What keeps a round from holding MOA

[StrayDog]

I have several rifles that are good shooters. Sub MOA at 100, 200, about right on MOA at 300.
But by 400 they are way out.
I read about guys holding MOA at much longer ranges, is it because of barrel weight? Or some other shooting mystery?

 

[sdiehn]

This is usely due to the bullet shape and design it is how the bullet will react with the loss of rotation example a rifle with marginal twist rate will not be as stable at longer ranges.

I have loads that wont shoot worth a spit a 100 yards 1.5 MOA but group size at 200 may only be 2 inches and not much bigger at 300 2.5 to much spin.

Barrel weight will afect accurcy but a good shooting barrel of any weight will shoot good at any range

 

[brian b]

straydog,
It is no mystery it is probably a Tasco scope or 3x9 syndrome. get a good scope and use better bullets
B

 

[JBM]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>This is usely due to the bullet shape and design it is how the bullet will react with the loss of rotation example a rifle with marginal twist rate will not be as stable at longer ranges.<HR></BLOCKQUOTE>

I'm curious to know why you say this. The forces acting to slow rotation are less than those trying to slow the bullet which means that the forces trying to overturn the bullet decrease faster as a bullet goes down range and therefore the bullet should get more stable (of course at the speed of sound, all bets are off).

 

[STL_Shooter]

Stray,

Accuracy is contributed to, or detracted from, by a whole host of issues.

Before you go off thinking that a rifle that shoots reasonably well at 100 yards falls apart at 400 because of a marginal twist rate, well - you'd better do some searching of the older posts on this site.

There's alot of wisdom that's been delivered over the last few years that you'd be better off gleaning from...

 

[Mysticplayer]

Straydog, assuming good quality bullets, I would steer you towards these areas: Velocity variations, shooting rests and technique, wind, and mirage.

It is not uncommon to see this type of situation. I can usually trace this back to poor powder burn/large vel. variations. Most commonly shown in ball powders especially older styles ie military surplus, and some extruded powders.

Used a ball powder in my hunting '06 that shot inside an inch at 200yds. Thought that would be great for LR. At 500yds, it wouldn't hit a 8X11 piece of paper.

Switching to a new type of consistently burning powder ie Hodgdon Extreme line or Reloader, problem goes away. I now use H4350 Extreme and get consistent sub MOA to as far as I want to shoot.

Are the groups stringing? If vertical stringing, then your load is probably at fault. If horizontally, it is probably the wind.

The further you shoot, the more important environmental conditions are. Mirage and wind can send you all over the map. Not easy to shoot MOA at LR even if your gun can.

If your load is stable and you are using quality bullets, once it gets to 300yds, it will continue to be accurate until it hits the ground. Bullets only show some dispersion when they go trans sonic (sometimes) which is a long ways from where you are.

How are your rests? Shooting technique? Try getting the most solid repeatable set up. A little variation like where you rest the rifle on the foreend from shot to shot, will make a big difference at long range. Rifle torque/roll during recoil can also 'throw' your shots off.

Good luck with developing this rifle. Shooting LR is not easy. That is why it is so addictive and fun.

Jerry

 

[LB]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>I have several rifles that are good shooters. Sub MOA at 100, 200, about right on MOA at 300.
But by 400 they are way out.
I read about guys holding MOA at much longer ranges, is it because of barrel weight? Or some other shooting mystery? <HR></BLOCKQUOTE>

In addition to what has already been said, I have two words: wind.

