Forums
New posts
Search forums
What's new
Articles
Latest reviews
Author list
Classifieds
Log in
Register
What's new
Search
Search
Search titles and first posts only
Search titles only
By:
New posts
Search forums
Menu
Log in
Register
Install the app
Install
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
revolutions per minute debate
JavaScript is disabled. For a better experience, please enable JavaScript in your browser before proceeding.
You are using an out of date browser. It may not display this or other websites correctly.
You should upgrade or use an
alternative browser
.
Reply to thread
Message
<blockquote data-quote="Buffalobob" data-source="post: 69388" data-attributes="member: 8"><p>The rate of decay is probably higher for low BC bullets than antbody has admitted. The extreme example would be a wadcutter or huge meplat bullet like the 45-70 Hammerheads. The front rotating plane (meplat) will encounter a significant resistance to spin from the perpendicular contact with air molecules. A very long ogive bullet will have almost no perpendicular surface for air to encounter and reduce spin, infact the long ogive will cause the air to move parallel to the surface so there is very little "normal" (perpendicular component) force and the air flow over the bullet is only interacting with the skin rotating under it. </p><p>The rifling groove on the skin create a very complicated interaction that could reinforces the spin and at the same time decays the spin. Number and shape of these grooves is important.</p><p></p><p>Think about the grooves this way. These groove are impressed into the bullet at an angle equal to the twist of the rifling, so they are not parallel with the axis of the bullet. If the bullet was slowly moving forward through a thick substance such as jello and the bullet had no spin, the grooves would cause the bullet to develop a spin in the jello. This is the same principle as a wood screw which rotates as it goes into the wood.</p><p></p><p>Of course this induced spin comes at the price of resistance to forward motion because air is impinging on one of the sidewalls of the grooves</p><p></p><p>The top edges of the grooves create a mechanical brake as has been mentioned before because as they rotate they are hitting the air that is flowing back along the bullet.</p></blockquote><p></p>
[QUOTE="Buffalobob, post: 69388, member: 8"] The rate of decay is probably higher for low BC bullets than antbody has admitted. The extreme example would be a wadcutter or huge meplat bullet like the 45-70 Hammerheads. The front rotating plane (meplat) will encounter a significant resistance to spin from the perpendicular contact with air molecules. A very long ogive bullet will have almost no perpendicular surface for air to encounter and reduce spin, infact the long ogive will cause the air to move parallel to the surface so there is very little "normal" (perpendicular component) force and the air flow over the bullet is only interacting with the skin rotating under it. The rifling groove on the skin create a very complicated interaction that could reinforces the spin and at the same time decays the spin. Number and shape of these grooves is important. Think about the grooves this way. These groove are impressed into the bullet at an angle equal to the twist of the rifling, so they are not parallel with the axis of the bullet. If the bullet was slowly moving forward through a thick substance such as jello and the bullet had no spin, the grooves would cause the bullet to develop a spin in the jello. This is the same principle as a wood screw which rotates as it goes into the wood. Of course this induced spin comes at the price of resistance to forward motion because air is impinging on one of the sidewalls of the grooves The top edges of the grooves create a mechanical brake as has been mentioned before because as they rotate they are hitting the air that is flowing back along the bullet. [/QUOTE]
Insert quotes…
Verification
Post reply
Forums
Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
revolutions per minute debate
Top