Agreed, I think the drill press will produce a better result. Or do a hybrid…use the bench grinder/drill approach to remove the bulk of the material. Then chuck the reamer into a drill press (or hand drill clamped to a surface) and spin it up, then slowly bring in a spinning emery wheel and just kiss the shoulder. Be patient and continue to just barely let the wheel abrade the shoulder so it takes down only the high spots. Eventually it will get to the point where it is touching all flutes equally for the full rotation. Usually can tell by the way it sounds. If uncertain, color the shoulder with a Sharpie (or blue layout dye) and spin it up again and briefly touch it with the emery wheel and stop to see if it removed the marking from all flutes.
Don,The length of the ramp into the lands is independent of caliber. Only the angle and land depth matter. As such, .177 and 22 barrels tend to have rifling that is half the depth of .357 and .45 barrels. This means the ramp length would be half as long - assuming the same standard reamer angle was used.
Guys the spindle bearings on drill presses, moto tools, etc aren't meant to handle the side torque you're talking about applying. A Bridgeport or similar knee mill would be a better choice but even there slop from wear and inaccuracies in original machining can foul you up before you even get started. Take a precision ground pin and chuck it up in a Bridgeport collet some time and put a tenth or half thou indicator and rotate the spindle by hand. And grinding requires rigidity or that wheel or grinding drum will start bouncing around like Roy Rodgers on Trigger!
You know, if you made a thimble for the actual "chamber" part - you wouldn't have to modify the reamer. Just push in the reamer until the lands are removed at the very end of the barrel and then attach it to a thimble.
FX uses a brass section which has the transfer port which is then attached to the barrel. Do they do the ramp transition in that brass piece ?
Quote from: nervoustrigger on November 05, 2021, 01:12:49 PMAgreed, I think the drill press will produce a better result. Or do a hybrid…use the bench grinder/drill approach to remove the bulk of the material. Then chuck the reamer into a drill press (or hand drill clamped to a surface) and spin it up, then slowly bring in a spinning emery wheel and just kiss the shoulder. Be patient and continue to just barely let the wheel abrade the shoulder so it takes down only the high spots. Eventually it will get to the point where it is touching all flutes equally for the full rotation. Usually can tell by the way it sounds. If uncertain, color the shoulder with a Sharpie (or blue layout dye) and spin it up again and briefly touch it with the emery wheel and stop to see if it removed the marking from all flutes.Guys the spindle bearings on drill presses, moto tools, etc aren't meant to handle the side torque you're talking about applying. A Bridgeport or similar knee mill would be a better choice but even there slop from wear and inaccuracies in original machining can foul you up before you even get started. Take a precision ground pin and chuck it up in a Bridgeport collet some time and put a tenth or half thou indicator and rotate the spindle by hand. And grinding requires rigidity or that wheel or grinding drum will start bouncing around like Roy Rodgers on Trigger! Now clear things up a bit. Are you trying to put in a short free bored throat A La' Roy Weatherby effectively creating a very short smoothbore before the projectile engages the rifling, also was commonly done in large artillery pieces for quite a time. (sounds kind of like it and that does boost velocity) or are you trying to cut and grind in a shallow long angled throat that will gradually constrict down to meet the inside groove diameter? For skirted pellets the initial air blast and breech pressure assures maximum ID bore dia. seal. You might grind in a tiny angled lead in the face of the lands? Simple polishing will go a ways towards accomplishing that. Precision seating seems like it might serve you better and with less "metal wrecking" -( trade slang for Machinist - Metal Wrecker) some Carm magazines and single shot loaders employ internal O-rings that gently center the pellet or slug before final seating. Doesn't FX have internalO=rings in their breeches that the probe pushes the round and itself through when it seats the projectile. It just seems to me you're going to great effort for something that may see minimal reward or go south and cost you for your efforts.