I have seen this happen before, but who has a theory for why a rifle that is 3/4 MOA at 100, but then shoots 1-1.25 at 200. I have a nice FN Mauser that does this day after day, a lot of groups in the 3/4 in. range at 200, never over 1.5, but it has absolutely never shot a .5 100 yard group. I have also seen some the other way, .5 at 100, 1.5 at 200, etc. The particular rifle I'm talking about now is a .338 WM loaded with RL19 and 210 TSX. I think the 3/4 at 200 will work on caribou and moose in a couple months. I've been shooting it every week for 6 months and the results are consistently in this pattern.

I witness this quite often. The reason why ,however, is beyond my scope of knowledge. There are days that it happens out to 400 yds.

Be that as it may it seems your concern stems from hunting accuracy. Well if your first shot falls within 3/4" of point of aim at 200 yds. I'd say you have arrived. roger

In Centerfire Benchrest shooting, I always shot better 200 yard groups than I did at the 100 yard line.
I think it has to do with the bullet going to sleep at about the 100 yard line, then flying true from there on.

bartsche

I guess it really isn't a concern, as far as hunting accuracy goes, just would like to know why. If I could find out the theory behind it, maybe I could cure the ones that group larger (relative to distance) at the longer ranges.
DMB
By using the term 'going to sleep' at 100 yards, do you think it is something similar to what a lightweight arrow does up close, wobbles a bit then straightens out at 15 yards or so. If so, then it may be due to the twist being a bit quick for the lighter bullets. What's your guess?

Does the sensitivity of scope focus and parallax adjustment at closer ranges have anything to do with it ?

Think the tolerances for those adjustments at longer ranges are broader.

My Savage in .270 WSM is not afflicted at all like that. Last time I was at the range, I was getting .25 MOA groups at 100 yards. I moved back to the 200 yard range and was getting .5 " groups. I bet if we had a 300 yard range, that day the group would have been .75 ". I think it all has to do with twist and bullet stabilization. Some bullets from some rifles may take longer to stabilize than others.

I am sure the bullet company employees could talk about this subject but they do not seem to join in here.
Someone could call Sierra.

Quite frankly, when it concerns bullet length and twist rate, which it does, I am a little gun shy at the moment.

heck, anyone noticed that if you sight in for low at 200, but better groups, the gun somestimes shoots better at 100?

HEH, here's a thought... try the same "shoots better at 200" rifle, and turn the scope down 2X (if it's on 9, turn to 7) and try shooting at 100 again....

i think alot of people "chase the gauge" with too high a power scope.

twist? only if shooting a long for calier bullet

quote:

twist? only if shooting a long for calier bullet

quote:

It was found that the faster a bullet is spun the larger the expected group size would be , given a predetermined amount of bullet imbalance.

Higher RPM can only be achieved from a given barrel by increasing speed. Speed can only be significantly increased if the bullet is lighter. For similarly constructed bullets, lighter bullets will be shorter.

quote:

too high a power scope

I do not think such a thing exists. On stationery targets, the better you can see, the tighter the groups will be.

I also agree that most of the phenomenon can be explained by scope characteristics, settings, and vision quality.

The only reason for this that I've heard simply comes down to WHEN the bullet becomes stable... Some bullets/weights may achieve their best stability out of your rifle past the hundred yard marker... Others may stabilize before...

Ken....

quote:

I think it has to do with the bullet going to sleep at about the 100 yard line, then flying true from there on.

This is the prevailing wisdom amongst Hi-Power Long Range shooters. Some of them think that it won't truly "go to sleep" until about 300 yards. Many long range (Palma) rifles will shoot better the farther out they go. When you are driving a 155 gr. MK at over 3000fps, that little bullet is yawing quite a bit until the velocity decreases some and becomes more gyroscopically stable.

I'd tend to think it was the shooter himself..

I have a depth perception problem.. but the further out I go, the less my eyes are affected...

I shoot better at 200 and 300 yds, than I do at 100 and 50 yds...

I have also noticed the differences in loads, that don't group well at 50, yet tighten right up at 100 yds...can be the powder, can be the bullet.. too many factors to come up with a hypothesis in my book...

