Almost certainly this is a gun problem. Get it checked.
You can't make a blanket assumption like this when using an economy grade ammunition. A poorly seated primer will produce what looks just like a light strike. Because all that "light" hit did was drive the primer deeper in the case.
In addition I've seen some rumors on the net that the White Box not marked USA is imported from China. I'm not going to place a lot of faith in that rumor, however might be possible it came from some rather poor contractor in Eastern Europe or south of the border.
To the OP, if you want to really determine if it's a gun or ammo issue, you'll need to use a first rank ammunition. One that I would suggest is Speer Lawman TMJ or FMJ.
I have 2 reasons for suggesting the Speer Lawman. One is the reputation on the net that Speer uses rather hard primers, so your insuring your gun will function properly with a premium grade of ammunition that uses a somewhat hard primer. BTW, I like Speer Gold Dots for defense, so reliability with Speer ammunition is critical for me.
The second is due to a recent session of benchrest shooting my model 620 after installing a new optical sight. I saw so little vertical stringing of the shots fired at 35 yards that I was amazed. Total vertical deviation for 5 rounds was less than 3/8 inch. Vertical stringing in a group shot from a sandbag rest is almost always due to a variation in the velocity of the fired round. Seeing such a small deviation in the vertical indicates that the ammunition is VERY consistent, both for ignition and load. Bottomline, this stuff is some of the best range ammo I've EVER shot. Another plus is it shot very clean. BTW, I'll also note that it "felt" a bit hot, more like a +P loading than most of the 38 spl. range ammo I've shot.
BTW, also tried 158 gr. LRN Blazer in the 620 and I won't ever make that mistake again, it was both dirty and leaded up the barrel worse than I've ever seen. Took a full 3 hours of patching the barrel with a peroxide/vinegar mix to get it clean. Speer should drop that round, it's just awful.