Home Forums Hunting & Shooting Long Range Hunting Smaller dispersion at longer range than at close range.

And it is a safe bet that they have the parallax sorted out too. I don't think benchrest shooters would be keen to shoot groups with a scope giving them parallax error at the distance they are shooting at.

All time records are, by definition, anomalous events. It would be unwise to make general judgments from them.

No, the aggregate figures are based on a collection of data and are statistical. Don't look at the other figures, look at the aggregates, as pointed out earlier.

I agree, aggregates are better to look at than records, records being anomalies as stated above.

Having said that, something to consider about the records listed in the link above is that (I'm 99% sure) the numbers are normalized to 100 yards. In other words, the records are reported in MOA not absolute inches. That's why you can have a single number represent an average for multiple ranges.

Example: Walt Berger, 5 10-shot groups at 100, 200 & 300, record is 0.3555. Not inches, but normalized to 100 yards.

I've seen BR match results reported this way, and I'm almost certain that's how these records are reported.

So, looking at it that way, the records are indicating (in almost every case) that the longer distance groups are proportionally larger than closer range groups.

-Bryan

I've still seen no evidence that those groups are smaller at long range than at closer range.

The fact they are similar in size isn't what's being claimed

No one has yet SHOWN evidence of a rifle that shoots a smaller group at 300 or longer yds than it can at 100 yds

They just keep saying they can do it

Take the test and there will be no mystery

I checked with our friends at 6mmmBR. The records are recorded in inches. The 200yds. record, in inches, is divided by two for a direct comparison to the 100yd. The respondent could not answer definitively re. the 300yd agg. record but is probably done in the same manner. Those things being true, the dispersion is linear with slight increases for the increased exposure to environmentals. Appears we still have no evidence of smaller groups at increased distances.

Maybe it's something that happens with firearms and ammo that are less than benchrest standard? SMLEs and M14s are not benchrest class.

I suspect it only "happens" on the internet, since there's no empirical evidence it's real at all

I think I know the likely answer to this observation now � it�s in the second webpage link that I included in an earlier post. And from my experience it seem now to relate to sporter/service weight rifles that must be using ammo that has somewhat more liberal velocity variations.

It seems that a slower velocity projectile will leave the barrel as it points slightly higher due to recoil and the fact that a slower projectile stays longer in the barrel. On the opposite hand, a higher velocity bullet will leave the barrel as it points slightly lower. This means that faster projectiles will hit the target lower than a slower one (same weight projectile and at close distance). Don�t know how true this is � don�t recall what happens when I work up loads.

Further down the line, the trajectories will intersect as the slower bullet (initially shooting high) will drop down across and below the trajectory of the faster bullet (initially shooting low).

I did some calculations using JBMBallistics on-line software, and some assumptions, and it does show increasing accuracy (decreasing MOA figure) out to the trajectory cross-over (of course). I assumed a 144gn 308 with a velocity of 2800fps nominal and +/- 100fps variation. I�ll post an image of the trajectory chart later.

Plugging numbers into a program isn't real world data

Also, comparing trajectories and the POI of different weight bullets still has nothing to do with the claims that a particular gun with a particular load will shoot smaller groups as distance increases

I've never seen a ballistics program that could predict "accuracy" (as in group size, not POI) at all, since unless the numbers change, theoretically they should all hit the same spot.

No, it's the same bullet weight but at different velocities. The different trajectories and cross over could be misconstrued as varying accuracy, which I suppose it is really. After all, accuracy comes from consistency.

It's really easy to test in real life too - you don't need to shoot through the same targets at multiple ranges. Just need to load up to give different velocities (ie decrease the powder charge) and compare the POI at different ranges.

People don't factor in the effect of recoil on the angle of departure (me either - sounds counter-intuitive that it would result in trajectory crossover, given that slower projectiles are supposed to shoot higher at close range as a result).

I'm going to test this one day.

{Edit - Oops, I hadn't linked the correct article, here's the one I meant. Please read the second paragraph carefully:

http://www.targetsportsmagazine.com/features/view/10157/303-british-compensation-claims/

Looks like the poms had it figured out for some time

You have just successfully described the whole concept of using a tuner as is commonly applied in benchrest rimfire. Without the ability to tune the barrel harmonics, and control bullet exit timing of
different velocity ammo, the match winning accuracy that displayed today wouldn't be possible.

