Double Barrel Divergence

[bamaranger]

I touched on this in my post regards the CZ o/U dedicated turkey gun, but thought the subject might deserve a separate thread.

How commonly is this quirk encountered? Has anyone discovered it to the degree that the gun has one barrel that is "off" enough effect good shooting? Is one system (O/U v. SxS) more prone to it than the other? Some type of industry standard, etc?

[Jim Watson]

Go through back numbers of American Rifleman for Dope Bag articles on doubles.
They show the pattern and the point of aim.

[44 AMP]

Double barrels, either type, are (or should be) regulated at the factory, so the patterns overlap at a given distance (typically 40yds).

However, best performance is only possible when using the same ammo that was used when the gun was regulated.

Most of the time, particularly with shotgun patterns, you will be using different ammunition (almost a certainty) it usually doesn't matter all that much, and the divergence isn't too much.

But, othertimes, it does.

[FITASC]

One reason many of us try to discourage the purchase of very inexpensive double guns is exactly what you are experiencing. Regulating barrels takes labor and that adds costs; one reason why the better double guns cost what they do. If it truly very bad, the only real solution is to have a gunsmith remove the ribs and relay the barrel/ribs while regulating them. One reason they get that way is the braising of the barrels during joining; the high heat can warp the barrels and if not corrected, the results can be poor regulation.

[bladesmith 1]

I could believe double barrel rifles are regulated, but not so much shotguns. Let's see, we have a 30" pattern and the barrels are what, a inch or two apart. So what if one barrel prints a pattern a inch and a half different than the other barrel. I'd have to believe any manufacture has formulas that tell them how far apart to make the barrels so they'll print the same. If you have a gun that prints too much apart to suit you, sell it. The cost for a SxS to take the ribs off and put back on, then reblue the gun is in the realm of 1000$. And that's not counting having to pattern it while it's apart. Maybe 1500 to 2000 total. Not too many mass produced guns worth that kind of money. If you're buying high end guns then I'm sure the seller would refund or give you a different gun if there was a problem.

[44 AMP]

Double rifles are regulated so that each barrel's bullet strikes within "x" amount of distance from the point of aim at a given range.

With double shotguns, the principle still holds, but it is the center of the pattern that matters. And, where that center is, relative to the bead (your sight) at a given range.

Call it regulated, or call it aligned, when the sight (blade or bead) is offset from barrel centerline, the barrels need to be aligned so that the bullet or center of the pattern strikes as close to where the sight indicates as practical. side to side AND vertical.

getting two shotgun barrels to shoot to the same place is easier (needing less work) to achieve than with rifle barrels, due to patterns vs single bullets, but it still needs to be done.

[stinkeypete]

One of the saving graces for double barrel shotguns is the random nature of the shotgun.

There is a random variation from shouldering, shot to shot.
There is a big variation in shot pattern, shot to shot.

In checking shot pattern, a minimum of 3 shots is needed to determine the pattern and poa. I bet you could not detect 5” deviation at 40 yards without serious range time and study. “Missing” by 5” is a downed bird.

But for a double rifle or Turkey gun.. that 5” matters.

[jmr40]

we have a 30" pattern and the barrels are what, a inch or two apart. So what if one barrel prints a pattern a inch and a half different than the other barrel.

If the barrels were parallel that would be the case. But they are not. At a certain range the barrels patterns should converge. At longer ranges the right barrel will be hitting left, and the left barrel to the right.

This could cause problems, especially on crossing shots at longer ranges. This is part of the reason you just don't see SXS shotguns used by serious clay shooters.

But for most upland hunters where shots tend to be close, and mostly straight away a SXS can be an advantage.

[bladesmith 1]

`No it's not the reason you don't see SxSs used by more serious clay shooters. Just about everybody today has been brought up shooting a single barrel gun - or O/U. The SxS sight picture looks entirely different and many shooters can't get use to it. It's just easier to look down one barrel than two. Why isn't there a problem with O/Us converging ? What about up and down conversion ? Shotguns, whether SxSs or O/Us both converge about 30 to 40 yards out. If anyone thinks for a minute that manufactures pay someone to test barrels over and over and then solder them together they're mistaken. It would be cost prohibitive. They use formulas to tell them how much to bring the barrels together. Hunters that use two triggers on their SxS can chose quickly what choke to use. A friend at the club has a O/U that shoots one barrel way off. Just some mistake when putting them together.

[44 AMP]

Spent a couple years early my teens with my Grandfather's Ithaca SxS. Later (at 16) got a Winchester Model 12.

If you're looking down a SxS and see two barrels, you're doing it wrong. You sight down the center rib, and focus on bead (and its relation to your target) not the barrels.

I can see where someone with little experience and only with a single barrel sight plane (which also includes O/U) might need a little time to adapt, but it shouldn't take much.

Point is, you look down the barrel(s) or rib, and sight with the bead.

[Jim Watson]

I have long read about doubles - especially double express rifles - being regulated to converge both barrels to the same POI at some arbitrary range. Beyond which, the shots "cross" and diverge. So if your barrels are an inch apart and they are set to converge at 100 yards, then they will only shoot an inch apart at 200 yards. Not a liability at iron sight hunting ranges.

But Ray Ordorica looked into that. He found that his double, I forget the make, shot parallel. His individual barrel groups remained that inch apart as far as he could get good hits. Jack Lott saw something close to that with an O/U that was good at scoped hunting rifle ranges.

This does not mean the barrels were installed parallel, they still had to be regulated because the barrels are offset from the line of sight and from the center of support against your shoulder and in-barrel recoil moves the gun differently. W.W. Greener had a customer who demanded parallel barrels and was disagreeably surprised by the poor shooting.

