Projectile with extreme speed causes bad auto-aiming in PrBoom

ZDoom had no trouble with aiming monsters with fast projectile. But whenever I test my map with PrBoom, the fast projectile couldn't track monsters properly
or even went to wrong direction although there's no living monsters in the way. A speed of projectile is 120 according to WhackEd4, while an original plasma one has 25.

A screenshot is attached below. While there's no living monsters, projectiles are heading to diagonal direction. (a red line is drawn to explain the direction)
This allows me to miss the shot even if I get close enough to monsters, except zero-point.

I figured out that in order to solve this issue, I just simply adjust the speed of projectile. A speed around 40 gives me a reasonable one, but I want to make my projectile faster with no problems in aiming.
Is there a solution about this one? Or not, how much is the maximum speed with proper aiming in PrBoom? Thanks.

As I recall, this is the case in vanilla doom, too. So ZDoom has fixed it and PrBoom inherits the behaviour from Vanilla. It's been 16+ years since I last tried this stuff myself, but I recall being disappointed as to what the top speed that was accurate was possible in vanilla (I remember wanting something like Quake's Enforce's laser, but it not being possible).

Maximum non-glitchy projectile speed in classic ports is 35.

Even in ZDoom you run into problems with projectiles of that speed, it's just likely you haven't noticed them as they're mostly related to vertical movement. It's still possible to make projectiles that fast in ZDoom, but you need to use DECORATE and make a child of the FastProjectile actor, since that uses different logic that can support fast speeds.

scifista42 said:

Maximum non-glitchy projectile speed in classic ports is 35.

That number is the answer I was looking for, many thanks! Also thanks to Jon and Arctangent for reply. :)

Sorry for the bump, but since I used this thread as a reference, I figured it'd be better if it contained the right answer.

 

On 29.09.2015 at 7:18 PM, scifista42 said:

Maximum non-glitchy projectile speed in classic ports is 35.

Right now I'm pretty sure it's 30. With this value, the projectiles always fly towards the crosshair in PrBoom+, or at least the error is so small that I can't see it.

 

Even 31 results in some inaccurate angles when you're not looking in a cardinal direction.

I was testing it back then, and though I forgot most details, I'm pretty sure that the distinction between speed 35 and 36 was not just that the angle imprecision became noticeable, but (at least under some specific conditions) the projectile's movement no longer followed a straight line and became completely erratic and unpredictable. I wasn't able to reproduce the issue (or recall what the specific conditions were) now, though.