Hi, I am new to an ar15 platform and I am in the process of learning the mechanic of the firearm bolt catch. I notice that some shooters prefer to pull back the charging handle than pushing the bolt release lever when doing a reload. When the shooters pull back the charging handle, what mechanism disengage the bolt catch and allow the bolt to go forward?
Thank you

The bolt catch spring keeps the bolt catch depressed unless it's either pushed up manually by the user, or there is an empty magazine follower pushing up on it from inside the magazine well.

Once engaged, the bolt catch is held to the bolt face by friction, until it is manually released, or the bolt is partially withdrawn, allowing the bolt catch spring to force the bolt catch down again.

This.

If you're familiar with how the slide catch works on most modern semiautomatic pistols, it's exactly the same.

Bolt catch is spring operated and there is a small metal plunger that sits in between the spring and bolt catch. You can release the friction on the BCG by pulling back on the charging handle just enough to disengage the bolt catch. Once that happens you let go of the charging handle and the buffer spring will push the BCG forward and chamber a new round. Honestly though, its just easier to re load a new mag and hit the bolt catch.