Nomercy448

Ogive shapes do matter when setting seating depth. You cannot seat two different bullets to the same COAL and assume that it will produce the same bullet jump (chamber leade).

Here's an example of a long radius spire point, for example a 16 ogive secant bullet vs. a rounder point, for example a 7 ogive tangent bullet. Examples A and B are seated to the same COAL, which produces an unsafe condition in condition B (unless the load is significantly reduced to account for the rifling jam), whereas Examples A & C are seated to produce the same bullet jump (when I drew these examples, the spire point actually IS a secant ogive), and the round nose actually IS a tangent ogive):



Most reloading manuals don't go into as much detail to describe secant vs. tangent ogive implications. Most do, however, provide specific COAL's for specific bullets, which will vary based on their relative bearing surface shoulder positions.

Beyond that, many manuals do cover how to determine maximum seating depth (depth to lands) for YOUR RIFLE CHAMBER. Most of these processes involve seating a bullet into an empty case and using it to determine maximum seating depth. Whether you 'soot' the bullet with a match (or magic marker) and crimp it tightly to let the rifling cut witness marks for depth, or seat it loosely and let the rifling press it into the case, or rely upon a tool like the Hornady Bullet Comparator to determine maximum seating depth, there are several ways to skin that particular cat.

In general, most folks start with a 0.005 to 0.01" jump, and work in or out to determine proper jump for best accuracy, of course watching for pressure signs as they go.

Also in general, you want at least one bullet diameter's worth of bearing surface length in your case neck to sufficiently hold the bullet properly, which limits how long you are able to seat the bullet.

Seating deeper, of course, eats up case capacity, as in the case of trying to load 90grn bullets in an AR-15, where magazine length limits COAL.

Long radius secant ogive bullets generally have better aerodynamics, but often require a bit more twist to stabilize because they are longer. These are often used by long range hunters for their advantageous flatter trajectory. They're more sensitive to seating depth and concentricity because of the angular disjoint between the bearing surface and the ogive.

Match bullets traditionally are tangent ogive, simply because they are so forgiving of throat jump and the distances are fixed (i.e. drop is known/constant). These are less sensitive because they have a smooth transition from ogive to bearing surface, letting them somewhat "self align" into the rifling.

Hybrid bullets (VLD's) offer a blended ogive with secant type tips and tangent type surfaces to join the tip to the bearing surface.

Rules of thumb for this topic:

• 1 dia of bearing surface in the neck for proper grip
• 0.005-0.01" jump
• Long ogive secant ogive bullets have longer COAL for the same bullet jump than tangent ogive bullets
• Long ogive secant ogive bullets have shorter bearing surfaces (full diameter straight sidewalls) than tangent ogive bullets
• Long ogive secant ogive bullets are more sensitive to seating depth/leade jump variation than tangent ogive bullets
• So called "hybrid ogive" bullets offer more forgiveness than pure secant ogive bullets, but with better aerodynamics than pure tangent ogive bullets
• Rules of thumb and theories are great, but they only take you so far - you have to experiment with YOUR RIFLE, YOUR BULLET, YOUR CASE, AND YOUR LOAD to find the proper combination

They should at least be verified. I always size and verify length on brass, even if it's new.

All cartridges are crimped to hold the bullets. A taper crimp might not look like it's crimped, but all cases have to be crimped to at least a minimum tension to hold the bullet in place. Degree of crimp tension and crimp TYPE depends on the application. Some factory rounds are "collet crimped," similar to what the Lee Factory Crimp Die produces. Revolver cartridges are inevitably roll crimped, pistol cartridges that headspace on the case mouth must only be taper crimped. A taper crimp with a light tension is generally all that is needed to hold match bullets for single shot bench rest rifles, but a heavy roll crimp might be required for a heavy recoiling revolver cartridge like 454Casull or a tube fed cartridge like 30-30win.