26 July 2007

What's that about Forsyth Rifling?

Recently I received an e-mail from a reader of this blog who asked about Forsyth rifling and why I use it in the rifles that I craft...

During the mid 19th Century, James Forsyth was a ballistician in the British army. As such he had a scientific understanding of the principles and dynamics that effect projectiles in flight. He was also an avid hunter and had the opportunity to hunt many species of game in India while he was stationed there. It was his keen interest in hunting, however, that spawned experimentation that led to his discovery of the most efficient rifling system for round ball hunting rifles.

Even way back then it was a well understood concept that the round ball was the best projectile for dispatching game in a quick and humane manner, while elongated projectiles were used in military rifles for the most part. Bullet expansion was not intended so it was not a factor in military bullet design. Today, however, jacketed (elongated) bullet makers strive for a design that will result in the perfectly expanded bullet. It’s interesting to note that the perfectly expanded bullet, as they depict it, attains the shape of a round ball… imagine that!

Forsyth also understood that bullet drop is a function of time, i.e. the quicker the bullet gets to the target the less time gravity has to act upon it. Therefore, a higher velocity bullet will shoot flatter than a lower velocity bullet of the same weight and shape thereby providing an extended point blank range wherein elevation guesstimation is less critical than with a slower moving bullet. But increasing the velocity of a round ball in a barrel possessing the conventional methods of rifling that were employed in most other sporting rifles resulted in merely stripping the ball from the patch and rifling and rendered horrid inaccuracy. Increased fouling from larger powder charges was also a result that made for difficult loading and further detracted from accuracy.

Being a hunter, Forsyth knew that most shots at game would be taken within a range of 200 yards maximum and usually under 100 yards. So the idea was to create a rifling design that would allow higher velocity, and thus an extended point-blank range, for those longer shots. Yet it had to provide accuracy sufficient enough to make those long shots “likely” instead of iffy. What resulted is Forsyth’s own design of rifling bearing wide shallow grooves of .005” - .007” depth with very narrow lands and a rate of rifling twist just sufficient to stabilize a large round ball for a short distance of under 200 yards.

Being a scientist, he understood that the round ball is a perfect geometric form and that a large round ball required very little rotational spin to stabilize its flight to the target. In fact, when one moves up to calibers of .58 and larger, a rifling twist of no faster than 1 turn in 100 inches will provide high velocity for flat shooting with very low stress on the rifle - with round balls and Forsyth rifling, that is. And because the grooves are wide and shallow and slow pitch, there is very little accumulation of fouling to adversely effect subsequent shots even with heavy powder charges.

The results are quite spectacular and do not exhibit any of the bad behavior that is attributed to most muzzleloading blackpowder rifles – that is difficulty in loading, accumulated fouling which leads to inaccuracy, which leads to the need of frequent cleaning, etc., etc.

The fact is, Forsyth had overcome all of our modern complaints about muzzleloading rifles over 140 years ago! So why didn’t we hear about this sooner? His wonderful book, The Sporting Rifle and Its Projectiles, was published just as cartridges were making their debut and most folks of the time quickly lost interest in muzzleloading arms. Hence, the book was lost in history and has remained virtually unknown for over a century and a half.

In my own experience of building rifles with Forsyth rifled barrels (about 200 so far), ranging from .58 to .82 caliber (but mostly .62), I have loaded and fired over 25 consecutive shots without cleaning or wiping of the bore in any manner; loading and seating the patched ball with nothing more than my thumb to start the ball into the muzzle and the loading rod to seat it upon the powder charge with one smooth stroke. Quick and simple.

“But, what about accuracy?” you ask. While my rifles will shoot very tight groups with target-loading techniques, in my opinion surgical accuracy is not needed in most big game hunting situations where shots are taken at under 100 yards. Power and ease (and quickness) of reloading were my primary objectives for a hunting rifle load.

However, shooting offhand (yes, I do test from the offhand position, too, as I need to know how well I can shoot from field positions as one rarely carries a shooting bench while stalking game) at a measured 100 yards, I could easily hit a cantaloupe-sized target with every shot. That is meat-in-the-freezer accuracy. A cantaloupe is about the size of the vital area of small deer-sized game. By the way, the vital area I'm talking about is the shoulder, not the heart/lungs as most hunters are instructed to shoot. That’ll probably raise hell with some, however, that’s another discussion for another time.

