I'm not much of a handy man but I just "successfully" made my own modified case guage that screws onto the hornady oal rod. I ended up just drilling an appropriate size hole in the base of a once fired 264 win mag case, ordered a tap to set the threads and "walla".... a modified case guage in 264 win mag.
The case is a little snug in the chamber so I'm not sure i've mastered the technique yet. But I am excited to know now I have everything I need to make modified case guages for any cartridge I want.
The one thing I wrestle with is whether or not to full length resize so the case fits in easily (but then the bullet wont slide thru the neck), or don't resize (so the bullet slides easily thru the neck) but the case is a little snug????

Congrats. Don't resize the case. Snug is good. If you want, try putting the case in a drill and polish it with some 00 steel wool at medium speed.

Where did you get the tap? The only place I could find one had a minimum order of $30 and I only needed one tap. Thanks

Congrats.
Could you share the thread size please.

Thanks

5/16 X 36, or 9/32 X 36 I've been told.

5/16-36 tap, seller jtsmach8xzw, 7.95 + 4.00 shipping (eBay ...jts machinery and supply co.), I think the drill bit I bought was 9/32nds ( I just took a modified case with me to lowes and found a bit that fit it the best).
Update on how it worked.....
Unsized, once fired case got stuck in chamber ( I pushed it in fairly hard to see what would happen. Had to put bolt in to grab it and pull it out).
SOLTION: full length resize, trim.
New problem: now bullet wouldn't slide thru neck.
NEW SOLUTION: repeatedly seat a bullet, then remove it with w kinetic hammer puller (4-5 times). Then wrap drill bit with course steel wool and spin it in the neck till bullet slides effortlessly (about 4 times, checking after each 30 seconds or so of drilling).
NOW, "WALLA"... Works like a charm, easy to insert/extract and bullets slide back and forth effortlessly.

RBH

Thanks for the info. I just ordered one for my self. Been wanting to make my own for some time. Made one for a 338-06AI using a 1/4" all thread seems to work OK but doesn't lock.

How did you hold the brass?

How did you hold it square to the drill/drill press?

I believe the best option is to use once fire brass from the specific rifle.

RBH,
You don't have to do the kinetic hammer thing....just put case in sizer and bring ram up until just the neck goes through the expander ball and stop go no further.

Me? I do my own too but I use once fired from the rifle I plan on using only thing I do is knock out primer and trim and polish......of course after drilling and tapping.

Tom, thanks for the heads up on the expander ball. I'll try that on my next one.

I just put brass head in a vice, lightly tightened, drilled slowly by hand with my free hand helping to hold the brass still and tapped by hand slowly, holding the brass the same way. Prolly not the most square but seems to work. Though gripping the brass with the vise may have contributed to its tightness in the chamber...?

thanks for the info!!

RC
I have used a drill press and those soft plastic inserts for a vise placed in a small drill press vice to hold the cartridge. These small vises work great for hand drilling also. Mine cost about $12 at Harbor Freight but many home improvement stores carry them also. As well as the soft plastic inserts. Start with a drill bit just a tiny bit larger than the primer hole and drill progressively larger holes till you get to the desired size. If you try to use too large a bit it will be more likely to gall and twist the case out of the vice. A few drops of cutting oil will also help. Good luck.

PS As an alternative you can drill a hole the size of the case in a block of wood then saw the block in half and clamp the case in the block with a pair of locking pliers (vise grips).