Bullet comparator use

[257 Ackley]

Alright guys, I'm full of all kinds of questions that I need help with. I bought a bullet comparator for my Stoney Point (Hornady) OAL gauge today. I didn't get any instructions for it and am wondering how you use it with the OAL gauge to get the correct lengths. I attached it to my calipers and measured to the ogive for a .28 caliber with the 140 grain AB. How does this length translate to the length I want to use for seating the bullet? The OAL without the comparator is 3.014 and with the comparator it is 3.45 (this is for a 7mm08). Thanks for your help.

 

[DrMike]

The simplest thing to do is to get an OAL gauge (also from Hornady) and a modified cartridge (https://www.hornady.com/shop/?ps_sessio ... aef6e83165). Use the comparator to measure the OAL of the cartridge as determined with the gauge. In lieu of this, measure the OAL of the cartridge when it has engaged the lands as per the description on page 43 of the Nosler Reloading Guide No. 6. With your bullet set, now measure the OAL to the olgive.

 

[257 Ackley]

DR -
Got the guage and modified cartridge. That's what I have been using to measure OAL until today. Most guys that use the guage told me you have to buy the comparator to get a true OAL instead of measuring to a bullet tip, since that can be different from one bullet to the next. I'm trying to figure out how to translate the length with the comparator on the calipers to the true OAL that the bullet can be seated to.

 

[YoteSmoker]

Measure the comparator once it's seated and locked down with the set screw on the caliper. Deduct this measurement from the measurement you get from ogive to case head.

 

[barge]

I posted a good site that has the information I think. check my post for the article. http://www.noslerreloading.com/phpBB2/v ... hp?t=10142 Hope this will help. For the most accuracy I take a fire formed case remove the primer and drill and tape so I can get the measurements from a case with proper shoulder dimension.

 

[barge]

that should read drill and tap.

 

[DrMike]

257 Ackley,

My mistake. I misread your question.

Indeed, the OAL may vary somewhat if you measure to the tip rather than measuring to the olgive. The measurement to the olgive gives you the length of the cartridge from the head to the olgive when it engages the lands. Determine how much off the lands you wish to seat your bullets, deduct that distance from the measurement made with the OAL gauge and bullet comparator. Set your seater die to seat to the desired olgive measurement. Don't worry too much about the length of the cartridge to the tip, provided the OAL does not exceed magazine depth.

The measurement you are using is a measurement to the olgive and not an actual cartridge overall length. However, it is the more consistent measurement.

Zero the calipers with the jaws closed on the comparator. Measure the distance to the olgive. Set your seater die. Depending on bullet design, the true cartridge overall length can vary considerably. Check your chosen bullet length to ensure that it fits the magazine. Then, enjoy the product of your labour.

Hopefully, this clears up the confusion. Again, I do apologise for failing to understand your original question. Thanks for clarifying.

 

[257 Ackley]

Dr Mike -
Thanks, that clears it up I think . No need to apologize, I may not have positioned the question correctly. The crazy thing about going through the exercise with the calipers and comparator last night is a moot point with many cartridges since the magazine length is going to determine what the OAL length is going to be anyhow :x .

 

[DrMike]

You are correct. In my 358 BLR, magazine depth is the determinate for OAL. The same is true in my 350 Remington Magnum Model 673, which has considerable freebore. However, when able, I appreciate being able to address seating depth. It allows a measure of fine tuning to get just the right combination for accuracy.

 

[nodak7mm]

257,

Doc Mike did an awesome job of explaining it so the there very little I can add. However, gonna try and help with my 0.02$. Now that you have that tool.

The measurements it takes are simply a REFERENCE point. From which you use to make comparisions.. Using the mod case and bullet, find the pt where touches the lands, consider this is your zero reference point.

All you are comparing is bullet seating depth when making die adjustments.. These measurements that will tell ya if you are 0.010, or 0.020 and so on from your zero reference point..

Gawd I hope I didnt muddy the waters..

Rod

 

[bobbyrum]

I also use the comparator myself. It works very well for me. Another suggestion that I heard someone put forward was that each time you buy a new box of bullets (different lot), go through the same procedure again :grin: