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Just ordered a 7/16 piloted counter bore for this. I will probably never use it again, but I want to do this right.
You need to make sure the diameter of the pilot on your counter bore is not larger than the diameter of your tap drill. Most musket nipples are 5/16-24. Tap drill for that thread pitch is letter L or .272, if the pilot diameter is smaller than .272 your good. 1/4 inch (counterbore) has a counter bore of 7/16 and a pilot diameter of .278 which is still closr enough. A 7/16 has a counterbore of 11/16 which will be way to big. Most standard counterbores are made for sockethead capscrews (SHCS). I usually use interchangable pilot counterbores. Hope you didn't order the wrong one. Before you do anything to your barrel you can PM me and I will give you my cell phone number and guide you thru the steps. I have built several hundred cannon barrels and offer my help if want it. I am retired and usually have lots of time on my hands, sorry I wasn't able to get more pictures up today, had a lot of irons in the fire and will have a lot of friends over tomorrow (ATV ride and SEC Championship game- ROLL TIDE), so Sunday or Monday I will try to post some pics of the cannon lock setup.
Yup thought of that. Bought a tap that takes the interchangable pilot and a 3/16 (.1875) pilot to use with it. I appreciate all your help/input, along with everyone else's! Also is there a standard size bit that would be close enough for me to use, or should I buy the "letter" drill? Bet I wont find those at Home Depot!!Drilling shouldn't be an issue. First the pilot hole (only deep enough for counter bore depth), then counter bore, followed by tap hole. Am I missing anything?
Sounds like your on the right track. I have found the best deal on drill bits is a 118 pc set. They cover fractional, number, and letter drills. For home shop use I buy the import sets in the $30 to $50 range. I made a typo on the drill size, it is not L(L is .290) it is an I drill (.272) assuming your musket nipple is 5/16-24, sorry for the typo. Once you drill for tap size you can chuck up a center drill (if you have one) and touch it just enough to give your tap a nice lead. I really dont recomend using a fractional drill for that size, they are just too far apart. Drill it oversize and the nipple has a loose fit(not safe), drill it undersize and you run the risk of breaking a the tap in your barrel which would be a pain in the butt to fix
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Some auto parts stores keep drill bit bins.
Another option is to use a 6mm or 1/4-28 nipple for using #10 or #11 percussion caps. The advantage is if anything happens to the threads (crossthread, stripped) it can easily be stepped up to 5/16-24. Some argue the smaller caps are not hot enough, but I have used them for years on small cannons with no problems.