Round Groove vs Square Groove Barrels

[zimmerstutzen]

This is a diagram I found on line posted by RSW over at the ASSRA forum Note that when done correctly, the middle of the groove is bore diameter.



This is the style rifling that Hopkins would cut for muzzle loaders with slightly deeper grooves and slower twist than used by Pope for bullets. and I can attest to it's superb accuracy with a PRB.

 

[Stumpkiller]

The rifle I have owned that gave me the most trouble to work up a good ball/patch combo was a square grove .50 cal with 1:48". Took me years.

 

[George]

To the board.

One thing I have trouble getting clear in my mind about all the various "best" rifling patterns, flat vs. round bottom, steady vs. gain wist, more or less grooves and lands, deeper or more shallow grooves, etc., etc., is how they are supposed to contribute to accuracy. As far as I know, the function of the rifling is to spin the bullet, and that's all. Period. What possible difference can it make how that spin is achieved as long as it is adequate for stabilization? Is there some kind of magical spin which works better? Is it possible to tell the difference between Pope spin and Wm. Large spin? Italian spin and American spin?

I'm going to go take an aspirin for this headache, now. :grin:

Spence

 

[zimmerstutzen]

That is a very good question spence. The round ball is an inefficient projectile at best and imparting the spin within the acceleration of the charge in the best way for accuracy is the goal. I have seen guys use mallets to mash tight patch ball combinations into a bore. So how much does the deformed bullet detract from accuracy over the span of 50 to 100 yds? Does the combination of lands dents and "patch weave imprint" on the ball have an effect of accuracy? Does the dents from wide lands or the imprinted design of the patching cause a deceleration of spin or flight. Do wide grooves lessen the effect? Do they lessen the effect of the dents from lands on the ball? We may be getting into the effect of the earth's rotation soon. I suspect that the imprint of the lands and patching on the ball, including the deformation when loading have a big effect.

 

[galamb]

If any of those styles/patterns was truly superior in "all cases" we wouldn't be having this discussion because there would only be one style of rifling.

If 1:70 twist will stabilize a 50 cal roundball (Green Mountain thinks so), then why does Rice use a 1:66, Colerain 1:56 and the Hawken Brothers, 1:48 twist (to add a historical barrel builder to the mix)????

And if Pope or Forsythe had found the "grail", then again, there would be no choice to make.

I take a more simple approach.

Instead of trying to come up with a "franken-barrel" that is gain twisted with round bottom groves greater than the lands, or whatever, I simply stick with barrels that produce results that I can live with.

If you pick a barrel that works "for most guys/gals" in the style of shooting you plan to do, it's kinda hard to go wrong.

If you are in that 1/2 of 1% that is looking for laser precision and that infinitesimal advantage over the "next competitor", then you really shouldn't be asking a group of hunters/plinkers.

 

[zimmerstutzen]

For one, I am not a plinker and only hunt infrequently. I shoot for the pure joy of shooting and trying to build the better muzzle loader. If you practice and become accomplished with a smoothbore, you can shoot 4 or 5 inch groups at 100 yds with no rifling, so why have any at all for hunting? That same logic would have us all shooting smoothbores.

Shooters have a result based upon the overall loading, sighting and squeezing techniques. The extent of their individual inconsistencies and limitations of their equipment restrict the potential for fine accuracy to a range that comes within their technique. Of the 32 (or so) factors that play into one shot being accurate, many shooters fall short in some or all of those factors resulting in a wider group. Equipment like barrels are only a small part of the overall picture. There are those who say this way is good enough. And that is as small as their groups will ever get. Even if there was a magic configuration for perfect accuracy, most shooters could not avail themselves of the advantage due to their shortcomings in the other aspects of loading, sighting and squeezing. A shooter that is inconsistent with his powder measuring throws all other skill to the wind. A shooter that soaks one patch and barely moistens the next will likewise have no basis to tell which rifling is better. A shooter with one of those 1/8 inch wide Renegade front sights would likewise be handicapped.

Saying this is "good enough", to me is like throwing in the towel. I am never satisfied that it is good enough. There is always that one little thing I can work on to improve accuracy.

Does the barrel make a difference. We know it does just from the fact that fast twist shallow rifling doesn't produce the best results for PRB's.

 

[George]

I've always had a problem with the million and one theories about what makes accuracy. It is that there seems to be a lot of magical thinking involved in them, and very little application of simple physics. I see discussions all the time about how patch lubes, patches, rifling style, cleaning methods, length of barrel, etc., you name it, will destroy or guarantee accuracy. I'm not a believer. My experience just doesn't show that. I switch patch material and thickness, patch lubes, powder brands, granulations and charges, whatever, and I see little effect. I shoot barrels with more or fewer lands and grooves, deeper or more shallow grooves, slower or faster twist rates, larger or smaller charges and I find that the one thing contributing to higher or lower scores is how I'm shooting that day.

An example to illustrate my point. Something interesting has been going on in the forum for the last few days. On one hand people declare how marvelous silicon patches are, that many championship shooters will use nothing else, and other people say silicon patches are far too slick, will destroy accuracy, and base a highly praised accuracy theory on controlling slickness with minimal dry lube. Both sides claim world-beater accuracy, and, significantly, give the credit to their particular theory. As the man famously said, they can't both be right. But, they could both be wrong, if slickness wasn't a factor.

