I would not chance ruining a $800 to $1000 suppressor trying to save a few dollars. The threads MUST be cut concentric to the bore of the rifle NOT to the outside of the barrel and with a tolerance of half a thousands. After doing hundreds of barrels, I have found that even the best quality barrels are off by a couple of thousands and factory barrels are the worst. Even if you use a bore riding pilot on the cutter the pilot has to be a perfect fit in the bore. You would have to make a pilot for each bore. Plus you would have to turn the outside of the barrel to the thread diameter concentric to the bore. If you do not have a lathe to do this properly it will not be done right. Plus if you leave the suppressor with the gun the gunsmith can size the threads to the suppressor threads and get a nice class 3 fit. Our preferred method.
If you strip the gun down to just the barrel or barrel with action most gunsmiths will cut you a break on the price since they will not have to disassemble the gun and then put it back together. It will save him time and Time is money.