Lands and Grooves

[El Chivo]

How deep are lands compared to grooves? Is it variable from gun to gun or is there an optimum relationship?

Why? As discussed earlier I'm thinking of reboring a 336 to .357 bore, and I want to make sure that .308 microgrooves would not be present in the lands of the rebored .357. Taking .024" off each land would wipe out all the old grooving, is that enough of a groove depth?

If a standard groove is less than that, I would be fine. Say, if a good groove depth is .020", then I'd have grooves of .357 and lands of .317. But if it needs to be more than that...

[Terry Murbach]

GROOVES AVERAGE .004" [ FOUR THOUSANDS OF AN INCH ] ON A SIDE. FOR INSTANCE : THIS IS WHY YOU SHOOT A .308" DIAMETER BULLET IN A .300" BORE.
WHERE IN THE WORLD DID YOU GET THE IDEA THAT MODERN GUNS HAD .020" DEEP GROOVES ??? MUZZLE LOADERS USED WITH THICK PATCHES COULD AND DID USE SUCH RIFLING. AND MAYBE THE BIG RIFLES ON THE USS IOWA DID, BUT I AM NOT SURE. I'LL BET THEIR'S WERE LOTS DEEPER.

[missionary5155]

Greetings
Books have been written on this subject but here is my short story.
If you were to want to shoot Paperpatched ammo the old barrels were made with shallow grooves (about .003) to accomidate this loading.
Bare lead bullets need substantial support or will skip, skid some down a barrel upon acceleration and / or if the barrel has a fast twist. As I shoot mostly my cast bullets, I like a barrel with about .006 groove (Ballard Type) rifling. I also size my cast bullets so I have a oversized fit bullet in the throat area to better seal that area at ignition.
For jacketed less is OK as the tough copper (or whatever material) is capable of gripping even Marlin's Microgrove without any skids. So that old .003 deep groove is more than enough for a properly fitted bullet. Sadly many companies purposly undersize thier bullets due to lawsuits and reloaders who like to full power + everything.
Mike in ILL

[El Chivo]

WHERE IN THE WORLD DID YOU GET THE IDEA THAT MODERN GUNS HAD .020" DEEP GROOVES ???

That was a hypothetical, because I had no idea.

But that helps me with my project, because anything less than that means the old rifling will be completely wiped out when I rebore. So it means my .357 rebore will have an inside diameter of .349-.345. I want it to shoot lead well so maybe I should ask for .006 grooves. Although the lead I plan to use is quite hard (Oregon Trail). I don't plan to cast my own.

Thanks!

[missionary5155]

Generally whoever you have do the job will already have his idea how deep to cut. But be sure you specify you want to shoot cast bullets.
No matter what cast lead bullets you use they will be no wheres close to the hardness of brass or even copper. What sellers call hard lead is about 28-30 on the hardness guages whereas even lowly copper is well into the hundreds. Also be aware a too small hard lead bullet is the worse thing to try to shoot. Fit is far more important than hardness. A soft but well fitted boolit with good and sufficient lube will not lead near as bad as a undersized hard bullet. I routinely launch 50-50 mix cast which are about 15 on the hardness guage to over 2000 fps from my Krags. Alot has to do with what pressure you are slamming into the base of the bullet and how well you can protect it from the slamming forces. Gas checks work very well. Even a lowly cerial box base wad gives a little help.
If you are serious about cast bullet shoting head over to the Castboolit site and take some time to read. Been there for numerous years myself and always a good idea floating about how to improve cast boolit accuracy.
Mike in ILL.

[JerryB]

missionary5155, are you in Peru now and can you have your firearms with and reloading stuff too? Just wondering, someof the missionaries our church supports in Latin America say they can't have guns, thanks.