I read this post a few days before buying a 20 bore investarm, and was slightly concerned, but went ahead with the purchase anyway, now used it today for the first time, and after firing the first two carts, opened it without remembering to fully cock it, two new carts were put in and I was about to close, stiffness/not wanting to shut can be felt at this stage, and I therefore realised what I'd done wrong, fully cocked the gun and closed safely, so I would put this problem of both barrels firing, as user error, rather than gun error, as not only can you feel that something is not right, but y