Tangent vs. Secant Ogive

[paplinker22]

I'm no mathematics professor or bullet manufacturer but understanding how bullet shape affects COL is a good thing to know when hand loading.

Pictured from left to right are 3 rounds that I chambered in my match AR:
1. 75 grain HPBT @ 2.250"
2. 52 grain HPBT @ 2.225"
3. 52 grain HPBT @ 2.182"

http://s1007.photobucket.com/user/bs...tml?sort=6&o=7

As you can see, the 52's tangent shape is well into the lands and is nearly impossible to manually extract. Despite being .025" longer, the 75 grain shows no evidence of touching the lands.

Tangent bullets have a much more "stout" shape whereas secant shaped bullets are much more "sleek." In other terms, the ogive of a tangent bullet is located closer to the tip of the projectile. Whereas the ogive of a secant bullet is much farther back.

Bill

[Edg]

I never really thought about it, but I guess thats why certain bullets have much smaller COL on load data then you would expect for their size. The Game Kings Im loading now, say to make them 2.21, When match bullets of similar weights are 2.26. Definitely will be thinking about it now when I bring a bullet out more.

[ettorment1916]

I'm no mathematics professor or bullet manufacturer but understanding how bullet shape affects COL is a good thing to know when hand loading.

Pictured from left to right are 3 rounds that I chambered in my match AR:
1. 75 grain HPBT @ 2.250"
2. 52 grain HPBT @ 2.225"
3. 52 grain HPBT @ 2.182"

http://s1007.photobucket.com/user/bs...tml?sort=3&o=0

As you can see, the 52's tangent shape is well into the lands and is nearly impossible to manually extract. Despite being .025" longer, the 75 grain shows no evidence of touching the lands.

Tangent bullets have a much more "stout" shape whereas secant shaped bullets are much more "sleek." In other terms, the ogive of a tangent bullet is located closer to the tip of the projectile. Whereas the ogive of a secant bullet is much farther back.
Bil

Good post.

Where did you get the OAL data for the 52gr. bullets?

Is there published data for this OAL that actually puts the bullet so far into the lands that you can actually see marks on the bullet and also have a tough time extracting the round?

[paplinker22]

Good post.

Where did you get the OAL data for the 52gr. bullets?

Is there published data for this OAL that actually puts the bullet so far into the lands that you can actually see marks on the bullet and also have a tough time extracting the round?

Keep in mind I have a match chamber that is unusually tight. As for the OAL, I generally just load everything to magazine length. Before I understood the difference in bullet shape, I assumed I could just load it to 2.250.

Bill

[bogey1]

What tool do you use to get the oal measurement from the ogive for a semi-auto? I'm considering making semi match ammo for my M1A but not familiar with semi-autos.

[paplinker22]

What tool do you use to get the oal measurement from the ogive for a semi-auto? I'm considering making semi match ammo for my M1A but not familiar with semi-autos.

I don't. I found this out through trial and error. I know people who use the hornady/stoney point gauge and speak well of it.

Bill

[bogey1]

Here's a good video for bolt guns.

[Little Cloud]

Interesting post.
I've noticed the same sort of geometry issues when reloading for rifles.

I usually just choke it up to different manufacturers and their mold geometry vs bullet mass.

I'm not nitpicking ... just curious, really.

Are these bullets from the same manufacturer?

[paplinker22]

Are these bullets from the same manufacturer?

Yessir. Both hornady match bullets.

Bill

[Tomcat088]

What tool do you use to get the oal measurement from the ogive for a semi-auto? I'm considering making semi match ammo for my M1A but not familiar with semi-autos.

They make a different overall length gauge for autos that really works the same way. This is what it looks like. http://www.midwayusa.com/product/479...c-lever-action

I'm no mathematics professor or bullet manufacturer but understanding how bullet shape affects COL is a good thing to know when hand loading.

Pictured from left to right are 3 rounds that I chambered in my match AR:
1. 75 grain HPBT @ 2.250"
2. 52 grain HPBT @ 2.225"
3. 52 grain HPBT @ 2.182"

http://s1007.photobucket.com/user/bs...tml?sort=3&o=0

As you can see, the 52's tangent shape is well into the lands and is nearly impossible to manually extract. Despite being .025" longer, the 75 grain shows no evidence of touching the lands.

Tangent bullets have a much more "stout" shape whereas secant shaped bullets are much more "sleek." In other terms, the ogive of a tangent bullet is located closer to the tip of the projectile. Whereas the ogive of a secant bullet is much farther back.

Bill

I'm glad that you brought this up because it's not something that lots of people are aware of. It definitely can make a difference in the way one is reloading. It's also part of the reason why you can't just substitute bullets of the same weight and expect the loads to be the same. The bullets usually have slightly different ogives, and they also can have different bearing surface lengths, and different tail designs and/or angles.

I did want to mention something though. The generalities about ogive shapes aren't exactly correct, they're just that, generalities. A tangent ogive has a very particular shape that is related to the nose length and a very particular radius. It's usually expressed as a ratio (whole number) relative to bore diameter. Anything that is less than that radius is technically "secant". So "secant" doesn't always necessarily mean that the bullet will be long and aerodynamic. Some manufacturers will use a more aggressive secant ogive than others. When you get them very aggressive is when the bullets get long and have less drag, and usually when people start talking about them being "secant". I just wanted to bring up these points because there are bullets that use very mild secant ogives, and the area on the ogive that makes the bore diameter isn't necessarily much further back. It's also worth mentioning that Berger now has bullets that have a "hybrid" ogive, and try to bring together the best of both worlds. I helped evaluate some of those bullets for Berger, and found them to perform exactly as advertised, and pretty amazing. For those that are interested in doing a bit more reading on this subject, Brian Litz (of Berger bullets) wrote a pretty great article on it. http://www.accurateshooter.com/balli...ogive-bullets/ .

We could get into all kinds of generalities about these designs and how close they like to be seated into the leads. It's important to remember that bullet seating depth DOES affect pressure, and that if you seat bullets into the lands, because they don't get a "running start" you can see pressure spikes. It's the reason that many of us will start on the lands with a load to know the maximum pressure, and then work the bullet deeper into the brass. While this DOES increase the internal pressure on the brass, it's usually a much safer way to do it than starting with a lower chamber pressure, thinking the load is safe, and then working all the way into the lands and getting a pressure spike that could be catastrophic. It's also important to keep in mind that when seating bullets out towards the lands, that you can actually get longer than the magazine length; that's not necessarily a bad thing but it will turn a repeater into a single shot. So make sure that things still run how you want and need them to run. After I know that I'm below magazine length, I don't worry about the COAL as a measure to the quality of my ammunition. I use the measurement for the consistency of bullet length relative to the ogive as the measure, since that's the part that will actually be engaging the rifling. Good posts and info.