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Mold size question for .40 cal

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32 Cal
May 15, 2024
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Hi, new member here.
A little history. 25+ years ago I used a flintlock all the time. Then had kids. That got put in the closet. I am now getting back into it. Back then I built from scratch a .62 cal. used it along with some kit flints. Back then I got all of the parts, stock (big square block of wood), barrel, furniture to build another flintlock .40 cal. Furniture is for a 1770 Bivins. I plan on start working on this one this summer, kids out of the house.

The barrel is 42" long, .940" on the flats, .393" on the groves in barrel, .420" in groves. Note that the measurements was done by me with my calipers. So could be off some.
I have the opportunity to have a friend help me make some lead round balls. I am looking at the molds. I found a .375" mold. would this be a good size?
Thought is that take advantage of this opportunity even though will not be shooting it for at least a year.
Thanks for advice.
Excited to get back into the flints.
I don't have any balls to test with.
I see a .380 mold for sale don't see any .390. Do you know anyone that has. 390 mold for sale?
@KSCrawford, a good choice would be to buy 2 boxes of balls. One box in 0.390 and one box of 0.395. Patches should be all cotton and about 0.015 to 0.018 inches thick. You will need a short starter to load balls of those diameters. The 0.395 might be too large and it is likely to be too soon to consider ordering a 0.385 from Larry Callahan.
I have shot my GM barreled .40 with .390, .395 and .400 balls and a .018 patch. My tournament champ friends shoots a .400 in his .40 but has to pound them in, as did I.

I prefer the .390 over everything else. All three sized balls shot just about a one-hole group at 50 yards with any powder load from 30gr to 60 gr (gotta' love a GM barrel). The .390 loaded easily and made my rifle into a tack driver so I stick with this size.

Track of the Wolf has Lee .390 molds in stock, eBay has a lot of them as well at the same price as TOW but with free shipping.
I shot swagged balls and the only thing I find is .395, I hate positioning that spur straight up on cast balls. If I could find .390 swagged I would try them and adjust the patch. So either will probably work, but one will shot better, probably not by much.
I don't have any balls to test with.
I see a .380 mold for sale don't see any .390. Do you know anyone that has. 390 mold for sale?
The only way to find the best for your barrel is to try different sizes. Unfortunately, in this game you are often not a seasoned ml'er until you have a library of many unused molds. We all go through it. Tanner makes any size you want.
I got two .40 calibers and they each will shoot both the .390" and .395" better than I can shoot them. I can push the .390" ball down the muzzle with a 0.020" - 0.023" wet patch down the bore without any trouble when started with a short starter. The 0.395" ball with a 0.015" - 0.018" wet patch will go down the bore when started with a short starter with a bit of effort. I also swab between shots. As others have already said buy a box of each diameter and try them yourself this way you will know what balls will work for you and your gun. Don't waste time and money without the rifle in hand first.
I suggest buying a few different sizes of balls from someone Like Track of the Wolf, or another supplier, to test which diameter of ball your barrel might like, before buying an assortment of expensive molds that probably won't work. I prefer slightly smaller balls, as in .015 to .020 smaller than bore diameter, to facilitate easier loading. I am not a precision, match shooter, so I don't feel the need to hammer balls down the barrel. I find smaller diameter balls load easier and shoot well enough for hunting and shooting steel targets, even at somewhat longer ranges. Pinpoint accuracy may suffer a bit, but, I'm not shooting for the X at 100 yards. IMHO, 40 cal has a reputation for being finicky about what loads they like. Be patient and work through the kinks methodically to find the sweet spot of patch, ball, and powder combination providing the level of accuracy you want.
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I'm running .395 Hornady balls through my Douglas 40 Cal or I use cast .395's from a Green Mountain Mould (wish they still made them) if anything the cast balls are more accurate than swaged. Won the Marlborough Round Ball Trophy last year with cast balls. I agree with previous post very tight loads are just not any more accurate enough (if at all) to justify the drama.
It all depends on groove depth. Good rifling is .010 deep so a larger ball is needed.
I remember Wes Kindig measuring my bore and selling me a bore size mold. Some barrels will just not take what the old Douglas barrels would.
Somehow I think that eventually this topic is going to result in a few members volunteering to send you some samples 😉
Thanks to all. I've been out of ml for some time. Reading through these posts makes me say oh yah i recall that now.
I have decided to get both .390 and .395 molds cast a bunch of each and see what one is better. Most likely i will say both are good enough for me. I am not precision more like i hit that tree rat man is this fun.
A man can never have too many molds.

While you are messing around with peliminaries , and find the right mold , make up a 10 or 12 shot thin wood loading block to make patched ball loading really easy. I know my old fingers will drop as many balls as I get patched into the muzzle. My .40 likes thinly greased patch material about .012 to .015. For plinking , paper , and steel targets , small game up to coyotes , gotta love .40. Built my .40 longrifle about 6 yrs. ago , using a Colerain , 3/4 " octagon 38" barrel. Ultra light , and deadly , more fun than an old guy should have.