Thanks for your kind words, Rich, Tim and Douglas; we do appreciate them. First of all we are happy to hear that D2 steel is actually used for punches and dies. Punching is probably closest to what we are trying to do with common boiler plate in our recreation of the old time armor penetration tests. Tim, we are very glad that you told us about it's actual use for this purpose. Machining the ratchet shapes in an annealed rod of the proper turned diameter should not be difficult and also drilling and tapping the central bolt hole followed by heat treatment in our Ebay furnace. Have to read up on that! According to Commander Brooke, in his testing on wrought iron armor plate, he made claims of 8" penetration at any range less than 500 yards with 120 lb, wrought iron bolts propelled by 20 lbs. of Navy BP. For us, that maximum charge would be 648 grains of Goex BP. Too cold and windy now; the Brooke Rifle VS Monitor turret tests will commence next summer.
As for accuracy, we really can't identify the single most important factor, but probably that $250 reamer has something to do with it and some very slow and careful reaming. Mike made a 30 lb. monoblock to hold the gun drills and reamers which helps dampen any minor vibration. The Sterling Gundrill Company supplied the water-sol coolant and misting pump unit which works like a champ. We never deviate from a set routine which uses optimum speeds and feeds for drilling or reaming. Eliminate the variables and a good result can be had.
We use both Mahr and Mitotoyo bore gages with minimum extensions and they calibrate good after each use. We check every inch and you are right, Tim, the spec is .0001" per inch max variation with a total of .0005" allowed. What we get, however, is much better than that at +/- .0001" for a total of .0002" in the entire bore length which is 22.667". We gundrill and ream a bore that is a full three inches longer, 25.667", than the finished 1/6th scale bore will be.
One further thing we do really gets rid of anomalies in the bore size. We part off the extra three inches of the tube after rifling is complete. The rifling head is partially, from 20 to 80%, unsupported in the last two inches so variation can and does occur. We take that two inches AND another full inch off to make darn sure that the all important muzzle area rifling is near perfect and NEVER larger than any other place in the bore. The solid steel bolts we use are made from 12L14 steel which can be easily and accurately turned to close tolerances and we do exactly that. Mike is trying to make a better than average machinist out of me, so I get this job quite often. I am much slower that he, but I rarely make mistakes. We inspect each piece as it is made, and typically reject one or two out of a batch of 30 that we make per 4 hour session. We weigh every powder charge and have standard patterns for the aluminum foil powder bags and a standard way of making each one. Other than the rooting out all the variables in every process, I don't think we have any real SECRET to tell you fellows.
Double D, we don't think that hitting a 1/6 scale whiskey barrel at 300 yards would be too much trouble, in fact we will try that at the Montana shoot, even if we have to make the small barrel !! That would be fun to try. As for the other pics of the trunnion detail, we can take the trunnion band off the tube to get some pics and also show how that piece is keyed into the second reinforcing band layer. The strap is only half formed, so it's connection to the yokes will have to wait until we make yet another fixture for the 20 ton press.
As for the barrel draining we will need some spectators to accomplish that task. Volunteers should not be hard to find. WOW, those are really nice barrels, Terry C. Top notch; they are so cute we would hate to put any holes in them.
Best regards,
Mike and Tracy
