Hornady OAL Modified Cases

[JohnWess]

Hello everyone,
I am a newbie on this forum and have a question for all of you with regards to the Hornady modified cases. Does it really matter if the case is the exact same size as one you will be loading and firing? I have heard some people say that in order to get the OAL properly you need to fire a case, resize it, then create a modified case based off of that fired piece of brass. But aren’t we just measuring from, in my case, the base to the ogive? There shouldn’t be much if any change there right? I may be wrong, but any feedback would be greatly appreciated.

 

[Howland]

With the OAL gauge, you're actually measuring from the chamber shoulder to where the ogive touches the lands because that is where your contact points are. To be precise you need to add the difference between case head to shoulder of the modified case to that of a case fully expanded in your chamber.

The modified case will almost always measure shorter from case head to shoulder.

Unless you want to take a fully fireformed case and drill and tap to make your own. Two ways to skin a cat.

 

[JohnWess]

With the OAL gauge, you're actually measuring from the chamber shoulder to where the ogive touches the lands because that is where your contact points are. To be precise you need to add the difference between case head to shoulder of the modified case to that of a case fully expanded in your chamber.

The modified case will almost always measure shorter from case head to shoulder.

Unless you want to take a fully fireformed case and drill and tap to make your own. Two ways to skin a cat.

Genius. Thank you so much! My mind did not even think that I am pushing the case in all the way until the shoulder hits the chamber. Very simple to just take my shoulder reading on a fired, resized, case and figure out the difference and add that to the reading. Thanks Again!

 

[Pvt.Donut]

If you want to be able to measure fire formed cases buy the Sinclair Seating Depth Gauge.

 

[Sheldon N]

Hello everyone,
I am a newbie on this forum and have a question for all of you with regards to the Hornady modified cases. Does it really matter if the case is the exact same size as one you will be loading and firing? I have heard some people say that in order to get the OAL properly you need to fire a case, resize it, then create a modified case based off of that fired piece of brass. But aren’t we just measuring from, in my case, the base to the ogive? There shouldn’t be much if any change there right? I may be wrong, but any feedback would be greatly appreciated.

If you've already got the Hornady comparator set, you can just measure the headpsace on your modified OAL case and compare it to a piece of deprimed/fired brass so you know the actual length difference between the two. Might be a couple thousandths, not much likely.

The Hornady tool isn't an exact science for finding where "touching" the lands is. I just jam a bullet hard into the lands with the tool, then write that down as my "hard jam" number. I"ll then back off 25-30 thou from there to start seating depth testing, which is probably similar to around 15-20 thou off "touch".

 

[JohnWess]

If you've already got the Hornady comparator set, you can just measure the headpsace on your modified OAL case and compare it to a piece of deprimed/fired brass so you know the actual length difference between the two. Might be a couple thousandths, not much likely.

The Hornady tool isn't an exact science for finding where "touching" the lands is. I just jam a bullet hard into the lands with the tool, then write that down as my "hard jam" number. I"ll then back off 25-30 thou from there to start seating depth testing, which is probably similar to around 15-20 thou off "touch".

Ever get the bullet stuck? Haha

 

[Sheldon N]

Ever get the bullet stuck? Haha

Sticks every time. I just tap out with a cleaning rod from the muzzle and then put in the OAL case and measure.

 

[JohnWess]

Sticks every time. I just tap out with a cleaning rod from the muzzle and then put in the OAL case and measure.

Ya, that’s what I figured. I have had to do that too without jamming it into the lands. I was just giving you a hard time.

 

[RackOpsTactical]

Using fired brass is better to get an exact measurement. You can drill and tap your own if you have the tools. However you dont need an exact measurement from shoulder to lands. What you are measuring is essentially a meaningless number as long as it's fairly consistant. The real number is from base to ojive so you can translate that to your jump.

Not sure if that makes sense. But if you measure from the real shoulder to lands or from a sami spec shoulder to lands it doesnt matter for the calculation.

 

[sabrecross]

If you have the Hornady OAL gauge, then buy this and tap/ drill a fireformed case and you're not left guessing... 5/16" - 36 HSS Right hand Thread Tap with 7.3mm Drill bit
The drill bit is very sharp and you can drill the case out with little effort. I just did one the other day.

 

[Midwestside]

I’ve drilled and tapped my own , but not everyone wants to bother with it.

A third option that has not been mentioned is that hornady will drill and tap your fired case for you in very short order for a reasonable fee.

It’s typically for wildcats that they don’t mass produce, but if you are concerned about the few thou’ difference in a fired case vs Sami it is certainly another option to consider.

 

[cmoore806]

sorry to resurrect an older thread but is a lathe NECESSARY to get the Fireformed modified case made or will my drill be centered enough in the primer pocket to get the job done? I have a mini mill but no room in the budget or the shop for a lathe.

 

[Midwestside]

I did it without a lathe. Centering& Concentricity was more challenging than I had thought it would be “chasing” the flash hole. It can be done though.

 

[ditter]

Send two fired cases to Hornady for 15 bucks or so. They have it back to you in less than a week.

 

[OldHistorian]

sorry to resurrect an older thread but is a lathe NECESSARY to get the Fireformed modified case made or will my drill be centered enough in the primer pocket to get the job done? I have a mini mill but no room in the budget or the shop for a lathe.

So, take a chunk of 2x4, and drill a hole in it that is between the shoulder diameter and the base diameter. put a piece of 180 grit sandpaper on a piece of scrap brass for that cailiber and use it as a tapered grinder to taper the hole to match the case. Once you have enough of a taper, set the case sans sandpaper in the hole, and make sure it is square to the wood.
This takes about 15 minutes. Place your once-fired case in the wood block, get the drill bit centered on the pocket, drill it, then use the drill press to center and hold the tap wrench to tap the hole. Done! total time less than an hour. I've made a bunch of these cases.

With regard to all who serve the Light,
Historian