Round groove vs square cut rifling?

[zimmerstutzen]

If you can, read about the different rifling configurations before buying . A narrow round groove rifling is more for ease of loading and cleaning.

Wide radius cut grooves are well proven for accuracy
By. Barrel makers like Alex Henry, harry pope and emil pachmayr. Their guns ruled the world competitions for decades.

 

[Col. Batguano]

Is there more labor involved in round bottom rifling? They're certainly more expensive.

 

[mhb]

I'm not sure I understand your explanation of varying depth of rifling grooves due to lack of support of the cutter in the cutter box.
I am a barrel maker, and make my own rifling heads, so have a good understanding of the design, geometry, fit and function of the parts.
The depth of cut is controlled by the contact between the cutter and the screw-driven wedge which supports and raises it in its seat in the cutter box/rifling head.
Hook cutters ride up the wedge to the full height permitted by the adjustment of the wedge and the hook's contact with the rear of the cutter box immediately on contact with the barrel on the cutting stroke, and are held there by the forces exerted on it in making the cut and the spring which pushes it rearward through the forward plunger which supports the 'toe' of the cutter. Any movement of the cutter in its box aside from this will be sideways, due to a less-than ideal fit in the cutter box, and can result in a 'tipped' cutter, which will make one side of the groove deeper than the other. Hook cutter rifling heads without the extra mechanism designed to retract the wedge, lowering the cutter for the return stroke still permit the cutter to ride down the wedge on the return stroke, but the forward spring and wedge will return it to full height for the next cutting pass.
Scrape cutters are usually supported by the wedge directly under the cutting edge, and, again, cannot ride down in the box below the height at which the wedge supports it for the cut.

mhb - Mike

 

[M. De Land]

It's just that when the head is not far enough into the bore to support the tooth or hook on both ends of the cutter window, (fore and aft) the head can tilt on a tangent away from the cutter tooth pressure the amount of the head clearance in the bore until it has been drawn far enough in to support behind the tooth pressure as well, same thing happens when withdrawn.
At least this is what I learned in a video from the man I bought my rifling machine plans from.
I have yet to rifle my first barrel but am tooling up for it and reading all I can find from various barrel makers.
My current reference author is Cliff LaBounty who is supposed to know of what he speaks.
I also am configuring this machine to set up for deep hole boring blanks as well as re-boring and re-rifling shot out barrels. Mike D.

 

[mhb]

M.D.:
I have never seen any evidence of this condition in rifling around a thousand barrels.
The only point at which the cutter contacts the bore surface is the tip of the hook or scrape cutter. Because of the geometry of the hook, the cutting face is some distance ahead of the rear of the opening in the cutter box, and it is supported directly by the wedge and its contact with the bottom of the slot in the box. The typical scrape cutter has its working edge even further forward, nearly in the center of the cutter slot, and it, too, is supported by the wedge and the bottom of the cutter box.
As the working clearance between the rifling head body and the bore is small (no more than .002", normally, though a somewhat smaller rifling head can be used in a slightly larger bore), and the same forces which work to seat the cutter in its slot also press the rifling head body into contact with the opposite side of the bore, it is difficult to see how the condition you describe might arise.
Also, since the rifling head body is fully hardened against wear (ca. 62 Rc), it won't stand being flexed at all, and any significant bending shock would snap it like uncooked spaghetti.
I've read Mr. LaBounty's book, which is excellent, but don't recall any mention of this syndrome there.
Ultimately, I don't think you'll find there is any need to be concerned about it, though I'll be interested to hear about your adventures in barrel making - it's fascinating work, and there's always something new to learn.

mhb - Mike

 

[M. De Land]

Thanks for the come back and have been looking for some one to chat with about barrel making.
I've been wanting to get going on this project for about ten years and have slowly been acquiring the material to make it.
The plans came from a hobbyest barrel maker by the name of Bill Webb via Guy Latard of Canada along with two Videos of him actually going through all the steps of deep hole boring, reaming and rifling. He uses hook cutters and goes into some of the pit falls he had to learn around from bad information he had received from others.
I hope to modify the plan to accommodate gain twist to experiment with.
Have no plans for any kind of production work but rather just keeping it on a hobby bases and to provide for my own needs as well as some close friends.
I will be making my own rifling heads and cutters as well of A-2 and HSS lathe bits but will probably buy the barrel drills with the oil tubes soldered on from Danjon if they are still in business.
Big dreams but it won't mean a thing unless I can learn to bore straight holes which I'm told is the hard part. Mike D.

