First thing to do is check your Sound Files, you need to make sure that all your sound files are PCM 16 bit Signed 44100khz sounds, if they are not, BF1942 will not play them. You also might want to make 22100khz and 111000khz versions for players who play on lower sound settings, all sound files are .wav in bf1942. You also need to make sure you have two versions of the same sound, one should be saved in Stereo format, and the other in Mono format. Stereo Format will be used for First Person sounds, and is enable by using the "stereo" line in the .ssc. Mono will be used for 3rd Person sounds, and is enabled by not including "stereo" to that sound patch in the .ssc.
You also need to make sure the sounds are their appropriate lengths. In Battlefield 2 you can use Loop Keys, which will tell the engine at what part of the sound to loop back to the beginning, and then on the ending of that sound trigger it'll just play the rest of the sample, However BF1942 doesnt use this system. In BF1942 you need to sink the length of your sound to the speed of your gun, so if your sound fires 600 rounds a minute, you should divide 60 by it. so:
60/600 = 0.1
so your sound should be 0.1 seconds in length to loop correctly. For faster weapons, like a MG-42 at 1200 rounds a minute, it will be better to use a sound loop, where a 1 or 2 second sound contains a looping sound over and over again, as opposed to a really short one. To get reverb on your weapons after you shoot, you will need to make another sound both for stereo and mono that plays after the weapon finishes firing.
And of course, make sure to use FinishSample for your stop type!