Why does the non premium kit not have the grooves in the mantlet for the bolt heads (I assume)I have looked at a lot of SU100 photos and all seem to have them , So I assume there was a model of the vehical which did not have them can anyone direct me to link to this tpe of vehical ?
TIA

Is it this one?



The kit allows to make a Su-100 or a Su-85 so there are two alternative gun matlets in the kit.
The matlet without the grooves is for the Su-85 M

cheers

No it is #6075 from the 39-45 series The box art shows the grooves but not on the kit part dont know how to post photos here of the box

I know which kit your are talking about. The #6359 is a re-issue of the kit that has been updated and reworked in several areas to address issues found in the #6075 kit.
Terry wrote up a nice little review comparing the Premium Edition to the former,
PMMS SU-100 review
but I don't think he mentioned the mantlet issue.

Dragon also shows both mantlets in its #6415 SU-85 kit,


Is your mantlet the version on the left?

SU-100 gun mantlet



SU-85



Does the kit part look like a wrong SU 100 mantlet or like a SU-85 one?

Yes the one on the left

Dragon 6075 is the original 1998 release. The grooves on the mantlet need to be added. This was a 15 minute job with a screwdriver and milliput

Judging from the photos the first initial model of SU-100 did not have those groves. But by the summer of 1944 they were already in place (production started only in September).