OAL Gauge question

[zenith]

I'm thinking of buying one of the hornaday lock and load overall length gauges and a comparator, but theres something im not sure about.

If I have set my rifle to minimum headspace during the barrel install with a go-gauge, will the modified case i use with the OAL gauge get me an accurate measurement? If the modified case is at all larger than minimum wouldnt that be a problem? Maybe theres some way to get a custom modified case?

Im still trying to fully wrap my head around the concept, maybe im missing something.

[thomae]

The gauges are designed for relative measurements (difference in two measurements) not for empirical data. They COMPARE measurements, hence the term "comparator."

You take a known (Your once fired brass, your bullet in your chamber pushed out to just contact the lands) and measure it using the comparator. Now you have YOUR measurement with that bullet of the length from base to a point on the ogive when touching the lands in your rifle. This is measurement 1.

Say you want your bullets to be 0.020" off the lands: You seat another bullet and measure the same thing as above...only you you keep seating the bullet deeper until your measurement is 0.020" shorter than measurement 1. In theory your bullet is now seated 0.020" off the lands.

[zenith]

That makes much more sense!

Thanks!

[thomae]

Remember that because the ogives are different, you will need a new "measurement 1" with each bullet.
Thus, if you switch from Nosler 150 grain boattail hollowpoint to a Hornady 150 grain boattail hollowpoint (just a hypothetical example), you will have to start over with your measurements. Does that make sense?

[FUBAR]

Thomae gave you a great example...

You might want to invest in a Bump Gauge to go with your comparator, that way you also know your fired case shoulder length, and of course you can bump brass if required.

[Texas Solo]

OK, I have a question on this. I just got my new comparator today (lost my old one in a move)
I measured two bullets only, Berger 80VLD and Sierra 80 BTHP MK. The two bullets gave me a base to ogive length within .002 of each other, CONSISTENTLY.
Then I used my OAL gauge in the chamber and measured case base to ogive with each bullet, and got .030" difference, CONSISTENTLY. ( 2.050 & 2.080 )
I repeated each measurement 3 times.

I can't figure out why the difference. If there's a .002" difference in the bullets themselves, shouldn't that equate to a .002" difference in the assembled round?

[FUBAR]

No, many things, but two of the big ones-- case head to shoulder, and of course bullet seating depth.

[helotaxi]

OK, I have a question on this. I just got my new comparator today (lost my old one in a move)
I measured two bullets only, Berger 80VLD and Sierra 80 BTHP MK. The two bullets gave me a base to ogive length within .002 of each other, CONSISTENTLY.
Then I used my OAL gauge in the chamber and measured case base to ogive with each bullet, and got .030" difference, CONSISTENTLY. ( 2.050 & 2.080 )
I repeated each measurement 3 times.

I can't figure out why the difference. If there's a .002" difference in the bullets themselves, shouldn't that equate to a .002" difference in the assembled round?
The comparator measurement gives you the point where the bullet begins to taper while the length that you get with the OAL gauge gives you the point where the bullet reaches the diameter of the lands. The ogive radius determines the difference between the comparator measurement of the bullet and the measurement to the lands. The difference that you're getting is because one bullet has a shorter ogive.

[supergolfer18]

I think the VLD has a different ogive design so it will not be the same as the SMK even though the ogive read the same before using the tool to find the distance to the lands. That is what my thought is?
I like to use a cleaning rod inserted in muzzle end to lightly push against the bullet when using the Hornady tool you mention. This ensures consistant readings and works better for me since I started using this method. I get exact same readings everytime. This also allows easy removal of the tool and bullet in one motion. Give it a try