Hornady Modified Case for OAL Gauge

Thanks for all the replies, I had considered doing it with a hand drill but for $10 it's worth sending it out to have done since I'd have to buy the tap anyway ... although then I'd have it for future cases. Decisions, decisions!
 
If you have a drill press, use 2 pieces of wood, clamp them in a press vice and drill a hole a little smaller than case diameter. This will allow better clamping of case for drilling and use press for running tap.
A used case with zero shoulder clearance is the most accurate. Any clearance between case shoulder and chamber will give you a shorter reading. I pick a used case the chambers with a very slight force to close bolt to insure its tight but not compressed.
 
Thanks for all the replies, I had considered doing it with a hand drill but for $10 it's worth sending it out to have done since I'd have to buy the tap anyway ... although then I'd have it for future cases. Decisions, decisions!

Can anyone tell me the tap size?

5/16-36, I got mine at Amazon for $10 >>> https://www.amazon.com/gp/product/B01N4PSBA8/?tag=lrhmag19-20

ADDED:

Just did one for my .30 Gibbs.

.30 GIBBS modified case.jpg
 
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I bought the tap, drilled out a small piece of pine stock equal case body (did not have any thing like a collet to use), placed in drill press vise, tightened enough where I could drill out in sequential drill sizes to minimize case slippage to the tap diameter I needed and then tapped using good lubricant. Just cleaned up the case in tumbler so nice and shiny, deprimed with universal Lee deprimer die. Just needed to be patient drilling since I really don't have the sophisticated machining tools available so make do with what I have to make it work.

But I have also sent in fired cases that Hornady tapped and sent back actually pretty fast return time so was very satisfied with their process as well.
I have done this for .30-06 with fired brass & .300 WSM with new FL sized brass that I stretched the neck with several insertions of a #3 phillips screwdriver and trued up the neck OD by cycling it several times in the subject rifle's chamber. Both methods work like a charm. Drilling is the hardest part. Sequential upsizing is the ticket IMO.
 
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