By the way, the sights on my rifle are part of the accuracy equation and consist of a simple silver blade up front and my own design "Peephorn" rear sight as seen below. The Peephorn looks like a typical buckhorn but works just like an aperture sight wherein the shooter simply centers the top of the blade in the crescent arms of the rear sight. For older eyes it's quick and accurate - especially in low light conditions.

The best performance and accuracy that I’ve experienced is obtained by using good quality blackpowder topped by an Ox-yoke wool Wonder Wad and an Ox-yoke .010" pre-lubed patch wrapped around our cast round ball. Loads easily, shoots clean and very accurately. And because there is almost no accumulated fouling in the bore, clean-up is a breeze.

If you're thinking that using a thicker patch will tighten up groups you're absolutely right. However that thicker patch also requires more effort in loading. For the ease and speed of a quicker reload while on the track of game, I'll stick with the .010" patch.

It is possible to attain 2000 fps from our .58 Faeton with the 270-grain patched round ball, and with a 100-yard zero, the mid-range trajectory is a mere +3.21 inches. This provides a point blank range of about 125 yards – just hold on center and shoot – no range calculation necessary. Some claim that if you shoot the “modern” sabot/bullet combos that they can shoot pretty flat, too.

While it's all the rage to shoot sabots and smaller bore bullets these days, I haven’t seen that all the extra fuss and gadgets have actually made for better hunters or more game in the freezer. Now don‘t get me wrong - I love to experiment, too. But, when reloading for a follow-up shot becomes so complicated or difficult that it takes your attention from the running and/or wounded game animal and has you futzing around trying to get a sabot started into the muzzle nice and straight (and then hope your bullet was properly seated therein), then straining your milk while trying to push that hard plastic pill down the bore with a too-thin ramrod all while your hands are probably cold, wet, stiff, or all the above, I can’t see any advantage.

For all the trouble involved, they won’t kill game any quicker or any deader than my round ball rifle. And in the event that I missed the mark with that first shot, I'll have my Faeton reloaded and be back on the game's trail before those other guys have reloaded and put away all their sabot-loading gadgets. Call me lazy, but I really appreciate simplicity.

For those who are still awake and curious about my experimentation...

As good as the big round ball is, sometimes I just get a wild hair to experiment. Recent inspirations were spawned from thoughts that a heavier bullet than a round ball might provide an edge on tougher game. The challenge is that a heavier bullet of the same calibre as our round ball is longer than a round ball if it is to have any significant increase in weight. And we already know that Forsyth rifling is too slow for most bullets that are much longer than a round ball. Unless, of course, that bullet is hollow based and has an extreme weight-forward design.

The photo above shows just such a bullet compared to a round ball. Both bullets are of .58 persuasion. The round ball weighs in at just under 270 grains while the wasp-waisted airgun pellet design, or "Forsyth Pellet" as I've dubbed it, tips my little Oehler at 320 grains – a significant increase over the round ball weight.

The Pellet is a two-diameter design wherein the front driving band is full groove diameter and is engraved by the rifling during the seating process. Loading it is a snap as there is little resistance in pushing the bullet down the Forsyth bore with its narrow lands. And we achieve perfect alignment in the bore every time with no effort due to the rear band being the diameter of the bore, thus it rides on the top of the lands during loading. The rear band skirt upsets upon firing to fill the grooves and provides a perfect gas seal.

And what about accuracy? My little .58 Faeton shoots both round ball and the Forsyth Pellet from an offhand pose into nice, neat 5-shot cloverleaf groups at 35 yards. The Pellet really wants to shoot accurately! It's group shot lower than the round ball group, which is to be expected, but it really wants to shoot into tight groups.

And speaking of versatility, did I mention that we can also shoot shot from the Forsyth bore?

No? Okay, maybe another time...

As I said before, Forsyth had it all figured out 150 years ago and it works well for me and mine!

For those open-minded folks who would like to read James Forsyth's wonderful book, The Sporting Rifle and Its Projectiles, the second edition is now in the public domain. If you're not able to locate it, feel free to e-mail me and I'll be happy to send it to you in e-book form.



Anonymous said...

This is a great website. I haven't found much information on underhammers on the internet that is very helpful.

Your explanation about the Forsyth system is interesting, but the problem is that the round ball loses too much energy too quickly to be really effective much beyond 60 or 70 yards.

Also, I believe the sabot bullets shoot more accurately than round balls at longer ranges.

I'd appreciate your comments.


Anonymous said...

