No, I don't mean that the bullet flies its trajectory with excessive yaw, nor do I mean shooting round corners!

Just been out shooting two 100grain bullets in the 243 - the pointed soft point shoots smack bang on zero windage, the round nose is consistently 1.25 inches left at 100 yards.

I can live with it but.......

why?

It's because of the difference in the induced vibrations of the two different loads. The bullets are leaving the barrel at different points in the vibration cycle.

Thanks Lar - I just knew it wouldn't be hard.

Add to what Lars said one bullet has more bearing surface inside the barrel, one spire point and the other round nose. Also are these reload's using the same powder or store bought?

[ 10-02-2003, 23:35: Message edited by: 4bambam ]

I'll buck the trend and say I think its your rifle. Horizonal strings are an indication your barrel needs to be floated. See what can happen is your barrel rests upon the stock and after each shot it rests at a different horizonal point. Therefore each bullet is launched in a different horizonal direction. Floating the barrel allows for the barrel to reach its natural resting point, which should be the same for all subsequent shots (assuming you aren't overheating it).

I had a new .270 which had this problem, had 3" horizonal strings. I floated the barrel and it dropped down to solid .7" groups. Terrific rifle now.

-DallanC

Been thinking alot about this. I am a physics type of dude being an engineer. Which means I think too much.

Ok, The vibration is started due to the load being fired. If a barrel is straigt and uniform and free floated, the vibration should be all around the barrel. Not whip the barrel one way or the other.

So if everyones theory on why POI changes with different bullets is correct. then that would mean the defects in the barrel shape is the reason for POI change. Cause the frequency of the vibration should be totally uniform around the barrel. If it was totally unform then it wouldn't matter which bullet you used, it wouldn't whip the barrel one way or another.

Did that make any sense?

Yes Bigcountry, it made sense.

What I think you overlook is that internally in a barrel are forces (stresses) left over from manufacturing which can cause the harmonics to change. Different bullets smack the riflings with different force according to case pressure etc etc causing harmonics to change. I was also a physics major

-DallanC

Bullet mat'l. length of bearing surface, take your pick. It is a great rifle that shoots all bullet types of the same weight into the same group.

If you have ever seen an ultra slow motion film of an arrow being shot at 290fps from an overdraw compound bow you wouldn't believe it. Nor would you ever shoot one without thinking about it. Man do they vibrate. Rifle barrels vibrate up, down and all around also. Thinner more than thicker. Smooth more than fluted or octagonal of the same thickness. Barrel harmonics are a hard thing to study as everything happens so fast. Some think the harder bullets ( barnes for instance ) cause more harmonics in most barrels an thus more rifles are picky about shooting them. Bearing surface; bullet hardness, degree of polish of lands and grooves, tight and loose spots in the barrel, copper fouling; etc all come into play in vibration and friction. Add it all together and it explains how different bullets shoot to different points. Even when they weight the same and all other components are the same.

[ 10-03-2003, 03:26: Message edited by: Old & Slow ]