Can this be correct?

[Robden]

I know they are only cheap and not precision instruments. I put two identical 12g cartridge bore lasers into my o/u shotgun. Once in the barrels they didn't move. Turning each one by hand they looked to be concentric.

At 10 feet the two laser dots were just over 2cm apart. At 30 feet they were 7cm apart. So it looks like, the further the distance the larger the gap. Shouldn't the barrels converge at some point?

Thanks for any help/advice.

[Rob85]

Are you sure they haven't actually crossed over each other at 30ft? Being only 2 cm apart at 10ft and converging, then triple the distance would mean it's not impossible that they may have crossed.

[scarecrow243]

barrels are roughly set at 40 yards to hit the same spot  so the bore laser dots should be very close at 40 yards

[Robden]

15 minutes ago, scarecrow243 said:

barrels are roughly set at 40 yards to hit the same spot  so the bore laser dots should be very close at 40 yards

That's what I was thinking but if I keep walking backwards from the target, to about 40 yards/120 feet the laser dots could be in different counties.

[Ultrastu]

What's the brand of shot gun ?

I guess to my mind the dots should be the distance between the centre of the 2 bores at the muzzle ie 1.5 cm or so and remain exactly that out to any distance .give of take a cm or so  .ie they shoot parallel  to each other .ideally  with 1 dot  above the other .

[Robden]

Zoli new last October. I phoned them and am waiting for them to call me back.

Of cause this is presuming that the cartridge chambers are true to the barrels.

[Smokersmith]

I'd be more concerned with where the patterns print.

The chambers only tell you about chamber alignment ... it's the barrels that throw the patterns.

[Robden]

29 minutes ago, Smokersmith said:

I'd be more concerned with where the patterns print.

The chambers only tell you about chamber alignment ... it's the barrels that throw the patterns.

Yes agreed. If I get time tomorrow I'll spend some time on the pattern plate.

[wymberley]

31 minutes ago, Smokersmith said:

I'd be more concerned with where the patterns print.

The chambers only tell you about chamber alignment ... it's the barrels that throw the patterns.

^^^This^^^

Also: 
Because we know about 16 yards and 1", we could use this as a guide but would need to remember that the majority of gun barrels would not be as long as 1 yard although on the other hand we're talking 40 yards and not 32. If 32 yards is to be zero, then 16 needs to be half of the converging figure which equates to about 0.8 of our 1/16". Obviously both barrrels need adjusting so that becomes 0.4. Half of that figure for the 16 yards therefore becomes 0.2 for each barrel. Our 0.0625 becomes 0.0125". If we now consider a, say, 30 barrel, but also the 40 yards it becomes obvious that 'cheap' - neither laser nor gun - ain't going to cut it.

[JohnfromUK]

32 minutes ago, Smokersmith said:

I'd be more concerned with where the patterns print.

/\ This.

With a shotgun, you have a pattern.  Typically it is approximately 30 inches at useful range, but much will depend on choke, shot size, pattern density to 'kill' your target/quarry etc.  7 cm apart at 30 feet is about 20 cm at 30 yards - which is about 1/3 of the pattern diameter. 

Whether you consider that significant is upo to you, but bearing in mind the lasers aren't 100% accurate, patterns are actually strings, and other factors - I can't see it as looking like 'a problem'.

IF you are concerned - pattern the gun, but you would be hard pressed to establish the centre of the pattern (which you do by eye estimate) with accuracy of much better than say 4 or 5 inches cm at 40 yards

[Robden]

As an aside, if I set the comb to get the sight picture I like , the red laser dot is dead on the front pip for the top barrel. The bottom barrel is 2.5cm lower.

[wymberley]

21 minutes ago, Robden said:

As an aside, if I set the comb to get the sight picture I like , the red laser dot is dead on the front pip for the top barrel. The bottom barrel is 2.5cm lower.

For this, it matters not where the barrels are pointing as we're simply looking at the relationship between the two barrels. For a 12 bore plus whatever is the barrel wall thickness plus any centre rib that would be about right.

[Westward]

4 hours ago, Ultrastu said:

I guess to my mind the dots should be the distance between the centre of the 2 bores at the muzzle ie 1.5 cm or so and remain exactly that out to any distance .give of take a cm or so  .ie they shoot parallel  to each other .ideally  with 1 dot  above the other .

The bores on an O/U are not parallel they are made to slightly merge towards the muzzles because there's more muzzle rise with the top barrel. London Best guns are hand regulated and you can specify where the patterns should merge but I believe with a typical factory made O/U, the intent is to merge at 35-40 yds. Different makers have different tolerances for barrel regulation, but Zolis are noted for their ballistics & regulation and are considered as good as or better than anything out there.

Personally I would trust Zoli's manufacturing a lot more than any LED sighting gizmo.

