Is my theory right?
- Thread starter Boer seun
- Start date
maybe at close ranges like that it will generally be true, but not always, and not with all shooters. My hunting load out of my ltr, for example, will shoot the same groups at 100m it does at 200m -- about .75inch.
At 300m I get these groups as well, but not with the same regularity, although when it is not regular, I often know that I screwed up. Then at 400m the are noticeably more open.
At 300m I get these groups as well, but not with the same regularity, although when it is not regular, I often know that I screwed up. Then at 400m the are noticeably more open.
martinbns said:
That doesnt make any sense whatsoever. If the bullet stabilised at say 150 yards any instability that made the group bigger at 100 yards would still cause the bullet to deviate, it would not return to its old flightpath just because the bullet is now somehow stablized.
Also if the bullet is not spinning fast enough to be stablized by the time it leaves the muzzle how would it become more stable as it slowed down?
I have to agree with Helno. I do understand though that a bulet will become more or less stable depending on it's velocity. But what ever deviation from the intended can not be recovered and the bullet, even in it's possibley more stable flight will continue on the incorrect tangent.
Myself I usually have trouble at really short ranges replicating my sight picture with a scope. i.e I have an easier time achieving the same hold on a 100 yard target with a 4x then say a 25 yard taget with a 9x. It could also be the elevation of the short range target compared to the longer range one. At our range the 200yd target is noticabley up hill from the 25 yard target. Therefore your hold on the rifle will different. Could be you are just better at shooting at that angle.
Have fun with it, that is why rifles are interesting
D
Myself I usually have trouble at really short ranges replicating my sight picture with a scope. i.e I have an easier time achieving the same hold on a 100 yard target with a 4x then say a 25 yard taget with a 9x. It could also be the elevation of the short range target compared to the longer range one. At our range the 200yd target is noticabley up hill from the 25 yard target. Therefore your hold on the rifle will different. Could be you are just better at shooting at that angle.
Have fun with it, that is why rifles are interesting
D
In theory, there should be a regular predictable enlargement in group size. Occasionally this is not observed, and groups appear to be smaller at longer range in terms of minutes of angle dispersion that would be expected. Frequently groups are larger in terms of moa as range increases - this results from wind, velocity variation, bullet imperfection, etc.
As bizarre as it sounds, bullets do tend to settle down in flight.
It can be compared to a spinning top. As soon as you pull the string and get it spinning, it wanders around a bit, but soon stabilizes.
I recall reading where the US Army did penetration tests on steel plate with AP ammo. They sometimes found that the bullet went in slightly off angle at 25 yards, but hit square on at 100 yards, and penetrated further.
It is important to keep in mind the difference between line of departure, which of course would expand the group as you go farther away, and the small but measureable "orbits" that the bullet does in flight.
If you were sighting in a laser gun (dead straight light beam, no wobble, etc.), then your theory would hold true.
In reality, you probably will have a reasonable clue as to how your load will do at longer ranges, but not an exact micrometer reading.
It can be compared to a spinning top. As soon as you pull the string and get it spinning, it wanders around a bit, but soon stabilizes.
I recall reading where the US Army did penetration tests on steel plate with AP ammo. They sometimes found that the bullet went in slightly off angle at 25 yards, but hit square on at 100 yards, and penetrated further.
It is important to keep in mind the difference between line of departure, which of course would expand the group as you go farther away, and the small but measureable "orbits" that the bullet does in flight.
If you were sighting in a laser gun (dead straight light beam, no wobble, etc.), then your theory would hold true.
In reality, you probably will have a reasonable clue as to how your load will do at longer ranges, but not an exact micrometer reading.
Tootall's explanation of the spinning top is about as accurate as you can get.
An unstable bullet (do to not enough twist), is a bullet that will want to tumble so the back of the bullets wants to be ahead of the front of the bullet. This will cause a keyhole effect on the target. Literally the bullet hitting sideways and will never be accurate.
Short range BR shooter usually pick a flatbase bullet over a boattail bullet becase they are more stable (the bullet not the shooter) or go to sleep faster then a BT.
However at longer range (over 300 yards) the BT bullet settles down and will out do a FB bullet.
With that said, a bullet or load that shoots a 2 MOA group at 100 yards will not be a 1/2 MOA at longer range. Think of water coming out of a hose.
An unstable bullet (do to not enough twist), is a bullet that will want to tumble so the back of the bullets wants to be ahead of the front of the bullet. This will cause a keyhole effect on the target. Literally the bullet hitting sideways and will never be accurate.
Short range BR shooter usually pick a flatbase bullet over a boattail bullet becase they are more stable (the bullet not the shooter) or go to sleep faster then a BT.
However at longer range (over 300 yards) the BT bullet settles down and will out do a FB bullet.
With that said, a bullet or load that shoots a 2 MOA group at 100 yards will not be a 1/2 MOA at longer range. Think of water coming out of a hose.
I should clarify my earlier statement about the better groups at 200 vs 100 yards. I was referring to MOA, a group that measured 1 inch accross at 100 yards, would routinely measure 1.5 at 200 yards. The groups didn't actually get smaller, they got relatively smaller.
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OK here is something that needs an expert.
Now when a bullet leaves the muzzle its going lets say 3000f/s and with a 1 in 10" twist that equates (click click click according to my calculator) 216000RPM
Now the bullet slows down due to drag but what about the RPM The drag is less so the RPMs should not decrease proportionatly with the bullet speed.
So all things being equal the bullet is actually spinning faster in reference to its forward speed.
This may account for a more stable bullet farther down range... right ??
my brain hurts.
Now when a bullet leaves the muzzle its going lets say 3000f/s and with a 1 in 10" twist that equates (click click click according to my calculator) 216000RPM
Now the bullet slows down due to drag but what about the RPM The drag is less so the RPMs should not decrease proportionatly with the bullet speed.
So all things being equal the bullet is actually spinning faster in reference to its forward speed.
This may account for a more stable bullet farther down range... right ??
my brain hurts.
Here's the best read on the subject I've seen. Download the whole thing first if you're on dial-up.
http://www.nennstiel-ruprecht.de/bullfly/index.htm
RJM
http://www.nennstiel-ruprecht.de/bullfly/index.htm
RJM