[stinkeypete]

Let’s talk about this idea of “parallel.”

To keep the numbers simple, let’s say we are looking at patterns at 30 yards from barrels that are 30 inches long.

30 yards x 3 yards/foot x 12 inch/foot is 1080 inches measured from the shooter

Let’s say we are looking for a 2” divergence to “focus” the patterns.

2/1080 = x/30
X = 0.050 inches
50 thousandths of an inch tilt from back to front! That’s about the thickness of a dime.

This assumes that thin wall steel tubing, 30 inches long, is perfectly straight. Watching any YouTube video of how they make double barrel shotguns, you’ll see highly skilled workers eyeball down the tubes, then whack and bend them against a padded post.

Then they weld tho of these together.

The thickness of the first spacer and last spacer can be easily controlled. It’s the straightness of the barrels that adds additional variables. Then the concentricity of the screw in chokes.

One could say “therefore, if I laser bore sight, I will always be perfectly sighted in!”

Well… close. Remember… if we are looking for 60 yards, 2 inch variance becomes .0025 inches. That’s some close tolerance manufacturing.

[Scorch]

Double barrels, either type, are (or should be) regulated at the factory,

The days of the gunmaker shooting a double rifle, desoldering the barrel, resoldering, rechecking POI are long gone. Nowadays they regulate barrels using laser bore sighters on expensive doubles, on cheap ones they don't (probably never did). It's too time consuming, and companies want to make money. If you're charging $15,000 per rifle you may have the time to do that, but not for mass-produced guns.

I have long read about doubles - especially double express rifles - being regulated to converge both barrels to the same POI at some arbitrary range.

Yes, typically 50 or 75 yards, but it depended on the distance it was intended to be used at. And POI was seldom the same, it was within their range of tolerances. A friend of mine had a H&H double rifle in .500/.450 #2, at 75 yds it printed the bullets within about 4", plenty close enough for rhino or hippo or buffalo.

Double rifles were the early repeaters, super reliable and sturdy enough to not be damaged by conditions in the field. After the turn of the 19th to 20th Century, bolt actions became more common due to ruggedness and lower price, beside the fact that they are lighter and hold more rounds that can be quickly brought to bear.

Then they weld tho of these together.

They don't weld the barrels together, that would damage the barrels. In the past, barrels were soft soldered together. But since the 1950s or so, barrels are brazed or silver soldered together (because soft solder won't stand up to caustic bluing salts). Nowadays, double gun barrels are brazed together in a fixture and the convergence is controlled with the amount of taper of the barrels.

[bladesmith 1]

Thank you Scorch. You said it so much better than me.

[44 AMP]

But Ray Ordorica looked into that. He found that his double, I forget the make, shot parallel. His individual barrel groups remained that inch apart as far as he could get good hits.

I have long read about doubles - especially double express rifles - being regulated to converge both barrels to the same POI at some arbitrary range.

I've read that kind of thing, too. Its's not quite correct.

Close POI, relative to the POA, but they aren't trying to put both shots in one hole ON the point of aim.

Double rifles are regulated so that each barrel's bullet strikes within "x" amount of distance from the point of aim at a given range.

Its a small detail and is often overlooked, or not mentioned. And most readers will assume the intent is to have both shots hit the exact same point.

Reality is, a bit different. There is no, and I doubt ever was any serious attempt to get both barrels to his exactly the same point. The point always was to get both barrels to shoot the same, relative to the point of aim, and close enough to it, and each other to do the job the gun is built to do.

Meaning, (for example) at your chosen distance, if the right barrel hits 2" off from the point of aim, the left barrel should do the same (or less). It can, and normally is in a different direction from the other barrel's hit, but it needs to be within the desired distance, this gives you a "group size".

Both barrels need to be about the same in their divergence from the point of aim. That's what regulating them does. Rt barrel 2" off, left barrel 2" off, ok. Rt barrel 2", left barrel 8" off, not good enough.
Remember what the primary objective is. The rifle must group (both barrel) well enough, absolute perfection is not needed. And not sought, as it is a waste of time, effort, and money.

When the required minimum is "minute of charging water buffalo" you're going to build guns that do that, or a bit better.

Whether it is done the old way, with soldering, test firing, adjustment, test firing, etc or done with laser pointers or done by just aligning the barrels in a fixture during assembly, it is still done. It is the end result that matters most.

[Jim Watson]

IMG_2883.JPG

Here is a "diagram" of a double express group, ca 1910.
Note that it is 8 bore smooth.

[dahermit]

I had an inexpensive 20 gauge (do not remember the brand name) back in the seventies. I could never hit anything with the second barrel. I finally sold it and got a pump, although I have never been a big fan of slide actions (rattle, noisy). A few years later I got a Browning Side by Side and was very happy with the barrel regulation... no problem whatsoever.

[44 AMP]

Browning has a long history and reputation for quality guns at quality gun prices.

[Unclenick]

The problem with parallel barrels is you have to pretend the shooter is a machine rest for the error to remain small. In practice, for non-rigid (i.e., human) support, the higher barrel in a typical O/U shotgun will produce more muzzle-raising torque around a horizontal axis moment of inertia, so it will tend to introduce vertical POI separation in flight. With an S-by-S, the left barrel will produce leftward torque, and the right barrel will produce rightward torque around a vertical axis moment of inertia, so barrel movement will tend to diverge the barrel's respective POIs horizontally. Understanding this and understanding that different shooters have different mass, strength, and rigidity, you can see any mass-manufactured double has to represent some sort of compromise in barrel regulation that is most universally useful to customers. That is one of several reasons custom bun makers still have work from those who can afford them.

This article may be of interest.