Author Topic: What groove depth for shooting patched RBs? (Read 1259 times)

Naphtali · « **on:** July 28, 2004, 07:03:14 AM »

I am having muzzleloading rifle barrels made by a custom barrel maker who has not made muzzleloading barrels before.

My intention is to use patched RBs in the barrels. Barrels bore IDs will be [nominally]: .38-, .62-, .65-, and .69-calibers.

I have no control over shape of grooves, so theres no point worrying about it.

I can use Greenhills Formula to identify correct rates of twist, but I have no idea about what groove depth to request. I own rifles that shoot RBs like a house afire whose groove depth is .007-inch, and one rifle whose groove depth is .012-inch. I use hefty loads in both powder resellers send me get well cards if they dont here from me every month.

I dont know whether how barrels are to be used makes a difference. The .38-caliber will become a squirrel rifle. The sixties will become heavy game rifles, loaded as heavy as I can stand for one shot.

All rifles are flintlock.

roundball · « **Reply #1 on:** July 28, 2004, 09:08:07 AM »

I'd tell you if I was an authority on the subject but I'm not...other than the obvious that "deep grooves seem better" for patched round balls, but I think you already know that.

So, how about this...I'm very impressed wth the accuracy of a .58cal Green Mountain 1:70" round ball barrel I got this spring, and while I haven't miced them, the grooves look extremely deep...deeper than my other TC 1:66" round ball barrels which I already know are .010" deep.

Give Green Mountain a general information call and ask how deep the grooves are on their .58 / .62cal round ball rifles...with their barrel reputation, the answer should be very telling

flintlock · « **Reply #2 on:** July 28, 2004, 09:26:55 AM »

Green Mountain patched round ball barrels are .012 deep...twist is 1 in 48 for .32, .36 and .40 caliber......1 in 60 for .45 and 1 in 70 for everything over .50...flintlock

filmokentucky · « **Reply #3 on:** July 28, 2004, 02:50:13 PM »

My .62 aqnd .58 calibers are .012" deep.

KING · « **Reply #4 on:** July 28, 2004, 05:01:36 PM »

Some people get to have all the fun,new toys to play with. In my experiance it seems that a groove depth of .010 to .012 will do whatever it is that you want it to. A little tighter patch might be called for but I also have one that mics out at .015 and it shoots like a champ. I think that this might be a little deep for a rb rifle but have seen them greater in depth. Good luck and keep posted as to how they shoot. stay safe.King :-D

crow_feather · « **Reply #5 on:** July 29, 2004, 05:12:51 AM »

It seems that the grooves are filled with the patch material, which then inparts the spin of the groove to the ball. If I was to shoot a rifle with a heavy charge behind the ball, I would want a good grab on the patch so that it could do it's job and not strip out of the groove due to the high pressure behind it.

two pennies

C F

HWooldridge · « **Reply #6 on:** July 29, 2004, 11:25:26 AM »

RB - .010 to .015 deep; bullets - .005 to .008. Twist for PRB in the 38 should be 1-48 to 1-60. The larger bores could be 1-60 to 1-80. If I was building a barrel in the 60 calibers, I'd probably go 1-80 with .015 grooves and be able to shoot 150 grs of powder with PRB. The longer twists seem to be more forgiving with a variety of loads.

Ramrod · « **Reply #7 on:** July 29, 2004, 11:55:13 AM »

From the older original roundball rifles I have seen, it seems they all have deep grooves, and rounded at the bottom. The lands were very narrow, and they had ALOT of grooves and lands. The twists are all over the map, depends on the maker. Square lands and grooves are a later invention to shoot slugs. I think the reason the 1-48 twist gets a bad rap as a roundball barrel is that the modern reproduction rifles are built on modern rifling machines, producing 6-8 groove, shallow, square rifling, fine for bullets, not good enough to grip a patch.

