17 HM2 case ruptures

[suhrken]

I have a converted 10/22 (New E. Authur Brown Barrel, and bolt handle) I took it to the range today and it ruptured the cases after about 20 or 30 rounds. Ran a cleaning rod with a brush on it the second time it did it, The third time it blew the magazine apart. I was using Hornady ammo. Had the rifle checked by a gunsmith he said everything appeared okay. Hornady wants to look at the cases, they blew at the rim or right by it. I havent been able to reach EA brown yet. Has anyone had this problem yet. the gun has had about 150 rounds through it all together