If you are new to handguns I expect that you'll report that it shoots low and left, a VERY common result for those new to handguns. The cause is "pulling" the barrel to the left at the end of the trigger stroke combined with a "push flinch" when anticipating the recoil. Note, the above is for right handed shooters, if you are a southpaw you'll tend to go low and right.
BTW, I first started shooting handguns in 1974 and still have a tendency to shoot low and left if I don't keep in practice. My solution when I find myself doing this is to use a bit of Zen and concentrate on achieving a relaxed state of mind and body at the instant the trigger releases. Some days I can get myself sorted out in 5 or 10 minutes and other times it can take me 2 or 3 weeks to start shooting well. It's all a matter of how long I've been away from handgun practice.
As for your slide rattle, that is something that is VERY common with many semi auto pistols and hard as it may seem to believe it has very little impact on accuracy. I carry a Sig Sauer P239 and if I cheat with readers and am in very good practice I can shoot 1.5 inch 5 shot groups at 50 feet with it using a sandbag rest. It also rattles nearly as loudly as a Castanet if there isn't a loaded magazine in the pistol. I've also put over 4000 rounds downrange without one single failure to feed, eject, or a jam of any description. What I've found to be most critical for accuracy with a semi auto is how snuggly the barrel engages into the slide. In the case of my P239 it's tight enough in this area that you cannot feel any movement of the barrel at either the front or rear lock when the barrel is seated in the slide. As a result the relationship between the barrel and the slide where the sights are mounted is very very consistent.
Yeah, more of an answer that you may have expected. The reason is very simple, just giving you a heads up on what is common for those new to handguns or "slow learners" like myself. Truth is that it is instinctual to flinch when hearing a loud noise and impact. We are programmed by evolution to do this and re-programing our responses takes PRACTICE PRACTICE PRACTICE.
Tips.
First, do your best to relax throughout the process of firing each shot. Doing this will take practice and concentration but learning this skills will both make you a better shooter and you'll find you leave the range in a more relaxed state of mind.
Second, I would suggest that you purchase a good double action revolver like a S&W 686. Because IMO there is NOTHING you can shoot with that will develop and refine your trigger skills more than shooting in Double Action properly. BTW, that is with a complete smooth trigger stroke. When you first start shooting in double action you will find that pausing just before the trigger breaks gives you better accuracy. This is called "Staging" the trigger and it's Cheating. Because it's not how you would shoot in combat and it won't allow you to learn how to stroke a long trigger pull smoothly without pulling your sights offline. Start with a slow steady stroke and gradually increase the rate of pull as you gain skill.
