Home Range Build

[CapnMac]

Can venting be cut into the CMU planks?

Yes, up to about 24" of the 48" plank width when centered in the plank.
Anything over 24", or near a plank edge ought to be communicated to the precaster so they can block the forms out.
You can split an opening between two planks, but, you have to make no larger a cut than 2x cover distance of the PVC cores (in a 6" thick plank, there's (nominally) 1.5" of "cover" concrete top & bottom, so you's want to stay at least 3" away from the cores).

 

[Palladan44]

Used search tool before making my own thread here.... I'm in the same boat here.. I'm confident in my backstop, which is 10 sheets of scrap OSB cut in 2'x2' pieces, duct taped together, then encapsulated in a cardboard box. The reason I do this is to keep the bullets whole rather than splattering them into oblivion on the steel trap. Also, the sound of the bullets hitting the steel is extremely loud in and of itself. It also cuts way down on aerosoled lead dust. This is inside an angled 1/2" steel bullet trap. I'm only using my range in my basement to chrono pistol handloads, or just fire a shot or 2 for the heck of it. I only use it when I'm the only one in the house and I'm certain there are no visitors on the way. I also lock all my doors to the house. I don't want anybody to surprise me, nor me them. I use my mini range very SPARINGLY. I have multiple dot stickers on the target on both sides so only a few rounds are fired on the same spot so bullets are not piling on each other in the OSB. I'm comfortable putting about 50-75 rounds in this target before I switch out the wood. Bullseye accuracy checks/chrono only. I fired 3 shots on it today, 9mm 147gr. Handloads.
All this said 99.9% of all my shooting happens at my local outdoor or indoor ranges, not at home.
Good luck with your project.
Safety safety safety.

 

[Atavar]

Having worked at a cannon manufacturer that had indoor tunnels in an urban environment I am going to suggest that all ventilation egress will need baffles and sound deadening if you want to reduce exterior noise.
Think like three or four switchbacks lined with acoustic foam.
Any straight line exhaust (or intake) will be a conduit allowing sound out to the environment.
The acoustic damping and air handling could easily turn into the greatest expense of the project. I suspect this cost is why we don’t see more inside personal firing ranges.