Hello Miguel,
No, L'Arsenal Richelieu turrets aren't "way underscale". They're designed to BOTH fit the Trumpeter kit barbette which is wrong in size AND to correct the wrong shape to be visually accurate.
I asked both l'Arsenal and Nicolas Dupont, the turrets designer.
These turrets have been designed
specifically for the Trumpeter kit. On this kit turrets had wrong shape AND dimensions, but resizing them to accurate 1:350 would have implied to completely rebuilding both barbettes, the superstructure behind #2 turret and so on.
So we had to make a compromise by doing the right shape of the angled facets and other details to be fitted on a WRONG barbette, so the SLIGHT difference in size.
BTW, this kit is widely known as plagued for bad shapes and dimensions all around, so if you wants to avoid 100% scratch building you'll have to make compromise.
Nicolas told me today they've been debates between him and Jacques Druel (l'Arsenal founder and former owner) when starting the project and it quickly became obvious a compromise had to be made.
Here is Nicolas model of Richelieu (as in 1952) which shows l'Arsenal's turrets in place:
And here is Nicolas Richelieu as in Dakar in 1941 (in progress) with the same resin turrets:
If these turrets had been at 1:400 scale as Robert suggested: their circular base (the top of barbette) would have measured 33mm in diameter instead of 37.7 mm on the resin part and would have left a 4.7mm gap in diameter to fit in on the barbette, which, by evidence, is not the case.
This raises a concern which should be always reminded: EVERY detail set maker (particularly with PE) has to somewhat alter scaled real dimensions of railings, fittings, etc. to cope with the kit on which the part will be fitted, should the kit being accurate or not.
The alternative is to supply corrected parts for everything... so a complete new kit.
Makers simply add on their box "designed for the Tamytrumpgawa kit", as l'Arsenal did.
One example: you can find super detail sets by the same maker under two references: one for Hasegawa, one for Tamiya and aimed at the SAME ship (I've Yukikaze in mind, also many 1:700 IJN ships )...
Of course you may want "totally" accurate building (I belong to this kind of rivet-counter, believe me, so is Nicolas): this will be at the cost of scratching soooo much of the ship that starting form a kit shouldn't be considered very efficient.
And we should keep in mind many of our fellow modelers might not want to go so far in rebuilding their kit, just want to have the best compromise between accurate dimensions and visual accuracy.
_Bruno