 

[mhb]

M.D.
Glad to share what I know.
You are wise to use air-hardening tool steel for the rifling heads - warpage is always a potential problem, and the air-hardening steel is, perhaps, a bit less prone to warpage in hardening.
I rough-machine the head, to include boringand reaming the hole through the body for the wedges, springs, etc., milling-out the cutter box a bit undersize, threading the tail end for the wedge-driving screw
(left hand thread, for the P&W machine), drilling the opposite end for the rifling rod, etc., leaving enough stock for final finishing by grinding the body between centers and working-out the cutter box to fit the hook, which is ground from HS steel. All the wedges and screws are made from oil-hardening tool steel, and left full hard for wear resistance, as is the cutter box.
It is a good idea to fit a block in the cutter box and wrap the head in stainless steel foil for hardening, to help control warpage and prevent oxidation.
The cutter slot is finished by hand with small diamond burrs and very fine slip stones, to achieve good fit and smooth finish and function.
The rifling head is mounted on aircraft tubing of appropriate diameters, and attached to the rifling rod with JB epoxy - and I've never had one pull off. When aircraft tubing is unavailable, I have used automotive brake tubing, which is somewhat less stiff, but works O.K..
Gun drills are bought mounted, and you will need to make a proper jig for sharpening them, since the geometry is complex.
Reamers are purchased, and also mounted on aircraft tubing - they must be kept straight, if they are to work properly. Bores are rough and finish reamed.
I sharpen the rifling hook on the top surface only, grinding only sufficiently to restore the sharp edge - you will also have to remove excess stock behind the cutting edge, if it is high enough to interfere with cutting. Metal buildup on the hook face should be carefully stoned off, maintaining the squareness of the cutter face and smooth finish. Cutter sharpening is done by grinding in a jig which holds the rifling head in v-blocks, which permit rotating the cutter on the correct radius to preserve the groove shape and depth. In our shop, both drill and cutter sharpening are done in a modified valve grinding machine, with micrometer advance to the wheels.
Mostly, you will develop your own ways of doing things, as you develop experience
In deep hole drilling, the most important factors are drilling speed, feed, and lubrication. The drill must be started centrally through a bushing, and the bar must be as straight as possible, if you want the hole to run straight. I believe it is useful to grind or turn a central rest surface in the center of the bar, and support the bar there, since this helps control deflection of the blank rotating at ca. 3,000 RPM. Our machine is set up to advance the drill .0003" per revolution, and lubricant pressure can run as high as 1200PSI, depending on the diameter of the drill: the absolute need is to flush the chips and prevent them from packing-up in the bore, which can break the drill, and will cause considerable runout over the length of the blank. When all works properly, a 30" blank will normally show total indicated runout of .010" or less, from breech to muzzle.
I find it best to drill the blank at full diameter, rough turn it to within ca. .030" externally, ream it to final diameter and finish, rifle it, and then finish the external dimensions and contours by turning and grinding between centers.
All blanks are stress relieved before any machining is done, and external machining/grinding is done under coolant flood, so little stress is induced likely to cause warpage, and barrels remain straight.
Good Luck!
mhb - Mike

 

[M. De Land]

Good stuff Mike! Read through the build instructions tonight again and watched the first video covering just about ever subject you touched on in your post.
I will give the hook five degrees positive rake and about three or four degrees top/back angle clearance. Webb suggested 1.5-2 degress side angle.
One thing I need to work out is the angle of cutter face to helix angle. Labounty says there should be a few degrees increase to achieve some shear for a smoother cut rather than 90 degrees to the helix angle. What have you found to work best?
I did just pick up some 320 and 600 grit diamond paste to make some radius tools for shaping the top of the hook and an undercut radius at the bottom for ease of sharpening.
Boy have I got a lot of work to do but it should be fun putting this thing together.
Already have the gear pump, 3/4 horse drive motor for it and a 3 horse motor for the spindle. The gear motor that drives the carriage for drilling and reaming is a fifth horse adjustable speed. I think the 3 horse should have plenty of power for the big holes.
This machine has a whip guide as well for the oil tubes. Mike D.

 

[mhb]

M.D.:
The various working angles and clearances on the hook are not particularly critical.

For the sake of convenience, and because all possible pitches are cut for special order barrels, I make the hook with the face square across the cutter box - in this way, I can cut right or left-hand grooves of any pitch within the range of the machine. Having calculated that a side clearance angle of 10 degrees would serve for any pitch between straight and about 5" (which is the fastest pitch the P&W will produce without modification), I place that clearance angle on both sides of the hook - if you plan to cut only right or left-hand pitches, you need not provide much clearance on the following side of the hook. Also, you need to make the working end of the hook of proper length to keep the back end of it, which locates the hook against the rear of the slot and rides-up the angle at the end of the slot sufficiently wide to provide good contact and control of the hook at that point.