The only real life test of the claims being made is for one of these folks to SHOOT that rifle at multiple distances with the same load on the same day with witnesses to verify the groups are consistantly smaller as range increases

All the calculations and load variations do NOT matter because it's not about "POI" of individual shots

It's only about group size, and no one will step up an take the test, even with a man offering to pay the expenses

The "compensation" effect in the link you posted, according to the author, only applied to the 303 Enfield, and not all rifles

Bear in mind, witness accounts are not entirely reliable. Speak to the police who have to interview witnesses after an accident or crime, and each witness's account will be different and conflict with the evidence from someone else. The trouble is that we interpret things and that affects what we "store" away in our memories.

The individual shots become the groups.

If no-one has come forward yet then I suspect that it is just a product of someones memory and interpretation ie not a reliable account.

Compensation for barrel flip applies to all firearms but the extent varies - it's physics.

From my experience/accounts/memories, I'm convinced that the velocity variation/recoil/vibration is the answer. It makes sense to me. I will test it myself one day but I'm not in a rush to do so - don't have the time or easy access to a long range.

Once again, each of those groups is an independent event. Such a trial, witnessed by 1 or 1 million, has absolutely no relevance to the posed hypothesis.

One must shoot a single string with every shot passing through targets spaced at a variety of distances. Each target will capture each shot. Then and only then can one claim that those groups describe a single event. He will have to show "dispersal" and then a subsequent "regrouping" as those slugs go down range. It's the ONLY way. I'd like a free trip, but don't have equipment that can do it.

Slugs dispersing from a common path at any point in their flight will never experience any sort of mid-flight correction capable of guiding them back to a common point. The processes depicted below cannot and will not ever happen.




Mauserand9mm: With some extremely serious science and velocity manipulations one can have vertical dispersion initiated at the launch point regroup as gravity and atmospheric effects expressed themselves. I.e. In BPCR a 45-70 shooter might use the upper path, and a 45-90 shooter the midline, and a 45-100 follow the lower with each launching slugs from a common rest for their muzzles. All arrive on target, but due to velocity differences follow separate paths. The paths depicted immediately above, however, would not be accurate renderings given that rates of fall would be more severe as we move downrange for the slower slugs. In practice though, we strive for a central aiming point and consistent velocity with our ammo. The central issue to the discussion here is mid-flight horizontal and vertical dispersal, followed by a regrouping in both axes. Just can't happen.

Too bad we can't get our boys in space to set up a range and eliminate atmospheric and gravity effects. It would be fun to "dial in" and test this at a range of several miles or so. Any budding astronauts out there or a shooter with connections to NASA?

I agree - but that would be only to prove if it were a spiral bullet path, which I now sincerely doubt. If it is a product of velocity variation/vibration then you don't have to shoot through multiple targets at different distances with the same project.

I'll post the graphs with explanation this evening when I get home (at work at the moment) - I hope this will better explain what I've found.

Deleted double post

I think it could help if results were consistant, and the farthest groups actually were smaller

The multiple targets could accomplish the task with fewer shots fired, but I imagine the shooters whose claim was disproved would then say the results were flawed because of the extra targets

But, as I said in the beginning, no one is going to take the test

Okay, this explanation satisfies my experience and what I have heard from others about increasing accuracy.

On the graph below, the green line is the trajectory for a nominal load (in this case a 308 144gn at 2800fps). The blue line is the trajectory of a 2700fps round assuming this variation with the ammo being used. The lower velocity means the bullet stays in the barrel longer and exits at a higher angle, due to recoil and muzzle flip.

The red line is a round at 2900fps once again assuming this variation (+/-100fps) with the ammo being used. It exits the barrel earlier and hence lower (less exposure to muzzle flip from recoil).

You can see that the trajectories intersect at around 325yds, so the MOA would be less here than at 100 or even 200yards - it looks like the accuracy is increasing.

http://i795.photobucket.com/albums/yy237/mauserand9mmagain/trajectories/0to500_zps8b316926.jpg

Of course this assumes no accuracy error at all ie the group size is dependant on the difference in point of impact dispersion only.

I modified the chart to add a range of accuracy (1MOA - consistent across all ranges) to each trajectory, and have calculated and added measured group sizes at each range in inches and MOA. You can see MOA increasing towards 325yds then start dropping off afterwards, as the trajectories start spreading further away from each other.

http://i795.photobucket.com/albums/...ajectories/0to500dispacc_zps319640b6.jpg

The purple line is group size (values on RH axis) and brown line is MOA (values also on RH axis).

You don't seriously think those guys are using ammo with a 100 fps velocity spread, do you?

The charts and graphs are pretty, but they prove nothing about THESE claims