Accuracy at distance

There are a lot of people who claim that some bullets aren't as accurate at 100 as they are at distance, well Bryan Litz wants you to prove it. He is providing use of his range and equipment to you but be aware he has yet to produce results that agree with this theory. Here is a link to one of the forums where he opens the challenge.

http://www.longrangehunting.com/forums/f19/applied-ballistics-shoot-thru-target-challenge-144359/

Parallax issues probably account for a lot of these reports.

Very nice!! I would like to make this road trip. I have seen this issue with the 208 A-max in a 308 Win, 115 DTAC in a 243 Win, and 180 VLD in a 7mm-08. We have shot some 208 A-max in a 1:12" and 1:11" twist out of a 308 Win and seen this problem. This is why I will NOT test long skinny bullets at 100 yards. I will test them at 200 or 300 yards for accuracy. I have had 2 customers that I have done custom load development with a 208 in a 308 Win short barrel (18" and 20" barrels) with 1:10" twist. The accuracy was great from 300 out to 700 yards. At 100 yards, the groups would be about 3/4". At 300, the groups would be less than an inch. The main problem we had though, was at 800 and out, the groups would open way up and not have any kind of grouping. It would be all around the target within several feet, and this was the case at 900 and 1K. Technically, the bullet is stable at these distances in a 1:10", and shot nice and tight from 300 to 700 yards. At 800 things opened up, and 900 to 1K was all over the place. I still do not know why these acted like this. And it was 2 separate customers with 2 different 308 Win rifles both 1:10" twist.

Sounds like you can get a free trip to play at somebodies range chad?! let us know lol

ok for real I read some of this and have a question. Chad you will probably be best to answer this.

Ok so assuming that you ARE having this issue, not parallax not aiming... nothing like that.

It seems these issues happen with more heavyish for size calibers from the posts. sooo HERE IS MY THOUGHT

so your shooting this heavy slug down the barrel, and you've probably got it loaded a on a little bit of a hot load. So the pressure is a high, not crazy high but could the bullet "jump" some of the rifling's? so that is starts spinning but doesn't get to the rpm that is SHOULD. because of this is has a bit of a knuckle ball thing going on early because of the slow spin, but as the bullet moves down range the spin corrects this and it gets its act back together.

So the issue is the combination of the lands, rifling, bullet, pressure combo. The only way I can figure to check this is figure out how to measure the spin on a bullet as is leaves the barrel and compare it to what it "should" be, OOR to capture the bullet downrange with NO damage and look at the cuts from the rifling's...

ok there is my W.A.G.

tell me where I messed up now

I can't see it gaining RPMs down range. Its as fast horizontally, and spinning as hard as it ever will at the muzzle.

Not gaining rpm. It's spinning slower, so it takes more time to stabilize that big bullet. It's impossible for it to gain energy I get that but a gyro has to spin up to stabilize. In this case time equals yardage cause it's moving pretty dang fast

First, bullet stability is based on bullet length, not weight. So the longer the bullet, the more twist needed to stabilize it. Generally, your heavy for caliber bullets are longer, like the 208 A-max.

When I load the 208 in a 308 Win, I have the bullet seated touching the lands, not jammed, but just touching. This does 2 things. It helps with the accuracy, and allows the most room for the powder. So, there is no jump to the rifling. The bullet will be spinning at whatever twist rate the barrel is (generally). I've seen some issues with the ratchet style rifling firing subs and such. That's another topic, though.

You are correct about the "theory" of epicyclic swerve, which is what Bryan is trying to reproduce in his challenge. Think of it like a spinning top that you played with when you were a kid. As soon as you spin the top and release it from your fingers, it has some wobble to it when it hits the table. After a split second of spinning, the top smooths out, and is perfectly balanced. This is the "theory" of epicyclic swerve with a bullet. The moment it leaves the barrel and at 100 yards, it is not perfectly on track in it's flight path and has some yaw to it. You see this in the accuracy of the bullet at 100 yards and compare it to the results you get at 300 yards. At 300 yards, the bullet has traveled far enough to be fully on track of it's flight path and have no yaw, or epicyclic swerve.


