What are the destruction mechanics for the doors in-game?
Do the doors splinter after a specific amount of damage is dealt? Or do some weapons more easily destroy doors than others?
How to doors be broken
playerunknowns-battlegrounds
Related Solutions
Since we're talking about an actual circle, I assume we want a circle that stops. (Otherwise, it continues closing until it finally becomes a line on the 9th contraction.)
here's some additional data on the circle.
According to the chart above, the answer OP is probably looking for is 50m.
There may just be coincidences with a lot of people having similar gear. I often see the same stuff because people aim to get the better gear and obviously level 3 gear will be the most benefit to you. The places with higher loot spawns, and better gear tend to have a high percentage of players dropping at so it's not unlikely you'll see a lot of players with that better gear.
As far as I known in my time playing, and from reading forums and threads about loot spawning, there doesn't seem to be any particular weight applied to certain things spawning in different matches.
Common loadouts are ARs with a shotgun or SMG, in my experience, which is why they're so commonly seen. The more powerful guns have less frequency so that also contributes to seeing more SMGs around the place.
Some early threads like these all mention how it's weighted towards certain zones having better loot, and the farther away you are from them, the more RNG is factoring in. In my experience the more isolated places tend to have some things in them, and a variety of gear, but there is the chance nothing/little amounts of things are there.
If you check out various loot spawn guides like this or this, they'll tell you that you're guaranteed better things at places like the Military Base, the School, or the Power Plant to name a few.
Here is an image which shows the general distribution, and as you can see, some places are much more weighted in the amount/quality of loot spawned. 
Best Answer
So I did dome testing on this topic and I must say, I was pretty surprised by the results!
I documented (almost) all of my testing and uploaded the video to YouTube here.
TL;DR:
Doors will only break, if you shoot them fast enough, the amount of damage dealt is not that important. Any weapon, able to shoot fairly fast, will be able to destroy a door easily.
"Just spam it!"
Destruction of doors:
Doors will always have 4 stages of destruction:
(only exception are grenades)
In every stage, apart from the last one, the door is still functional.
Damaging:
As you can see in the first clip of my Video, I shoot the door a total of 40 times with an AR, but the door still doesn't break. Note that I shoot one bullet per ~0.85s.
Then I switch to a faster shooting pace and it only takes 3 bullets to destroy a part of the door. (Door is now in stage 2)
For the other half of the door I will also only need 3 rapidly fired bullets.
Firing Rate needed:
I did some very simple calculations on how many bullets per second must be fired in order to break a part of a door:
(These are the results of the M416)
So it's safe to say, that by shooting 3 bullets within 1 second you will break a part of the door. (using an M416!)
Different Weapons:
Any weapon, able to shoot "fast enough", can destroy a door. Here's a list of weapons:
This list is not complete! I haven't had the opportunity yet to test all of the weapons.
PLEASE READ:
Because testing something like this is very time consuming and based on a lot of luck (finding the right weapons whilst not dying) this is all I can answer so far.
I will definitely update my answer in the future.
EDIT: By "I will definitely update my answer" I mean, that I might update my answer...