Yes, the case will headspace now at the end of the bottleneck, so when you make the bottleneck with the 32ACP die if you create too long a bottleneck, the headspace will be off. What I meant really by 'specific gun' is use the barrel of the gun you are making the shot shells for and check the headspace of the case before going forward. If there is too much headspace you could have dangerous pressure, but more likely the issue is the round will not fire because excess headspace, it will miss the primer or be a weak primer hit. Also, make sure the length is not too long for the magazine.
Before you load up live rounds, I would make dummy rounds and get them to cycle. Also making dummy rounds will be good practice as getting the headspace right by the time you crimp can be tricky at first.
Heres what I do -
Cut .223 brass down to size - try longer at .950 to start and you can trim and crimp to size - cut too short an its scrap brass
Run cut 223 brass through 380 full size die
Chamfer the inside case mouth well, and lube the mouth
Create bottleneck with 32acp die - go slow and if you get resistance turn the case and apply pressure
Check for headspace fit and mag fit - get it right
Add powder charge
Use a scrap 223 brass and sharpen mouth with trimmer to make card punch for over powder and over shot cards
Make cards from light cardboard or plastic such as a birthday card or plastic notebook covers
Insert a tight fitting over powder card into the case
Use a dowel to carefully get the card even and level over the powder and get it over the powder firmly and tight fitting
Load shot almost to top
Place over shot card
Crimp with 45acp bullet seating die
This is all experimental, and I'm working these ideas from scaling down successful 45acp shot shell as the model.The basic OAL that cycled in my Kahr CT380 were .911 through .945. Too long for the magazine was .973. I will eventually narrow this range down quite a bit, but again still experimenting. You have to use your gun and your mags, to get reliable cycling. Just like certain guns dont like certain factory ammo yet other ammo is great - the same concept will apply here. When you crimp, try to get the mouth perfectly rounded and not squared even a little as that will effect cycling. I'm not listing any specific loads, but I would look up info on 45ACP shotshell. Many publications published and use 6 grains of W231, so use that as reference and scale down the load. I would be interested in anyone who is doing this and what their methods and results are -