Round groove vs square cut rifling?

[zimmerstutzen]

The question of round or square bottom rifling is too simplistic to answer. Round bottom has it's advantages, but the radius of the "round bottom" and the width of the grooves vs the lands plays far more into accuracy. Most round bottom rifling is cut with a cutter having a radius that is smaller than the radius of the bore. As a result, the barrel has corners of round bottom trenches with wide lands on which the tops match the curve of the bore.

The grooves cut should be rounded, but not necessarily on a circular curve. The grooves should be much wider and the arc of the cutter curve should be based on a larger curve than the bore radius NOT smaller. The ideal shape would be like half of an oval laid on it's side. The grooves should be at least twice as wide as the lands. That is the type of rifling that Hoppy at H&H barrels came up with about 35 years ago. H&H barrels are still known as excellent match shooters even though they haven't been made in about 20 years.

Anybody considering making a type of rifling needs to study the type of rifling (grooves width vs lands and groove shape vs lands) Study Alexander Henry rifling and Pope rifling. It is far more complex than simply round or square bottom. Alex Henry rifling was a complex system of swales and the Martini Henry rifles bores had two chokes. Harry Popes rifling has grooves that were shallower in the middle than at the edges. (Due the the radius of his cutter) Pope's rifling used groves that were six times wider than the lands.

H&H used a Pope idea modified for PRB shooting and their rifling is the best I have ever seen for match shooting PRB's.

However, a lot of folks can SAY they notice no difference between round bottom or square bottom. That opinion is only good as long as all other things related to loading and shooting the barrels are consistent. The very best barrel on earth will make little difference if the shooter measures his powder inconsistently with a difference of 5 grains from shot to shot, or his patch is so wet with lube that varying amounts of powder becomes fouled before the shot if fired, or if the patch ball combination is so tight that the ball is mashed and deformed upon starting at the muzzle. Or shots are fired on a day with gusty cross winds.

Harry Pope guaranteed his barrels could shoot 2.5 inch ten shot groups at 200 yards.

Also when a person says they notice no difference. Have they fired one hundred shots in each from a bench on windless days to see if there is a four or five point difference over 100 shots?

I tend to cringe every time this round or square bottom issue comes up because it doesn't consider the issue of width, or shape of the grooves and lands.

 

[M. De Land]

Good post and I agree with the premise of rifling form that has much wider grooves than lands. I have a mechanical drawing in one of my many books of Popes rifling form. It looks like he basically used flat bottom or much larger radius rifling with rounded corners. A circumference circle would make contact in the middle of his grooves but not on either side in the corners.
It must be remembered though that Popes barrels were designed for shooting lead bullets ,some times paper patched, not cloth patched round balls. Still the idea is to impart rotation and minimize projectile deformation. MD

 

[Hunter John]

Lots of good info in your post...thanks for sharing. Been considering ordering a custom round bottom barrel myself for RB shooting.

Of today's custom barrel makers, any idea if any follow Harry Pope's from a technical perspective?

Put differently, who would you recommend for a custom barrel maker who specializes in making round ball bottom patch RB shooters?

Thanks again for your info.

 

[zimmerstutzen]

I still shoot my H&H barrel in light bench. I don't know of anyone that cuts a barrel like that, although Bobby Hoyt probably could and would.

I have heard that Hoppy of H&H barrels is still alive somewhere in Florida. It would be great to talk to him and he may know if anyone is copying his barrel style.

There is a little about styles of rifling in Greener's The Gun and it's Development, but keep in mind, that Greener wrote at a time before Pope perfected his rifling. Of all the shooters in the world, there are only a very few who even understand that differences exist. A higher percentage of the muzzle loading crowd understand it than modern shooters.

I once heard a person say that a gun had Ballard style rifling. When I asked what that meant and how it was different from Forsyth, Henry, or Pope rifling, the person just had a blank stare.

The styles of rifling really don't have much meaning to modern shooters with their copper jacketed bullets. I also shoot BPCR, and prefer a deeper rifling and shooting pure lead bullets than most.