The way I see it, after the ball leaves the muzzle it absolutely does not matter how it got there. If the weight of the ball and the velocity at the muzzle are the same every time, the trajectory will be the same, as will POI. It matters not a bit what patch you used, what lube, what the rifling configuration was, or anything else. Weight and velocity, and with a rifle, spin within the proper range for stabilization. If I didn't hit the target, it's because I wasn't point the gun at it when the shot broke, not because I put 30% beeswax in this new batch of lube instead of the 40% last time.

Incoming. :grin:

Spence

 

[bpd303]

Have to agree with you. :thumbsup:

 

[Zonie]

I think you meant to say, Teflon patches rather than silicone patches. :hmm:

 

[zimmerstutzen]

Teflon patches are very old news. Saw them used 30 years ago up at Blue Mountain's bench rest match. Those guys stopped using them within a few months.

 

[George]

Yes, you are right, thanks for catching that. My bad.

Spence

 

[zimmerstutzen]

Spense said: I find that the one thing contributing to higher or lower scores is how I'm shooting that day.

But in offhand shooting most would not notice a difference, they simply aren't accurate enough to notice a difference. When you shrink your 100 yds groups to under 1.5 inches, let us know. Other wise it is, as I said, settling for "good enough."

 

[galamb]

The point I was trying to get at is, for the "average guy/gal" asking "what's good/better/best" it's impossible to give them an answer.

They don't provide enough information in their question to even begin to give the answer that they actually need.

If they want to shoot every conceivable projectile from a single barrel then in that single case perhaps a gain twist barrel would be the "only option" that would give them overall "mediocre" results.

Would they get laser accuracy - NO - but that style of rifling would give them the means to shoot a PRB or a very long, very heavy conical from a single barrel.

If they only wanted to shoot PRB in a sub-45 caliber, then Forsythe rifling, which works best in large bores with kegs of powder is probably not what is "best" for them - their accuracy would suck compared to the cheapest India built barrel.

A 1 1/4" ATF, 45 caliber barrel on a 25 pound chunk gun might put all the balls through a nickel sized hole at 200 yards but try carrying that 2 miles overland to your hunting spot.

I "hunt" my rifles. They have barrel lengths from 28" to 42" - some are straight, others swamped and a couple tapers. They range in caliber from 40 thru 54. Some are round rifled others are square. The rifling depth amongst the bunch runs between .008" and .016"

They were built by Lyman, Rice, Green Mountain, Colerain and Oregon. Two were custom orders the others were "as they made them".

I buy whichever balls are available (swagged from Speer or Hornady) at .005" below bore size. They get wrapped with either .018 pre-lube pillow tick or .010" cotton pre-lube from Ox-Yoke (depending on the rifling depth).

My latest order is for a 38 cal, round rifled, .010", 1:48 twist from FCI/Charlie Burton - why? because I prefer round rifling (just because) and Greenhill (modified) says that a 1:46.8 twist is optimal for a .375" roundball.

I don't weigh/measure the balls, I don't mic the patches and I don't cook up concoctions on the kitchen stove to lube things.

I clean my barrels with cold water and a drop of soap - then they get a shot of WD 40 to keep the rust away.

I have never lost an animal I hit, but have never taken a shot longer than 37 yards - never had to.

So for me what's more accurate and what shoots better? ALL OF THE ABOVE

I might build a rifle with a gain twist barrel for the "novelty" of it, not that I think it would do anything for accuracy etc.

If I wanted a conical shooter I would have a very shallow (.003/.004") square rifled barrel cut at whatever twist the Greenhill formula said was the best twist for the caliber and length of the bullet.

That barrel could potentially give accuracy well under 1" at 100 yards but would be of NO VALUE to a roundball shooter.

Without context then you can never give "the correct" answer because you don't know how/why/what they are going to shoot and at what...

 

[roundball]

Spence, I happen to agree with virtually every point you made...and will offer a related point of consideration. And it's one I can turn on and off at the range like a light switch to recreate the situation...and that has to do with the "amount" of lube.

My .40cal late Lancaster will shoot a single ragged hole all day long using a .395" ball and T/C's precut / pre-lubed .018" pillow ticking patches.
However, when I melted some 'mink oil' into a few bags that I thought felt unusually dry, I got too much lube on them...(both visibly and that they were greasy to the touch)...group sizes opened up to a couple inches.
Switched back to a good normal factory bag of T/C pre-cut / pre-lubed patches and went back to a ragged hole again.
Tried the greasy patches again and got 2" groups again.
Everything else the same right there at the range.
Have double checked that test on at least one other range trip and resigned myself to the fact that I'll just use up those greasy Mink Oil patches shooting steel targets instead of looking for smallest bullseye groups.

Similar experience using PRBs out of my .54cal Early Virginia 'smoothbore'. Oxyoke prelubed patches shot very well...but when I added some Hoppes liquid due to very low humidity one trip in early spring, the group opened up and I had a POI shift. Turkey target below shows the POI with Hoppes added moved up high right.

So at least my experience has been that excessive patch lube can affect accuracy, from both rifled and smoothbore barrels.