Riddle me this……?

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General Skanky

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Jul 22, 2024
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I was going to Google this but decided to see what you guys think first.

How do two barrels work vrs one?

An O/U surely will have a different POI as they are approx an inch or two apart? So therefore different. Physics then dictates that the lower barrel will shoot lower than the upper barrel.

A single barrel semi for example will always shoot in the same place.

So why do we not all use single barrel guns?

I see single barrel guns from Browning for example that give you the option to switch to a double. But why?

Genuine question. Please be kind.

For ref I own a 694 and 2 x A400 guns.I prefer and shoot better with the semis. 💁‍♂️ That is the only time I will be blasphemous .
 
The barrels will be regulated to hit the same spot at a specific distance. I would expect a skeet gun its 21 yards and a sporter about 30 but a gunsmith would know more. With the pattern and slight choke variations its negligible at the clay.

The single barrel guns are for single shot trap - big in America I think ?? Set of O/U barrels for general use.

And I suppose if we were not so stuck with over & unders (or down & outs as the SXS users call them) there is a good argument for a semi being the best (technical) option - never seen anyone make a competition semi with serious intent however.
 
Aren't the barrels of an O/U ever so slightly angled towards each other on the vertical plane? The aim being that the POIs converge at a fixed point. I would assume that it's around 30m or so.

If I use a bore laser on my 694 the bottom barrel POI is slightly above the bead at around 40m with the top barrel POI being obscured by the bead. Exact POIs being a few inches apart at that distance.

An average pattern at 40m is going to be 30 inches plus in diameter anyway so a few inches is neither here nor there.
 
I'm not an expert by any means, however this is my understanding.

Double barrels are regulated during manufacture so that they converge at a set distance. I don't know what that distance is or if it varies for different types of gun (e.g further for trap or closer for skeet). I think this combined with the fact that the gun is firing a column of shot and not a single projectile means that generally speaking unless it's completely out of specification, it doesn't really make a difference in reality.
Again just my humble opinion and I am happy to be corrected.

EDIT;
just seen other members have posted similar whilst I was typing my reply above.
 
Last edited:
I did suspect an ever such slight optimum cross over point.

However there is the. The immediate question of how much of a deviation, if at all significant, is there before and after that sweet spot?

Of course there are multiple world champions with O/U so this really is a question about trigonometry I guess……
 
General Skanky said:
I did suspect an ever such slight optimum cross over point.

However there is the. The immediate question of how much of a deviation, if at all significant, is there before and after that sweet spot?

Of course there are multiple world champions with O/U so this really is a question about trigonometry I guess……
Click to expand...
So, Intrigued by your question I've had the gun and bore sighting laser out as it was just getting dark enough to see the laser and still see the trees in the background. I have some trees at approximately 20m, 40m and 100m away from the standing position and a garage wall at 5m. Gun used was a 694 sporter.

At 5m the POI from both top and bottom barrels are well below the bead near enough in line with the center of each barrel as you would expect.

At 20m and 40m the POI from both barrels is basically at the bead with the bottom barrel slightly above and top barrel slightly below the bead. I would guess the convergence point is somewhere around 30m.

At 100m the POI for both barrels is slightly above the bead at approx 0.5m at the 100m mark. Likely the result of the difference in angle of the eye above the rib of the gun.

Good question nonetheless and I'm all to eager to waste an hour looking into it. The wife is away and I have nothing better to do.
 
There are quite a few stories - and I think one on here involving a 694 (?) - where the regulation has been off by some degree.

The problem with laser bore guides is they are not that well made and the bores are not the crucial part - it's the barrels. I have not played with them much so you might have a good one etc.

I know of one - used to great effect for 20 years - which was three feet off left to right. You can imagine the outcome - the owner wished he had never checked it !!! I am not meaning (for one moment) to draw an end to what might be a very interesting discussion, but I expect someone will soon say - pattern the gun and be done with it !!!.
 
I can recall the guys at Longthorne conducting a similar experiment using several different makes of guns, from the bargain basement, right through to very expensive over and unders. The results were quite enlightening, apparently. Obviously this was an experiment to show how accurate Longthorne's unique barrel making system is, rather than exposing the inaccuracies of other makers. But it did seem to highlight an issue.
My PERSONAL view is, and has always been, why do I need to worry ? The same applies to patterning my guns.......I DON'T. If, when shooting, I observe that the target 'breaks' are chippy, and not as I would expect, I avoid that brand of cartridge. When I find one that works, then I stick with it.
I do believe that some shooters can 'overthink' things, worrying about a problem that does NOT really exist.
LIFE IS TOO SHORT !
 

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Even if they are perfectly parallel, without any convergence built in at all, the less than an inch difference is going to have bugger all effect on hitting a clay when you take the size of the cloud of pellets into account.
 
Exactly what Bebo says. You are shooting a pattern of pellets at a moving clay target, whilst moving the gun. The question of OU barrel divergence is wholly academic, and moot for the actualities of shooting clay. Ymmv, but your time may be better spent on practicing, even if dry mounting at home.
 
On the one occasion I had the misfortune to be looking down the wrong end of a 12 bore, I don't recall thinking "Bloomin eck....those barrels don't converge" !!
I think it went more "Oh manure ! Pass me my brown trousers " 🙄
 
The laser experiments forget that the shot drops off over distance. At 100m it's travelled in an arc and is well below the laser point.
If you start with a barrel angled further up,then the drop is lessened proportionally.
Of course the reality is that eye position makes more difference than barrel angle especially as you are looking along a bead while looking for a moving target.
 
A laser will give you only a reference point +/- and L/R in relation to the point of aim you have taken down the rib . The point of impact can’t be established until you have shot at that point of aim from various distances. Depending on the gun it will have been set at the factory to place the pattern in a specific manner for example 50/50 or 60/40 even 70/30 above the nominal point of aim at a specific distance . Whether all that matters when you are shooting the gun is a moot point .
 
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