OK I have not read all the posts here but let me give you my observations.
I've been meaning to buy a Viper III, so I did. I've also wanted to toy with fixed cannons. Yes, I know the cannon is a difficult weapon to hit with and must be use at relatively close range but I can usually hit with a center mounted fixed cannon from <= 1Km.
So loaded up 4 fixed cannons on my shiny new Viper III, 2 small 2 medium. The projectile speed is not that difference between the 2 so it should not make much difference.
What I observed is this.
Target a Cobra III whose profile to me is from the rear or side (thin profile), piper dead on the LCOS circle, fire all 4 cannons, one hit! the other 3 miss by varying degrees. Try several times the most I land is 2.
Maneuver so the cobra's profile is flat to me, seeing the top of the ship, piper on the circle, fire all 4, 2 hit, 2 miss. I got lucky once and got 3, never got all 4.
Tried this on several different targets of different sizes, On small ship targets getting all 4 cannons to hit was extremely difficult even at very close range unless the target was showing their entire flat side to me. (i.e. top of ship, I was able land all 4 on an ASP several times with this profile) Even then it was hit or miss, mostly miss. Large targets, depending on the ship was better but not consistent. On a Clipper you would see rounds miss even when targeting was spot on due to the slim profile. I even tried targeting subsystems and it did not help.
Conclusion, this makes this load out pretty much useless. I am finding fixed multi-cannons and fixed cannons pretty much useless IMO. It is more effective to wait out the chaff and then get a lock than it is to load up these fixed weapons. 4 gimbled Multi-cannons is an effective load-out. Have not tried 4 gimbled cannons yet.
Without some kind of convergence (horizontal in the case of the Viper, vertical is constrained by the ships hull) landing all 4 guns on target is very difficult and does not result in enough damage to make these weapons worth carrying.
In the case of the cannons, if these weapons were set to converge at about 800m then getting projectiles on target would be very effective from a range of 600m-1000m. Anything further out than this your target can maneuver out of the projectile path due to projectile speed.
Even if this were the hard default convergence set on these weapons it would improve effectiveness of these weapons greatly. As I said, the cannon is an up close and personal weapon, but when your rounds just fly past your target when your aim is dead on is just stupid. No combat pilot would put up with this and he'd have some ship mechanic rig these with the convergence he needs.
The only effective place for fixed Cannons/multi-cannon is a center mounted hard point.
I have never tried more than one PA but I have flown between PA rounds shot at me by larger ships,right through the middle even in my Python so convergence there is an issue.
Rail guns do not seem to have this issue IMO, so if we have convergence on Rails why not on other weapons.
