100 yard groups same as 200 yard groups

[RH45]

I bought one of their uppers when they first came out. A freind of mine liked the way mine looked so much that he bought one too. Since then two of my other fellow shooters have bought them, but, I haven't heard how they like them.

I think I might have recieved a prototype. Mine is the only one I've seen with a black bolt. All others I've seen have had a chrome bolt. They are "supposed" to have a 1/2" group guarentee, but, mine won't do under 3/4" at 100 yards with any of like 30 loads tested. But, with Hornady v-max, or Hornady 68 grain match hollowpoints, it will also hold 3/4" at 200 yards. My freinds Gator will hold under 1/2" at 100 yards with several loads I tested through it. When I was trying to find the most accurate load for it, I called Clark, and was told that 55 grain ballistic tips were the most accurate, but, that has not been what we found. When I told the lady that the best it would do at 100 yards was 3/4' and that my freind's shot under 1/2", she said that was too bad. I guess I expected that she would have me send it in, but, she didn't seem to think it was a problem. I also had the glue on the carbon fibre hand guard come loose, and was sliding around. When I called about that, she said I should get some epoxy and re-glue it, which I did.

Other than those problems, it has been running 100%, even with a broken gas ring, which seem to have broke at the 2004 DPMS tri-gun challenge. DPMS replaced the set of rings, on the spot at no charge. I think it is supposed to be some kind of secret, but, DPMS makes the Gators for Clark.

[reneet]

They are "supposed" to have a 1/2" group guarentee, but, mine won't do under 3/4" at 100 yards with any of like 30 loads tested. But, with Hornady v-max, or Hornady 68 grain match hollowpoints, it will also hold 3/4" at 200 yards.

We guarantee a 1/2 MOA. If your rifle doesn't shoot that ... send it in for evaluation.

Renee Tyson

Clark Custom Guns, Inc.

[George]

Someone doesn't understand that 3/4" at 200 yards is a bit smaller than 1/2 moa ;-)

It is typical for rifles that hold small moa at distance with .223 heavy bullets (62 gr and up) to be a little sloppy at 1 hunnert'. The bullets haven't stabilized yet. 3/4 at 2 hunnert' is bragging level stuff.

[John Heiter]

If your gun will hold 3/4" at 200 yards then it seems to me that it would almost have to hold less than that at 100. All of the bullets are originating from the same point so to create a 3/4" group at 100 means that the bullets are diverting from the theoretically ideal flight path for some reason (variations in bullet weights, densities, powder charges, barrel temps, wind, humidity, etc.). The further downrange they go, the more they are going to spread apart as they each travel their own path. The combination of factors required to cause those diverging bullets which have a 3/4" spread at 100 to suddenly stop diverging and then travel parallel courses for the next 100 yards (or somehow alter course and converge again) is one I can't really imagine. I won't say it can't happen once, but I will say it's highly unlikely. If yours can do it consistently then don't send it in to be fixed because you've already got a magic barrel and Clark is usually sold out of those.

I think the most likely scenario is that there are some inconsistencies in your tests. Maybe the rounds you shot on your 100 yard tests happened to have more variation than the random selection of 200 yard test ammo, maybe your scope focuses better at 200 so you had a better hold, etc. I'm not saying you should be satisfied w/ 3/4" at 200 if your goal is to be better than that. Do what you've got to do. I'm just saying that if we could have measured your 200 yard 3/4" group when it was at 100, I'm betting it was pretty tight.

John

[George]

Nah, it's perfectly normal for heavy .223 projectiles to not be stabilized at 100 and be looser than farther out as far as MOA goes.

The lighter ones are less likely to do it as much as the big VLD's, but they will do it in certain bbl's.

[John Heiter]

Hi George,

I can buy that it takes longer for heavier bullets to stabilize but I'm not sure I get how a group can consistently grow smaller further out. Can you explain that one to me?

[EricW]

Gyroscopic precession is the only explanation I have. The bullets spiral around the trajectory defined by bore axis and as the spin rate slows, they converge onto central flight path.

All I know is that the phenomena Geo is talking about *seems* to happen with my AR with 69 grain sierras. Groups at 100 are loose, but lock right into place at 200. I would have said the same thing as John until I experienced it first hand.

