JGFLHunter

Is this tool worth getting for an AR? I have been seeing mixed reviews. I know it will be worth it for bolt rifles like my 257 Weatherby. I think I'm getting it anyway, But just seeing about another option for making seating depth easier to determine. I think the PRI mag in 6.8 can be loaded to approximatey 2.3".

Nomercy448

It really doesn't work that well.

Here's the problem - you slip the modified case into the chamber and it headspaces on the datum-line of the shoulder. You push your bullet against the lands, and you note the spindle reading. All you really know is the non-calibrated COAL for that bullet in the HORNADY MODIFIED CASE!!!

So if you don't set your dies size to the EXACT SAME headspace length as the Hornady modified case, the measurement is purely bogus. I have NEVER had any of the hornady modified cases headspace exactly correctly for any of the rifles I've checked them. They're a generic SAAMI spec, but when I'm looking for a 10thou jump and you consider that SAAMI spec has a 10thou tolerance (say, for a .30-06) in headspace, then I really don't know WTF the gauge is telling me. So really the only dimension that you're getting right with the Hornady OAL gauge is the bullet seating depth - but the gauge doesn't measure that, it measures an arbitrary length from the modified case's base to the lands. There's no guarantee that when your bolt is locked in battery, that headspace length will be correct.

Now, if you used a tool like the Hornady headspace gauge or RCBS Precision Mic's or Wilson Headspace Gauge to measure the calibration length of your properly sized case (once fired case in a bolt gun, once fired then resized with a 0.003" shoulder bump in an AR) against the hornady modified case, OR if you drill and thread your OWN properly sized case, THEN AND ONLY THEN is the gauge worth a $hit.

Or, you can save yourself some money and just do it the old fashioned way. I'll try to find a link to a thread that Ridge Runner and I posted on a while back giving options for this process.

Nomercy448

Here are two methods that Ridge Runner and I posted on a different thread a while back for determining proper seating depth and COAL for any given bullet in any given rifle.

JGFLHunter

As you know with my other thread with shoulder bumping, I did finally figure it out and I dogs end up getting the head space Guage by Hornady. So I guess I will try and find one since I use the head space Guage and will be worth it. Will the straight model or curved model be better? I have 2 AR. 1 bolt. These are my primary firearms.

Mr. Longbeard

I tried RR method but I have a ?... When taking the measurement to face of bolt... How do you allow for the thickness of the base of brass casting... My base is like 40 thousands thick???

Nomercy448

Ridge's "dip rod" test gives you a COAL - you mark the rod when inserted down the barrel and held against an empty bolt face, then you mark the rod while inserted and held against the tip of a bullet, held in against the rifling with a pencil. The measurement between those two marks will tell you the distance between your closed bolt and the tip of your bullet (Max COAL to kiss lands) if you were to seat the bullet to the lands.

You do not need to make any correction at all for base thickness - your only adjustment to that measurement is your desired bullet jump.

The Curved hornady COAL gauge is designed for levers and autos, or basically any other model that doesn't allow ready access to the boreline from the rear. I've used a straight model in AR's in the past, just remove the upper from the lower.

For me, the Hornady OAL gauges are useless tools. For it to be useful requires far more work and calculation than it is worth, and takes longer than doing it the old fashioned way.

You'll spend a lot more time calibrating your hornady modified cases to your properly sized brass then using the gauge and punching numbers in your calculator than it would take to have simply done Ridge's dip test or my smoking test. Waste of money.

JGFLHunter

I'll give it a shot and see what happens, I should use the head space Guage though to find the coal? Or just by the caliper itself?

Nomercy448

I'll assume it's safe to assume (so if I'm wrong, I'm an @ss twice) that you're talking about the Hornady HS guage...

So the Headspace gauge inserts are too large for bullet comparing - If you're using that tool, you'll need the bullet comparator set. The headspace gauge is used to measure the headspace of the case to allow you to optimize your resizing and shoulder bump, and does not touch the bullet. The bullet comparator set would let you measure your ogive-to-base length, which is analogous to your COAL, but more relevant.

COAL is easy to measure, so we measure it. But it's largely irrelevant in the grand scheme of things.

Your seating die seats the bullet by the ogive (assuming it's a proper seating plug for your bullet), and your rifling contacts the ogive shoulder through the bearing surface of the bullet. The tip of the bullet is simply free hanging in space through it's entire life, except for when it touches your calipers. The portion of the bullet from the ogive to the tip really doesn't matter, and it's really nothing more than an opportunity to introduce error into your measurements.

You can use different tools from the RCBS Precision Mic's or PTG or Hornady's Bullet Comparators to measure your ogive-to-base length. None of them are really perfect, but all of them work well enough.

So... You do Ridge Runner's dip rod test, and you find your MAX COAL with THAT BULLET.

First - subtract your desired bullet jump from that measured MAX COAL to get your TARGET COAL.

Say it was 3" with a 10thou desired jump, now we're at 2.990" TARGET COAL.

Slip that bullet into a bullet comparator and determine the tip length vs. bullet length. Subtract that tip length from your Target COAL, and you'll know your ogive-to-base length. Seat bullets and measure them with your Hornady Bullet Comparator installed until you hit that ogive-to-base length.

Write down that ogive-to-base length for that rifle, as you can use it for any bullet you use in that rifle.

Here's the weakness of the Bullet comparators - they use a reference diameter (at least TARGET a reference diameter - however accurately they actually machined it), that SHOULD be equal to your rifle's land diameter. However, if their diameter and your rifle's is not the same, you're really not measuring the actual ogive position when you seat the bullets.

Now, the reality is that you're measuring a reference diameter on the ogive that will be more accurate than if you simply measure COAL from the tip of the bullet, since ogive inconsistencies are more rare than tip inconsistencies. So this is still a good practice. But you need to use the same comparator every time - if you have two hornady kits, unless both have EXACTLY the same diameter, you won't get the same ogive-to-base length because of the machining variation.

HNI Thread: Using oal gauge comparator 30-06

I don't recall exactly what this thread covered, but I put up a couple diagrams for using the Comparator that might illustrate what I'm talking about.

JGFLHunter

I think I did it right. I did it the way in the video somewhat. I barely placed bullet in my case and seated it. After doing the process I noticed markings And then a little ring, which I would guess be the land? There is no way in my AR to make that length possible because magazine allows 2.290". Will I still be able to use the load I developed and not worry about pressure? I will load to that length and see what happens. I am going to gain investment in a comparator to make seating depth easier because the tips of bullets have varied and is aggrevating a little.

Topgun 3006

For your AR I think you'll have to seat them to the depth that the magazine will accept them and call it good. I believe that is generally always a shorter OAL than what you found doing like the video showed or what NM447 and RR were talking about doing. If I'm wrong, I'm sure he will correct me. That video was for a bolt rifle and I missed the fact you had an AR.