not sure I believe that is what is causing my issue. Wouldn't there still be some consistency to the error? would a worst case scenario harmonic toss rounds off POA by 4-6 inches at 100 yards?? If people say yes then I will consider that but it doesn't "seem" right.

    I wish I had taken pics of the M193 spread to show. Those were bad. The TMK I still think something was off but maybe it was me I dont know.

    UPDATED WITH PICKS OF GROUP MEASUREMENTS:

    1st = Browning (Not Brownells) 50 gr Varminter.
    2nd =.BH 69 gr TMK.
    3rd = Went back to 50 gr and feathered the rifle.
    4th = Top left Pro shooting my TMK from his rifle, Top right shooting the last of my TMK, Bottom left me shooting his 53 gr hand loads.
    5th = 20 rounds of Gold Dot LE 75 gr Soft Point
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    Last edited by little_scrapper; 05-20-2017 at 06:02 PM.
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  11. #10
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    OK Im starting to believe. I have been reading and it sounds like a couple MOA shift in POI on some loads is not uncommon. Maybe the NATO ammo is just finding the sweet spot in a bad way.

    However, I still havent been able to get a definitive answer to the following question: In a worst case scenario, how far can harmonics in an 18" medium profile barrel shift the POI? Thats what i would like to know.

    If you guys say 4-5 IS possible at 100 yards then I will assume thats it.
    "I saw some girl texting and driving the other day and it really pissed me off, so I rolled down my window and threw my beer at her!" LOLz

    "If I don't shoot you now, you're never going to learn." ~ me

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