Another thing to remember is that, with any given hook, the width of the groove decreases as the pitch is increased, because of the change of aspect angle on the face of the hook. If you make a hook for a specific pitch and width, and cut only that one, there will be no such effect, but if you make a hook such as I described, to produce a groove 3 times the width of the lands, you will still maintain a good groove-land ratio throughout the probable range of pitches to be rifled. And, of course, you need to make the hook width of proper dimensions for the number of grooves to be cut - I normally make 6-groove barrels, but have used the same hooks to make 4-groove ones.

The rake angle of 5 degrees is satisfactory, but you need to remember that this actually changes as the cutter rises higher out of the box with increased cutting depth and as the hook is shortened by sharpening - you need to verify that positive rake is present when the cutter is installed in its slot in the rifling head at the lowest it will go the box while still protruding above the box high enough to cut. It needs to be capable of being set at or below the surface of the cutter box, so that you can set the rifling rod up in the rifling machine and allow it to pass through the barrel before beginning to raise the hook into contact with the bore.
Small caliber rifling heads are more difficult to make, because the internal parts must be proportional to the physical dimensions of the rifling head: wedges, screws, springs and the cutter itself are all smaller and more delicate. The slot must be of proper dimensions so that the walls of the box are not excessively thin, and, due to the shorter overall height of the hook, it cannot be re-sharpened as many times as one for a larger caliber rifling head. I've made rifling heads from .22 to .54, but don't intend to attempt anything smaller than .22 - that's what buttons and hammer-forging are for!

I don't know how your rifling machine will be driven, but cutting speed is a factor to be considered. I operate the P&W at about 5 cutting strokes per minute, which results in a cutting speed of ca. 30 SFM, which is much slower than the machine can be operated for greatest production, but I'm trying to make the best possible barrels, not the greatest number in the shortest time. Also, the increase of cutter height for each successive set of passes can be varied, but I raise the hook only about .0001" per cycle. This means it takes a while to completely rifle a barrel, but gives a better finish and dimensional control. You will learn by experience how long it takes to rifle a barrel, but I recommend that you proceed slowly at first, and check progress frequently. Lubrication is essential, and it is best to feed cutting oil through the rifling rod, and arrange additional floods at both ends of the cutting stroke to help clear chips from the cutter box as it passes out of the bore at breech and muzzle. It is important that the cutter box slot and the hook clear the blank at both ends, but the rifling head should not be allowed to pass completely out of the bore, of course.

Much of this you will discover for yourself, the hard way, but it's probably worthwhile to tell you about some of it in advance.

Hope I'm not telling more than you want to know.

mhb - Mike

 

[M. De Land]

Nope, I'm eating it up and have read up on all that you have mentioned. Just last week when going through Labouty's book I learned of what you said about the sharper the pitch angle the narrower the groove. Had never even heard of that before.
This machine is hand powered for the rifling operation and gives very good feel of the cutting stroke.
My cats head spindle is 30 inches long so should be able to accommodate fairly long barrels.
I do need to figure out maximum length of traverse I want which will directly effect length of the carriage rods I will need.I will be using two 1.250 ground rod stock with oilite lite bronze bushings for the carriage and whip guide.
I'll set up the index head for 3,4,5,6,8 grooving.
Still need to design a better chip box than these plans show with a larger discharge barrel.
Plans show a pretty effective weir and filter arraignment for filtering the cutting fluid.
The gear pump I have will generate a 1000 psi at 4 gallon per minute so I think it will have enough capacity for the job.
I think this size machine will be just about right for my hobby requirements and still capable of producing match grade barrels if the operator can get his stuff together. Mike D

 

[hanshi]

Wow! This is all much too technical for my old brain. All I can say is my vote is round bottom for hunting and general purpose and square groove for a dedicated target rifle.

 

[mhb]

M.D.:
Sounds like you're on the right track - it can be (certainly will be!) frustrating, but with patience and a firm hold on what you want to achieve, you can make fine barrels with simple gear.
FWIW: another feature of gain-twist rifling which is seldom or never discussed (and is one more reason why you can't lap such a barrel in the conventional way) is that the groove width changes with the change in pitch - widest at the breech and narrowest at the muzzle (and, of course, just the reverse for the land width), for the same reason (change in aspect on the cutter face) discussed earlier.
I don't believe (personal opinion) that gain twist is capable of better accuracy than a conventionally rifled barrel of proper pitch for the bullet and velocity, if made with equal care. Harry Pope was (deservedly!)famous for his gain twist cast bullet breech/ML rifles, but for jacketed bullets and high velocities, he also made fixed-pitch barrels, which were just as accurate, having been made with equal care and workmanship.
Rather than continuing my hijacking of this thread, I'll await any specific questions you may have, which you may post directly or via PM or email.

mhb - Mike

 

[FishDFly]

mhb and M.D.,

Nice education for us here, thank you. I have no idea of what you speak, but thanks.

