GURPS high tech has fairly extensive lists of specialty grenade and shotgun ammo, and different shotgun shell chamberings listed on rare occasion (the 3" magnum is listed only for the Banelli M1 Super 90, despite the fact that about half the guns on the list are now available in 3" magnum. That might not be their fault due to changes after the book was written, though).
On top of that, Ultra-Tech has a great many specialty warheads and loadings, and some of the numbers seem to work right and others.... not so much, at least not by comparison to the round they would scale from in High Tech. In some cases, optional warheads aren't available for things where they were in High Tech, or neither book features specialty rounds in calibers where they exist already
On top of that, lots of options are only given at one tech level or another, not showing anything for higher TL version (the HE Shotgrenade is listed only at TL7).
Still other options should probably exist but don't.
Anything that would be loaded with filler is going to be modified according to the following data.
Most TL7 explosive fillers are REF 1.4
Most TL8 explosive fillers are REF 2.25 (1.61x the power of TL7 filler)
The listed TL9 explosive filler is REF 4, (1.78x the power of TL8 filler)
First off, some comparisons, using stuff as listed, then according to Adjusting Damage rules to double check the numbers.
40mm High Explosive.
TL7 HE 40mm: 4d-1 [2d] cr ex
TL8 HE 40mm: 6d+2 [2d] cr ex
TL9 HE 40mm: 8d [2d] cr ex
Using Adjusting Damage rules to check
TL8 HE 40mm turns into 6d [2d] cr ex
TL9 HE 40mm turns into 12d-1 [2d] cr ex if starting with 6d+2 or 11d-1  if starting with 6d
40mm Shaped Charge
TL7 40mm HEDP: 4d(10) cr ex + 4d+2 [2d] cr ex linked
TL8 40mm HEDP: 7d(10) cr ex + 6d [2d] cr ex linked
TL9 40mm HEDP*: 6dx4(10) cr einc + 4d [2d] cr ex linked
TL9 lists Shaped Charge as an dual purpose round, rather than pure shaped charge, but much heavier on the shaped charge as you'd expect the 4d [2d] fragmentation effect to be closer to 8d, per HE.
This one's harder to convert using Adjusting Damage because there's more at play in the power of the shaped charge than raw explosive power, but lets just see what we get,shall we?
TL8 40mm HEDP turns into 6d+2(10) cr ex + 7d+1 [2d] cr ex linked
TL9 40mm HEDP turns into 6d2(10) cr ex + 11d-1 [2d] cr ex linked
As you can see, if you treat Shaped Charge as the next evolution of HEDP, things go screwy, with you getting half the listed shaped charge power, and nearly triple the HE blast. There's a High Explosive MultiPurpose warhead (HEMP), but it doesn't come until TL10 for reasons unexplained.
25mm HEDP vs. 25mm Shaped Charge nets similar results
TL8 25mm HEDP: 4d+2(10) cr ex + 3d-1 [1d+1] cr ex linked
TL9 25mm HEDP*: 5dx3(10) cr inc + 2d [1d+1] cr ex linked
Again, between TL8 and TL9, the fragmentation explosion drops, with a substantially higher power shaped charge.
Using Adjusting Damage rules from the TL8 25mm yields the following
25mm HEDP: 8d(10) cr ex + 5d-1 [1d+1] cr ex linked.
In both cases, the ultratech Shaped Charge is approximately 2x the shaped charge damage and 1/2 the fragmentation/dual purpose blast (but no less fragmentation effect). Given the easily acquired nature of DR at TL9+, this makes a lot of sense.
One thing Ultra-Tech DOESN'T have that High Tech does? A shotgun HEAT shell. High Tech has various HE and HEAT shells, but some are only one TL or another, and they vary in size
Based on my research, 3" magnum shotshells tend to have 1.5x to 1.67x the projectile load of a 2.75" shell, and 3.5" supermagnum shells have a full 2x (potentially even more, if you sacrifice some powder charge to drive it). Because the projectiles are approximately cylinders, and the diameter doesn't change, this makes it real easy to scale things up. Interestingly, 3" magnum has the same listed max chamber pressure as a 2.75" shell, but a heavier projectile or going beyond SAAMI spec can both boost power a bit.
Items marked with ^ are custom, made using Adjusting Damage rules.
TL7 HE 2.75" shotgrenade: 4d(0.5) pi++ + 1d-1 [1d] cr ex follow-up.
