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Problem with bump gauge insert

thedude824

Sergeant of the Hide
Full Member
Minuteman
Oct 7, 2020
310
228
Tampa FL
I recently decided to try making more accurate 556 ammo by sorting brass, measuring shoulder from cases fired in my rifle, using bushing and micrometer dies, etc. Unfortunately, unlike my other Sinclair bump gage inserts, the 556 #23 will not pass over the case mouth of brass from my AR. It works as it should on new or sized brass. I only have the full length bushing die. Did I get the wrong insert? It really does me no good if it doesn’t fit fired cases. I have inserts for 338 Lapua, 308, and 6.5 Grendel and all work on fired brass as they should.
 
23 degrees is the correct insert. Couple of things could be going on, but it sounds like your chamber (223 Wylde?) has a larger neck diameter than the gauge insert ID.

Can you measure the OD of the neck on undented fired brass?

IMG_7360.jpeg
 
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Take your calipers, and check the ID of the end of the gauge insert that goes into the 'body'. See what that measures.

I just walked out to the shop, and checked mine: it measures 0.274" inside - which should be *plenty* for any brass coming out of a .223 / 5.56 chamber.

Unless it's been dented or otherwise deformed. ARs do tend to be hard on the case mouths/necks to begin with, but sometimes brass gets flung into a concrete wall, or stepped on, and then all bets are off as far as it 'fitting' in anything until it's been through a sizing die. I'm assuming you're bright enough to not try to measure one of those, and then complain about it here ;)