Shooters always need to rule out the shooter first, when something isn't going according to plan...

The spin rate in relation to the bullet length is what causes it. My .220 swift, pre 64 model 70 never shot under 1" AT 100 YD's, but I shot several 1/4" groups at 350 YD'S. I killed chucks to 600 yd's with it. Over spinning the bullet makes close range large groups and when the bullet goes to sleep it will group better. If you could watch bullet flight, you would see it yaw around the flight path until it becomes stable.

Seafire

I don't have that problem. On the same day, I can shoot my 7x57, it will shoot 3/4 at 100 and 1.5-2 in. at 200. There is no consistency with this happening with me, some rifles are that way others I have are the other way, some are 1MOA at all distances. This .338 will flat shoot as good at 200 as at 100. I suspect the high power shooters have the best idea. A slight bit of yaw up close that evens out. Somewhere I think I remember reading where someone tested BC's on bullets from 0-100 yards and from 100-200 yards and they were different. Their explanation was a slight amt. of yaw.

Well I can imagine a bullet "wobbleing" for a while, but when you think of the speed it's spinning, I have trouble imagineing the bullet leaving its actual path to give a worse group at 100 than 300. If that was the case why would the off line bullet magically realign to the same path at greater distances?

Heck, I've had keyhole bullets still accurate enough to stay in the bullseye at 900 yards.

Still, too many people have reported it for it not to be happening sometimes.

Optics and shooter focus are my pet theory. The parallex setting on most scopes are supposably set at 100yds for non AO scopes. It could be with some scopes that in the manufacturing process, the scope parallex setting was set at a point that would correct beyond 100yds.
I cannot visualize a bullet that is off in the x or y at 100yds drifting into center at greater distances with wind and such being the same for all bullets within the group.
I take more time and focus to shoot 200yds (range max) and that might give my barrel more time to cool down between shots. Even so, my 200yds groups are usually double what I get at 100.

Like JAL and sonar59, I have a problem with a bullet that has moved off the original flight path having any tendency to return to that flight path. So yaw and "going to sleep" doesn't do it for me.

Parallax seems the likely culprit. Even though most of my scopes have a parallax adjustment and I make an effort to position my eye in the same spot each time, some of my rifles do seem to group better (MOA) at 200 than at 100 yds.

Just to muudy the water a bit, the scope power and reticle and the target itself are also factors. Just how precisely can you hold that same point of aim at different distances?

When larger minute of angle groups occur at closer range than further out, it is not because the bullet goes off the flight path and then returns, it is actually corckscrewing around the flight path. There are two oscillations and they may worsen as in the case of the illustrations below, opening the group as distance increases, or they may dampen out, as may be the case with the 7mmRM under discussion, improving the grouping further out. All this is twist and bullet length/shape related. Note that the illustrations show a spiral shaped bullet path, not up and down as it seems at first glance. Illustrations are from "How Do Bullets Fly?"

Very good. We have observed this through a spotting scope with S&W .44's where the bullet rotated around the flight path. ( they looked like a corkscrew.) Going to a heavier bullet eliminated the problem.

Gerard is thinking along my lines. The thing I'm describing is not optics related. If you have one that does this, you can change scopes till death and change nothing. I recently reread an article someone had a report on the new Savage target rifle. Some of their loads shot 1.25 at 100 and were sub-MOA at 500 yards, exactly what I am describing. None were consistent in size from 100-500 yards and this was a rifle that was shooting some 1-2 in. groups at 500.

My guess is that a bullet that is not spinning is less aerodynamic and does not have a CONSTANT flight path.

Thanks for the illustrations and link Gerard. After looking at the web pages and illustrations though, the diagrams would seem to be even more complex when the trajectory is drawn in. The first example of a .38 cal wadcutter would probaby drop greater than 30 inches within that 8000 caliber distance. I'll have to hope my rifle and bullet combo shoots more like the second example. From the illustrations can anyone decipher what the unit of measurement is on the left X and Y axis?

quote:

Originally posted by sonar59:
Thanks for the illustrations and link Gerard. After looking at the web pages and illustrations though, the diagrams would seem to be even more complex when the trajectory is drawn in. The first example of a .38 cal wadcutter would probaby drop greater than 30 inches within that 8000 caliber distance. I'll have to hope my rifle and bullet combo shoots more like the second example. From the illustrations can anyone decipher what the unit of measurement is on the left X and Y axis?

