I'll give you a little info on suppressors before you get into something and are disappointed.
I have a 22 caliber suppressor that I use on my AR's and can also use on 22 rimfires. What a suppressor does is dampens the muzzle blast, but if the bullet is going supersonic (over ~1200 fps) then you will still get a loud crack from the bullet breaking the sound barrier. On my AR's, the sound is low enough that you can shoot without muffs, but it isn't really comfortable, it's about like shooting a 22 Magnum. I have done it some, but wouldn't do it for an extended period of time or a lot of shooting. When I shoot standard velocity 22 rimfire it is subsonic, about the only thing you hear are the hammer fall and the bullet strike on target. Hi Velocity 22LR still breaks the sound barrier and has the loud crack, but it isn't as loud as unsuppressed 22LR.
I'm not sure exactly what you are going to put the suppressor on, but if it is the 300 UM, you might need to check and see if it will handle the pressure of that round. I DO know that there are suppressors for the 7.62x51 (308 Win). By no means do I want to talk you out of the suppressor, but another alternative might be a 308 with a 24 of 26 inch barrel. That would help get the muzzle blast a little farther out, and the 308 wouldn't have near the blast of the big magnums. You will also have to have your barrel threaded, and it will need to be done by someone familiar with suppressors and that can do the threading properly and in perfect line with the bore. Otherwise, the first time you pull the trigger you can get an endcap strike and have a nice pretty EXTRA hole in the end of your $750 suppressor. You'll need to sight your rifle in with the suppressor on, because there could be a change in the point of impact with it on and off. On my AR that I usually run the suppressor on, the POI change was only about a half inch down and left at 100 yards. Every gun is different.
Now on to the legal side. You will fill out an ATF Form 4 for the transfer of the suppressor. You will have to find a Class 3 dealer, tell him what you want, and then pay for it. He will order it from the manufacturer, get it transferred to him, and then the paperwork will start. You will send in 2 F4's, 2 Citizenship forms, 2 ATF fingerprint cards, and 2 photos. You'll also have to get the CLEO of the county you reside in to sign the waiver on the back of the F4 stating that he knows of no reason that you can't legally possess the C3 item. If the CLEO is gun friendly, he will sign, if he's not and won't sign, there are ways around him. (Ask me how I know...) Also a check for $200, which is a 1 time fee. Once you are approved, they will send the F4 to the dealer with your canceled tax stamp, the dealer will call you, and then you can go take possession of your new toy. NFA items must be locked up when not in use, and no one except the person whom it is "registered" to can have access to the locked area that the NFA item is stored in. This means that your wife can't have access to it, your son can't have access to it, no one can have access to it without you being there with them. Any time you are in possession of the C3 item, you MUST have your paperwork with you at all times to prove that it is in your legal possession. This seems like a lot of hassle, but it really isn't, if your mind is made up to know the law and follow it. One last thing, you can't take it out of state without filing a form with the ATF before you travel, and if suppressors aren't legal in the state you want to travel to, you can't take it there.
The $200 fee is not actually a "registration" as so many people think it is, it is actually a $200 Tax that you are paying on the item. You will have a canceled $200 stamp on your original form that they send you, just as the US Mail has a canceled 41 cent stamp on it. You will make copies of the ATF form and put the original in a safe place (I use a safe deposit box).
If you really think you might be interested, and if you get up this way, we can take mine out and let you see what it is all about. Also, there are some other things I could talk to you about if you really think you might pursue a suppressor. If so, we'll talk on the phone.
I'm sure I am missing something here, and with this information, you'll probably have more questions. Feel free to ask and I'll help any way I can.