Is it safe to use a full-auto bolt carrier group with an H buffer in a middy?

Is it safe to use a full-auto bolt carrier group with an H buffer in a middy?
First, I know very little/nothing about full auto - I'm assuming this is for a semi-auto AR-15-type rifle...
That being said, sure - there is no reason why one CAN'T "safely" use a full auto BCG with an H buffer in a mid-length gas system rifle.

However, make note of two things...

First, by using a full auto BCG, you are IN A SENSE already using a heavier buffer...because full auto BCGs weigh more than semi-auto BCGs. So, the use of the H buffer MAY not be "necessary."

Second, there is no set, scientific formula for determining which buffer and buffer /action spring "should" be used in any particular AR to achieve the "best" performance.

Generally, you have to experiment a bit with different buffers and buffer springs to figure out which is "best" for any particular rifle. I keep using quotations around "best" because it really depends on what you want. For example, rifles that cycle a bit hard, or "jump" a lot, MAY be a bit more reliable than those that don't...UNLESS the BCG is being slammed back into battery so hard that it is bouncing off the front of the receiver...

You can cushion the recoil and/or slow the cycling rate down by using a stronger recoil spring (more for cushioning recoil) and/or using a heavier buffer (more for slowing cycling rate). This will make the rifle shoot "smoother," and make it easier to keep on target for follow up shots.

HOWEVER, with too strong of a recoil spring and/or too heavy of a buffer, the rifle MAY not cycle properly, at least some of the time (i.e., you may lose some reliability).

So, the bottom line is that you may have to experiment a bit to find the BCG, buffer, and buffer spring combo that is "best" for you.