@ 08:53 pm (GMT)
Nathan FosterUncle Nick would know (Nick Harvey).
OK, just a bit more to add to this thread.
The above photo shows a Sako suffering from severe copper fouling on the lands. Other rifles may show the same in the grooves. This coating is in essence fused to the bore. Think of it as being pretty much guilded / braised in place.
If we put Sweets through this bore and leave it for an hour, the Sweets will have worked on the top most layer, the reaction dies off, then no further copper removal occurs. So leaving it sit is not ideal.
So, in order to cut through this layer, we need mechanical etching from a bronze brush, plus regular doses of fresh Sweets etc. I do not simply leave the bore to sit, slowly corroding away.
"But what if I was to use KG-12 or Eliminator?"
Well- Its the same deal. These fair no better when it comes to a braised on layer such as this. I have also noticed with KG-12, that if you walk away and come back later- and if it is a hot day, the KG-12 will turn to varnish. If you do not break this varnish layer up with a bronze brush, then you will be in real trouble next time you go to shoot. That said, BoreTech is advertised as being OK for lengthy soaking periods (even if the action / reaction is no longer effective).
The trick is to stay close to the rifle, work on copper removal for as long as it takes, then work on rectifying the causes of severe copper fouling.
Time can be a great issue. The reality is, as much as it would be nice to stand at the ready and pump fresh solvent through the problematic bore every 10 minutes, we may have a very busy schedule following our hunt / range day,...a work day ahead of us...kids need to be taken to sports etc etc. In other words, there are times when things don't go to plan and we don't follow an ideal method.
I can tell you that from my talks with customers over the years, that there have been folk who have left solvents in the bore for whole days. One target shooter would leave Sweets in his heavy fouling stainless bore from Sunday afternoon until the following Saturday morning.
You would expect that a person in my position must deal with nice rifles. Well, that just isn't the case. People don't send me good rifles (unless its a custom job). I get to see all the problem rifles. Being willing to work on problem rifles is what got me here. That and having to buy some real dogs ourselves in order to be able to afford all the testing we wanted to perform.
There are times (such as the above pictured rifle) when you get to a point where the manufacturers recommendations mean very little in light of the job at hand. It is not as if you can make the problem bore any worse than it already is. The same goes for polishing routines.
While one gunsmith may sneer at DIY polishing methods (black arts should be left to the wizzards, not you small people who can't be trusted to tie a shoe lace, oh look I just farted and it smells like Lavender), well its all the same. When a bore is causing such problems and shooting 3-5" groups after it fouls, it is not going to magically rectify itself or come clean with a bottle of smug.