My SOP is to start with the Ammo.
After you try some known high-quality ammo, you then
start looking for gun problems.
Cheap ammo often gives oddball problems...
Take Remington Golden Bullet .22lr...most inconsistant ammo I've ever run across.
You can't get consistant chrony reads off a whole bulk pack. They're all over the place, and that ain't all.
Short powder loads,
No powder loads,
No primer loads,
Insufficient Primer in case,
Badly done crimping,
Different bullet diameters,
Probably why folks call 'em Remington Golden Bullsquish
Reminiscent of Thunderbolts (Thunderduds)
I constantly see people cussing their guns...when I wander over to check out the issue, it's most often the ammo that's the problem...closely followed by the trigger nut. After you rule out those two issues, diagnosis gets easier