A group that bad at 10 yards from a full size gun, slow fire, is either a terrible shooter simply not having the sights on when the trigger is pulled ... or a mechanical issue ... It's unlikely ammo could get that bad.
We can rule out ammo because OP produced a tight group using same ammo at same distance with a different pistol shooting off hand.
OP is a match shooter proficient with shooting basics and in PM verified the front sight does not move when the striker is released.
Ok, but what is making the muzzle jump? What can one do to correct a pistol whose muzzle is jumping? Are we talking about the trigger (or trigger finger) bottoming out on the frame when the striker drops? Are we talking about the trigger finger pushing the muzzle to one side, and when the striker is released the gun jumps the other way? In your opinion what’s going on inside the gun? In your opinion what is the actual cause?
I have been in PMs with OP for some time working on different pistol/match shooting issues and this was part of PM I sent last night.
"... once you start pulling/pressing back on the trigger, due to trigger parts overcoming inherent safeties and metal-to-metal parts engaging each other, there will be small movements you will dynamically correct/compensate to maintain the front sight steady until the striker falls. So the front sight is continuously moving while you work to steady it until the bullet exits the muzzle."
Glock utilizes partially compressed striker that continues to compress as the trigger is pressed. As the trigger is pressed further, drop safety is disengaged by the back of the trigger bar and striker pin safety is disengaged by front portion of the trigger bar and at the end of the trigger press, trigger bar drops below the striker pin to release it forward through the striker channel sleeve and striker pin slams on the back of the breech wall face as
illustrated by this animation video.
During this time, various spring tensions and metal-to-metal contact/sliding will put the front sight in motion (Yes, the front sight is always in motion until the bullet exits the muzzle) and efforts to overcome/counter these motions by trigger finger, shooting/support hand/fingers - grip, forearm/shoulder/chest/back/abdominal muscles WILL ADD input to trigger/grip and move the front sight.
OP likely produced a tighter group with a different pistol using the same reloads because Taurus PT 100 is fired using single action trigger (not like modified "DAO" Glock trigger), so it requires less effort and counteractions to release the hammer/firing pin.
That's why I asked OP to shoot with eyes closed once sights were aligned on a dot at 5 yards, to see if OP was adding input to the trigger/grip to move the POI away from the POA. If POI consistently deviates from POA, then we know it's trigger/grip input as the cause. What I am hoping to find from OP shooting with eyes closed is whether POI randomly deviates from POA or whether POI groups consistently away from the POA. Depending on the range report, we'll go from there (I already PMed detailed information to synchronize POI to POA for OP to try).
Going from match 1911 with a 2.5 lb trigger job that was glass break clean and smooth and light to Glock trigger took some getting used to. Even factory Sig/RIA 1911 triggers are cleaner compared to Glock's "spongy" trigger feel that is from compressing the striker pin spring and overcoming two internal safeties while trigger bar rubs metal parts. But having said that, when I first shot a Glock 17 on a match practice stage, I got comparable double taps as my P226 I was very proficient with and got faster stage time. Yes, this was with a Glock I never shot before. Surprised, repeating the stage run produced comparable double taps with faster and faster stage times. What can I say, holes on target speak volumes and timers don't lie.
What I found with Glock triggers is that when new, until the trigger parts break in, can be firmer with hard release and jarring striker pin hit on the breech wall face causing significant jerk/jump of the front sight. If efforts to compensate move the front sight before the bullet exits the muzzle, holes can appear wildly away from POA, as experienced by OP. BUT, with many shooters, especially new shooters, I have found shooting under stress/pressure of time, Glock triggers tended to produce more consistently smaller groups when trigger was jerked quickly compared to other striker pistols. And as trigger parts break in and become smoother, can produce very consistent 4.5 lb trigger for accuracy.
These are reasons why I now recommend people dry fire before they buy any pistol while watching the front sight to ensure it does not move or buy one that minimally moves the front sight. IMO, starting out with a pistol that does not move the front sight will result in more accurate pistol as pistol parts break in. And now when I train/share with people defensive point shooting, I have them dry fire their pistols several hundred times before the first range session. This will not only help them become proficient with trigger control/grip but also makes trigger parts smoother. When I trained a coworker who never shot before with inspiration to shoot matches (He was blown away by how I could point the pen laser held in my hand consistently at various objects in the office within an inch - I told him practice), he bought a new Glock 34 and to my surprise, dry fired over 1000 times before the first range session. When I checked the front sight and trigger, it was very smooth and front sight did not move, like my Glock 22 with well broken in trigger. He then proceeded to produce 2"-3" tight groups point shooting with his eyes closed at 5 yards and eyes open point shooting at 7 yards at multiple targets (Remember, he never shot before that day).
To many not familiar, OP has been trying to address brass to face (BTF) issue with his Gen3 Glocks with factory and 40-9 conversion barrels replacing ejectors/trigger assemblies and extractors. I think some of the accuracy issues could be attributed to newness of the pistol and parts which should improve as pistol breaks in.