Just ordered a Mauser "Pre fit". Question is, can you truly install these without a chamber reamer or is it best to have one? Never used the Pac Nor before, so somewhat unfamiliar with the process.

If its long chambered, you don't need a reamer, but you may need to move the barrel shoulder back and will need to face the barrel to to control the headspace. You will need a good depth mike and must know how to use it. You will need the proper headspace guages a good Lathe and a properly ground very sharp square bit.I frankly don't like this system as the threads are cut on a production lathe and the chamber reamed in Production mode,however,it does avoid the cost of a reamer and the skill to cut threads up to a shoulder. It's probably fine for a hunting gun. You still need a Lathe though. Please don't try and do this with a dremel tool as some poster here described awhile back.-Rob

I have used several of the "pre thread, pre chambered" barrels. They are top notch. They will be short chambered and you will need a finish reamer and headspace guages. I never used a lathe, I never had to go in more than .003's so I just thread the barrel on and use a "T" handle with extension.

Sooner

Humm... Now I'm a bit confused. I ASSumed it would be long chambered, and I would use the method you described. But, now I'm not sure. Guess I need to talk to PacNor. But, while on the subject, would a carbide tool work or would it be better to use HSS?

Pac-Nor usually sells Long Chambered barrels. I've used a few of their barrels ,although, I've always done my own threading and chambering. Their steel is a proprietary alloy and it cuts beautifully. A sharp HSS Tool works fine.
I don't know if they sell short Chambered barrels that are Pre-Fit or not. To fit a short chambered barrel you will need a STOCK action which has not been faced and/or trued. This is very important as the shank depth and shoulder are cut for the minimum for either a Mauser 96 or 98 or Rem 700 action. If your action varies significantly or has been faced or trued you are in deep doo-doo with this approach. You will need a reamer and a headspace guage. Depending on the cartridge and how they short reamed it, one could use a hand reaming tool, as described above although doing this in the Lathe is a much more appropriate method. I should warn you that undoubtably your reamer will not be identical to the reamer used to short chamber the barrel and a ring in the chamber may occur. Most of the time this can be polished out or is accepted as a cosmetic problem only unless it interferes with the ejection of the brass.
Frankly, both of the approaches described above are made available by the barrel makers for folks who are essentially building hunting type rifles and are usually very concerned about costs. Hope this helps.-Rob

Thanks for the tips: With me, it's a hobby. I've done a number of the "short chambered" route, mostly with good results, never tried the "long chamber" route. It's a learning process. Perhaps the next project I'll feel comfortable enough with my threading ability to start with a blank, but not yet!

Just remember on a Mauser98 the primary locking surface is the inner ring not the receiver shoulder. Make sure you have a solid lock up on tightening on that surface. This usually involves about a .002 crush fit to set the threads. I set the barrel shoulder to just lock up on a trued receiver face. The rest should be easy.-Rob