sleepy bullets and group size

[milanuk]

OK. Here's one for the hardcore ballistics gurus:

I've heard the theory batted around about some guns having a tendency to shoot somewhat smaller groups proportionally at distance than they do up close. Seems to be more prevalent w/ the long spiky high B.C. VLD style bullets out of fast twist barrels.

I've seen something that certainly looked like that, where I had a gun, in .308 Win, that would fairly regularly shoot say, a 3/4" group at 100yds (0.75 MOA), then 1-1/4" group @ 200 (0.63MOA) and 1-1/2" @ 300 (0.5MOA). Somewhere btwn 300 and 600 the group size started opening up 'normally' to where it was a little over 0.75MOA @ 600yds. I've also followed threads where it would appear that this happens somewhat regularly to others. Even in shooting sports like HP, competitors are often cautioned to do their load workup @ distance, as their best 600yd load may not look that hot @ 300, and vice versa - a load that looks sweet @ 300 may not hold together for the long yard line. Ditto for Palma distances (800,900,1k) compared to 600.

Recently I've encountered a fellow who apparently has access to several Oehler 43's or else has acquaintenances who do, and is quite adamant that there is no way in heck that that could possibly take place, as it's never been documented to his knowledge over 'real' targets in the form of acoustic or radar targets; that the groups always get bigger, *always*. Given the 'anecdotal evidence' as he refers to it of my experiences, I get a lot of talk about unstable bullets making ragged holes at shorter ranges. When I point out that other people have seen this as well, I get some babble about how other people have seen aliens and believe in them as well. So at this point we've just agreed to disagree

It does have me curious, though. Have any of you long-rangers seen anything to make you believe one way or the other? I don't really care who is wrong or right, but darn it, if I'm wrong, I *really* want to know what was going on those days at the range

TIA,

Monte

 

[Kevin]

Very Interesting topic,

From what I have seen I would say it is possible for a gun to shoot better in terms of MOA at range. I cannot see where it would be possible to shoot a better group, that would mean that the bullet is making a sidways arc and therefor would really only be on zero in regaurds to windage at one range. But I do think that it is possible to shoot say .75in groups at 100yards and 1" groups at 200 yards and 2" groups at 400 yards. Because I have seen it. I think this happens when a bullet is just on the verg of stabilization. MY gun that does this is a 220 Swift AI. The barrel is 16 twist and I shoot 55gr bullets around 4250fps.

 

[Brent]

Milanuk,
I was going to ask you if you were familiar with the Oehler 43's acoustic target, but you went on to actually mention it.

I actually have one and am getting ready to run this very test here in less than a week or two. I've got a broken leg of PVC pipe on it right now, almost cut the wires running through the PVC my pistol when I hit it!

I could get set up and test tomarrow if I ran to the hardware store and got another stick of PVC, but it's my Dad's B-Day tomarro and we're already to go and have a bunch planned to shoot already.

I'm fixin to set the acoustic target up at 100 yards, then the target frame at 300 yards to try and lay this to rest for myself, I have seen it happen too. I don;t remember which loads, but it was with a 12 twist 308 and possibly even my 416 wby, but I'll just have to shoot for a while to see what I find. The nice thing about the acoustic target is that it doesn't interfere with the bullet in flight.

It will tell the tale if it happens.

I've shot enough groups with the 210 JLK now that I think it's not an issue with it in my 11 twist, it shoots too tight at 100, and pretty much extrapalates to my 300 yard groups.

I'm not convinced I'll even find anything interesting the first time out trying this, and more than likely it will take seeing it happen at some point down the road then further range tests with the acoustic target to validate, or dismiss it.

 

[jb1000br]

Keep us updated Brent--Im interested too

JB

 

[MAX]

There is a very recent and long discussion on this subject on page 2 of this forum, "Bullet Stabilization Question", posted by Wyoming Whisper. It may provide some answers to your question.

The factors at play are fairly complex, and most of the top echelon ballisticians say "No.", but they are looking at it purely from the aspect of bullet dispersion. The one precession cycle that does null in the bullets flight is very small and likely of small influence, but it does occur in the first 200-300 yards of flight. A more likely thing(s) that influences this to my thinking is parallax, changing wind, and variations of load/bullet balance that will occur from one round to the next.

