Some folks
don’t realize that smooth twist barrels are glass mirror smooth inside because in manufacturing the insides of them never see tooling. FX have multi-million dollar CNC machines that produce absolutely perfect barrels and liners that are totally free of burrs and imperfections, I chuckle to myself when I read that someone comments that they pollished a FX barrel by hand
. They probably cause more harm then help. Just my opinion, I’ve been wrong before.
I'm going to nitpick here, because I must. First, CNC doesn't assure quality, nor does the cost of the machine itself. All it takes is one stubborn little piece of swarf, a flaw in the tooling, etc and that precision can rapidly go out the window. A multimillion dollar state-of-the-art CNC machine, of whatever flavor, is no better than the operator's or tooling manufacturer's worst day. Something to keep in mind.
Second, mirror finish may or may not truly be optimal. For example, inside a regulator, you DON'T want a mirror finish, and in fact a lot of the skill in making them is consistently achieving the correct level of polish/scratch. Why? Because those scratches help retain lubricant. Similarly, in your barrel, a perfect mirror on mirror contact between the lead and the steel can potentially result in something called vacuum welding. Without going into too much detail, essentially metals without some sort of boundary layer can cold-weld to each other, and it is a real problem in a huge variety of different and interesting applications. To be clear I'm not saying a perfect mirror bore is good or bad, I'm simply saying I don't know what you want exactly and the correct answer is non-obvious.
Third my understanding of the Smooth-Twist manufacturing process is they start with a circular bore, which they take advantage of to (probably) rotary hone it. Either way polishing a circular bore with precision is a LOT easier than a rifled barrel, and my understanding is they polish the barrel at this stage. Then, after that, a clamping device presses or "cold forges" the barrel into its polygonal shape. This pressing process WILL affect the surface finish inside. Micro-fissures have a very real possibility of opening up depending on grade of steel, heat treat, etc. I would assume that minimizing this was part of FX's development process, and so it should be a non-issue, but defects are certainly still possible everywhere from their manufacturing end to whatever steel mill they source the raw tube stock from. Again, imperfections and batch errors are certainly possible if not probable, and you can't assume that something which was perfect as a cylinder could be significantly deformed and remain perfect as a polygon. Further FX sells these barrel liners for a mere 100$ each, which I'm very thankful for. To us, the end line user, that offers incredible versatility at an unbelievably low price. However at that low price I highly doubt FX is able to afford someone with a bore-scope spending 20 minutes on each and every barrel to ensure they are all perfect. More likely they do what most companies do which is batch testing, that is to say picking a few from each run, and check them to ensure no systemic errors.
None of this is meant as a criticism of FX by any stretch, all manufacturers are bound to reality, I'm simply pointing out that FX is no more a guarantee of perfection than any other brand. I'd also add that there appears to be a significant minority of people on here who seem to find their STX barrels need cleaning on a surprisingly regular basis. I don't know why exactly this is, it might be that we few have higher expectations for accuracy and possibly longer ranges, or it could be that FX had an issue with some barrels. Until several of us purchase "identical" liners, install them, and test back to back it is very difficult to say whether or not the phenomenon is from the user or FX let alone determining the cause.
My 25c (because this post was too long to be just 2c) I genuinely hope there was something of interest or use in there.