I have used Tubb's final finish, Tubb's throat maintenance system, as well as used bore lapping compound on cast bullets. I have had success with all 3, though I would be very cautious about using anything abrasive for barrel break-in. Reason being, there are some drawbacks to using these abrasive bullets. You will lose some throat, no way around it. They can make a good shooter worse, I have only used them when I had few other options and accuracy was an issue.
I used the cast bullet method on a few Mosin Nagants, which have an oversize bore anyway and require bullets from .310 to .312. I would likely only use this method on pitted barrels or on older mil-surps with oversize bores that have bore issues. The method offered by David Tubb are far better suited to a standard diameter barrel and are more precise and consistent as well. You also avoid any potential issues with leading in the rough bore, which adds some time to the process as well. But it is one of few options when dealing with an oversize bore and you want to avoid any potential issues or when you need to be very aggressive with a pitted bore.
The Tubb's Final Finish works very well if you use it by the directions and understand the drawbacks and only use it when necessary. If you have a badly fouling barrel or one that shoots inconsistently, they may be an option. But go slow and do accuracy testing to see if things are improving or getting worse before you go too far. I have used them to improve a 1.5 to 2 MOA rifle to a fairly consistent 1 MOA rifle, and also solved a severe fouling issue in another rifle.
The Tubb's throat maintenance system is a bit less abrasive and won't eat away at the barrel nearly as fast. I have used them to help smooth a throat in a rifle firing a hot round (6-284) and was able to see a bit of improvement when bore scoping afterward. It is not a miracle cure, but it did smooth the throat a bit when it initially started fire-cracking as well as help remove some deposits that were difficult to remove. I feel I may have had better results had I not let it go as far as it had before using them.
I have been using the Throat Maintenance System in my current .243 a bit as well. When the rifle needs to be cleaned (every 50-80 rounds) I will give it a scrubbing at the range and then fire 1 or 2 of the TMS bullets through the bore to remove any stubborn fouling and really clean the throat out. I then fully clean the bore when I return home. I have yet to see any significant loss of throat and it has made cleaning very easy. I have bore scoped it twice now, and the throat still looks excellent after about 250 rounds and the entire bore has smoothed out significantly since I first purchased it, as well as it is shooting much better as well. I just keep a box of 20 loaded TMS rounds in my range box so I can keep up with it.
Fire-Lapping can be beneficial if used when necessary. I would very cautious to use it as a "break-in" method, and I would likely use normal bullets for the shoot 1 and clean portion, and then shoot 5 round groups with the first bullet or the group being a final finish or TMS bullet and stop as soon as fouling went away.
Just use these bullets with caution and also very sparingly and you can have good results. They are not a "magic bullet" to make your factory barrel into a hand lapped custom. But they can be beneficial when you have a badly fouling or poorly shooting barrel, but still need to be used with caution. I would suggest bore scoping before to be sure the bore is rough, and again after to see how it has improved or degraded. Slugging is also recommended before and after.
Good luck.
Kenny
EDIT: I will agree that if nail driving accuracy is your goal and the factory barrel isn't a shooter, a custom barrel is the BEST option. The lapping systems can help, but will never make a bad barrel into a great one, or even a good barrel into a great one. They can however, make an OK barrel into a decent to good barrel, but again, they will never produce miracles.