[Gunman]

6 hours ago, scarecrow243 said:

barrels are roughly set at 40 yards to hit the same spot  so the bore laser dots should be very close at 40 yards

It all depends on the length of the barrels and the distance between the centres at the breech and the muzzles .

So the same  gun with 26" barrels will converge at a lesser distance than a gun with 32" barrels .

[Robden]

58 minutes ago, Westward said:

The bores on an O/U are not parallel they are made to slightly merge towards the muzzles because there's more muzzle rise with the top barrel. London Best guns are hand regulated and you can specify where the patterns should merge but I believe with a typical factory made O/U, the intent is to merge at 35-40 yds. Different makers have different tolerances for barrel regulation, but Zolis are noted for their ballistics & regulation and are considered as good as or better than anything out there.

Personally I would trust Zoli's manufacturing a lot more than any LED sighting gizmo.

Totally agree but when I get something in my head regarding shooting, I have to keep at it until it's no longer a problem/thought.

This all started with a "I wonder" moment. I fear I've created a thought/problem that wasn't there before, but, thanks to you lot, I've just about worked through it now.

Many thanks all. 

[Ultrastu]

Can anybody tell between 2 patterns at 40 yards that the center of one is 2 centimeters higher than the other ? 

What a load of rubbish this converging barrels waffle is  

Make them shoot parallel .and all will be fine .

[Old farrier]

16 minutes ago, Ultrastu said:

Can anybody tell between 2 patterns at 40 yards that the center of one is 2 centimeters higher than the other ? 

What a load of rubbish this converging barrels waffle is  

Make them shoot parallel .and all will be fine .

With the greatest respect here if barrels arnt set up to converge at some point they could go totally different ways there has to be a datum point to work from or to for a gun maker 

 

[Ultrastu]

Oh I agree .they need to both point in the same direction and pattern in the same place at all ranges .that's what parallel barrels will do .presuming the choke doesn't make the shot go off on a tangent .and is what a gun gun Smith will achieve by trueing  The barrels .

But the notion of convergence is bizarre. 

Yes with a doubled barreled rifle  or possibly with a shot gun designed to shoot slugs .but I've never seen a slug hold an inch group at 50 yds and I've not seen any one use an ou for slugs .  Do they ? 

So parallel barrels  - patterns in the same place  - job done .

[TIGHTCHOKE]

All very interesting, but, I would set the pair of barrels on something like a black and Decker Workmate.

Ideally in a dark garage, then place one of the laser devices in each barrel in turn and mark where the spot is from both barrels on a piece of paper hung on the door.

Then repeat with the second laser and compare.

The OP could also gently rotate the devices in order to highlight any error of alignment.

Or just get on and practice with one laser which is perfectly acceptable for getting in the swing.

[wymberley]

11 minutes ago, Ultrastu said:

Oh I agree .they need to both point in the same direction and pattern in the same place at all ranges .that's what parallel barrels will do .presuming the choke doesn't make the shot go off on a tangent .and is what a gun gun Smith will achieve by trueing  The barrels .

But the notion of convergence is bizarre. 

Yes with a doubled barreled rifle  or possibly with a shot gun designed to shoot slugs .but I've never seen a slug hold an inch group at 50 yds and I've not seen any one use an ou for slugs .  Do they ? 

So parallel barrels  - patterns in the same place  - job done .

Toe in.

[ditchman]

put some packing behind the lasers....some toilet paper.....so the rim is tight against the extractor's....then try again...........really all the lasers are telling you is the alignment of the throat of the barrel................as mentioned before.....its the barrel/choke alignment which will dictate where the culminating point is.....

[Walker570]

7 hours ago, Ultrastu said:

What's the brand of shot gun ?

I guess to my mind the dots should be the distance between the centre of the 2 bores at the muzzle ie 1.5 cm or so and remain exactly that out to any distance .give of take a cm or so  .ie they shoot parallel  to each other .ideally  with 1 dot  above the other .

As above.

21 minutes ago, ditchman said:

put some packing behind the lasers....some toilet paper.....so the rim is tight against the extractor's....then try again...........really all the lasers are telling you is the alignment of the throat of the barrel................as mentioned before.....its the barrel/choke alignment which will dictate where the culminating point is.....

and as above

Fnally thrrow the laser gismo away and just pattern your barrels at 40yrds, job done. THEN it is up to you to put the bird in that pattern and no laser is going to help you do that.

[London Best]

Or, just stop overthinking things and go shooting.

[Westley]

8 minutes ago, London Best said:

Or, just stop overthinking things and go shooting.

Thank You, THAT is the most sensible answer  !

[Scully]

1 minute ago, London Best said:

Or, just stop overthinking things and go shooting.

Hallelujah! Common sense! It never ceases to amaze me the lengths people will go to, to create problems for themselves which don’t exist!