Will the 4 ohm double if I bridge my Mcintosh???

Jalen- The ability of an amplifier (solidstate) to double power output when the load is halved, usually indicates a very healthy power supply. The Mc7100 can't do this in stereo mode, and certainly can't do this in bridged mode. This doesn't mean that it may not sound good on the right speakers, but it isn't intended to drive difficult loads (<4 ohms) and still perform at its best when pushed. Of course, there are certainly amplifiers that can double their output power into halved loads that don't sound particularly good, so don't let just this one characteristic determine your appreciation of the amp. Let your ears be the final judge as to the amplifier\speaker combination. Good luck.

Virtually no amplifier actually doubles power into 4 ohms.
Many amplifiers may claim this, but, typically, they are under-rated into 8 ohms, and slightly over-rated into 4 ohms. Unless they have no current limiting, in which case the reliability may come into question. On to your answer...

The mc7100, if bridged , is not designed to operate into 4 ohms. It might overheat and you would be stressing it if operated for extended time at full power. If you do NOT listen very loud, though, and just want a lot of power for peaks, then it will be fine.

Do not stack anything on it, give it a few inches to breath.

The reason that most amps aren't rated at 4 Ohms when bridged is that bridging effectively drops the load in half. In other words, the "300 watts bridged into 8 Ohms" is twice the "150 watts into 4 Ohms" rating, because both channels are driving half of one 8 Ohm speaker. Putting a 4 Ohm load across a bridged amp makes each channel think it is actually driving 2 Ohms. The amp isn't rated for it, and will likely get very hot if you drive it at high levels (which is usually the justification for bridging in the first place).