It is the result of a manufacturing process for match bullets.The 75gr bthp is Not really intended for anything other than target shooting.

It's a remnant of how the jacket is drawn and shift weight to the back of the bullet.

So here is a picture of an "OTM" Notice that the jacket is pretty uniform in thickness from the base ot the tip. The actual "hollow" is pretty flat, all that's for is to give the bullet more length. The opening of the tip itself as you've noticed is very small.




That being said, they can fragment like CRAZY from what I've been looking at.


Anyways, here's a pic of some actual designed for expansion HP's, big open noses, and deep cavities to aid expansion. Other styles include thinner jackets at the front to aid in everything opening up.

good post nicely explained

The spitzer bullet was designed for higher aerodynamic efficiency. The design makes the bullets travel farther with the same propellant charge, or as far with less. When they were invented in the late 19th century, they were stunning-the revolutionized cartridge design very quickly. It was also found that there was a side effect of their design: they tumble on impact. The tumbling is dependent on bullet weight and velocity, so a 150gr M2 Ball bullet doesn't tumble quite as dramatically as a 62gr M855 bullet at similar ranges, but it still tumbles.

Target and high-precision bullets with an "open tip" are made that way to produce a very consistent BASE, which assists in increasing accuracy immensely. This is because with a consistent base, the gasses leave the barrel behind the bullet the same in all directions. With a less consistent base shape (cough...Winchester bulk 55gr bullets...cough, cough), there can be a variety of different places on the base that muzzle gasses could be withheld or allowed out differently from other places, which is effectively a gas jet that deflects the bullet. Maybe not much, but maybe a lot, and that causes those inconsistent base bullets to be "broad side of a barn" accurate.

The open tip is, as noted earlier, a side effect of the bullet's construction. The jacket is formed as a cup closed at the base, and the core is then placed in it and the jacket is formed down onto the core. This means that there will be a small opening left at the tip, which both a) has no negative effect on aerodynamics and b) absolutely does not cause, enhance, lead to, or allow bullet expansion. Some "hollow point" rifle bullets ARE built to expand, but they are made with different tip shapes and substantially larger openings, along with (most likely) thinner jackets that facilitate this expansion.

Wow––I think I've learned something! Lemme see if I can summarize...

People assume a HP bullet is meant to expand, so with these bullets it would be better to refer to them as OTM to avoid confusion. They may or may not expand, but they weren't designed the same as a HP bullet.

A "closed base" bullet is filled with lead from the base up and is this more consistent at the base, the last part to exit my rifle. The result of this manufacturing process is the little .035" hole at the tip. An "open base" bullet is filled with lead from the top down and then closed up, resulting in slight differences from bullet to bullet and not as predictable accuracy.

The authors of the Ammo Oracle all recommend OTM as their choice for defense bullet. This is because of superior terminal ballistics at longer distances (I guess).

Not always the case with .308 Sierra SMKs in 168gr. Sometimes they fragment/expand but others they just sail through like a FMJ.

Its more steps,

for standard top down bullets, the Gilding metal is drawn through multiple die steps into a cup with the final shape that of the bullet being made. A slug of lead cut from from a coiled lead wire is then pressed into a bullet cup, that is in a die with the final shape of the bullet. The gilding metal is then crimped over the end of the lead slug. Cheap and fast.

OTMs have all the same steps and more,

instead of pressing the lead slug in back to front, it's front to rear. The open ended front thus needs to be massaged into an ogive and meplat, this is done with more swaging steps. In manufacturing anything, more steps = more money.

The end of a conventional top down bullet is simply gilding metal crimped over the lead slug into a base, usually flat bottomed, thats a lot easier to do them forming an ogive and meplat.

Lots and lots of detail can be found here: http://www.corbins.com/fjfb-3.htm

I think this link does a good job of explaining that open-tip is just one of many choices for how to form the ogive of a bullet when you are building closed base bullet. It has nothing to do with aerodynamics or "air pockets" or what not. You simply have to make a choice at the end of the swaging process, and there are several choices. Now just imagine this on the scale of a manufacturer where they are making thousands per hour.

I also found this is a useful overview of the differences between casting, machining, and swaging bullets: http://www.corbins.com/intro.htm Also does a good job explaining how boat-tail and rebated boat-tail bullets work.

Before I asked in this thread, I had never even heard of swaging. Now i knows somethin'.

I dunno. What do you think it is?

This.

I'm not trying to be argumentative––just trying to learn. Here's the thing: I can't find any bullet manufacturer or expert who will say that the OT is there to cause an air pocket or alter the boundary layer. If it does, and again, I can't find a named source other than forum posters, it doesn't help anything. In fact, it would lower the BC.

I've even found a die maker that sells a product for benchrest shooters to reduce the size of the OT "by half its diameter" so it will be more accurate: http://www.whiddengunworks.net/pointingdie.html

So maybe air pockets do exist forward of an OT bullet. If so, I'm trying to learn if such an air pocket is intentional. Everything I've seen thus far says that the OT is a result of the closed-end manufacturing process, and if they could get rid of the OT economically, they would. Of course, they could build the bullet top-down and not have an OT, but the resulting loss of accuracy from the inconsistent bases of the bullets is worse than having an OT. That's how I"m reading the various white papers out there, anyway.

I've also learned that within 200 meters or so, it doesn't matter the bullet design. At least not in a way the vast majority of shooters could discern without scientific equipment.

Ok, sorry didn't mean to be a jerk with you. The other poster really pissed me off though. As another said above I don't know if the hollow point was intended to create the boundary layer or if it was just a "oh wow look what else it does" moment?