I think most barrel makers cut what they are able to, but not necessarily to be the best. It takes a barrel maker that understands the different styles and purposes. H & H actually had a choke bore in their muzzle loading rifle barrels, the last few inches before the muzzle. How many do that today? It seems counter productive to load a ball through a choke bore and fire it down a slightly more loose barrel. But if the ignition force obturates the soft lead ball enough to fill that .002 difference and then it chokes it at the muzzle, it does what is intended.

In talking to Bob Hoyt many years ago, he said he would cut some BPCR barrels with false muzzles and pope style rifling, so he understands the difference. I'd call him and see if he can cut such a barrel. He may already have made such cutters.

 

[M. De Land]

Choking or tapering in bores is measured in tenths and are generally lapped in which causes it's own trouble if the rifling is gain twist as lead slug laps cannot be used. Pope chambered his barrels and then lapped in taper after gain twist rifling them using leather washers that polished the land tops but not much could be done in the gain twist groove bottoms. He used a series of slightly tapered steel plug gauges that would drop to a specified portion of the bore when the lap contoured it to that point. A thirty inch barrel required 30 one inch tapered steel plug gauges that would drop to their assigned depth when the bore was lapped enough.
Good barrels of the old school were often lapped after reaming before rifling to insure a level bore for the rifling head to traverse and then were generally scraped rifled although some were hooked. A straight and level reamed bore is the foundation for any precise rifling to be cut.
Also when a rifling head is used in scrape or hooked rifling the groove depth will be shallow when the head is introduced into the bore and again when it is removed at the muzzle end. This is because the cutter is not supported on both sides of the cutter box at each end of the barrel until it is two thirds in the bore. This can be used to advantage at the muzzle if one wants taper/choke in the grooves as well as the bore. MD

 

[roundball]

As one reference, I bought my .45 and .58 round bottom groove barrels from Rice barrel company.

 

[dcriner]

Related Question:

I have an original .58-cal, 1864-dated Springfield rifle musket. It was designed for Minie balls, and the square rifling is quite shallow. I have shot both Minie balls and PRBs in it, but I haven't done any extensive testing of the accuracy of one versus the other.

I thought Minie balls were preferred in the Civil War because loading is faster than ramming a tightly patched round ball. (I'm also aware that Minies, because of their shape, could be heavier, and thus more lethal, than the same caliber PRB, right?)

But, back to the comparative accuracy - what are the opinions here about using PRBs in my Springfield vs. Minie balls? I don't cast my own balls, and Minies are a bit more expensive than round balls.

 

[zimmerstutzen]

Roundball how does the width of the grooves compare to the lands? is the radius of the groove curve smaller than the bore or larger? Saying it is round groove means little without the rest of the information.

 

[zimmerstutzen]

dcriner I have no experience with a Springfield, but I have shot a Zoli Zouave for years.

Yes it has shallow rifling. And it will shoot a PRB very accurately, with charges in the service load range.

The original service charges for the 58 Springfield, 53 pattern Enfield and Zouave were between 55 and 70 grains of powder. Even under a 500 grain minnie. More than 85 or 90 grains often leads to blown out skirts. Because of the shallow rifling, they don't shoot accurately with mush more than the same charge of powder under a PRB. I have the list of changes from the British War Department for the 53 pattern Enfield and it was the same as the official US charge and CSA charges for the Enfield. The Springfield is not significantly different in it's shooting characteristics.

 

[Larry Pletcher]

In 2006 at Friendship a panel discussion was held on the back of Gunmakers Hall. L C Rice of Rice Barrels was one of the participants, along with Jim Chambers, Bob Harn, Mark Silver, and Wallace Gusler. In the discussion, L C talked about round vs square rifling. His response to the idea of a "all out match grade ML barrel" with round rifling, he replied, "the H#11 you say!" He clearly felt that for match quality shooting square rifling should be chosen.

If any of you know L C, you realize he didn't mince words. I won't speculate on the validity of his comments - I don't know enough - just reporting what he said.

The panel discussion is recorded as an MP3 at the link below. The discussion is divided into 6 parts because of its length. The link is to part 1, which is when LC's comments are (I think).

Link

Regards,
Pletch

 

[zimmerstutzen]

I will listen with interest. I know what Mike Bell and others were able to do with H&H barrels. I know that as lousy a shooter I have been, how much my score improved in light bench matches. I have seen the targets shot with Harry Pope's muzzle loading rifle barrels.

