I was just thinking, how hard are the "drop in" from top magazine adapters to get in and out past the bolt catch?

You push the magazine catch button when you put the adaptor in or take it out.
Easy.

Misunderstood the question.

Get a bottom loading one if you plan to remove and install it often.

Impossible.  If you plan to swap back and forth, this is a good place to have a threaded pin on the bolt catch pivot.

https://www.brownells.com/rifle-parts/receiver-parts/receiver-hardware/receiver-pins/ar-15-m4e1-lower-bolt-catch-pin-prod132472.aspx

It will be a regular mag catch, not the long one.

I guess I don't understand the premise of the question about the bolt catch. The bolt catch is at the very top and you insert the adapter from the bottom, where AR magazine goes. So it slides up until it contacts the bolt catch and stops there. The adapter is called "drop in" but you don't actually drop it in, unless the gun is upside down.

You have to press the magazine catch while inserting the adapter.

There are literally "drop in from top" adapters and insert from bottom. I am specifically asking about the top load blocks like Hahn makes because I understand they are tool less required to swap in and out. I will be swapping between 9mm and 22lr a lot with the lower. The top insert blocks are supposed to be easy to change but do not do lrbho.
 I was only wondering were tolerances so tight would a standard bolt catch stop it from easy removal and installation.

Still need to remove the standard bolt catch.  The adapter has a moving element that is between the 9 mag follower and the standard bolt catch.  This way the 9 mag will do a last round bolt hold open.  Since it must push the catch up to engage the bolt, the adapter must fit under the bolt catch.

I called Hahn. Their "Drop in from top" block is cut to allow tool less removal and installation without interference from the bolt catch. All you have to do is open the back hinge pin and put the block in or pull it out. No tools. It will not do lrbho with a standard bolt catch. That is fine for my purpose.  The bottom insert type will but require tools to swap in and out.

That is for a bottom load

Uh, no.  I have this Hahn unit. It drops in from the top.  It has lrbho. A must as far as I was concerned.

That is the "Dedicated" it is not made for fast changes.

This is the other Top Load one that is "tool less".

" Tool less / Top Load"

But if it had the "long 9mm bolt catch" it would be trapped from quick removal by that bolt catch.

Just setting you straight. Mine is not a bottom load as you state.  Mine is a top load as you stated you wanted in OP.  Mine is as I describe and confirmed by Hahn’s webpage.  Just not the one Hahn calls a “top load”.  A link to what you were looking at would have proved helpful and cleared up any confusion on my part.

You did not indicate lrbho was unnecessary in your first post.  I want my 9 to exactly emulate my 5.56. Your needs may vary.

The "Dedicated" is also top load. That is undoubtedly the best block for dedicated lowers. I am going to be switching this lower a lot between 22lr, 9mm and who knows what so the "tool less" is what I am after.

Just thread the rear bolt catch boss and use the threaded pin.  Your manual of arms will now be identical across all your ARs.  Another couple minutes for the swap out is all that’s lost.

Rock River just uses a set screw.

Dedicated Hahn for me !  On a new lower drop from where you want!  no screws and 100% reliable with fmj….. expensive…. But ??

H

Hahn has two versions of the top loader, dedicated and non-dedicated. Or at least they used to.
I have the non-dedicated top loader, drops in and out by just hitting the mag release button, no change of the bolt catch. NO LRHO.

Later I made mine dedicated by changing my std. 5.56 bolt catch with a Colt long finger catch to give me LRHO. The long finger catch keeps the adaptor in place even when hitting the mag release.

Before the long finger catch I’d regularly switch between 5.56 & 9mm uppers with the Hahn non-dedicated top loader, swapping was as fast as a mag change. Be aware that the Hahn top loaders are famous for running great with Metalform mags (the best IMHO) but not with other brands.

Normally I can take or leave LRHO but inserting a full 30 round Colt SMG mag on a closed bolt is very hard and I’d often have a mag that wouldn’t feed cause it wasn’t latched. 9mm Colt SMG is the only setup that has to have LRHO for me.