[George]

S'truth. There are several promising explanations, but the only correlations are that it does happen with the heavies which are typically longer. The highpower boys noticed it first of course as the benchresters don't care about anything but 1 hunnert' and shoot flat base shorties for that reason.

I personally lean towards the "wobbling a bit fore and aft so they sorta' swim around until the spin rate actually points the base straight back" theory. Eric's is another contender too. No matter the reason, it does happen with the heavie's.

[John Heiter]

Well, RH and all, you have my apologies then. Won't bother to edit my original post because I said it...still not sure about understanding it, but I'll take your experiences for what they are and let it go.

[George]

BTW, the group does not actually grow smaller, it's just that it stays static for 200 yards, then diverges. Think of it as a 200 yard long bbl and the dispersion starts when it leaves the muzzle ;-)

[EricW]

Geo,

Gyroscopic precession *is* why they "wobble." Every, unrestrained rotating object in a gravitational field does it to some degree. What's happening cannot be random, or the groups would disperse over distance, not tighten up, then disperse.

GP is why the constellations in the Zodiac change over time. The earth effectively "wobbles" on it's rotational axis, thus pointing the north pole to different stars over time. Polaris' reign as the "North Star" is only temporary thanks to GP.

What's happening with longer bullets is that the extra length accentuates the distance the tip and tail of the bullet travel through and that is why the phenomena is noticeable.

I don't have definitive proof or a set of equations, but physically, that's the only systematic explanation I can think of. One of these days I'll try to draw a picture, which will be much more explanatory.

Edited April 6, 2006 by EricW

[RH45]

Someone doesn't understand that 3/4" at 200 yards is a bit smaller than 1/2 moa ;-)

It is typical for rifles that hold small moa at distance with .223 heavy bullets (62 gr and up) to be a little sloppy at 1 hunnert'. The bullets haven't stabilized yet. 3/4 at 2 hunnert' is bragging level stuff.

That is the conclusion I came up with too, but, although I've never shot my freind's Gator at 200 yards, it will shoot groups half the size of mine with most of the ammo I've run through it. We awere both running Leupold 6.5-20 scopes for the testing.

[George]

There is also some credence to the possibility of the boat tail shape of the rear allowing the butt to stick out into the slipstream slightly as GP wobbles it without it getting beat back into place like a flat base edge profile would. That's another postulate about why they are able to be swimmin' about at a hunnert' instead of being pushed into line by the slipstream along the sides at the tail immediately upon leaving the bbl.

[tightloop]

The bullet yaws coming out of the barrel and does not fully stabalize in the first 100 yds but between 100 and 200 everything falls into place and total dispersion is usually less at the longer distance than the shorter one... Usually with heavier bullets...the faster twist plays hell with the heavy bullets as they leave the bbl...that is why all the bench shooters shoot with a bbl that is on the ragged edge of stabilization for a particular bullet weight..

[Bill H]

It could be that he has a percieved smaller aiming point at 200. Aim small miss small.

[Dan Sierpina]

S'truth. There are several promising explanations, but the only correlations are that it does happen with the heavies which are typically longer. The highpower boys noticed it first of course as the benchresters don't care about anything but 1 hunnert' and shoot flat base shorties for that reason.

I personally lean towards the "wobbling a bit fore and aft so they sorta' swim around until the spin rate actually points the base straight back" theory. Eric's is another contender too. No matter the reason, it does happen with the heavie's.

What ever the explanation is, it does happen. A friend's Rem 700 with Krieger 7" twist, shooting 107 Sierras shoots 3/4" at 200 and 3/4" at 300 yards. The barrel on my AR is a Wilson 9" twist, that someone said didn't shoot. I put a Douglas on his AR and he was happy. I then took the "bad" barrel and shortened it to 18 1/2" and it shoots under 3/8" at 100 with H335 and 52 grain Sierras. Sooo....I kept the junky barrel. Maybe shortening it changed the harmonics, don't know why it shoots now as opposed to when it was 20".

[BPiatt]

Dan,

Maybe all it needed was a re-crowning.

I too have a .308 that shoots around 1 1/2 inches at 100 meters

and shoots 2" at 385 meters. I haven't played with too many bullets.

If you're just a 100 yard shooter, I hear flat base bullets do better up close but I haven't confirmed that myself.

Edited April 7, 2006 by BPiatt

[RH45]

Dan,

Maybe all it needed was a re-crowning.