It is likely that this debate will continue for all time as the resoultion to the question involves far too many variables to control. I'm no rocket scientist, but that's my opinion.

 

[MAX]

Luck to you Brent. It is a thing of very fine discrimination that you tackle here. Do you per chance have of of Vern Jeunke's concentricity devices? I'd think sorting the bullets would be an advantage. Wish I had your "facilities" for load testing. Sounds nice.

 

[Brent]

Max,
Yes, I have an I.C.C here too. I'll do that.

 

[5Redman8]

I would have to blame it on parallax.

Kyle

 

[Mikecr]

What I see from gurus are pictures taken in houses which aren't haunted. "see...no ghosts".
I'm glad to see Brent is actually LOOKING for the ghost before taking pictures. Thats gonna be the only way to catch it.
I wish I could test one of my rifles there. It's zero'd@250, and has always shot tighter there than 100(in moa).
Good luck to ya

 

[Michael Eichele]

I cant explain it, but I was shooting a month or so ago testing the 155 AMAX. At 100-600 yards the groups were all between .75 and 1.0 MOA. When I went to 1K (same day and time frame) it shot 3.5 Inches. I figured it must be a coincidence. I went back to 1K and shot a 4.5" group. No coincidence there! No I was not high, drunk or under the influence of any aliens or the such...These phenomenons exist. Why?? Nobody has yet to explain it, or at least prove it scientifecly.

Bear in mind that the example above was not different days or in differant weather. It was all on the same day. All groups were fired within minutes of eachother. It will repeat this craziness almost daily.

[ 02-27-2004: Message edited by: meichele ]

 

[4mesh063]

Monte,

I have a couple targets hanging on my reloading room wall. They were shot after a great amount of time and effort setting up an experiment. I shot 2 10 shot groups at 100/200/300 yards onto 8-1/2x11 targets. These were shot with some initial setup so the bullets would all be on paper. What I did was arrange the targets on tripods with transpartent targets. (thin paper targets with no backer). The same bullets traveled through all 3 targets and the same group showed up at 100/200/300 yards.

The test showed that THE SAME BULLETS after passing through a sheet of paper arrived at a tigheter MOA at 300 than they did at 200 and a tighter MOA at 200 than they did at 100. Now, this is not my immagination and I'm getting a little tired of people who say that they can't believe this when they have never tested it for themselves. Perhaps my 10 shot groups (2 of them) shot this way (it took an entire day to set up and get results). is an accident. I don't think so. My inclination before this and my entire reasoning for doing the test was that I had seen this phenomenom regularly and had no choice but to test for this very condition. I found it to be true. My 1K guns show this every week as do yours.

It never fails to amaze me how people can shoot guns regularly and do all of it with thier eyes closed.

 

[Blaine Fields]

I've seen a number of attempts to explain this apparent phenomenon, but I think that the answer may lie in a topic that I've never seen discussed in these forums. The cause may originate from "aerodynamic jump" which is a lateral displacement of the bullet that occurs at the muzzle due to bullet tip in the chamber, i.e., the lack of concentricity of the bullet and the bore. As I understand it, the bullet exits the muzzle and immediately must deal with an abnormally high yaw angle. This angle causes a sideways movement, but then the bullet stabilizes and heads down range. The jump is not trivial in terms of distance and may explain why group size in terms of MOA can actually get smaller with range.

[ 02-28-2004: Message edited by: Blaine Fields ]

 

[Brent]

Max,
I'll be shooting more than one group to decide this one for myself. 3-5 groups all indicating the same exact thing would peak my interest, like 1.5 MOA at 100, then 1.5 or 2 MOA at 300 would be something to consider, if wind wasn't an issue that is. Our shooting 300 yard range at Birchwood is pretty protected, and windless days are found a good share of the time but, that's not really the case on the river bar I do a lot of shooting on. There are good calm days, but wind is still moving at times up to 1-2 MPH here and there, on occation it's dead calm.

 

[Brent]

At one point along the way I was getting this impression groups were often better at 300 that they were expected to be from my previous 100 yard groups, and it didn't take long for me to realize if the air was calm, I could at least, for the most part, elliminate throwing out a possible good load, if this were to be happening by testing at 300, not 100.

I still hate shooting at 100.

Shot a 1.2", 3 shot group at 300 today with the kids 308. Wish I could say they were all that good, but another 2.75" and 4.25" was reality talking!