OAL hornady bullet comparator

**cardonasharp** · March 25th, 2016, 09:32 PM

I need some assistance from experience re loaders. When I measure the reloaded round it always has a different measurement. I am reloading for 308 Winchester. Someone said the measurement will be different because of the bullet head not being the same. That I should be measuring from the ogive of the bullet not from the tip. I bought a Hornady bullet comparator.
All of the hornady bullets measure differently from .619 to .625 and 3 of them well over .635. I also have a OAL gage and a modified case from hornady to measure the correct bullet length from my chamber. Now if I use the OAL gauge with different size bullets will it effect my OAl from my reading.

**Lycanthrope** · March 25th, 2016, 10:35 PM

Make sure you put the comparator seated snug and flat on your calipers. Also make sure your sizing die is set to cam over on the press and you trim to the same length.

If you use different bullets they usually have a different ogives so they will differ. You just need to seat bullets where your guns likes them and then take readings with the comparator because the bullet tips are often deformed and give poor readings.

Bullets that are not match quality are often varied in terms of construction. You won't get great readings out of bulk heads.

You may want to invest in a competition seating die. I prefer Forster myself.......

Lycanplacestostartthrope

**cardonasharp** · March 25th, 2016, 11:34 PM

they are match from hornady. All bullet vary by .615 to .622 to .630. When I place the bullet in my OAL from Hornady I will not have a correct OAL. Because the bullet have a different size.

**Twoboxer** · March 26th, 2016, 12:42 AM

Originally Posted by cardonasharp

I need some assistance from experience re loaders. When I measure the reloaded round it always has a different measurement. I am reloading for 308 Winchester. Someone said the measurement will be different because of the bullet head not being the same. That I should be measuring from the ogive of the bullet not from the tip. I bought a Hornady bullet comparator.
All of the hornady bullets measure differently from .619 to .625 and 3 of them well over .635. I also have a OAL gage and a modified case from hornady to measure the correct bullet length from my chamber. Now if I use the OAL gauge with different size bullets will it effect my OAl from my reading.

Short answer to your last question is "Yes".

Here's the problem: Some bullets will have different shapes near or at the tips. Some bullets will have different lengths from their base to their ogive. And your seater die does not strike either of those two points when pressing the bullet into a case.

So your cartridge length would probably be very consistent if you could measure from the base to where the seater stem hits the bullet. But you can't measure that. So people use either COL (base to tip; caliper) or BTO (base to ogive; caliper + comparator tool).

COL is likely to vary much more than BTO measurements. But because most batches of most bullets aren't perfectly consistent from the BULLET'S base to the bullet ogive, even this measurement will vary. I had a batch of 100 Sierra 168 MKs that had 4 distinctly different base-to-ogive measurements 0.012" apart. OTOH, I just measured a batch of 500 Sierra 175gr TMKs, and all 500 were within 0.001".

Precision freaks will separate bullets by their base-to-ogive lengths, and only use similar bullets to make a batch for the range. The rest of the folks realize the issues involved and just work with an average, or load to make sure they fit in the magazine.

When using the comparator tool to find the distance to your lands, you obviously have same issues to deal with. Further, if you take 5 measurements using the SAME bullet, you are likely to get 5 different measurements and will have to use an average number. And yes, every time you change the bullet type, you must assume you will have a different measurement to the lands.

So you've tumbled into all of the issues and you can decide just how far you want to go.

Measure all your bullets base-to-ogive, use only similar bullets to make a batch of cartridges, and your BTOs are likely to be quite similar . . . but not exactly the same. Or construct some average number you are comfortable with and live with the variations. Or find a method somewhere in between.

**dmac7979** · March 26th, 2016, 03:24 AM

What I do is take a handful of bullets out of my batch and measure those base to tip. Find the longest and use that one to seat first.

When that one is at the proper length I measure the cartridge at the ogive and go from there.

I use an AR10 and AR15 so I measure OAL to fit in the magazine.

**Gunsnwater** · March 26th, 2016, 04:02 AM

I like cannelure bullets for this reason, and for auto loaders a crimped in bullet is best to fight setback. Trim the cases to the cannelure for an over all length to fit the mag. Bench rest reloading would drive me crazy.

**bogey1** · March 26th, 2016, 08:21 AM

Heres a little video to help out.

**BobGun** · March 26th, 2016, 09:42 AM

Originally Posted by cardonasharp

they are match from hornady. All bullet vary by .615 to .622 to .630. When I place the bullet in my OAL from Hornady I will not have a correct OAL. Because the bullet have a different size.

Are all the bullets you are using the same product number. I can not see a match bullet varying that much unless they are different products. Say a 168 gr match as compared to a 175 gr. they will have different lengths.