Odd grouping


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wgp
January 7, 2013, 10:52 AM
I tried out a new (to me) Savage .308 yesterday at my range, using handloads that have performed well in another of my rifles. Perfect day, no wind, from a bench. I got consistent 1 1/2" 3-shot groups at 100 yards. But, when I tried 200 yards, the groups tightened to 1", some shots almost touching. This has never happened to me before, groups getting tighter at longer range. Thoughts? Did I just happen to shoot those 200 yard shots better or does somebody have experience that might explain such a thing?

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USSR
January 7, 2013, 11:05 AM
You said you got "consistent 1 1/2" 3-shot groups at 100 yards", but nothing about "consistent" 1" groups at 200 yards. I suspect you shot one 200 yard group that was extremely good, and you will not be able to shoot consistent 1" groups at 200 yards. Also, 3-shot groups are not the norm. Typically at least 5-shot groups are recognized as being valid.

Don

ironworkerwill
January 7, 2013, 11:17 AM
you may have a parallax issue with that scope. I held a Nikon once that had a wandering point of impact less than 100 yds, it wasn't much but i could tell the difference may be a 1/2'' or so. also I think 3 shot groups are fine for deer. If your a bench shooter one inch 3 shot groups at 200 yards would be lackluster any way.

Centurian22
January 7, 2013, 11:17 AM
I'll be interested to hear the experienced shooters weigh in on this. I have heard of this happening before where certain rounds (and I believe it was .308) didn't 'settle in' until beyond 100 yards. The concept baffles me but then so did barrel harmonics the first time I heard about it.

hardluk1
January 7, 2013, 11:19 AM
With a new rifles shooting and cleaning can make for solid groups 20 to 50 rounds later. Not before. groups may shoot well and may not. Give it time to break in before worry'n about groups. NO break in , better get that barrel cleaned. The size of your target can effect how stead you hold on a center aiming pin. Some target types, like a 4" circle fit the scopes retical better at longer distances and that can allow for a tighter grouping. Also dumb luck helps sometimes. Keep moveing the yardage out. See what happens at 400 yards.

Hunting rifle ?? Don't worry about three shot groups . make note when you go to the range what the first shoot does then the next shoots. For hunting that cold barrel clean and dirty mains everthing to a good clean kill and a bad shot.

wgp
January 7, 2013, 11:43 AM
Helpful comments, keep them coming. This is a used rifle, I have cleaned it thoroughly and the bore looks good and the crown of the muzzle also looks good but beyond that I have no knowledge of how it was treated by the previous owner(s). The scope is a cheapie that came with it, it will be replaced.

I am particularly fond of the "dumb luck" comment, that may turn out to be the best analysis. Further shooting will tell me.

With my hunting rifles, my practice for a range session is to watch carefully where that first shot from a cold barrel goes -- no question that is the standard.

Trent
January 7, 2013, 11:45 AM
You may be experiencing a peculiar phenomenon associated with bullet runout, first noticed by the British when developing the 303. They noted a peculiarity with bullets "Settling In" as they travel downrange, becoming more accurate as they traveled.

Bullet which are "tilted" ever so slightly as they engage the rifling will remain so when they travel down the rifling, and leave the muzzle slightly crooked.

These bullets then start to "spiral" once they leave the muzzle.

As the bullets fly downrange, the spiral diminishes and the bullets "settle in" to a stable flight path.

This causes bullets at shorter ranges to shoot larger MOA groups than bullets at longer ranges.

It's harmelss; for the most part, but you aren't getting optimum accuracy at shorter ranges.

Make sure your sizing and seating dies are squared up properly.

Otherwise, not much you can do.

murf
January 7, 2013, 11:53 AM
wgp,

what is the load? bullet, powder and primer used

murf

ironworkerwill
January 7, 2013, 02:07 PM
rounds don't get more accurate as the go down range. we can have some fantastic imaginings of mechanical phenomena. First its a savage and second its a .308. This thing aught to be able to shoot sub moa all day long.

Trent
January 7, 2013, 02:21 PM
rounds don't get more accurate as the go down range. we can have some fantastic imaginings of mechanical phenomena. First its a savage and second its a .308. This thing aught to be able to shoot sub moa all day long.

Incorrect.

Several extensive studies have been done on this; go read Dr. Mann's work for a starting point.

Trent
January 7, 2013, 02:24 PM
1909, Dr. Mann "The bullet's Flight, from powder to target"

http://books.google.com/books/about/The_bullet_s_flight_from_powder_to_targe.html?id=QdQqAAAAYAAJ

One of his experiments was to put very thin sheets of paper at ranges along the bullet's flight path; it demonstrated that bullets DO spiral in flight, and that they CAN settle down to a stable flight path.

ironworkerwill
January 7, 2013, 02:35 PM
I know bullets dont seat in the riflings properly on occasion. I also am not saying bullets wont self stabilize from a WOBBLE. However when the projectile is moved out of intended point of impact it will NOT correct its self. IF it does I want some.

Trent
January 7, 2013, 02:42 PM
Look up "Helical flight path."

This has been studied to death for over a hundred years, has a sound physics model, and was observed in doppler radar testing by the army. You need a 6 axis ballistic simulator to predict the flight path, all commercial ones that I know of are only 3 axis.

Dr. FW Mann first published findings on the phenomenon back in 1909, it as since been a subject firmly beat to death by physics students. :)

When a bullet leaves the muzzle tilted, precession can cause the bullet to engage in a helical flight path (a spiral, as it were). This flight path causes the bullet to "orbit" the true trajectory. In the end it either destabilizes or settles in, depending on many factors (including severity of the precession).

So yes, bullets can, and do, get "more accurate" down range, under certain circumstances.

It's become part of the standard accepted theory on exterior ballistics, and part of the reason why such emphasis is placed on creating "true" concentric bullets and precision reloading dies.

ironworkerwill
January 7, 2013, 02:59 PM
I understand completely the nature of your post. I also understand helical flight paths completely. I disagree with the assumption of "more accurate down range". It is more feasible to assume parallax is the issue.

Trent
January 7, 2013, 04:13 PM
0.5" tightening of groups is well within the possibility of a helical flight path. It's about the max of what could stabilize; much more than that and it's just going to destabilize and "pick a direction" at random.

If it was 2.5" or some other absurdly large change, it would be ruled out completely.

But, parallax is a possibility. :)

Ramone
January 7, 2013, 05:27 PM
I refuse to believe that a bullet will 'settle in' and become more accurate at a greater distance.

BUT I have seen it, with my very own eyes. The groups did not get smaller -that is 1" at 100 yards did not become .75" at 200, but instead of 1" at 100 yards becoming 2" at 200, it became 1.5". This was repeated with the same rifle and the same loads on 3 separate occasions.

SO, I got nuthin.

adelbridge
January 7, 2013, 05:31 PM
If someone was shooting a muzzle braked .300 win mag next to you at 100 and no one was at the 200 bench I could easily see your groups improving.

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