Putting together the test rifle was easy. It's a standard push-feed budget production "Ranger" Winchester model 70, chambered for the venerable, and long obsolete, .30-06 US service cartridge. I topped the rifle with a variable power telescopic sight capable of focusing at close targets, crossed my fingers, and gathered materials for another pass at making the sub-caliber inserts.
In the photo above, you can see the inserts prepped for blank test firing. That is, firing large rifle primers without the ratshot balls. These inserts have also not yet been reamed or rifled.
Testing showed that the new method of producing these inserts is better, but still far from successful. The good news is that the new type of spent primer removal plier and corresponding case head cuts work well as a system. The bad news is that proper alignment of the miniscule barrels remains extremely difficult and the accuracy of rifling remains highly questionable. Other bad news, the worst of it at the moment, is that problems with stuck inserts due to pressure effects remain a serious problem. The one live load fired produced excessive primer set-back and a stuck case. I suppose the good news is that the barrel / insert bond did not fail and the projectile did depart the bore. The primer set back and vented via the primer extraction cuts made in the case head. That's preferrable to having the insert self-destruct, but it's still frustrating.
Also, it appears that the cutting head I made for the first set of inserts wore down enough during production of those inserts that it must now be replaced. This is going to be an unavoidable consequence of the spring-tension abrasion method I'm using to cut the two-groove semi-ovoid rifling with a modified sewing needle (the abrasive heads are formed out of a fork made by cutting the end off of the needle's eye). Bore diameter is approximately 1.25mm (difficult to measure). The lead ratshot balls are breech-loaded and deform to the bore's dimensions -- dimensions that are a bit uncertain and are guaranteed to vary a bit from one insert to the next. For the sake of simplicity, I'm calling this a 1.25mm sub-caliber insert.
I'm going to see if large pistol primers can be successfully substituted for the large rifle primers. The pistol primers are not as deep/long, so this may not work, but I would like to reduce the pressures. These inserts simply don't need the pressures generated by a large rifle primer, and that pressure is tearing and jamming everything up. Believe it or not, I can see the muzzle flash of the large rifle primers even though the inserts are only 63mm long and the barrel is a standard length (about 22 or 24 inches). Penetration is also far greater than I need for hunting insects with these inserts. So, I'm hoping the pistol primers will work out.
What would be really great is to find a barrel maker out there who'd be interested in taking this idea and running with it. I will probably eventually prove that this can be done as a DIY project, but the advantages of high quality production of a solid steel insert with an expansion chamber to buffer gas expansion is undeniable. Perhaps I'll save up some bucks and have a few made. But not anytime soon.