Hey guys,

I was wondering what effect bullet design has on cartridge oal. For instance, will a bullet with a sleek design like say the nosler ballistic tip, have to be seated out farther(longer oal) in order to be near the lands when compared to a bullet that is less aerodynamic like the tbbc, grand slam, northfork, a-frame, etc. Here is my predicament. My box mag is not long enough to permit me to seat partition spitzers anywhere near the lands (we are talking in terms of a couple of mm). Will switching to one of the above mentioned bullet designs help me get closer to the lands? The rifle by the way is an a-bolt.

quote:

Originally posted by molar1:
Hey guys,

I was wondering what effect bullet design has on cartridge oal. For instance, will a bullet with a sleek design like say the nosler ballistic tip, have to be seated out farther(longer oal) in order to be near the lands when compared to a bullet that is less aerodynamic like the tbbc, grand slam, northfork, a-frame, etc. Here is my predicament. My box mag is not long enough to permit me to seat partition spitzers anywhere near the lands (we are talking in terms of a couple of mm). Will switching to one of the above mentioned bullet designs help me get closer to the lands? The rifle by the way is an a-bolt.

Molar, your are correct. bullet design does affect seating depth. You can make the OAL whatever you like, but bullet design will affect the distance between bullet and lands.

Another thing to remember, some rifles shoot really well seated farther from the lands than close to the lands. I often find good results when starting with the recommended seating depth listed in the loading manual.

But I also check to see where a particular bullet will engage the lands and record that in my records... just to know the actual seating depth I am using.

I hope this helps.

quote:

Originally posted by molar1:
Will switching to one of the above mentioned bullet designs help me get closer to the lands? The rifle by the way is an a-bolt.

Hey molar

The answer to your question is yes, the bullet design does allow you to seat closer to the lands at the same OAL.

But you are thinking about it backwards. Bullets like the TBBC, Swift A Frame and others like those will allow you to seat closer to the lands at the same OAL.

Think of it this way, it is distance between the ogive and the tip of the bullet that makes the difference. The TBBC, Nosler Partition Protected Point and others like that have a shorter distance from the ogive to the point. You seat your bullets at a given distance from the case head to the ogive on any given load. The shorter distance from the ogive to the meplat (bullet tip) allows you to load a shorter OAL and get closer to the lands.

Even bullets of the same type but of different weights can make a difference. For example I had a 270 that would allow me to seat a 140 TSX within .05" of the lands but the 130 would only seat to .065". They put the extra 10 grains of weight on the 140 gr and moved the ogive forward on the bullet.

IOW, the ballistic tip type profiles are the worst for what you are trying to do.

All bullets of different weight, brands, etc are different COL when measureing to the lands. I measurse all my different bullet/cartrige combos and the only 2 I have found to be the same were the nosler BT and accubond of same wieght/cal.

You will find that the blunt round or round nosed profiles permit seating the contact area further forward. Similar to cutting off about 1/4" of the nose of a Ballistic Tip.

quote:

the only 2 I have found to be the same were the nosler BT and accubond of same wieght/cal.

Just thought I'd mention that in 30 cal, AB's are longer than BT's of the same weight.

This makes me a little suspicious of the Ballistic Coefficient of the AB being listed as identical to the BT.



.

There is a super easy way to measure the OAL for a particular bullet where it contacts the lands:

Take a bullet and drop it nose first into the breech. Push it into place where the lands stop the bullet, with a rod. (Just dropping it carefully in may serve the same purpose.) Either support it some way, as with a rod pressing against it from behind, or just let it lightly jam into the rifling origin and very carefully push a rod down the muzzle until it touches the tip of the bullet nose without dislodging it. Mark the rod with a piece of tape at the muzzle. Remove the bullet from the barrel and close the breech of the gun. Push the rod down till it touches the breech face. Mark the rod again. Measure the distance between the marks and you have the overall length for that cartridge and bullet that puts the bullet right into the start of the rifling. Seat the bullet deeper than that (shorter OAL) for any specified distance of the bullet off of the lands. Or for any arbitrary OAL shorter than the measurement, the difference is the distance of the bullet from the lands for that load. The test is easy to repeat and will need to be repeated frequently if you want to maintain a particular distance off the lands, as this changes with throat erosion as you shoot.