Home Forums Reloading Big Game Rifles Base to Ogive measurements with different bullets

What's the most bto difference that you've seen when seating different bullets to reach the lands in the same rifle?

When I set up up my stoney point gauge to kiss 147 eld's I find the bto measures .017" shorter than with 139 scenars. I expect different shaped ogives to engage the rifling a little differently, but that struck me as a big difference. I just started using the stoney point, but I'm able to replicate the measurements very reliably so I think it's good to go there. Thoughts?

I think that measurement should be consistent. The problem is probably a little different diameter bullets. Hasbeen

Depends on the rifle and which set of bullets you're comparing but a quick check of notes for four different rifles and a max of 8 different bullets in two of them shows .068" to be the max difference in a couple of .30-06's - that's between a Hornady 165 BTSP as the shortest and a Remington 150 Bronze Point as the longest. To be real precise one Model 70 shows exactly .065" and another Model 70 shows .068" difference. A .260 and .243 show lesser spreads between shortest and longest.

I mostly use Hornady Spire Points and just looking at those in the 06's the difference is a max of .021" between a 180 SP and a 165 BTSP, with lengths for a 165 SP and 150 SP falling within that range.

These numbers are based on what I call the "Stoney length", which is the distance from the base of a modified cartridge to where the comparator hits on the individual bullet set out to touch the lands. The comparator insert is smaller than the actual caliber, e.g. a 28 caliber insert is about .271" iinside diameter, so it's hitting the ogive somewhere above the actual full caliber portion of the shank. The raw measurements might be something like 3.760" or 3.780" which include the length of part of the comparator itself and are obviously much longer than the OAL of a loaded round. It's just a number which is used to set my seating dies.

This is a long read but worth it. Hasbeen

http://www.bergerbullets.com/effect...and-cartridge-base-to-ogive-cbto-part-2/

hasbeen - thanks for the link, I'll check it out.

Jim in Idaho - just to confirm, you're seating two different bullets in the stoney to kiss the lands in the same rifle, but when you remove the stoney and measure with your calipers you get two different bto lengths? That's what I'm experiencing, but apparently to a much smaller degree than some of the examples you've cited.

As far as the comparator goes, I understand it's smaller than the designated caliber with some allowance/recess to account for the taper of the ogive. It really is just a tool to repeat the bullet position in the modified case. I do adjust my loaded rounds to account for the difference in headspace between my fired brass and the modified case.

Thanks much for the detailed info.

I use the Stoney Point OAL gauge with a modified case to seat a bullet out to hit the lands, then tighten down the lock screw. Then I remove the gauge/case/bullet and measure that with a Stoney Point comparator insert mounted on the jaws of my caliper and that's the "stoney" measurement. It's actually the measurement to some point on the ogive above where it actually hits the lands but nose shape is pretty consistent from bullet to bullet within a particular lot - although it does change occasionally so you have to remeasure with new lots. As noted, it's just a reference number. E.g., if I want to seat a bullet .020" off the lands I'll just seat it so the "stoney measurement" is .020" shorter then it was with the bullet in full contact with the lands.

Jim, I've been using the same method for years. Hard to judge how far you stick the bullet in the lands. I just try to be consistent. Hasbeen

I'm using the same method, too. I was just surprised... both bullets in the stoney are supposedly kissing the lands, so it seems the length to ogive should be the same when measured in the comparator. I guess the take away is that it's all relative, and the measurements you obtain are only good for a specific bullet.

The distance is set up by the reamer when the rifle is chambered. It does not change. The difference is in the bullet. Shape and diameter. I've noticed a little difference in bullets from the same lot. You can check this with your comparator and caliper.

Some more good info on precession reloading.
http://www.wheeleraccuracy.com/videos

The OAL of the 140 SST bullets my Tikka 6.5X55 likes best is much longer than the 129 Hornady Spire Points I also load. The case head to cannelure is similarly different. I don't change the die seating depth. However, the length from case head to the end of the bullet jacket is identical.