Reaching out to you guys because I just can’t seem to make heads or tails of the numbers I’m getting. I’ve been using the Hornady bushing to measure shoulder bump since I started reloading around 2 years ago. Seemed to work alright for me so far. That is until I broke out my Wilson micrometer head yesterday. Initially I just wanted to play with the Wilson gauge (which I forgot I purchased a year ago) and to verify that my shoulder bump was matching what the Hornady bushing was showing. I was resizing 223 and set the RCBS FL sizer to bump the shoulders 0.004”(via my Hornady bushing). I then checked each case with the Wilson micrometer head & the Wilson gauge I was getting 7-8 thousands shoulder bump. Kind of a headscratcher but since I was just loading some plinking 223 with mixed headstamp brass I didn’t give much though to it.


Fast forward to today and I’m sizing my 9x fired Hornady 6.5 Creedmoor brass. My die HAD been setup to bump the shoulders 0.002” when measuring with the Hornady .400 bushing with no real issue in the past. But when I started sizing today I pulled out the Wilson micrometer head again to see if I could get it to confirm the delta from the bushing. The Wilson gauge was very repeatable, showing 0.006” shoulder bump. I got on the phone with Wilson in the hopes that I may have been missing something obvious and didn’t come up with anything. So, to test, I then backed the sizing die out until the Wilson gauge showed I was bumping the shoulder back a very repeatable 2 thousands. These rounds chambered in my rifle just fine. The problem is when I size 0.002” based off the Wilson gauge reading my brass grows by 0.002” from the fired state according to the Hornady bushing. I tried swapping the .400 bushing with the .375 bushing with the same results, I’ve got a good set of Mitutoyo calipers & I’m conscious and try to be consistent on how much pressure I’m putting on the caliper jaws. So I’m left trying to make sense of what’s going on.

I attached a link to a photo and description of the Wilson micrometer head so you guys could get a better idea as to what it does (incase you haven't seen it before). The micrometer head is an accessory to the case gauges that acts as a comparator.LE Wilson Micrometer Head


I'm well aware that the Hornady bushing are just used as a comparison measurement from fired to sized brass, all I'm using is the delta. I was taking a before and after measurement of my brass during sizing with the Hornady bushing insert. That's where I was initially getting a .002" shoulder bump, according to my calipers. The issue I'm having is when I tried to verify that shoulder bump with my LE Wilson case gauge and micrometer head, which is nothing more than a comparator itself, it was showing .006" shoulder bump, when compared to the same fired case in the same gauge before firing.

I guess what I'm trying to say is the delta should be the delta no matter which comparator I'm using. But in my case it's not. I'm inclined to believe the Wilson because my .002 bump in the Wilson still chambers in my rifle.

Any help will be appreciated!

Comparing and measuring are two different things. Different calipers with different hornady guages aren't gonna read the same.
Sneak up on the correct shoulder needed to lock without scrubbing & use one or the other.
I suppose you could note the reading from each & recognized which one you've chosen to use.

The Delta reading based on the 0.4" dia datum or the 0.375" dia datum, gets you part way to the answers but doesn't account for full surfaces on the shoulder or the body.

The Shoulder Diameter alone can cause the difference between the Hornady and the Wilson, so checking both is better than not knowing about those differences but it would take all the body measurements to know the full picture.

If a case gage touches on just the shoulder datum diameter, it will likely give a very close answer to the Hornady bushing gage tool. If it references more of a surface and includes the body diameters, all bets between those two methods matching up are off.

Your technique is not to blame, it is a difference between the shapes of those Hornady gage bushings and the Wilson case gage that cause the potential major disconnect.

Many gunsmiths, will double check function with a dummy case and the chamber setup with Go-No-Go gages, and then add a layer of Scotch Tape to the back of a dummy case to see if the bolt closure is affected.

They can then do the same with those case gages to check to make sure their gages are picking up on a well formed case. (They, (Go-No-Go gages), are not necessary for casual folks, but many serious folks own their reamers as well as Go-No-Go gages and we can use them to cross check out other tools. Even having just the Go gage is useful.)

Some practice with a case that has been fireformed several cycles while using the tape trick in the chamber, plus the gages, is a good exercise. It is also good to check as many of the SAAMI spec datums as you can to see how well your dies and chamber are going to play together. For example those shoulder diameters I mentioned earlier as well as the 0.2 Datum if your particular design has one. Learn to track those diameters and lengths from virgin brass and after several fire form cycles while being careful to neck size only, then again after your first shoulder bump attempt. Remember, a caliper is okay for datum lengths, but you will want a micrometer for diameters, and more than likely one with blade anvils to make it easier. A regular one works fine in a pinch.

It is good that you are paying attention to details.

Yeah Op, went thru this with a buddy..Hornaday sets their gauge up to measure off #C 375 comparator bushing..

Attached File


But SAAMI measures the datum at .400"

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I went with SAAMI and used hornaday #D 400 bushing.. what matters is what you measure before and after sizing with the same bushing..My guess is Wilson is also measuring off the .375 datum...

Attached File


I actually emailed Hornaday about it..they didn't really have an explanation more than "because" Technically either way will work, it just matters that you know and stick to one or the other and not intermingle...

I prefer Mo DeFina's gages and have two sets in .223 and .308 (got the second set cheap used) and neither gage gives me identical measurements. I used a touch of whiteout to mark SAAMI minimum headspace on all of them using a PT&G "go-gage" for both calibers.

Drop in gages are nearly useless IMO. I need a measurement in .001" increments to work with.