Making 300 Blackout Brass. Neck Diameter Issues.

I learnt something last night which you guys might be interested in if you are making or going to make 300 aac brass from 223 brass.
I have a case gauge but this only checks the head space and the length. It does not check the neck diameter.
Long story short, I ended up with about 100 rounds that wont chamber because the neck diameter is too large. Out with the bullet puller and 10 minutes latter it was time to start again with a different type of brass.
The brass that caused the issue was RG. Changing to FC solved the issue. Neck turning would have solved the issue too but this is way too much work.
This is a good video on the issue I had.
https://www.youtube.com/watch?v=_08yZXnk7ro

In short American sourced brass should be fine. The European brass is likely not suitable to be made into 300 Blackout without a lot of additional work.
Think I might try and buy one of these as they do check the neck diameter.
Sheridan Engineering - Ammunition Gauges

Just been in the man cave cutting 400 LC cases with a Dremmal and trimming the cases, I get low ES 16fps with LC brass.
Very interesting about RG brass as I was thinking of getting some but I don't want to go to the trouble of neck turning brass. The Sheridan 300blk gauge would be handy instead of chambering them all to fit.

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Originally Posted by Simon

I learnt something last night which you guys might be interested in if you are making or going to make 300 aac brass from 223 brass.
I have a case gauge but this only checks the head space and the length. It does not check the neck diameter.
Long story short, I ended up with about 100 rounds that wont chamber because the neck diameter is too large. Out with the bullet puller and 10 minutes latter it was time to start again with a different type of brass.
The brass that caused the issue was RG. Changing to FC solved the issue. Neck turning would have solved the issue too but this is way too much work.
This is a good video on the issue I had.
https://www.youtube.com/watch?v=_08yZXnk7ro

In short American sourced brass should be fine. The European brass is likely not suitable to be made into 300 Blackout without a lot of additional work.
Think I might try and buy one of these as they do check the neck diameter.
Sheridan Engineering - Ammunition Gauges

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Same as when I turned 350 FC .270 cases into .308, they were fine, but heavier PMC brass with thicker walls couldn't even fit into the .308 F/L die as the neck (former wall) was too thick, let alone actually seating a projectile.
RG being ex milsurp 5.56x45 ammo would be thicker brass.