i shot my custom 7mm rem mag,factory ammo 100yds 1.5 inch groups @ 100yds and 3/4 in. groups @ 200 yds i thought this was supposed to be the other way around,my sendero in .300 win mag did the very same thing.any explanation would be helpful, i think it may have something to do with bullet stabilization??

Yes - I have heard of this in Benchrest circles - The only way it was ever explained to me is that the bullet needs to "go to sleep" and is doing that once it passes 100 yards - curious are you using any wierd twists?

Any signs of keyholeing or wierd holes at 100?

no keyholes or weird barrel twists pac-nor told me exactly what to get for the bullet weight i'm using, my sendero shoots 190's only will not digest anything else worth a hoot.

Wow - that is wierd - does it happen with different lots of bullets? IE Lot number 123 does it but lot number 456 does not. What about changes in load- does it happen with every load you have tried - how hot are you pushing them?

Thinking you got some wierd bullets - I don't know - I have heard of it and can not remember the cause or solution - just one of those wierd bit you pick up and never really remember.

Parallax. Your scope is likely parallax free at 200yds, and not so at 100.

Chuck

My CZ 550 in .308 will do that. Better groups at 200 that 100 altho sometimes their close.

I have a mildot scope with AO. I think the bullet stablizies past 100 yards.

A 5 shot 100 yard group by steve y trying out my CZ.



Some of my 3 shot 200 yard groups (if I hold my mouth right )

For a good explanation of this phenomenon, go to Yahoo!Groups, then to JGBS (Jos�'s Gallery of Bullet Science), then to Links. Under the Links listings, you will find a German Ballistics program/tutorial How Bullets Fly. Click on it.



It explains how under certain circumstances bullets fly in decreasing diameter spirals (sometimes compound spirals, that is, spirals within spirals), resulting in smaller groups as distance increases...up to a point...then at still longer distances, groups open up again just as one would expect.



Alberta Canuck

To save everyone the hassle of having to go through Yahoo! Groups, here is the actual link

"PCB Piezotronics Ballistics site
This is the best site I know of for learning about the flight of projectiles through air, in plain English. It is sponsored & maintained by a major German producer of ballistics instrumentation, and an international forensic ballistics association. Their equipment is in current use by NASA, law enforcement agencies, and various nations' military establishments throughout the world. All told, the site prints-out at about 100 pages or more of top quality, readable bullet science."
http://www.nennstiel-ruprecht.de/bullfly/index.htm

Alberta Canuck

My AccuMark, .300 Wby does this with 165gr Ballistic tips. Have not obsevered this with 180gr Partitions. My understanding is this happens more with boattails than with flat base bullets.

Save yourself the trouble, we are talking about a 1.5" group, people: bullets do NOT make 1.5" "spirals" through the air! Any "wobble" or "spiral" would be much less than one bullet diameter.

The only likely cause has already been mentioned. Scope parallax. The view at 100 is distorted, but the view at 200 is dead on. An inch of parallax is not unusual at all. FWIW, Dutch.

I've noticed the same thing with my Mod. 70 beanfield gun. It shoots @1" groups at 200 yrd.s with 175 grain Fed. Prem.and about the same at 100 yrd.s. I've read a lot this year on the topic and it's like Alberta Canuck's article says. An ultra-light version of the article might say, "Like arrows, bullets need to fly a while before they fully stabilize. Some may fly further than you'd think.

My solution for eastern whitetail involves scouting with my rangefinder and depends on what I figure the max. range is likely to be: Inside 125 yrd.s my 12 ga. rifled slug gun, inside 250 yrd.s my light-weight 7mm 08, inside 325 yrd.s my .270, and inside @500 yrd.s my 7mm Mag. I don't shoot enough beyond 400 to be comfortable shooting at a deer beyond that. But then I do really, really love guns.

Obviously you did not go to the site and look at the data there...bullets make much larger than 1" spirals through the air under certain conditions. And, I note, we are not talkng about "wobble" here. That is an entirely different phenomenon.



Also, the spiralling is additive to all the other dispersion factors of the load, and even when substantially eliminated will not (of course) give a 0.0" group. Elimination or reduction of it during flight can, however, cause a rifle to shoot smaller groups at 200 yards than at 100 yards.



Often the spiraling can't be eliminated with the components at hand. But knowledge that rifles CAN shoot smaller groups at 200 than at 100 does at least suggest to people who want to hunt and shoot animals at longer ranges, that they should actually TRY their loads at those longer ranges, rather than just chuck them away because they won't shoot sub-1" groups at 100 yards.



Alberta Canuck

It's not neccesarily parallax .



Bob Hagel wrote about this phenomenom years ago , it's not uncommon with 7mm mags and long heavy bullets . As teal 325 said , the bullet has not quite settled down yet at the shorter ranges.



If it is parallax , a change to a shorter , lighter bullet would not tighten up the the short range groups

This is not at all uncommon, and it happens with many rifles...

It takes awhile for a bullet to stablilize, depending on the bullet..Mostly has to do with the base of the bullet it seems and the harmonics of a barrel I suppose....

In my experience bullet dispersion is only rarely linear. I have more than a few rifles that group better on a MOA basis at 200, 300, 500 and 600 than they do at 100. FWIW, 100 yards is a poor test of a rifle's accuracy potential. Most rifle don't really exhibit their true accuracy capabilities until you get out to and beyond 300 yards.

And yes bullets really do "fly" in the purest sense of the word. How well they fly is a function of many factors including how well the bullet is made, ballistic coeffecient, and whether they are launched from a platform that is consistent and true among others.

Alberta Canuck,
You'd be even more alarmed by my synopsis of everything I ever read about bullet performance.

Bullet performance on game is affected by so many variables it is almost impossible to predict accurately although idle shooting buffs entertain themselves endlessly in the pursuit. Hunters can make more efficient use of their energy by using enough gun and shooting a reasonable bullet that shoots well in it.

Holzauge -



I certainly agree with & appreciate your synopsis of bullet performance.



There are so many variables in almost all facets of shooting science that it is almost dumbfounding...and that's probably the reason it is so attractive to so many of us. Kinda like a chinese puzzle within a mystery, within a riddle, within an enigma...not sure we can even take it apart, let alone put it all back together again on demand.



The older I get and the more I learn about shooting, the more I personally lean toward a "performance objective" orientation...that is, the more I ask myself the question, "What do I really need performance-wise to accomplish the purpose to which I am going to shoot this gun?"



Then, once I get there, it is time to go shooting and enjoy the sport, and not to fret over .0000321794" more induced accuracy, or .0000777111-framises more bullet penetration, expansion, or weight retention.



And, ya know what? That more and more drives me toward guns that will reliably shoot 1-1/2" groups, with bullets of 200 grs. or more weight, at velocites between 1,000 and 2,400 fps. Welcome to the early 1900's era, eh?



Best wishes,



Alberta Canuck

Right you are! Shooting is like quicksand waiting to suck you in. Frankly, it's one of the reasons I've never started reloading. It takes more time and energy than I can spare now to keep up with all the other aspects of hunting for me to develop a new obsession. One of my hunting buddies has gone your route. He has a half dozen custom Sharps reproductions, casts his own bullets, and spends hours smelting, alloying, and fiddling around trying to shoot as well at 100 yrd.s as any modern factory gun will with the right factory ammo at 200 yrd.s. I've gone a different route and focus on others aspects of the sport. I've given up things like blackpower in favor of stainles steel, centerfire guns with composite stocks, shooting factory ammo. Then I obsess over the difference between 3/8" and 1/2". If I only had a 300 or 400 yrd. range nearby! I guess you pick your own poison.