TL8 HE 2.75" shotgrenade^: 4d(0.5) pi++ + 1d+1 [1d] cr ex follow-up
TL8 HE 3.00" shotgrenade^: 4d(0.5) pi++ + 2d [1d] cr ex follow-up
TL8 HE 3.50" shotgrenade^: 4d(0.5) pi++ + 2d+2 [1d] cr ex follow-up
TL9 HE 2.75" shotgrenade: 5d(0.5) pi++ + 2d+2 [1d] cr ex follow-up
TL9 HE 3.00" shotgrenade^: 5d(0.5) pi++ + 4d+1 [1d] cr ex follow-up
TL9 HE 3.50" shotgrenade^: 5d(0.5) pi++ +5d [1d] cr ex follow-up
TL9 3.00" shotgrenades have as much raw explosive power as a TL7 HE 40mm grenade, though less fragmentation effect.
TL8 HEAT 3.00" shotgrenade: 1d(10) cr ex + 1d-1 cr ex linked
TL8 HEAT 3.50" shotgrenade^: 1d+1(10) cr ex + 1d-1 cr ex linked
TL9 HEAT 3.00" shotgrenade^: 2d-1(10) cr ex +1d+1 cr ex linked
TL9 HEAT 3.50" shotgrenade^: 2d+1(10) cr ex + 1d+1 cr ex linked
HEAT shotgrenades are simultaneously lackluster yet potent. They also don't maintain the effectiveness of other things in Ultra-Tech of being a little over half the effective power of 25mm warheads when customed up to TL9 versions. Still, they might warrant a single shot underbarrel shotgrenade launcher for a primary weapon, and offer enough power to potentially damage the joints and other weakspots of even a heavy combat walker, or power armor of all sorts.
18.5mm/12g Buckshot, all TLs
2.75" Shotshell: 1d+1 per pellet, 9 pellets per shotshell
3.00" Shotshell^: 1d+1 per pellet, 15 pellets per shotshell
3.00" Shotshell: 1d+2 per pellet, 12 pellets per shotshell
3.50" Shotshell^: 2d-1 per pellet, 9 pellets per shotshell
3.50" Shotshell^: 1d+2 per pellet, 15 pellets per shotshell
3.50" Shotshell^: 1d+1 per pellet, 18 pellets per shotshell
Additionally, buckshot rounds for 40mm are listed but lackluster in High Tech, and nothing is given for 25mm buckshot. Given stronger barrels able to withstand full pressure, TL9 buckshot grenades might look as follows. 25mm buckshot is based on the russian 23mm shotgun.
TL7 40mm birdshot: 1d-1(0.5) pi-, acc 2, 20 pellets per shot
TL8 40mm birdshot: 1d-1(0.5) pi-, acc 2, 50 pellets per shot
TL9 40mm buckshot: 1d+1 pi, 40 pellets per shot
TL9 40mm heavy buckshot: 2d-1 pi, 30 pellets per shell
Grenade Launcher Buckshot
25mm Heavy Buckshot: 2d+1, 12 pellets per shell
25mm Heavier Buckshot: 3d-1, 8 pellets per shell
40mm Heavy Buckshot: 2d+1, 20 pellets per shell
40mm Heavier Buckshot: 3d-1, 16 pellets per shell
Given the nature and easy availability of armor in the future, and even at TL8, buckshot loses effectiveness rapidly. A way around this is to use heavy flechettes, maintaining the number of projectiles but turning them into fin stabilized armor piercing darts.
Turn damage from pi to pi-, add (2) armor divisor, no other changes.
Depleted Uranium adds +1 per dart at this level, and optionally increases the armor divisor up to (3) if using my other homebrew rules.
Custom Depleted Uranium, based on Depleted Uranium from High-Tech and Armor Piercing Enhanced Penetrator from Ultra-Tech
Add Armor divisor of (3), +10% dmg, +30% range. Reduce damage type by one step if below 20mm. On penetrating hard armor with DR10+, add an incendiary [1d(2)] attack with fragments cycling every 10 seconds for 30 seconds. DX roll can brush fragments away if they're accessible.
18.5mm/12g Slugs, all TLs
2.75" Slug: 4d+4 pi++ (combines to 5d pi++)
3.00" Slug^: 4d+8 pi++ (combines to 6d pi++)
3.50" Slug^: 8d-4 pi++ (combines to 7d pi++)
I was going to add more to this, but I think that's enough for one post.