9mm fragmenting out of 16" barrel

Hi everyone! I have been loading RMR 124gr FMJ RN with 4.1gr W231 at 1.135 which I have used on a variety of pistols and a CX-4 Storm. I recently picked up an AR9 with a 16" barrel and my 9mm is fragmenting out of this rifle. From what I can tell, the only possible difference between the CX-4 and this AR9 is the barrel twist rate. I think the CX-4 has 1:16 while this Ballistic Performance barrel may have 1:10.

The ammo passes the plunk test on the AR9 and spins freely. No issues with cycling, feeding, ejecting, etc.

I’d like to continue using 124gr FMJ. Do I just have to slow it down?

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Do you have any kind of muzzle attachment screwed on? A friend of mine was having a similar problem with his 9mm CZ Scorpion. Upon examination, it was evident the bullet was hitting the flash hider he had screwed on. Tried it without the flash hider and problem went away. He bought another flash hider and no problems since.


That was my first thought, twist. I load my 9. 115 and 5.1 gr. Maybe drop it to 115.

PS do you have a chron to get the velocity?

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Thank you. It was the muzzle brake. So slight that I could not see any marks when I took it off. But it shot fine without it.


Good deal! :+1:

Even a blind squirrel finds a nut every now and then :grinning: