Colerain .40 cal. radius-cut barrel question?

[Curt LaManna]

I slugged this barrel, and was surprised to find these measurements:
Lands .400
Radius-cut grooves .435
Being this grove to land diameter is that large of a difference, what thickness (compressed) should be used to start?
I'd like to know if anyone using this same barrel would please share their findings.
RB size on hand to test are .390 weighed.
Thank you for you input.

 

[longrifle78]

With 390 balls I'd try to find some patch material around .020 - .025.
I have a colerain 45 & it shoots pretty good with a .445 ball and a .017 patch.

 

[Grenadier1758]

I think I would try a 0.390" diameter ball with 0.020" to 0.025" patches. That will be a tight load but you should have some thicker patch material to get into the 0.0175" deep grooves.

 

[ohio ramrod]

For that deep of groves I would recomend an over the powder wad of either leather (prefered) or felt. to help prevent blow by. :idunno:

 

[Grizzly Adams]

Mine likes a .395 and .018" pillow ticking.

 

[jamesthomas]

I go up to a .395 ball and use a .20 patch myself.

 

[Vaino]

Doing the arithmetic yields a minimum patch thickness of .0225 which probably won't obturate the grooves. So...a thicker patch is req'd....028 thick would fill the grooves w/ some compression, but might be hard loading. .390 plus .056 double patch thickness equals .446, so there would be .023 patch land compression in a .400 bore.

Could use a .395 RB which would help some, but might make loading more difficult.

Really don't know why the bbl makers cut such deep grooves....008-.010 deep grooves work fine and w/o the difficulty of sealing the grooves.....Fred

 

[Tom Compton]

I've never shot any caliber in a barrel w radius grooves so there u go. I order barrels w .012 deep square groove rifling and use .015 compressed or thicker material with a ball .005 under bore.

So a .395 ball + .015 + .015 = .425. Barely exceeds the groove to groove measurement.

 

[don hepler]

I don't have a 40, but I'm guessing that regardless of caliber, Colerain barrels share the same type of rifling. My 50 radius-cut likes .022.

Trial and error to find the best combination. However, looks like everyone is leaning toward thicker patching.

 

[galamb]

Mine likes a .395 and .018" pillow ticking.

Mine as well. Been shooting my 40 Colerain with this combo for a good number of years now.

But I also generally "load loose" - you don't need a mallet, even a little one, to get my patched balls down the tube...

 

[George]

So a .395 ball + .015 + .015 = .425. Barely exceeds the groove to groove measurement.

If you could lay that out flat so that only one thickness of patch was always between the ball and the bore, it might be marginal, but you can't do that. Any flat patch material wrapped around a spherical ball will bunch up like crazy and have double thickness in many places. Flexibility and compressibility of the cloth comes into play, too. I've never been comfortable just doing the math and deciding what patch thickness is needed, I try it in the field.

My Douglas .40 has grooves .012" deep, and I shoot balls .005" smaller than land diameter, .395". The math would tell me to shoot patches at least .017" thick, but I have always shot plain cotton patches in the .010"-.015" range, and they are snug to start, consistently very accurate.

Spence

 

[Curt LaManna]

Thank you all for the replies. I will be ordering some .395" RBs to work up loads. I'll try the .390"s with some thick patch material to at least fire them.

 

[Curt]

i use a 380 swaged RB and a 25thou canvas duck patch lubed with coconut oil and it shoots very accurate.and i have the targets to prove it .I use a short starter also .Curt

 

[hanshi]

I have two radius groove barrels and get fine results with .311" ball in the .32 and a .490" in the .50. The patch size for both is .024" material. Snug but not too tight.

 

[Pete G]

Denim can make a good thick patching material, usually thicker than ticking and holds plenty of lube. Wash it first to remove the starch put in for sizing. Resist the temptation to use old jeans. They are usually too worn for good patching material.