Good hunting. LB

 

[StrayDog]

The 400 yard groups 6 shot groups are usually a horizontal oval shape (wind) and I do have the 3 x 9 syndrome and hunting bullets, not target bullets.
You guys mentioned variable velocity rates, which could also be contributing, because I don't yet have a chrony.
So there is hope of improvement.
Thanks guys

 

[sdiehn]

Stray what kinda rig is this cartrige and rifle if you know the twist rate and what bullets are you useing

JBM I would realy love to hear you make these arguments to some of my shooting buddies one who I belive to be the best barrel maker in the world bar none.Second if twist rate is not a factor why do we have difrent twist rates I gave a example of a under rotation problem now how about a over 155 palma bullet out of a 1-10 and beef up the load the bullet will hold together but is as accurate as a pig in a poke. Lets also not forget hatchers note book and a section on spin drift!! what about the green hill formula

[ 10-28-2004: Message edited by: sdiehn ]

 

[sdiehn]

the bullet will lose the amount of rotation that is need to keep it stable.This is why you have difrent twist rates for difrent leanght bullets

I have shot the 107 seirras out of a 243 witha twist of 1-11 at 100 yards they were tack drivers but at 200 they were all over the place this is a extreme case as the bullet should be shot threw a 1-9 twist and 10 would be marginal.

I would be willing to bet if you looked close at the targets when the load loses accuracy at a spacific range say a 400 yard target that you find that the holes are not round. you wil need to keep a specific RPS to keep the bullet stable

 

[JBM]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>the bullet will lose the amount of rotation that is need to keep it stable.This is why you have difrent twist rates for difrent leanght bullets <HR></BLOCKQUOTE>

Yes, it loses rotation, but it also loses velocity. The forces that are attempting to yaw the bullet come from forward velocity. The forces maintaining stability come from rotation. The velocity forces fall faster than the rotation forces so the stability goes up as the bullet goes down range.

 

[JBM]

<BLOCKQUOTE><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><HR>JBM I would realy love to hear you make these arguments to some of my shooting buddies one who I belive to be the best barrel maker in the world bar none.Second if twist rate is not a factor why do we have difrent twist rates I gave a example of a under rotation problem now how about a over 155 palma bullet out of a 1-10 and beef up the load the bullet will hold together but is as accurate as a pig in a poke. Lets also not forget hatchers note book and a section on spin drift!! what about the green hill formula<HR></BLOCKQUOTE>

I never said that it wasn't a factor. I said that bullets that are stable at the muzzle tend to stay stable going downrange (again, all bets are off as they cross through the speed of sound). We have different twists to make different bullets stable at the muzzle. I don't deny spin drift exists - I've seen it with my .338/.416. Greenhill's formula I can do without. There are much better programs/formulas available.

 

[BountyHunter]

Number of reasons.

bag technique is more critical at long ranges

bullet variance in base to ogive

load variations that give large ES

poor quality scopes

Pick a reason and most of the time, combination of several.

Popular misconception, groups can tighten up at longer distance. Yes, and it is called a "freak accident", but it will not happen normally or more important repeatedly. if it will not shoot good at 100, no way it will shoot good at 500 or 1000.

BH

 

[sdiehn]

What i was orginaly trying to get at was that a lot of times when you find a load out of a good gun that shoots great out to 300 -400 yards you will usely find that the bullet is marginal for the twist.Now if its a gun that has some throat erosion this will compond the problem

one of the guys i use to work with had a 240 NM with a 10 twist (this gun shot sub .250 5 shot groups) and shot the international 3 postion he went and practiced at 300 yards before going to Fort Benning the difrence was 300 yards to 300 meters that difrence with the fact the throat was on the way out was masive. He set the barrel back .060 not much for a bad throat and the gun begain to shot again this rifle even when he first built it would not shoot 600.

There are a lot of pricopals and formulas that peaple use as a absulute hard and fast rules. this has to be because the math or computer says so. But in all acuality the practical use and experiances are tottaly difrent.

My guess is that stray is useing a lite bullet in a faster twist barrel say 130`s in 30 cal. and a 10 twist or heavy bullets in a slow twist say 80 grainers in 223 cal. out of a 10 or slower twist.

When I try to diganose a problem their is a process that I go threw steps to find out what may be the problem one of the most commom problems you find is that shooters are useing the wrong bullets for what the barrel is set up for varmint bullets out of heavy game barrels or heavy game bullets out of varmint barrels