Ignorant question fer the day...

noahmercy

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So I had my Bushy Varminter (24 inch heavy fluted barrel) out to the range for the first time today. I had put together some ammo with 25 grains of Varget under 69 grain Nosler Competition BTHPs lit by Remington 7 1/2 primers in Remington cases. The brass was well prepped; trimmed to length, mouth inside and outside chamfered, pockets uniformed, and flash holes deburred. The charges were weighed, not just thrown. Bullets were seated with an RCBS Competition Seating Die. For now, I have a Burris Fullfield II 3-9 X 40 Ballistic Plex mounted.

My groups were only so-so at 100 yards, averaging around an inch. When I moved out to 200 yards, however, my groups were dramatically <span style="font-style: italic">smaller</span>. I mean like the bullets were falling pretty much on top of one another (I was shooting steel, so I couldn't get an actual group measurement).

WTF?

My ig'nint question is this: What could cause this? I didn't detect any major parallax in the scope. I shot under identical conditions at both distances...same bench, rest, ammo, conditions, etc.

I've shot guns that grouped the same at 200 as at 100. I attributed that to delayed bullet stability, but it doesn't seem like that could result in <span style="font-style: italic">smaller</span> groups at longer distances.
 

bohem

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Re: Ignorant question fer the day...

What's the twist rate of that barrel?

There's some talk (and some very convincing substantiation as well) that our common boat tailed, long, high BC bullets precess about the axis of flight for a hundred to 300 yards before "settling" down and grouping tightly.

VLD's are notorious for this. I have seen my 9 twist 7mm barrel shoot the 162 Amax on top of each other at 100yd while the 180 Bergers shoot about 1/2" or 5/8" groups. At 300yd though the bergers are shooting inside of an inch still and the Amax's are about 1-1.25" for 5 shots.
 

noahmercy

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Re: Ignorant question fer the day...

Twist is 1:9. The Nosler Custom Competition 69 grain .224" bullet is only .900" long, so it should stabilize fine in my barrel.

I guess I'll have to load up another fifty of these things and go paper them at 100, 200, and 300. If they don't group well at 100, it's no big. I use my CZ 22LR for varmints inside 150 anyway, but I've just never seen a group <span style="font-style: italic">shrink</span> at a longer range.

Weird shinola...
 

sinister

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Re: Ignorant question fer the day...

Precisely -- which is why the overwhelming majority of benchrest shooters fire lightweight flat base bullets at 100 and 200 yards.
 

krink85

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Re: Ignorant question fer the day...

Not trying to sound like a d**k but maybe you just shot better (position, trigger pull, breathing) at the 200 than you did at the 100.
 

rth1800

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    Re: Ignorant question fer the day...

    I am wondering how you could tell a 1" group of several shots from a "small" group on steel. With 5 shots splattering around, it seems like it would be hard to tell. Not trying to dispute at all, just seems odd.
     

    noahmercy

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    Re: Ignorant question fer the day...

    Don't sound like a penile protuberance a'tall, krink.
    wink.gif


    There could be the possibility that I did everything "righter" at 200, but all I did was shift the position of the front rest about six inches to the right. I didn't even get up from the bench, and to be honest, I can reliably "call" my flyers. I've shot enough to know when I'm on and when I should just pack it in and call it a day. All my shots felt good and my paper groups were within a quarter inch of one another, which I feel is respectably consistent.
     

    noahmercy

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    Re: Ignorant question fer the day...

    The 100 yard groups were shot on paper, so spreads were easy to determine. And at 200, there weren't a bunch of shots splattered around...just one slight dimple about an inch across. Newly painted target, so I know all my shots went right there.

    As I said, I need to load up about fifty more of these and paper them at 200 and 300. Five five-shot groups at each range should be pretty difinitive. If I get any sort of interesting results, I'll post them up.
     

    noahmercy

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    Re: Ignorant question fer the day...

    RJ, I've actually had great results from some old flat-based Speer TNT 50 grainers at closer ranges, so I know what you mean about flats for 100-200 yard shooting. In this case I'm looking for something to shoot 'yotes, prairie poodles, and targets out at 5-600 yards.
     

    Rovieairto

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    Re: Ignorant question fer the day...

    The phenomenon that you described is fairly normal.
    It often seems more exaggerated as the caliber increases.
    Many folks describe it as the bullet going to sleep.
    The precessive wobble damps out over time.