I too have a .308 that shoots around 1 1/2 inches at 100 meters

and shoots 2" at 385 meters. I haven't played with too many bullets.

If you're just a 100 yard shooter, I hear flat base bullets do better up close but I haven't confirmed that myself.

I did have it re-crowned. Before that, it wouldn't put any load under an inch at 100 yards.

I didn't realize that the brake was pinned in place at the time and messed up the threads on the barrel a little bit too.

[Dan Sierpina]

Dan,

Maybe all it needed was a re-crowning.

I too have a .308 that shoots around 1 1/2 inches at 100 meters

and shoots 2" at 385 meters. I haven't played with too many bullets.

If you're just a 100 yard shooter, I hear flat base bullets do better up close but I haven't confirmed that myself.

Bruce,

That barrel was one from an AR when I was sponsoring the rifle match at the Miller. The winner of it, was someone from down South. I felt obligated to change the barrel for him and keep him happy, which he was with the Douglas that I put on. The 243 I refered to, was Mark M's. He also had me shorten the barrel of a Model 70 that he picked up, that didn't shoot so well, at least not to his expectations. After shortening the tube to 22", groups at 200 were cut in half with the same load. The wierd thing is that he just tossed the scope back on, and the first shot cut dead center of his aiming point at 200 yards. The headstock on my lathe is short enough that I didn't have to pull the barrel to do the work. There are theories about the best barrel length for a given cartridge. Again, the barrel harmonics. If that is the case, who knows, just shortening the muzzle brake could make a differnce.

[kellyn]

BTW, the group does not actually grow smaller, it's just that it stays static for 200 yards, then diverges. Think of it as a 200 yard long bbl and the dispersion starts when it leaves the muzzle ;-)

+1 on that observation.

[Run n Gun]

Wow! This is a great (if horribly drifted) thread. I FINALLY get an explaination as to why my rifle groups are 3/4" at BOTH 50 and 100 yards!

Thanks guys,

Ed

[George]

I hear flat base bullets do better up close but I haven't confirmed that myself

I have and they are. I am not sure if the lack of a boat tail (see my earlier post on this), or the shorter length are the main factors, but for whatever individual, or group of reasons, they do stabilize right out of the bbl unlike longer, heavier boat tail profile projectiles. The Flat Base testing I have done in my CTR-02 delivered one 1/4" hole at 50 yards and just under 1/2" at 100, but grouped almost 1.5" at 200 with the SMK 53gr FB. Whereas the boat tail SMK 77's that ran 3/4 inch at 50 and at 100, also ran just under an inch at 200 yards.

[EricW]

If a bullet group maintains the same diameter of dispersion for a particular distance (say 200 yds) the *angle* of dispersion is getting *smaller* over that distance.

S = R * theta

[George]

When the projectiles are in a pre-stabilization mode, I don't think the term dispersion has any real meaning until they change the mode and stop yawing. Until the yawing gets under the amount that masks the dispersion rate , dispersion doesn't exist in a realworld measurable form, they really are acting like they are inside of a finite diameter tube and bouncing randomly off the walls as they careen down the pike.

In this case the walls of the tube/bbl are the wind slipstream that touches the base when it yaws out into it. The tip of the projectile opens up a wavefront disturbance in the air and creates a zone of calm the sides of the projectile are usually in. Outside if that is a hard wall of static air molecules that is in effect a boundary layer not much different than the inside of a tube at the velocities in question.

[EricW]

Geo,

I'm sorry to call you wrong, but that can't be happening. It *seems* like it is but it ain't. It just ain't.

What is going on is NOT random. And the projectiles are NOT unstabilized. Repeat: the projectiles are NOT UNSTABILIZED!!!!!! An unstabilized projectile will always produce an increasing angular dispersion over distance. The involved forces do *NOT* magically cancel one another. Random process do not magically combine to produce total dispersions less than any one of the processes involved. If they do, they are NOT random, they are systematic.

What people are observing is SYSTEMATIC.

The term "dispersion" has just as much meaning 2" from the muzzle as 600 yards.

I am not a benchrest shooter, nor a highpower shooter, nor a good rifle shooter. I am someone who has a degree in physics and engineering and I can tell you for a fact that random processes do not behave in the manner that is being observed. But, I know this is the internet and you and everyone else have the right not to believe me, and I'm sure that no one will.

Edited April 7, 2006 by EricW