Lots of players can't wrap their head around how some of those ridiculous top scores can be possible. First of all let me assure you, that they aren't impossible to achieve, Noble Empire (this game's developer) has the means to check the minimum possible times for all guns.

Here are some tips you are probably not aware of yet, but might clear your doubt on what is actually feasible:

Having your camera flying about whenever you click a part is going to cost you lots of time.



While navigating the map press the leftmost button in the upper left corner to switch to fullscreen.



Force this through your graphics card's settings for an overall smoother experience.
(Click picture to zoom)

Save big, easy to reach parts with a somewhat longer animation like magazines, slides, barrels or parts with multiple screws being removed in one go for when you may need to reposition the camera accurately.

Pins and the likes are especially hard to catch during hectic movement, having your cursor hovering over them while another part is still being removed really helps.

You'd be surprised how little movement there's actually needed once you've found some sweet angles. (See below)

Press the P key to bring up the pause menu. As long as it's open the clock will stop and the camera slowly rotates. Use this if you need a breather, have to think about that single part you're still missing or simply want to reset your point of view.

Assume a small delay on your behalf of 0.2 seconds per click at about 35 parts. 0.2 seconds doesn't sound like much, but that's times 35 activations on average, times 2 (you need to reassemble after all) totalling a difference of 14 seconds just because you didn't click fast enough. There is a way to shave off some extra time:

Pressing Spacebar while having a part selected will activate it. Not only is it likely to improve your times, but it may also prevent unwanted camera movement double-clicks tend to incur. Just click on a part once while mashing Spacebar.

While you are holding the Ctrl or Alt key, camera movement will be disabled. This may prove especially helpful in super-hardcore, wherein a single mouse click activates parts and the above-mentioned Spacebar key won't be of any help.

Readjusting your camera angle costs time, leads to misclicks and lots of curses.

Take this shot of the S&W M&P .40:



It allows me to remove the magazine and the slide:



As well as all pins (the rightmost being hard to reach otherwise) and the only part on the bottom of the gun:



You can even finish most of the slide, especially the sights which are forgotten all too often:



From the same angle you can also gut the innards of the grip and remove its back.
The whole gun can be easily disassembled with a total of 4 camera angles, one of which is needed for the sear pin alone.

If all you want to do is get the champion achievement for a gun, check its daily highscore multiple times a day.
Player's daily highscores are saved individually for 24 hours. So if you made it in second place, you may be bumped to first simply because another player's score "expired"! All you have to do then is to beat your own score in the gamemode you just rose to the top of.

If you aren't confident about your clicking skills and not sure about bothering to attempt a highscore for a gun you unlocked or are about to unlock in the first place, compare its daily highscore with the all-time highscore. When both are just a fraction of a second apart and waaay off your own personal highscore, you might want to try a different gun - at least for today. This method won't help you much with often frequented guns like the AK-47, MP5 or TEC-9, of course.