    If you get a chance to spot bullet trace on this load, you will likely be able to see it in action.
    High BC boat tails seem (to me anyway) to wobble for longer distances.
    Flat base bullets seem to not wobble much at all.

    I think that minimizing bullet run-out will be your best bet at reducing this phenomenon.

    If shooting really tight groups at close range is important to you than these bullets are usually the place to start.

    Medium to long range groups are usually best with high BC BT designs.
     

    gator2k

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RJ Hunter</div><div class="ubbcode-body">Try the 53grn SMK flat base - short range - one hole. </div></div>

    Do the 53 grn SMKs work okay in a 9 twist?
     

    gator2k

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Precisely -- which is why the overwhelming majority of benchrest shooters fire lightweight flat base bullets at 100 and 200 yards. </div></div>

    Do you have a particular bullet in mind for a 5.56 9 twist?
     

    splean

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    Re: Ignorant question fer the day...

    This is an interesting thread. I have experienced the same thing with my 300WM. I loaded 208gr SMKs that grouped better at 200 yards than at 100 yards. I was a little perplexed aswell. I just figured I shot a better group at 200 yards. Does this phenomenon have a name? Any suggested reading or resources concerning said?
     

    Lt. Arclight

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: splean</div><div class="ubbcode-body">This is an interesting thread. I have experienced the same thing with my 300WM. I loaded 208gr SMKs that grouped better at 200 yards than at 100 yards. I was a little perplexed aswell. I just figured I shot a better group at 200 yards. Does this phenomenon have a name? Any suggested reading or resources concerning said? </div></div>

    New Exact Small Arms Ballistics: The Source Book For Riflemen
    Author: Arthur J. Pejsa
     
    G

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: splean</div><div class="ubbcode-body"> Does this phenomenon have a name? </div></div>

    None that I know of but it is a combo of, Boat tail vs Crown vs bullet weight, vs twist rate, vs gas exit pressure.

    When loading if you mark the trans area between the body an B/T you will get this 100% of the time. Depending twist rate, gas pressure at muzzle exit, bullet weight an total yaw, the stabilization range can be short or long.

    The higher gas pressure at exit the worst yaw becomes, an the farther it takes spin to stop it. Slower twist, and/or heavy bullets, can take longer as well.
    One way to reduce this in hand loading is to always seat the bullet brass to copper, no carbon in the neck. Use a VLD on the neck then spin the neck with a bore brush to remove any marking from the VLD. Or have a die set up to just open the first 0.010 of the case mouth 0.003 over bullet body size. Don't worry your seating die will close this up.

    Next time your loading load 10 rds, 5 your normal way, then mark the trans area on the next 5. Shoot the two groups an see for yourself.

    As already stated, if your looking for tight groups under 300yds shoot Flat Base only. Flat base bullets have more going for them than most everyone gives credit to.
     

    noahmercy

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Gunfighter14e2</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: splean</div><div class="ubbcode-body"> Does this phenomenon have a name? </div></div>

    None that I know of but it is a combo of, Boat tail vs Crown vs bullet weight, vs twist rate, vs gas exit pressure.

    When loading if you mark the trans area between the body an B/T you will get this 100% of the time. Depending twist rate, gas pressure at muzzle exit, bullet weight an total yaw, the stabilization range can be short or long.

    The higher gas pressure at exit the worst yaw becomes, an the farther it takes spin to stop it. Slower twist, and/or heavy bullets, can take longer as well.
    One way to reduce this in hand loading is to always seat the bullet brass to copper, no carbon in the neck. Use a VLD on the neck then spin the neck with a bore brush to remove any marking from the VLD. Or have a die set up to just open the first 0.010 of the case mouth 0.003 over bullet body size. Don't worry your seating die will close this up.

    Next time your loading load 10 rds, 5 your normal way, then mark the trans area on the next 5. Shoot the two groups an see for yourself.

    As already stated, if your looking for tight groups under 300yds shoot Flat Base only. Flat base bullets have more going for them than most everyone gives credit to. </div></div>

    Hmmm...I never thought about small nicks in the transition from BT to bearing surface having much of an effect, but knowing what I do about how much impact a small ding on the base of a cast bullet can have on accuracy, it makes sense. I do use a VLD reamer as well as use a competition seating die which ensures alignment of the bullet with the neck while seating. However, I have not been cleaning the inside of the case neck beyond a thorough tumbling, so there is a possibility that the transition area is getting scuffed during seating from carbon deposits. I'll polish the inside of the necks prior to the next loading and see if there's any difference. Can't hurt...