Mr. Renner,

I found your post on the Underhammer Society site. I was curious if you have done any underhammer work in the smaller calibers, specifically the .32. I am the proud owner of one of your Zephyr rifles in .62 cal. ( had it for about 12 years I guess) but find this to be somewhat excessive for the local squirrel population. The big game season in my area is relatively short. I like the fine handling quality's of the underhammers and would like to be able to continue using this style rifle in the small game season.

I have used my Zephyr as a shotgun, no.6 shot in front of 95grs. FFG with plastic shotcup and wonderwad. This works good out to about 35 yards but when the leaves fall off the trees (North Carolina) 50 yards becomes more the norm. Hard to sneak up on them in crunchy leaves. A scoped .22 is ideal, but I am looking for something with a little more challenge.

A .32 cal. would be about perfect, being able to use no.1 buckshot at about 40grs and a .010 patch. This would simplify bullet production and a couple pounds would last me a lifetime!

Any thoughts would be appreciated,
S. Boyle
(proud owner of a Zephyr)

As an interesting side note (I am not certain the design was intentional) I have the peephorn rear sight, at 50 yards' the rifle is at zero with the top of the front blade in the center of the peephorn. if you line up the "wings" of the front sight with the centerline of the rear sight it is dead on at 100 yrds. This also aids in keeping the rifle from tilting acting as a spirit level. I have added sight white to the wings of the front sight and the line in the center of the rear sight. This arrangement has proven very effective for quick sight alignment in less than perfect light situations. This is with a load of 150grs. FFG, wonderwad and .010 patch.

Anonymous said...

Mr. Renner,

When you load the Forcythe Pellet....do you patch it or load it bare??

R.J. Renner said...

The Forsyth Pellet shoots very well both with and without lube. If I planned to spend the afternoon shooting them I would roll the bullet in a bit of lube to cover the driving bands.

However,if I was afield and hunting, where I would be taking one or two shots during the hunt, I would lube the first one loaded and carry a spare or two unlubed. The lube tends to pick up stuff that I don't want in my rifle bore while its in your pocket, possibles bag, or where ever you might carry it.

But then, that's me.

Experiment and see what your rifle likes best and do that.

BTW, I do recommend that you load an Ox Yoke pre-lubed Wonder Wad over the powder before loading the Forsyth Pellet.

I haven't tried their thicker, pre-lubed shotgun wads, but that might be another experiment. Probably would work well with heavier powder charges that might deform the Pellet's skirt.

Good luck!

RJ Renner

R.J. Renner said...

Hey, I just remembered your question was about a patch...

(Sorry about that. I'm in old age training.)

No patch is needed, just the Wonder Wad over the powder.


Unknown said...

Mr. Renner,
I was reading your article on Forsyth rifling and had a question about your pellets. I've heard about the greenhill formula for calculating barrel twist. When you where testing/designing your pellet did you use this formula to determine optimum twist? If so, for length did you look at the area that was engaging the rifling or did you look at the entire length?


Roger Renner said...

Ah yes, the Greenhill Formula...

No, I didn't consider the Greenhill Formula because that would be too limiting. It's purpose it to determine the optimum twist for a specific length of bullet fired within a narrow spectrum of velocity which is determined by the powder charge of the case and the bullet weight.

The barrel length also plays a part in this equation due to the fact that (generally) the longer the barrel, the greater the velocity imparted to the bullet.

If that sounds complicated it's only because it is. And I like to adhere to the KISS principle.

The point of the Forsyth Pellet is to shoot straight at almost any velocity. In order to accomplish this, it must first fly straight with no spin. This is accomplished by an extreme weight-forward design. The hollow base extends all the way to its wasp waist which shifts the weight forward of the center of form on its longitudinal axis, much like a badminton shuttlecock.

The design allows the Forsyth Pellet to shoot straight even from a smooth-bored gun. The slight rotation provided by my Forsyth rifling just adds even more stability to an already stable projectile.

Technically, the Greenhill Formula must consider the full length of the projectile and not just the area that engages the rifling.

Hope that's helpful.


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About Me

Roger Renner

Hi. I've been a student, admirer, and designer/builder of underhammer guns for over 30 years. In that span I've built over 200 semi-custom underhammers exploring the possibilities from the ordinary to the exotic. In 1996 I founded Pacific Rifle Company to explore the market's interest in a high-quality underhammer rifle. Thankfully, that interest was, and still is, there. I sold PRC in 2006 but continue to craft high-end underhammers as I am truly afflicted with underhammeritis - which can be contagious!