Rifling ratios

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Elvishead

Moderator
I been thinking for the last few years that rifling ratio (1:16 ratio for example), what it meant. Was 1 one full spin for every 16 inch's of travel, or is it an aspect ratio were the bullet spins 1 inch for every 16 inch's of travel?

BTW 45ACPs are close to that, were is 9mm are close to 10:1 ratio's.

Sorry I hope I made sense, but I'm tired and I'm ready to go to bed but I've been thinking about this for a while.
 
Not sure if I got that straight, but the aspect ratio's are percentages, so I'm going to bed soon and I'll see what you all think about that concept.:confused:
 
I been thinking for the last few years that rifling ratio (1:16 ratio for example), what it meant. Was 1 one full spin for every 16 inch's of travel, or is it an aspect ratio were the bullet spins 1 inch for every 16 inch's of travel?
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You are correct in your first statement. If the twist (it is commonly called "twist rate" not "ratio") is 1:16, it means the bullet would make one complete revolution in each 16 inches of travel down a barrel (and beyond the barrel).
 
I hope it's okay to add on here. So what does that translate to in terms of capability or rifle strengths? the higher ratio, the better for lighter weight bullets?
 
You're trying to stabilize a projectile so you spin it just like throwing a football ! The longer the bullet the tighter the twist necessary. Yes it's length not weight. So a 150gr pointed bullet needs tighter twist than a 150 gr round nose bullet.
The 223 and 5.56 originally came with twists of 1:14" and 1:12" but now the twist may be as tight as 1:7" to stabilize the longest military bullets.
 
ABC's Of Reloading Has An Explination

In the book "ABC's of Reloading" 8th Edition, Chapter 6 defines rifling twist, has what I think is a good explination of twist rate in relation to bullet length and gives a standard formula for calculating optimum twist rate for a bullet.

I am sure there are many other sources but this is the one I have been reading lately.

Have a good day.
James
 
Yes it's length not weight.
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They actually both come into play eventually.

The Greenhill formula contains some inherent assumptions about stability margin and projectile density (and thus polar moment of inertia).

Stray very far from the assumptions used and you can have problems.

For most common bullets we can purchase higher weight is longer length.
At the margins bullet shape can affect length in the same weight (spitzer vs. round nose) and cause problems if you are near the edge.

Changing form a barely stable round nose to an equal weight spitzer might cross the boundary and not be stable.
 
And you still have to ask your gun what it likes ! :rolleyes:
BTW it can take some distance to stabilize a bullet .In other words you may get a 100 yd 1" group and a 200 yd 1.5" group.Especially with a very heavy bullet like a 160 gr 6.5 or 175 7mm bullet. Can anyone tell me the proper term for this ?? I can't remember.
 
term

BTW it can take some distance to stabilize a bullet .In other words you may get a 100 yd 1" group and a 200 yd 1.5" group.Especially with a very heavy bullet like a 160 gr 6.5 or 175 7mm bullet. Can anyone tell me the proper term for this ?? I can't remember.
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Think your talking minute of angle (moa)
 
The correct term for that is BS. Or maybe selective memory or data doping.

The concept of bullets "going to sleep" or "stabilizing" in mid air and getting more accurate with range is common and a lot of people have fired individual targets that seem to demonstrate it. They will be along shortly to defend the notion.

I read of a benchrest shooter who set one of the Oehler accoustic targets up at 100 yards and a paper target at 335 yards (300 metres, maybe). That let him plot the same bullets at two different ranges. He said he never, over some long period of time and many groups, saw a single case of the 335 yard group being smaller than the 100 yard group when figured in MOA.
 
It's theoretically possible for a bullet to go from being under-stabilized to being stabilized during the time of flight, but it would have to be a very long-range shot to give the forward velocity time to decay, and you'd practically have to design the load for the sole purpose of demonstrating the effect.

Also, it doesn't mean that the groupings would be better at longer ranges than shorter ranges, because by the time the bullet goes from being under-stabilized to stabilized, the damage has already been done,accuracy-wise. The stabilization isn't going to "guide the bullet" back onto the point of aim.
 
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The stabilization isn't going to "guide the bullet" back onto the point of aim.
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Amen.

What most people call "stabilization" is the initial yaw movement damping out as the bullet travels. NRA once said the "air spiral" was on the order of .10". All these diagrams you see of a bullet flying in a corkscrew helix are greatly exaggerated. There is no physical force to cause a bullet to move in a circle centered outside its shape and there is no physical force to cause a bullet to move back towards the original launch axis once it has left it.
 
iirc bullet stability is also affected by barrel length and velocity in the barrel. A bullet will stabilize with a slower twist out of a longer barrel or at a greater velocity that would not stabilize out of a shorter barrel with the same twist or at a lower velocity with the same twist.

Once a bullet has left the barrel stability doesn't necessarily mean straight along the ballistic path. Just like the football analogy the bullet stabilizes with a certain amount of pitch or yaw.
For a bullet to return to a straight and level attitude after leaving the barrel would require an act of physics that I can't work out.
 
BS?

the yaw, if i recall correctly is also called key holing...

best description:
http://en.wikipedia.org/wiki/Rifling


some call it BS i think the engineers call it other things...
I have no idea.. but what i think is this...

no matter how far and what groups.. rounds, velocity, and the rest.. all make a difference.. if it didn't .. scientest wouldn't study it..

the effects of all this explain why people reload... they try to find the best fit for rounds/seed that give their gun the best accuracy... ask any competition shoot and they will likely confirm: there is a different load for every gun that works best... Most i have spoken don't know why(the science behind it), and really don't care... they just know it works.


I could be wrong.. but a bullet that yaws, keyholes, will not be as accurate over any long distance.. and if twist rate is wrong.... will be off even in short distance..
 
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