What does HMHP (Heavy Match Hollow Point?) BTHP JHP SMK stand for and what just exactly what does that all mean? I think the HP stands for hollow point, but the what do the other prefixes mean. SMK = Sierra Match King? Is that a trade name for the same as a FMJ? I think I read in another post that SMK is good for target shooting while the HP's are more of a lethal round. Am I correct? How about accuracy; is one bullet type more accurate than the other?
BTHP = Boat Tail Hollow Point
JHP = Jacketed Hollow Point
SMK = Sierra (a company that makes bullets) Match King (a product line of match grade BTHP bullets. They are precisely made which makes them ideal for use in target matches)
Hollow points are generally created with expansion in mind. When the bullet impacts, there will be a pocket of air inside the cavity, between the bullet and whatever it hits. This air causes the bullet to mushroom out, causing a larger wound channel.
Hollow points can also be more accurate, as with less mass up front, the center of mass of the bullet is a bit more rearward, which aids in the stability of the bullet in flight, if I'm not mistaken.
Just note that in the case of 5.56mm NATO ammunition, the bullets are designed to fragment. This is the primary wounding method of the bullets. Hollow points can often prevent this fragmentation, unless they are designed to still allow it. It's kind of confusing, I know.
the air has nothing to do with it.
you are mistaken.
you are confused.
(1) true JHP bullets expand ("mushroom") because the opening at the front of the bullet creates an internal pocket by which the struck matter (flesh, etc) can apply force to internal surfaces of the pocket. this causes the jacket and lead core to deform radially, increasing the apparent size of the projectile, and (hopefully) leading to a quicker demise of the target (deer, enemy, etc) via exsanguination.
(2) regarding a BTHP... a copper jacket can be drawn over a lead projectile in one of two ways: front to back, and back to front. with the former, an area at the rear of the bullet has exposed lead, and the rear of the finished bullet is somewhat non-uniform. recall that this is the part the gas is pushing against. when the copper is drawn back to front, as in a BTHP projectile, the rear of the bullet can be perfectly uniform, and this aids in homogeneity of pressure as the bullet exits the muzzle and interacts with the crown -- this interaction is a critical aspect of absolute accuracy and precision (repeatabilty).
note that a BTHP bullet is not designed for increased wound size a la a true JHP bullet; the aperture of the front opening is typically insufficient for the stuck flesh to force further opening. the primary wounding mechanism of a BTHP is usually through fragmentation due to shear forces incurred as the bullet tries to yaw in the denser medium (flesh). this is no different than standard FMJ ball ammo (in 5.56mm: M193, M855). and as with standard FMJ ball ammo, a BTHP will only make a tidy .22cal hole if the target is struck at insufficient velocity (due to range and/or barrel length).
(3) the US military, like others, obeys international conventions on "humane warfare" -- whatever that means these days. as such, hollow point bullets are not used. a BTHP, as noted above, is not a JHP and does not wound via expansion. a BTHP wounds via fragmentation, as noted above. while this distinction may be important to the lawyers and humanitarians, i doubt very much that the enemy would rather be struck by one type versus the other. BTHP bullets are more accurate than FMJ, and this is why the military uses them for precision applications.
note that in some literature you may see "OTM" = open tip match. IMHO, this is the "more correct" definition of a projectile wherein the copper jacket is drawn back to front.
Wow, lots of great information here. I now have a much better understanding. It looks like when I start reloading my own, SMK/BTHP bullets are the best of both worlds; accuracy and destruction even though the JHP's sound like a more destructive bullet.
I just purchased some 69G SMK's so I will get a chance to see how these work out. Many thanks to everyone especially AR-Jedi.