Bullet RPM formula: Bullet RPM = MV X 720/Twist Rate (in inches)

In theory if you weren't spinning the top by hand "read human error" would it take time for it to stabilize? or would it be stable from the get go?

Could it be cases by imperfections in the crown/barrel throwing it off and making the bullet have to re-stabilize.

chevy, as for the human error thing I think it would. You still have lateral energy to get the top going and at "pull" would have an equal and opposite reaction, which in turn would be stabilized by the gyroscopic force.(unless I missed something)

They talk about the crown being an issue latter on in that forum post the op put up. and they make some pretty good arguments against it. But the guy says if your rifle shows it bring it on.

CHAD... Question, ok so stability is a result of bullet LENGTH? Ok yes bullet weight would directly correlate to the length... but if I put a hollow bullet with the same profile in the rifle. wouldn't the bullet balance differently with the spin? I mean we talk about some rifling's stabilizing bullets better I feel like this is just an extension of this?

these are questions... I LOVE this stuff... The fact that chad makes a living with this kinda stuff makes me very very jealous lol

Chad since you've experienced it what do you think it is?

Elliptical dispersion or yaw is said to be minimal. Usually 1/10th of one caliber is the referenced number but that's not enough to cause the difference.

cat,

What you are referring to is the center of gravity (COG) vs. the center of pressure (COP) for the bullet. Take a shorter, flat base, spire pointed or round nose hunting bullet vs a bthp bullet. The distance between the COG and COP will be greater on the bthp compared to the SP or RN bullet, which will require more spin to stabilize the longer bullet. Think of a .308 Sierra 220 RN vs a 220 bthp. The bthp is longer and will require more twist to stabilize. Also, the greater the distance between the COP and COG makes the bullet less stable. This is why the heavy solid copper bullets need more twist than the lead bullets of same weight. The copper bullets are longer than the same weight lead bullets, and need more twist. Copper is less dense than lead.

220 RN
https://www.sierrabullets.com/store/product.cfm/sn/2180/308-dia-220-gr-RN

220 BTHP
https://www.sierrabullets.com/store/product.cfm/sn/2240/308-dia-220-gr-HPBT-MatchKing



Not always, but generally yes. See the 220 RN vs 220 bthp links above.

I am fairly certain I can show this yaw issue between 100 and 300 yards. I don't think 200 yards is far enough distance to get all the yaw out completely. But 100 to 300 I'm pretty confident. I've already been emailing Bryan and talking to him about this. He said he has not tested the 208 A-max in a 308 Win like this. In my personal 308 Win with 1:11" twist, the 208 A-max is just barely stable enough to work, and it would be a great example for this project. I need to push it around 2400-2450 fps and I think it will work.

Chad is your typical experience with long bullets that are marginally stabilized or have some had more than a high enough sg?

Chad,
are you interested in trying Bryan's challenge?

If I know that the bullet is questionable on stability, I generally won't use it or recommend shooting it. But in this case, the 208 A-max out of a 308 Win in 1:11" twist has a 1.27 stability factor at 2450 fps. You want a 1.4 or more for proper stability. The problem will be the slow fps of the bullet at about 2450 fps will have slower rpm's, which will effect the stability. A 208 A-max out of a 300WM being launched at 2950 fps, the rpm's are high enough for good stability, even going through the transonic stages at around 1500 yards or so. They will still shoot very well beyond this distance. But I may have an issue in the 308, but I will test it to know for sure.

So, for the theory, do you select a bullet and cartridge combo that gives you plenty of stability above the 1.4, or do you play with something that is marginally stable at the 1.27? That's what I need to figure out. I know the 208 A-max will have the yaw at 100 yards, but do you shoot it in a 308 or a 300WM? I think the 308 would show it more, since it's less stable. But does that go against the idea here? Do you want the bullet to be fully stable? I have both rifles and both are a 1:11" twist. I wish I owned a custom 7 Rem Mag to shoot the 180 VLD's or 243 Win shooting the 115 DTAC's, and I'm certain I can make it happen. These 2 will easily show the yaw at 100.