Naphtali · « **Reply #8 on:** July 30, 2004, 04:36:38 AM »

HWooldridge: I appreciate your information and will furnish some in return. Rather than depend on anecdotal data to identify correct rate of twist, I rely on Greenhill's Formula. Despite my ongoing inability to remember that I must convert "twist in calibers" to "twist in inches," the formula is accurate, has been since 1879.
*********
crow_feather: Regarding deep versus shallow grooves -- watch closely as I insert foot in mouth -- deep grooves appear to be an older method of compensating for too rapid rate of twist. That is, the lead projectile would normally/experientially strip the rifling at velocity, so deeper grooves allowed the lead to remain gripped (through patching). The downside is that deeper grooves deforms projectile, and deformed bullets are less accurate than those undeformed.

I have no test results that verify the previous paragraph. I tend to believe it in the absence of contrary evidence.
*********
I am hopeful someone HAS tested this variable before I invest -- no fibbing -- nearly $600 per barrel. My instinct tells me that shallow grooves should "grab" as well as deep ones were twist correct. But perhaps, shallow grooves require cleaning more frequently? When target shooting or hunting, more frequent cleaning is no big deal.

When people relied on muzzleloaders for staying alive, perhaps, ability to fire many "acceptably accurate" shots without cleaning was more important than best possible accuracy?

flintlock · « **Reply #9 on:** July 30, 2004, 07:09:28 AM »

At $600 a barrel...believe I'd buy a Getz, Colerain, Green Mountain or Rayl...they know what they are doing...I've won countless matches with both my custom .40 and .54...both have Rayls...both are .012 if I remember correctly... .40 is one in 48....54 is one in 70...I wouldn't experiment with $600.......Accuracy with open sights will be better than you can see....There is more to a rb barrel than depth of rifling and twist rate...Softness of material used and smoothness of bore come to mind..

Someone suggested calling Green Mountain...good idea...Ed Rayl in West VA, Jim Chambers in NC or Vernon Davis in Ohio, could also help...If you will call...flintlock

roundball · « **Reply #10 on:** July 30, 2004, 12:58:17 PM »

Quote from: Naphtali

My instinct tells me that shallow grooves should "grab" as well as deep ones were twist correct.

My instincts tell me that I think you need to rethink your thinking... :grin:

Ramrod · « **Reply #11 on:** July 30, 2004, 06:28:44 PM »

Yes-sir roundball! what Mr. Naphtali is missing is that Mr. Greenhill developed his formula for artillery shells, which were all elongated projectiles by 1879. This has absolutely nothing to do with roundballs.
Although he is correct in that the deep grooves were mostly there to give the fouling a place to collect so cleaning was not needed between shots. It is the many narrow lands that grab the patch. Can you imagine one of our internet wonder shooters being transported back to 1750 or so. "Excuse me Mr. Redskin, please don't take my scalp while I'm cleaning my weapon. I know i only fired one shot, but I read that I can't hit anything if i don't clean it before I fire another one." And no excuse given for missing with the first one. ( must have been because of a clean barrel) !

roundball · « **Reply #12 on:** July 31, 2004, 12:23:47 AM »

I've never seen rifling marks on a lead ball...I've seen patch/ball combinations tight enough to leave a patch weave imprint on the lead, but never rifling marks.
The patch material wads itself down into the grooves and locks up the relationship of the ball to the rifling to impart the twist, without the ball going into the rifling.....balls ride lands like a train rides rails

crow_feather · « **Reply #13 on:** July 31, 2004, 03:44:40 AM »

If you do not see patch imprints on a fired ball, or a ball that has been loaded and pulled, you had best get a thicker patch or a bigger pall. Ball grabbin by the patch is one of the necessities of round ball/patch/rifle shootin.

