I had about 1500 brass I had run through my Adams Arms AR and reloaded them as usual. No problems experienced on my next trip to the range.

I bought a BRN-180S with a 10.5" Wylde chamber that must be very tight as I discovered my rounds would fail to fire and had to be mortared out to eject them. Did my research and discovered I need a small base resizing die. I ordered one from RCBS which should remedy the issue.

Rather than pull down all the bullets, I discovered not all had this issue so I set those aside. During this checking I discovered by chance that if I place the bullet by hand into the chamber and release the bolt that it slams it home and that somehow sizes it down and it is then easily extracted. Did this will all rounds that were hard to extract and loaded them back into a mag and they all chambered just fine after that.

Observations:
All rounds were gauged and passed in my Dillon case gauge.
Apparently a case gauge for Wylde chambers is needed. Do they make them?

There is no "Wylde chamber issue".

You may have just got an overly tight chambered barrel, it has nothing to do with the type of chamber. Or you didn't get the brass sized well enough for the new chamber, which is more common, especially if you were sizing for a different looser chamber. Measuring shoulder bump goes a long way to making sure the rounds fit, and that's your most likely issue, but there is an outside possibility you actually need small base dies (and not just talking about the bad advice so many give about small base dies being needed for all semi autos).

This is also the reason that a case gauge is a crappy way to go. You're not measuring rounds for your barrel, you're measuring for a gauge that may or may not represent your barrel, as you discovered. Much better to check and control shoulder bump for your barrel and verify that shoulder and base diameters are sized down enough to chamber freely. If you do those things, you can scrap the case gauge which isn't helping you anyway. And yeah, I know a lot of people like case gauges. That doesn't mean they're the best way to go. Hopefully I am helping you understand the problem with them.

Well it’s probably too late now, but when you discovered that you had some cartridges that chambered and some that didn’t – that’s when you should have stopped and made some measurements to see how those cartridges differed.

Something to put in your tool box for next time.

Another thing to point out - if you were able to "resize" your cartridges by slamming the bolt closed, and then they extracted easily - that's an indication you didn't have shoulders bumped back far enough. If it were a base or shoulder diameter issue, it'd have locked up your gun so tight you wouldn't have tried it a second time. I've done that accidentally, and it sucks.

It's possible your chamber has short headspace (more than you could adjust with an unmodified sizing die), but more likely you just didn't have the ammo sized well enough to fit that chamber. This has nothing to do with small base dies at all (those size the base diameter smaller), and everything to do with not screwing the die into the press far enough to push the shoulders back to the correct dimension.

I need to disagree with that. Sure, a case gauge may not be the be-all, end-all, but it's a lot better than just using a single barrel as a gauge. (Unless that ammo will truly never be used in any other gun.)



But I heartily agree with this! I'm so tired of "small base dies" being the internet answer to every rifle reloading problem!

I'd also be looking at pushing the shoulder back a little (adjusting sizing die down), to see if that will help.

I'd be hesitant to do this at home . . . slam-fires do occasionally happen with free-floating firing pins.



Just to specifically ask . . . does this include checking the shoulder setback by making sure that the base of the case is flush with the gauge?

Listen to the advice and information given above. It is spot on....
Case gauges are an imperfect tool at best
Way too many reloaders rely on them as the end all for checking their reloads.

I load 1000's of precision 223 /5.56 rounds every year. Wait for it.......
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I do not use a case gauge EVER.....I own several but simply don't find a need to use them......SHOCKING....

OP, I had this same problem with some 5.56 brass that I found in a box marked "Fully Processed". I loaded them up with my proven recipe of 25g of CFE223/55g Hornady FMJ's and went to the range. I was embarrassed as my SIL and his friend watching the constant mortaring on my new 223/556 pistol build.
I found that some gauged and some didn't so I separated them and started the investigation. Out of 150 rounds there were 90+ that did not gauge properly so I did the thunk (chamber) test on a matching pistol barrel and some that case gauged didn't pass either. I pulled the bad ones down and resized them (with the decapping pin pulled) and checked every one in the chamber test. The remainder of this reworked batch all went bag.
Moral of my story is "set up the resizing die properly".

Thanks for all the tips! To clarify, I measured them with my calipers. I also verified my sizing dies are fully sizing the case and that the neck bump was not impacted.

I discovered the issue at the range and have noticed they all feed and cycle without issue in my Adams Arms 5.56 upper. I acquired an SB sizing die and that did the trick. Apparently my chamber is undersized.

These reloads are from brass that I initially fired in my 5.56 and reloaded to fire in my Wylde upper.

What exactly did you measure, and what "neck bump" are you talking about? If you didn't actually measure the shoulder bump (it definitely should be "impacted") with a case comparator tool you probably didn't have the die screwed in far enough to bump the shoulders back for that chamber. It's extremely unlikely that you needed small base dies.