We're left with 33 of which 24 are actively used by the three RCHA regiments, with the rest as spares and with the RCAS.
The project is a major gain in operational guns. How big a gain depends on how many are bought at the end of the day and whether or not the M777s will be retained or disposed of.
The 105 calibre hasn't been an operational gun since 2005. It's used for training and as a saluting gun only.
The 120mm mortars are also a net gain. We haven't had that calibre since the 1960s (and also 4.2 inch) and its needed to support our battalions. The issue is whether it will be given to the reformed mortar platoons in infantry battalions or assigned to artillery reserve units. Again, a question is what will be done with the 81mm mortars that we have.
The CAF likes to simplify maintenance and supply and make room in ammo dumps for new calibres. IMHO, no it is not necessary to replace the 105mm calibre. It has its uses as a less expensive training round but the guns are on their last legs. The C3 since the 1950s (with new barrels in the 1990s) and the LG1 since the 1990s. Both have numerous issues which need resolving. Avalanche control needs a 105mm. Salutes need a 105mm. Those are problematic issues.
Lets do some simple math. The 24 M777s right now have PYs for detachments of ten. With a new SP, one could get by with 5 man detachments split between the gun and ammo an ammo limber (more would be better depending on the ammo handling system). That means we could double the guns in RegF regiments to 48 which is just short of the 54 needed to create three 18-gun regiments. But three six-gun battery regiments would also need quite a few more folks for recce, command posts, A echelons etc. Bottom line one either needs more PYs or one needs to create a stable RegF/ResF hybrid regiment concept.
Moreover, even at 54 guns, and lets say 8 at the school and tech spares, we have more guns left over. Probably a six and a spare or two would be predeployed forward to Latvia. That leaves between 10 to 20 which could be assigned to ResF training centres.
I really want to see the M777s retained. With only a little manipulation of how you organize regiments in a peacetime setting - for example in a hybrid regiment where you have one or two fully equipped full-time batteries and one or two ResF batteries that share equipment, you could equip 14 batteries which could form anywhere from seven to 14 regiments with modern equipment rather than the three we have. Add to that STA batteries/troops and loitering munition batteries and SUAS and MRR batteries and air defence and you'd be hard pressed to man them with the current PY and ARes positions available right now.
There are some terrific possibilities right now if we take advantage of them.