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Bullet Stabilization Questions

 
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  #22  
Old 01-23-2004, 09:08 AM
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Re: Bullet Stabilization Questions

"I have talked to a few guys who make bullets and to a man, each has tried shooting bullets backwards. Even at 1000 yds, they see no difference in accuracy."

Damn, sure hope I get some of those "backward bullet shooters" on my next relays. That is one thing, I have got to see to believe!!!!!

BH
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  #23  
Old 01-23-2004, 02:00 PM
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Re: Bullet Stabilization Questions

JR

You trying to take all the fun out of it.

I still want them guys on my relay if they want to try it, but at other end of the line.

BH
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  #24  
Old 01-23-2004, 09:57 PM
MAX MAX is offline
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Re: Bullet Stabilization Questions

Well now, backwards bullets eh?! One of my specialties for "short range shooting"! [img]images/icons/grin.gif[/img] I've yet to compute drift or drop, but a Hornady 148 gr HBWC loaded backerds over 3.0 gr of Bullseye will flat screw up an armadillo! Field tested out to about 10 yards so far. Shoots to same POA too! [img]images/icons/cool.gif[/img]

Actually, I did load some 40 gr. Speer spire points backwards once for a Hornet whilst trying to develope some squirrel loads, and they shot well out to 50 yds but I didn't try further.

The "going to sleep thing"... According to Vaughn and a few others, most bullets exit the muzzle with at least two(epicyclic) precession modes, one fast, the other slow, and the resultant motion is a rosette pattern. Sort of a long arc interspaced with short loops. The short loops are the fast cycle precession which is the one that damps out for the most part around 200 yards or so, depending on GS. The slow cycle mode has a dimension of that may shrink in circumstance of high GS, or grow somewhat with marginal or low GS. Slow precession cycles do not null, and are continuous for the duration of the bullet's flight. At ranges typical of benchrest competition these issues are of small import, however, the precession cycle represents yaw from flight path, hence DRAG. It reduces BC. This is one reason that short range bench shooters may prefer flat base bullets and slow twists, whereas you fellows might like to err on the side of faster twists and higher GS. Do I need add High BC?

All yaw or precession cycles have a resultant value, that is, an average value. Even though a bullet may have an epicyclic(dual) precession mode, or tricyclic(3 or more) mode, and yaw of repose is in play, it all boils down into a single resultant value. As velocity changes, so too does the GS and this in itself results in more "trouble". How do we ever hit anything with a bullet? [img]images/icons/confused.gif[/img] [img]images/icons/grin.gif[/img] This is one reason the 6DOF programs were developed and are so useful in ballistics research. Hope you have a supercomputer handy...

To clarify one comment I made above, I do not know how to quantify or express "turbulence" that may be associated with transonic flight. The region of highest DRAG that will be encountered in the atmosphere occurs between Mach .75 thru approx. Mach 1.3, and for most forms drag DECREASES as Mach increases above this speed range. I know things happen when a bullet slows thru this range, but not what or why.

It's Miller Time...
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  #25  
Old 01-24-2004, 12:08 AM
JR JR is offline
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Re: Bullet Stabilization Questions

Bounty Hunter,

When he says there was no difference in accuracy, maybe he meant didn't hit the target whether the pointy end was out or in, therefore neither was more accurate than the other..ha..

Right..here's my take on why some shoot better at 1K than 100yds..when a bullet exits the muzzle, it leaves with a slight angle of yaw, where a force acts upon a point on the Center of Pressure, which wants to make the bullet want to overturn on that axis and, well tumble..The spinning motion of the bullet should negate this effect, bringing gyroscopic stability, and the bullets precess around it's center of gravity, giving you nice neat little 1/2 minuter's.

Basically, the more wobble the bullet has as it leaves the muzzle, the longer it will take for the spin to correct..If the spin can not correct in the distance you are shooting, due to barrel whip, due to imperfections in the crown which deflect the bullet slightly off a reasonable angle of yaw, aerodynamically the bullet is presenting more surface to drag forces, which will in turn affect the BC, which will lead to spotty shooting..

Also, if you have a reasonable 100 yds shooter that won't group at 1K could be because the bullet is understabilised, or even overstabilised..WHOAH!! ha..

Keyholes at 1K are often due to the bullet's stability thru the transonic zone, a region right at the speed of sound, which is one the most horrendous afflictions to flight. Not just necessarily that it must be going 'x' fps, but have a bullet with a high BC and a spin rate to match, to cut thru the cheese.. using .223's(AR) shooting 90gr JLK's at 1000, have found that a 1/6.5" twist is preferable to drive this round thru accurately..1/7" just doesn't seem to cut it..It is preferable to remain supersonic at your yardage..ha..

but, I digress with my hoo-ha..

JR
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  #26  
Old 01-24-2004, 12:51 AM
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Re: Bullet Stabilization Questions

I think MAX has made some pretty good sense here. I also have used 3-5 grains of bulls eye!! I filled 2 cases with epoxy resin up to the bottom of the neck and drilled out for a flash hole. Sounds like a cap gun. He he he!! [img]images/icons/grin.gif[/img]

I think some bullets will stabilize quicker than others. I have noticed higer BCs in some bullets between 100 and 300 where as others didnt have much of a BC till after 300. An interesting side point, in the Sierra manual, they disscuss what each bullet was desighned for. Some are stated to have an optimum accuracy range of 100-600 yards, like the 168. Others are 100-1000 yards like the 155 and 175. Some are 300-1000 yards like the 180 and 190. I think the 240 was 600-1000 yards. Obviously bullet design and ballance have a little to do with it. Come to think of it my experianc with the 168 and 155 and 175 and 190 seems to be concistent with their statments. Also as far as bullets being fired backwards, the twist will stabilize them the same. They might wake up faster though. If you think about it, they might stay stable longer because of the forward weight. Ever shoot an arrow w/o vanes?? It works because of the forward weight. It might not be as accurate but it does work.

[ 01-24-2004: Message edited by: meichele ]
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  #27  
Old 01-24-2004, 09:59 AM
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Re: Bullet Stabilization Questions

I would like to see those backwards bullet targets myself.
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  #28  
Old 01-24-2004, 11:16 AM
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Re: Bullet Stabilization Questions

I am a little curious. Some here have said in 1 post that there is NO relationship between GS and BC. In others its stated that BR shooters use differant twists to offer differant GSF for shorter ranges.

If this is the case than it obviously matters what the GSF is to get a another BC.

Many shooters and even some bullet manufactures have done tests to show that in most cases using typical bullets that when a major change in GS occurs, a change in BC ocurrs as well. This would indicate that GS has a relationship with BC.

Think of this. If a bullet continued to wobble slightly for 600 yards before it settled down, what do you think that would do to its BC?
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Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
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