Can Noveske .300 FB barrels use 5.56 brass?

[Garrett]

Okay folks - here is what I found out. It wasn't the Noveske barrel. It was just certain brands of brass. And these particular rounds would not chamber in my Contender, either.

The ammo I'd had issues with was all new-formed brass, made from mixed .223 and 5.56 brass. These were just to be for plinking ammo, using surplus 147 gr. bullets.

I took some random samples of the different neck ODs of the loaded ammo I still have on hand, and found the following:

.223 brass
Fiocchi: .330 - .334
PMC: .330 - .331
BHA: .328
R-P: .329
S&B: .335 - .336
Win: .330

5.56 brass
LC: .329 - .330
PPU: .334
WCC: .329

From some of my 220 gr. SMK loads, I measured:

PMC: .330 - .331
Rem .221 FB brass: .329 - .334

The PPU and S&B loads would not chamber in my SSK .300 Whisper Contender barrel, any better than they would in my Noveske .300 FB barrel. They were both very consistent, but too thick. I'm thinking either of these would make good "match" brass if you were to turn the necks.

The PMC brass gave good consistency, and these seem to chamber just fine. I might have to see how much more of this brass I have on hand. LC and WCC military brass were also both good and were both very consistent.

.221 Fireball brass seems to be the least consistent. This did not surprise me, though. When you form the cases, the brass does not stretch consistently. You can measure the neck thickness at 4 or 5 points around the case mouth and it can vary .005" from thickest to thinnest.

eta:
I just measured some factory .300 Whisper ammo from CorBon. I have a box from a couple of years ago, with brass headstamped "300 WSPR". I also have a box from 5 or 6 years ago, which uses new LC brass. Both are loaded with 220 gr. SMK bullets. Several measurements on both give a neck OD of .328 - .329