Just bought a brand new NAA Black Widow in 22 lr. only. Took it out tothe range yesterday and fired off about fifty rounds. I noticed some of my .22 lr cases had slight hairline ruptures in the casings after I took them out (I fired about 50 rounds; 3 rounds had the ruptured cases). They did not all rupture in the same chamber, nor did the rupturing cause the gun to misfire. Tell me - is this normal/safe or is this an issue?