    As for flat-based, you are absolutely correct about them...they tend to be accurate and (in cup-and-core style non-bonded hunting bullets) have less of a tendency to shed their cores than a comparable boattail. Also, for 99% of hunters, the difference in ballistics will never be noticed...the couple additional inches of drop at 300 yards will be impossible for them to detect or take advantage of under field conditions.

    In the case of this AR, I want it to perform at 5-600 yards, hence the heaviest and most aerodynamic bullet I can stabilize with my twist. I 'spect this load is about the outer limit for my rig.
     

    Rovieairto

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Da_Gator</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Precisely -- which is why the overwhelming majority of benchrest shooters fire lightweight flat base bullets at 100 and 200 yards. </div></div>

    Do you have a particular bullet in mind for a 5.56 9 twist? </div></div>

    For a 1:9, I'd try a Hornady 60 grain v-max.
    A full case of Varget, or RL15 (26 grains or more).
     

    gator2k

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: splean</div><div class="ubbcode-body">This is an interesting thread. I have experienced the same thing with my 300WM. I loaded 208gr SMKs that grouped better at 200 yards than at 100 yards. I was a little perplexed aswell. I just figured I shot a better group at 200 yards. Does this phenomenon have a name? Any suggested reading or resources concerning said? </div></div>

    Mel Gibson said it best in "The Patriot" when he reminded his son to aim small/miss small. Works for me - if I use a tiny target dot I see a lot of improvement on my group sizes - I guess it gives me something to focus my aim on. When I'm using a high powered scope (20 power), I start with a 30 cal sized hole as my target and fire all shots at that same hole.
     

    gator2k

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: RJ Hunter</div><div class="ubbcode-body">http://en.wikipedia.org/wiki/Nutation

    I like it.

    DA_Gator - the 53 SMK shoot great in both my 1-9 and 1-8. </div></div>

    Thanks RJ Hunter, I'm on travel now but when I get home, I'll try some out and give you some feedback.
     

    gator2k

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Da_Gator</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Precisely -- which is why the overwhelming majority of benchrest shooters fire lightweight flat base bullets at 100 and 200 yards. </div></div>

    Do you have a particular bullet in mind for a 5.56 9 twist? </div></div>

    For a 1:9, I'd try a Hornady 60 grain v-max.
    A full case of Varget, or RL15 (26 grains or more). </div></div>

    Thanks for the load data Hamilton, I'll try out this load in a few weeks and give you some feedback. Got anything special for a 1 in 7 twist 5.56?
     

    Greg Langelius *

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    Re: Ignorant question fer the day...

    I think we could all be barking off in the direction of the wrong hare.

    After consulting the Burris site for the scope in question, I note that despite it's healthy pricetag, the scope does not provide a means of compensating for parallax.

    Scopes which lack such compensation adjustment are typically set at the factory for an arbitrary distance, typically somewhere around 200yd.

    I think the disparity is due to parallax.

    Greg
     

    samnev

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    Re: Ignorant question fer the day...

    I found the 52 grain HPBT SMK's shoot a tad better in my 1:7 and 1:9 twist riles than the 53 grain SMK's and are easier to seat as well.
     

    Rovieairto

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    Re: Ignorant question fer the day...

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Da_Gator</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Hamilton</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Da_Gator</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sinister</div><div class="ubbcode-body">Precisely -- which is why the overwhelming majority of benchrest shooters fire lightweight flat base bullets at 100 and 200 yards. </div></div>

    Do you have a particular bullet in mind for a 5.56 9 twist? </div></div>

    For a 1:9, I'd try a Hornady 60 grain v-max.
    A full case of Varget, or RL15 (26 grains or more). </div></div>

    Thanks for the load data Hamilton, I'll try out this load in a few weeks and give you some feedback. Got anything special for a 1 in 7 twist 5.56? </div></div>

    I've been running the 69 Sierra matchking with 25.5 of either RL-15 or Varget, Rem 7 1/2 primer, and an LC case.
    Never crimped.
    Velocity and accuracy are excellent.
    Pressure is very acceptable.

    If you can/wish to load long, then any of the 80's I've tried (I love the 80 A-max), with 24.0 grains of either RL15, or Varget, weighed cases, Rem 7 1/2 primer, 10-20 thousandths off the lands.

    They really shoot as well as a .308 shooting 155 palma bullets.
    Accurate as all hell, and handle the wind very well for their caliber.
    Pressure is medium high.
    No primer pocket expansion in any of my loads.