Hmm - missiles by nature need an engine to propel them, so strictly speaking its GOT to have an engine.......however, you could erase the vapour trail on the thing i should think...............
Might be this sort of thing:
const_effect = li_missile02_drive
just make it another projectile effect.......but i aint sure about that. Do you mean that you have got rid of the motor then? Cause you sound like you want a gun which the projectiles from are missiles.......... Never tried that either! Experimentation is the key though!

Its simple. Just copy the archetype for the missile over to the weapon entry you are using. Thats all you need.

I'll try that, just don't want it to look like a missile thats all. But I still need the explosion and damage effects.

Here is a tutorial I wrote about making guns, you will find a collection of all projectile effects I found in the game(also several other useful lists of sounds, impact effects, look of guns,...).

look at the list of
'const_effect = ', that defines the "visual look" of your projectile.
I haven't found any that looks like a "real" projectile or something that would fit to an autocannon for example.
It's possible to change the effects but I didn't have any success in creating a "shell", some sort of massive projectile.

here's my tut:
http://www.klngarthur.com/forum/viewtopic.php?t=1549

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modder on www.excelcia.org

Here again we come to the "rail gun" concept. I have made a couple of these using the rail guns supplied with the game, though mine tend to be very powerful for use on ships like the Corvette. Here is one I have been using...

[Munition ;<==you will have to watch out and close this closed bracket.
nickname = jsg_railgun_ammo
hp_type = hp_gun
requires_ammo = false
hit_pts = 2
hull_damage = 1200
energy_damage = 900
weapon_type = W_Particle01
one_shot_sound = fire_photon4
munition_hit_effect = pi_photon_03_impact ;trying this out... 8/21/03
;munition_hit_effect = br_missile02_impact ;the last one used... another large white impact
;munition_hit_effect = ku_missile02_impact ;<==rather large white impact, pretty good looking.
;munition_hit_effect = ku_photon_04_impact ;<==small yellow impact
;const_effect = ku_photon_04_proj ;nice small yellow 4 pointed star flash
const_effect = ku_gunboat_maingun ;<==trying this out
lifetime = 2.000 ;was 1.000
force_gun_ori = false
mass = 1
volume = 0.000100

[Gun ;<==you will have to watch out and close this closed bracket too.
nickname = jsg_railgun
ids_name = 524351 ;<==this number is for an 8th dll I have, change it to
ids_info = 524451 ;suit your application
DA_archetype = equipment\models\weapons\co_raildaddy.cmp ;<==just trying out this look...
material_library = equipment\models\ge_equip.mat ;ditto...
HP_child = HPConnect
hit_pts = 16860
explosion_resistance = 1.000000
debris_type = debris_turret_small
hp_gun_type = hp_gun_special_10
parent_impulse = 20
child_impulse = 80
volume = 50.000000
mass = 10
damage_per_fire = 0
power_usage = 1
refire_delay = 0.125 ;was 0.2500
muzzle_velocity = 1000
toughness = 4.000000
flash_particle_name = br_particle_04_flash
flash_radius = 15
light_anim = l_gun01_flash
projectile_archetype = jsg_railgun_ammo
separation_explosion = sever_debris
auto_turret = false
turn_rate = 90
lootable = false
LODranges = 0, 10

You can of course modify the refire rate and damage ratinigs to suit your own application, but it has a cool firing effect.

Use this: ku_capgun_01_proj
Someone supplied me with a reworked version of Leonhart's Swordfish Mk. II ship and it came with specially made guns for it. They look like yellow, perhaps somewhat large, but nonetheless accurate, machinegun tracers. Naturally, they also included sound effects. If you email me, I'll send it to you cuz I've reworked the machinegun noise to sound deeper and a little better.