The line denotes to path of the tip of the bullet, X and Y are Horizontal&Vertical yaw degrees(the odd symbol in the middle is the symbol for yaw). The bullet path itself is approx down the center of the spiral. Both illustrations are for dynamicaly unstable bullets.

Very fastinating article, and explaigns very nicely why bullets "go to sleep" at a certain point very well. I had always assumed it was transference of angular velocity arround the bullet path that caused groups to spread or tighten at different ranges, I never would have geussed that bullets have so much yaw as they travel.

It seems to argue for heavy bullets, high twist rates and high velocities for short range and lighter bullets, low twist rates and moderate velocities at long range. Lots of food for thought here.

I'm getting a headache....

AD

Wow was my math off last night! Working the numbers thru the 8000 calibre distance would be 80yds, not 240 (a figure I saw on the webpage). A total vertical bullet drop of only 3.0 inches and bullet yaw angle of possibly 15 degrees. That explains the wadcutter bullets Ive seen at the 50 yard target board stuck non perpendicular.

quote:

Originally posted by Allan DeGroot:
I'm getting a headache....

I've got one. OK I'll believe anything done as a scientific drawing, esp where I can't understand it.
But thank goodness my "accurate" rifles, don't seem to act up. Either with fouling needs for accuracy or damn corkscrews.

A 1-12 .223R 55gr shot into 7/16 @ 100 yards yesterday (again). And factory 46gr goes 5/8 at 100 and double that at 200.

A 1-9 .223R 80gr isn't meant for 100 yd shooting but stays under 1" and 69gr are better.
From 200 yards out it must have gone to sleep cause from 300 yards it's a keeper.

I'm happy others have all the problems.

JAL,
You put your finger right on the point. When all is within spec and the way it should be, there are no problems. Rifles act the way they should when the dimensions come together as the designers intended them to be. When things do go wrong, there is always a reason for it and the quickest way to the solution is to check the equipment against the specs. In rifles, the spec that is most often off, is twist rate. After that comes the chamber neck diameter and then a host of other stuff such as bore/groove diameter, bore taper, squareness and concentricity.

There are often very good pointers when a troublesome rifle comes my way. For example, if the target shows mostly horizontal dispersion, I start with the rifle. If the dispersion is largely vertical, I start with the ammunition. Reasonable groups with the odd flier, points to ammunition first (easy to check) and, if not found there, the rifle second (more difficult to isolate).

The funniest things I ever watched through a scope was when a friend was shooting 200 meter rams with his TC 30-30. I would watch his bullet go all the way over to the next ram in line and swing back and hit the one he was shooting at. I never figured out how he hit anything.
We were shooting at a black spot at over 200 yd's, offhand, just for fun one day when the sun was just right. We had a .44 SBH and a S&W 29 with 240 gr bullets. You could watch the bullet go all the way down because the sun lit the bases of the bullet. Looked like tracers. Bullets from the Ruger ran a straight path but from the Smith, the bases flashed all over because of the corkscrew flight path. We had seen this many times in a spotting scope at the range. We found going to a 250 gr or heavier bullet in the Smith would make a straight path. The funny thing about the Smith was that I shot a lot of 50 meter groups that measured 1/2" with 240 gr Hornady's. It sure never hurt the accuracy but the Model 29 was super grip sensitive and I never shot a good score with any of them.

See: https://forums.accuratereloading.com/eve/forums/a/tpc/f/5611043/m/185106546/p/1

Simultaneous firing thru paper testing should be done, both normal guns and rail type.

Lets see someone pick the theory that makes the most sense out of this pile of junk.

OK - now explain why I've got a 204 that will shoot about .4 at 100, 1.3 at 200 and 1" at 300. Now try that out on you headache only thing is all them bullets hit the prairie dog

I WISH I had such problems.
I have been waiting for 2 weeks for the wind to die down.