Yes, I am already emailing with him about it. I will begin testing some loads in my 308 Win with the 208 A-max when I have time. If I can get it to do it in the 308 Win, I will test it in my 300WM. I would like to set up a paper target at 100 that I can shoot through and record the same rounds on paper at 300 yards. I'm just wondering if shooting through paper at 100 will effect the groups at 300. I need to try this. I want to capture the groups at 100 and 300 at the same time.

following chad... idk how long this stuff is gona take buuuuut I want to hear updates lol

Let me know if you need help. I've been curious about this, but always assumed it was parallax, so I am watching his experiments. I'm willing to pick you and up and drive if you want to and it works with my work schedule.

Road trip!!

Well crap, I want to go!

Chad, can you get these loads built before you come out on Tuesday? So we can run the test then. Also, I have the custom 7 Rem Mag shooting 180 gr. VLDs. How did you forget that?

Sure! I want to build a target stand to shoot through at 100, and also catch the same rounds at 300 yards. I need targets at both spots. The 100 yard one can be small, as I can easily line it up over the 300 yard target.

I've got the mobile paper holder that can be put at the 300 yard berm (it's hiding behind 500 right now). And making a small paper holder for 100 to line up with 300 won't take very long at all. It'll take both of us to line them up due to the platform height off the ground, as you well know.

Wouldn't a Berger 230 hybrid also work? I think it's a hair longer...

I wonder if there is a way to focus or aim on the farther target to eliminate the possibility of a paralax issue.

My plan is to make the 100 yard target above my line of sight to see my 300 yard aiming point and catch the groups on paper at 100. I will be impacting about 4-6 inches high at 100 with a 300 yard zero. I may even plan to impact higher at 300 to get more room on the 100 yard target. I'll try to shoot next week.

Yes, the 230 Berger is much longer than the 208 A-max. At the speeds I'm looking at (2400-2450 fps in a 308 Win), it shows a 1.05 stability factor. That's not enough. (Plus, this bullet is twice as expensive as the 208!!) With the 208, I'm looking at a stability factor of 1.27, which should be ok. 1.4 or greater is for sure stability, and the 1.3 area will also work, but is getting away from the 1.4 area. I don't like to go less than 1.3. My 208 out of my 300WM is a 1.35 at 2950 fps, which I've taken out to 1780 yards, and works well. The 1.27 should be ok. I think it's just right for this test.

That's the way I was thinking it could be done. It will be interesting to see the results.

Just out of curiosity why the 208 vs 178 if it seems you are having challenges stabilizing it?

I think the lack of stability, or right on the edge of stability is what exhibits this issue the best. Plus, I've already seen this issue with the 208 in a 308 before.

The way I read everything is that the bullet is the best stabilized leaving the barrel. So it's either stable or not.

A 178 out of a .308 Win will print small at 100 as well as 300.

The wobble on a top is caused by off axis torque (OAT), which is the same thing that causes a frisbee (one of my other hobbies is disc sports) to wobble when released. OAT is defined as unbalanced force applied in a direction other than the axis of travel.

To explain further -- imagine if you were dropping a top rather than spinning it on the table -- the axis of travel is vertical and any force on that axis will not cause wobble. Unbalanced force along the X or Y axes will result in wobble.

How could this happen in a firearm? My first thought is barrel harmonics causing unbalanced force on the bullet (as it is riding the wave it's being pushed up/down/side to side) in a direction perpendicular to the direction of flight. poorly cut/crowned barrels will do the same by allowing gas to exit on one side of the bullet before the other.

(edit to add details past here)

Further -- just as a top and a disc will quickly lose that wobble if they have enough spin, the gyroscopic inertia of a bullet will self correct and remove the wobble during its flight. That straightening/correcting force is not "free" however, and necessarily slows down the rotation of the spinning object as force is exerted.

I went to the range yesterday to get started on this project. My first load with the 208 A-max out of my 308 was a little hot. So I need to pull some bullets and reload them. I'll try it again in the next few days.