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Problem With AN AR-15 Build ?

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Ok, I've built numerous AR's but never had a problem like this..


I ordered a recieved an upper from Model 1 Sales. It was chambered in 300 Fireball.


I ordered Hornady 300 Blackout Brass for reloading as I was told that they are interchangeable.


At the range today several rounds didn't fire. The firing pin NEVER struck the primer. Then the round didn't extract. It wasn't jammed in the chamber, the extractor just didn't grab the rim..


My theory(s) are:


The 300 Fireball chamber is longer and allowing the rds. to chamber deeper to where the extractor doesn't grab the rim, and the firing pin doesn't contact the Primer




The headspace is off allowing the case to seat too deep in the Chamber..




On the plus side, when it worked it shot 2" groups with a EOTECH Red dot scope at 100yds.. And 6 different loads shot to the same point of impact. From 125gr. - 180gr. Out of a 16" Barrel .

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Hi Paul, how've you been?


Is it possible that the Blackout Brass is intended to be run through a Fireball sizing die before firing through the Fireball upper? Reason I as is I have a 6MMAR that is based on 6.5 Grendel brass but needs to be necked down before loading. In any event it sounds like a F/L sizing issue. I wouldnt think you have that much variability in your headspacing.

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My response from MODEL 1 Sales :


Thank you for your purchase


The brass is not interchangeable. The .300 Blackout Brass is longer. What you are experiencing is the bolt is not fully locked which is why it will not extract or fire. When it did fire, you are pushing case past the slight shoulder in the chamber causing the weapon to fire out of battery, which would explain the cartridge burst as the bolt was not fully locked into the barrel extension.

The lead is also shorter. Using .300 blackout cartridges in a .300 whisper, 300/221 or fireball chamber is not safe.


Thank you

Model 1 Sales



Soooooooooooo.. I just ordered 200rds. of 300 WHISPER from SSK Industries, the designer of the 300 Whisper/Fireball rd.


I guess this solves the mystery ..

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