I have seen the terms highwall and lowwall and don't know the difference or if one is better than the other. Also if this is the lower that we are talking about, are the uppers interchangable between a highwall and lowwall. Thanks....

All AR-15 lowers are interchangeable, as far as dropping AR-15 uppers onto them -- with one exception. Some of the older Colt lowers have large pivot pins. These lowers require a cheap adapter pin to use mil-spec small pivot uppers.

I have no idea what high/low wall is in reference to.

Quoted: I have seen the terms highwall and lowwall and don't know the difference or if one is better than the other. Also if this is the lower that we are talking about, are the uppers interchangable between a highwall and lowwall. Thanks....

The only rifle I've ever heard called highwall and low wall are the old Browning and Sharps black powder cartridge single shot rifles.

I think you're mixing up guns.

I think you mean high shelf/ low shelf.  The "walls" generally refer to 19th century Winchester single shot rifles.

The shelf designaters refer to the surface under the rear lug of the upper. Drop In Auto Sears (DIAS's) were designed to fit under the lugs of the original Colt SP1s and 2s. in which there is enough space between the lug and the upper surface of the recess in the lower to allow them to fit.

In more recent years, in order to prevent the use of such a device, different lower makers have devised various ways to block the ability to insert the DIAS. One of these, used by Continental Machine, which makes the lowers for Rock River, Stag, Century, and probably others, is simply to make that shelf higher.  That prevents the insertion of a DIAS.

For 99.9% of all AR owners/shooters, it' s totally irrelevent difference, since they don't own a DIAS in the first place.  For the few that do legally own one, it restricts their choice of lowers to build an AR; or requires them to have a high shelf lower milled to a lower profile

Quoted: I think you mean high shelf/ low shelf.  The "walls" generally refer to 19th century Winchester single shot rifles. The shelf designaters refer to the surface under the rear lug of the upper. Drop In Auto Sears (DIAS's) were designed to fit under the lugs of the original Colt SP1s and 2s. in which there is enough space between the lug and the upper surface of the recess in the lower to allow them to fit. In more recent years, in order to prevent the use of such a device, different lower makers have devised various ways to block the ability to insert the DIAS. One of these, used by Continental Machine, which makes the lowers for Rock River, Stag, Century, and probably others, is simply to make that shelf higher.  That prevents the insertion of a DIAS. For 99.9% of all AR owners/shooters, it' s totally irrelevent difference, since they don't own a DIAS in the first place.  For the few that do legally own one, it restricts their choice of lowers to build an AR; or requires them to have a high shelf lower milled to a lower profile

+1

I think you mean high shelf/ low shelf. The "walls" generally refer to 19th century Winchester single shot rifles

You sir are correct, I was thinking "shelf" and wrote "wall". Thanks so much for the explination.