All cable locks will let it open.
You're supposed to use a padlock on those front corner holes to keep it closed.
(I just usecheesy $5 luggage locks, because the plastic case is the weak point anyway)
Cable lock would go through the holes on the hinge side of the case, and be used to secure the case to something, like the seat bracket in your vehicle when you're transporting.
These are my go to for just about everything.
Master Lock 131Q Covered Aluminum Padlock with Key, Black, 4 Pack https://www.amazon.com/dp/B00004Y8D4/ref=cm_sw_r_apan_glt_fabc_0NY5HW2Y276Y1Q7SZ73D
Buy a set of locks that only you have the key for and use at least 2 on the rifle case and one on the POD.
https://smile.amazon.com/dp/B00004Y8D4/ref=cm_sw_r_cp_apa_glt_fabc_4BYC72EQAT4TD3RRE9AC
First I would definitely check the laws in your location (assuming USA?.. so your State). .and find out if possessing Lock Picks is legal or not. I live in Colorado and Lock Picks are legal (possessing them (by itself) is not evidence you plan to use them for crime.
What I did when I started,. was:
buy a cheap set of Lock Picks off Amazon (You can find fairly decent ones for less than $30
and then I went to Home Depot and just browsed their Lock section and purchased a variety of Locks (from very small to medium)
Very small locks (like these: https://www.amazon.com/Master-Lock-Padlock-Aluminum-131Q/dp/B00004Y8D4) .. only have 2 or 3 pins and no security mechanisms.. so they're easy to learn on.
Slightly larger Locks (like these: https://www.amazon.com/Master-Lock-Padlock-120Q-4-Keyed/dp/B00004Y8CQ/) .. still fairly easy to do. If I remember only like 3 or 4 pins and smooth (no security pins,etc)
Once you start getting into normal Masterlock size (such as these: https://www.amazon.com/Master-Lock-3TRILF-Laminated-Padlock/dp/B0009V1WIY) .. those are still do-able (I think fastest I've ever popped one of those was in about 35seconds) It does take some practice but definitely do-able.
I'm a little rusty and out of practice now.. but I used to just keep it all in a plastic tupperware bin and sit around with it sometimes playing with different Locks. I grab extra Locks when I can (if I find them discarded on the street or old bike-chains or whatever).. just as challenges to try on.
it's actually come up at work a few times where HR Dept has locked some hallway-cabinets and then lost the key. Luckily those were the tiny Masterlocks (linked above).. so popping them open was pretty easy peasy.
I bought these. Great because they are small enough to not get in the way and all four locks are keyed alike.