Distance to the lands

[m1ajunkie]

So I received a hornady overall length gauge this week for use on my 6 cm, the reason are discussed in a separate thread. Now that I've got the tool in and I'm using it in conjunction with my hornady comparator to measure length to the ogive of a loaded round I've got a question.

Using a 105 berger hydrid bullet, my tools give me a reading of 2.255 to the lands in my barrel.

However, when I use a hornady 105 bthp, I get a measurement of 2.242 to the lands in my barrel.

So my question is, why are different bullets giving me different measurements? In my mind, the distance should be the same regardless of bullet? Judging by the feel I get in the OAL gauge and the cleaning rod, I'm getting both bullets set firmly into the rifling, I can't push the BTHP in any further.

Moral of the story, my barrel is getting pretty worn, I'm trying to determine if I can work up a new load with bullets seated further out and this new gauge is helping me in the process.

 

[GhengisAhn175]

Different bullets = different profiles.

on top of that, each lot may be slightly different so ALWAYS check each box.

distance to the lands is always checked when you do the following:

every 500 rounds (my rule)
each new box of bullets (regardless of same lot)

in Hornady for example, there isn't 500ct boxes. So if you buy a pack of 500, open each pack and check two bullets per box to verify distance to the lands.

In a box of 500 (say bergers) check 10-20 bullets. Normally there's 2-3 piles you'd make.

Good of luck with sierras

 

[Citius7]

What he said. Bottom of bullet to ogive will be different for each bullet profile. And lot to lot variation. Hope this helps. I personally don't measure for every box. I'm not danger close to the lands and have tested 5 thou each way to see how the bullet reacts. I suggest you do the same once you have things situated. If u don't have noticeable variation from one setting to the next, than I'd say not to worry about box to box. But that's me. I'd rather shoot than measure.

 

[m1ajunkie]

Cool, I figured my distance to the lands thinking might be slightly altered when the bullet profiles are factored in.... didn't think about variation among bullets in the same lot though. Good information guys, thanks.

 

[eicas]

There is a write up in the latest Berger Blog on just this subject if youre interested.

 

[m1ajunkie]

Eicas I'll check it out. Thanks for the heads up