All due deference to Mr. Rice, I don't think the final chapter on accurate rifling for muzzle loading has been finished yet. Through the 1980's barrel makers kept experimenting with rifling. The experimenting has died off some what, but still exists in many who compete at friendship.

The true test indicator may fall to an indoor range with a machine rest like Dr. Mann, Harry Pope and others used. With powder weighed to a tenth of a grain, etc. Patches weighed, etc.

One of the things I learned decades ago, is that good shooting with a muzzle loader is the culmination of many things, barrel, lock, sights, trigger, stock fit, loading technique (to the point of being anal) breath control, posture, muscle tone, eyesight, ambient light contrast, etc. None of them is most important, all of them are of equal importance. A good match barrel is a small part of the equation. It does not make a mediocre shooter a master. A good shooter has mastered and pays attention to every part of the process. When all the other dozens of things are equal, the barrel can make a small difference.

 

[roundball]

When I had my first discussion with L. C. Rice, then Jason...about buying a round bottom groove barrel or not, asked if there was any difference in accuracy, etc.

He asked me:
"Do you regularly compete at the national level"

I said:
"no"

He said:
"you'll never see a difference in accuracy"

I bought it in .58cal and it was as tight group accurate as my previous GM .58cal square groove barrel;

I then bought another one in .45cal...same result.

I then had a 42" long / too nose heavy .45cal square groove barrel bored out to a .50cal and re-rifled with round bottom grooves...same result.

I'm definitely not a match target shooter but I do expect excellent accuracy and every one of them has been as accurate as any square groove barrel I've ever used.

 

[roundball]

EXAMPLE:
My Early Virginia / Rice .58cal round bottom groove barrel...this may not be good enough for everyone else, but I'm fine with it:

 

[zimmerstutzen]

Yep. Imagine what you could do with a barrel rifled for target shooting.

BTW, I';; ask again. Are the grooves cut with a radius larger or smaller than the bore radius? How does the groove width compare to the width of the lands? I didn't think they were difficult questions.

As I said above, it is easy to say you don't notice a difference. That is hardly proof that there is no difference. only testing over a long series of shots under identical conditions will show the answer.

 

[Larry Pletcher]

Roundball,
I should have said that I have three barrels with round rifling - two are Rice and one Getz. I like them all. The .54 I may try chunk shooting with.

If I were a National Match quality shooter, I'd probably buy square rifled barrels for chunk or bench. But I'm not. My eyes are my problem - not my barrel, or my lock for that matter. My targets are not as good as yours, but I'd never think to blame it on round bottom rifling. I'm my own worst variable.

Regards,
Pletch
PS I reckon I'm more productive with a flintlock hooked to my computer than I am shooting. But-- if I ever get to SC, it would be fun to shoot with you.

 

[roundball]

Just to be clear, that target was benched...I wanted to see what to see what 120grns Goex 2f would do.
I use a 1/8" .62cal lubed felt was over powder to help seal those .016" deep grooves better

 

[zimmerstutzen]

third request

Roundball how does the width of the grooves compare to the lands? is the radius of the groove curve smaller than the bore or larger? Saying it is round groove means little without the rest of the information.

 

[Larry Pletcher]

third request

Roundball how does the width of the grooves compare to the lands? is the radius of the groove curve smaller than the bore or larger? Saying it is round groove means little without the rest of the information.

I have the same .54 Rice that Roundball has. I'm also away from my gun, so this is what sticks in my mind. I believe it has equal lands and grooves, and a rifling radius the same as the bore. That last part I have NOT seen in Rice's information, but I think it's right.
Regards,
Pletch

 

[zimmerstutzen]

Thankyou

 

[Billnpatti]

I do not have, nor have I ever had, a rifle with round bottom rifling so I cannot tell you from personal experience what the advantages are. But, I have done a bit of reading about that kind of rifling and it seems that the main advantages of round bottom rifling is ease of loading and ease of cleaning. I have not read where anyone has done a real scientific study of how round bottom rifling effects accuracy. Such a study may well have been done, but I have not seen it so I assume that the round bottom rifling is mainly just easier to load and clean. If I ever build another rifle, I plan to use a Rice barrel with round bottom rifling because I do not own such a rifle and I would like to have one.