....But the only 105mm anywhere that can get near 20 miles (32km), is the S.Afrikan G7 LEO, and no one yet seems impressed enough with it to buy one!

...Would make for an interesting modern-day Abbot SP gun (benefit being it carries more rounds than a much more massive 155mm SP gun).

And like was previously mentioned: precision is becoming more favorable than overall blast coverage area: develop a decent 105mm arty PGM ("soft launch" it at lower velocities like those Russian 100mm ATGMs, but maybe rocket boost them for greater range) and you've got something.

Argument seems to suggest that 120mm mortars may often lack sufficient range.

And it was suggested about maybe using 120mm as a new artillery caliber since 120mm is NATO standard for tanks...except NATO-standard tank guns are smoothbore, like most mortars are  (only the Chally 1 & 2 have rifled guns, but recently a C2 was trialled with a Rheinmetall smoothie). And I think smoothbore actually may be more favorable for PGMs (less stress on the round because there's no friction to turn a driving band?): Israel's LAHAT and several other projects in the works are already giving us PGMs for 120mm guns... That US BLOS (Beyond Line Of Sight) round we want for the FCS would be an ideal closer-ranged (self defensive?) weapon for an SP gun (otherwise, you can get by with a mortar PGM, many of which have about the same 10-12 km range we anticipate for BLOS).

...Reason I suggest the S. Afrikan G7 LEO 105 as a fine SP gun: at 30km, it outranges any other tube artillery caliber up through 130mm (excluding 5" PGMs designed for naval guns), and most 122mm class rocket artillery.

But of course, that's with standard long range ammo: I imagine they will try and do VLAPs in 105 also, easily giving it better range than any 39-45 cal 155mm guns (40+km easily, if the 155 VLAP reached a record 75km). But without some type of guidance/control or course-correcting fuze, its accuracy would probably be haneous.

Does Norway need to defend Norway or is looking to equipng its forces for Peacekeeping missions elswhere?  Probably both.   From my own experience with its terrain I would recommend  a towed light 105mm-L119/M-119 and 120mm mortars (like Afghanistan extreme high angle fire would be needed in some of that terrain).  Granted a towed 155 would be nice but considering probable available lift assets with weight of gun and weight of ammuntion it could boil down to moving 155s with a few rounds of ammuntion or moving 105s and supplying them with a lot more ammuntion.  On the other end HIMARS and a Caesar type 155 preferably  something like an M777 mated to a HIMARS chasis. Both would provide a good amount of firepower and have great strategic mobility.