When both of you have time, could you please devote some time to barrel coning?

I have a feeling it is important element of rifling since the ball first sees the cone before the rifling and the last thing when leaving the rifling.

Thanks

rde

 

[M. De Land]

I was thinking perhaps some confusion could be averted if we used the terms round groove rifling ,radius groove rifling and flat bottom rifling.
Just a suggestion.
Mike, I like the practicality of making the face of the cutter square with the box. Makes a great deal of horse sense for sharpening and use in right or left hand twist.
So appreciative of your willingness to help me get going as this will save me huge amounts of time and frustration. Makes the learning curve much faster and the road less bumpy.
The five degree rake I believe was chosen in these drawings as it allows for some positive rake at all possible hook heights.
Webb,the guy who's plans I'm using, says he gets well under .010 run out normally. His best was .0006 in 27 inches.
I'll be making mostly larger holes .35 cal through .45 cal initially if all goes according to plan. Mike D.

 

[M. De Land]

Richard, you probably know more about muzzle coning than I do as I have never cut it into any barrel I've crowned although I don't see it really as a mysterious or particularly difficult machining operation to do. I doubt I would taper bore it on my lathe but rather make a piloted reamer for the barrel in question and ream it by hand, set up in the lathe using a floating chamber reamer attachment, in the tail stock. I also think it would need to be radially lapped with a brass lap and some lapping compound ,just as forcing cones are in pistol barrels.
I have read some on it in a distant Muzzle Blast Magazine some years back and apparently it was rather common in golden age of muzzle loading. Some of them were coned 2-3 inches deep from what I remember of the article and still demonstrated good accuracy supposedly.
Can't imagine a match rifle so configured but it probably has been tried. Mike D.

 

[mhb]

Richard:
I have no strong feeling about(or much experience with)coned ML barrels.
I have only one longrifle with a coned muzzle, and it shoots as well as my rifles without the cone. As I use a short starter for loading my rifles, I don't feel I gain any great benefit from the coning.
In a general sense, as a barrel maker, I would state only that the accuracy of the coned barrel depends on the care that goes into the alteration: it should preferably be done with a piloted reamer, and, with great care to be certain that the cone is smooth, properly centered and symmetrical.
The muzzle itself should, as always, be square with the bore and crowned properly (I use a slight radius for the muzzle crown on my ML barrels).
Further deponent sayeth not.

mhb - Mike

 

[FishDFly]

Richard, you probably know more about muzzle coning than I do as I have never cut it into any barrel I've crowned although I don't see it really as a mysterious or particularly difficult machining operation to do.
I have read some on it in a distant Muzzle Blast Magazine some years back and apparently it was rather common in golden age of muzzle loading. Some of them were coned 2-3 inches deep from what I remember of the article and still demonstrated good accuracy supposedly.
Can't imagine a match rifle so configured but it probably has been tried. Mike D.

M.D.,

Here we go, possibles or hunting bags, coning or crowning, shotguns or shotties, Remingtons or Remmies? Terminology/slang sure gets me confused.

I do not know the difference between coning and crowning at all, I can tell the difference between a bull and cow though, just lift up the tail and count the holes.

What is coning and what is crowning? I assumed the terms were interchangeable

Folks say if a rifle is properly done at the muzzle, a round ball can be seated with thumb pressure. A properly done muzzle will not cut patches when seating balls with or without a short starter.

Which is the definition of each and what are the advantages to each?

Thanks

 

[M. De Land]

Crowning is machining the muzzle of any barrel square with the bore using any a number of different profiles.It deals only with the end of the barrel.
Coning is cutting a taper down the bore from the muzzle to facilitate loading without a short starter.
Most of the ones I've seen were .500 to .750 beginning to end of taper. The idea is to be able to thumb the patched ball far enough into the bore to only need the ram rod to finish the job of ball seating on the charge. Usually this is a hunters set up. Mike D.

 

[FishDFly]

Thank you, I have a feeling you educated a lot of folks along with me on what the proper terms actually mean, I appreciate it

 

[M. De Land]

What are you using for barrel steel and where are you getting it? We have several steel brokers here in town but I have not approached them yet about getting 1137 or 4140 CM stress relieved certified steel rounds 1.125 in diameter. MD