C F

Naphtali · « **Reply #14 on:** July 31, 2004, 05:59:17 AM »

Ramrod: You are correct that Greenhill created his formula for elongated artillery projectiles. Fortunately, RB calculations remain valid -- that is, experience and Greenhill result match closely. If anything, rate of calculated twist may be slightly too quick.
********
SO --

So far the consensus is:

Deeper grooves (0.12.015) -- that is, higher lands?? -- better than shallower (.007.010).

More grooves are better than fewer.

Buying ultra-expensive barrels 100 percent finished is not my most cost effective purchase.

Rely on anecdotal twist rates rather than questionable formula.

Patching, material AND thickness, make or break an otherwise first-class barrel.

Is this an accurate summary?

filmokentucky · « **Reply #15 on:** July 31, 2004, 07:38:54 AM »

Well, ball size is pretty important, too.
Rather than "anecdotal twist rates", rely on empirical experience-centuries of practical and successful use. This will give you the best possible results and save you enough money to buy yourself a fine custom made rifle-a good result all by itself in my book.

cbagman · « **Reply #16 on:** August 27, 2004, 05:50:58 PM »

:-) Gefeltifish!! Been shooting round ball in sanctioned matches for 22 years.. I routinely load a .395 ball in my greenmountain barrels with the thickest denim made..Sometimes even a .400 ball.. and even a .410 ball.. I shoot a .350 in the 36 caliber Douglas barrel with thick denim patching.. All these barrels have square bottom deep grooves .010 of a bit more. The ball engraves in the rifling, but it is hard to show unless you blow one out with a CO2 charge.. My hunt guns are loaded with pillow ticking patching and sometimes denim but with a combo that can be started with a short starter fairly easily and sent home with the ole hickory stick.. At the range we use a very tight load for accuracy.. Now a custom round ball barrel with round bottom grooves will not be as easy to load a tight comdo as the patching fills the grooves to capacity.. Generally speaking, use as tight a setup as you can and wipe between every shot...:wink: cbagman

roundball · « **Reply #17 on:** August 28, 2004, 03:03:20 AM »

Rely on anecdotal twist rates?

=======================

IMHO, I worry that this issue is being disected disproportionately to it's simplicity.

Twist rates and groove depths have been etablished for centuries and the the choices are really very few, simple and straight forward.
The major, successful barrel makers have been making their high quality barrels using these proven, established twist rates and groove depths corresponding to the use of round balls or bullets.

If a round ball barrel is desired, any barrel maker will tell you what is appropriate, what they build, etc, and as previously stated by those who have purchased and used them, .010-.012" grooves are desirable for round balls.

My .58cal GM 1:70" flint barrel has very deep .012" grooves and a .570 ball using .018" pillow ticking patches simply eats out a single ragged hole at 50yds...My .50cal and .54cal TC 1:66" round ball barrels with .010" grooves do the same thing...and I'm just an average weekend shooter.

As round ball flint barrels they cost about $180...percussions are a little less expensive...I bought them, cleaned them, installed them, and they shoot perfectly with round balls which is what I bought them to do.

Longcruise · « **Reply #18 on:** August 29, 2004, 09:21:24 PM »

I'll go along with the std .010 to .012 grooves, but I gotta tell ya that my Lyman GPR shoots pretty good and those grooves don't look to be any more than .004 to .006 deep if that.

I can't imagine $600 bucks for an ML barrel. Especially from a barrel maker who is not a BP barrel specialist. What is he promising that makes his product worth $600? :shock: You can buy a common barrel for less than $100 or you can spend another $100 or $150 and get a hand lapped barrel. A goodioen barrel probably gets about as much handwork as can be done to an ml barrel as far as functionality goes. Guess you could spend more money and go with some engraving, but it's not going to make it any more accurate.

As far as Greenhill goes, if you apply it to some common calibers you come up with:

.38 cal 1/57
.50 cal 1/75
.58 cal 1/87
.62 cal 1/93
.69 cal 1/103

Those are slower than the common slow twist barrels but would probably work just fine. OTOH there is nothing magical about those twists and probably not worth $600 bucks at least IMO