What's the couse?

[Double Lab]

Angel,
Your 1oz loads are not likely the culprit. Try some of RST's lite 7/8oz. loads for the 16. You and the gun will love it and they crush targets as well as the 1oz. loads. Bill is right. Gunk. Most times the simplest solution is usually the answer. Good Luck.
Daryl.

[Angel Cruz Ortiz]

Daryl, that's what I use on my Damascus 16ga.

[Jim DiSpagno]

Dirt the most likely culprit. After sitting unfired for 50 years, my Pop's GHE 12 did that to me and after taking it to a reputable gunsmith, the problem was solved with a thorough cleaning. The smith actually replaced the screws to the original timed position.