Hornady OAL Gauge help

[drfroglegs]

I haven't been able to find the answer to my question and hope you guys can help...

I have the Hornady OAL gauge and the corresponding modified cases. My question is, should I adjust the shoulder on my actual cases such that they match the shoulder (headspace measurement) of the modified case. I'm using the hornady headspace gauge to minimize working my brass. If the shoulder is what rests on the chamber, you would think any differing value in the case headspace would affect the length of the bullet (when using the OAL gauge).

In other words, if the cartridge measures 1.300" to from base to ogive that same cartridge would measure 1.290" if the shoulder is bumped back 0.010". So if my cases don't match the modified cases from hornady perfectly, will the measurements be 100% accurate?

I hope my question makes sense, if not I can reword it Thanks everyone for your assistance, I'm pretty new to reloading (going on year 2)...

 

[IndispensableDestiny]

If you want to bump back the shoulder 0.010 inches, then use the headspace gauge to measure a fired case. Then adjust your resizing die to reduce that measurement by 0.010. You don't need the OAL gauge.

A bullet comparator measures from the ogive to base using your cases. It is useful in setting up your seating die. It is also used with the OAL gauge.

The Hornady OAL gauge measures from the ogive to to base using the modified case. It is used determine the OAL to the lands of your bore. I have an earlier post that describes how to make your own modified case, which should give your truer measurements.

 

[drfroglegs]

Thanks Destiny. I understand I don't need the OAL gauge to measure the bumped back shoulder. My question is if my bumped back shoulder does not match the shoulder on the modified case, how can these two measurements be compared?!

If I make a cartridge with the same bullet, but 2 different cases with different shoulder lengths (headspaces) the two cartridges will not be identical (nor will the measurements be identical with the OAL gauge).

I actually made a few modified cases, but my tap broke and the stupid company wont replace it (even though I paid $25 for the tap).. I hate poor customer service!

 

[IndispensableDestiny]

When you use the OAL gauge and comparator together, you are measuring from the ogive to the base of the modified cartridge. When you use the OAL gauge in your rifle, there is no assurance that the shoulder of the modified case is touching the chamber. It does not need to, and may be best that it does not.

That's the reason some people make their own modified cases using brass fired in that rifle. I may give you another 0.001 or so of accuracy.

If you search on making your own modified cases, you'll run into a discussion or two as to why do so.

 

[drfroglegs]

Ok.. The picture might help explain what I'm asking...

Both of these cartridges would read exactly the same on the Hornady OAL gauge. However, if the modified case on the right was used to calculate the optimum OAL and your actual cases have shoulders significantly less, the cartridge you make with the correct OAL will actually yield a bullet that is digging into the lands/grooves...

 

[IndispensableDestiny]

You are thinking too much. First of all, you have no idea what the optimal OAL for your gun is until you shoot it. The OAL gauge is to measure the distance to the lands. You can compare the headspace between your modified case and actual case using a headspace gauge. Hornady sells bodies that work with the bullet comparator.

I just came up from my basement . . .

Using a Hornady No.400 headspace body, for .308 Winchester, I get:

1.619 - Hornady Modified .308 case
1.624 - Home made modified case
1.623 - Full length resized case

Those differences are not significant. Here's why:

My gun measures 2.280 to the lands. If I loaded to that, the cartridge would not fit in the magazine (may not be an issue for you). I developed a load with a COAL of 2.810, a measured OAL to the ogive of 2.212. Next, I'll load some with with a longer OAL, starting with the maximum magazine length, to find my "optimum."

You can try finding the distance to the lands the old fashioned way. Slightly crimp an empty case with pliers, start a bullet, and chamber it. It will be to the lands.

Bottom line is don't worry too much about it.

 

[drfroglegs]

Thanks for the very detailed reply, I do have the headspace gauge and the OAL gauge from Hornady. The company I was complaining about actually emailed me this morning with a replacement tap, so I'll be able to make my own cases again!

I didn't realize there was such a small difference in the headspace between the modified and the fireformed cases, I guess that's why I've never really seen anyone complain about this topic! I see what you're saying with the COAL and the magazine, I don't use the magazine and just feed 1 at a time, I would rather do that anyways because you don't have to worry about crimping (the magnum calibers).

I did screw up once by resizing my modified case, then I couldn't expand the neck so the bullet would fit back in. Any tips for expanding the neck after you resize (so the bullet will move freely). Thanks again for all your help/advice!