I understand that the general concensus among many here is that a light profile barrel can be just as accurate as a heavy profile barrel, and I believe this to be true. But that it also heats up faster causing potential POI shifts, I also understand (I think) that a free floating rail system will allow uniform expansion of the barrel, thus precluding POI shifts. Another disadvantage of light profile barrels is the risk of cook off. So my questions are as follows.

1. With a pencil barrel, how many shots can you fire rapidly before you notice a marked shift in POI? Both with and without a free float rail.

2. Same as above but with an HBAR.

3. How many FA shots, fired successively,  does it take to get a light barrel to start cooking off? How about an HBAR?

Thanks in advance for any help.