Velocette Posted February 5, 2018 Report Share Posted February 5, 2018 In broad terms, a 12g shotgun has a nominal bore size of .729 which would be a cylinder bore and choke is "added" in 10thou increments to give the range of chokes we all know and love. If a 12g had a nominal bore of .719 such as Baikal O/U have and it had been shortened to 26" leaving no choked barrel left,,would this be regarded as an Imp. Cylinder or quarter choke in this state. It looks to me like a very long Imp. cylinder but I have thought a little too long about it to be sure. Any ideas ? Quote Link to comment Share on other sites More sharing options...
panoma1 Posted February 5, 2018 Report Share Posted February 5, 2018 (edited) Choke is determined by the amount of constriction at the muzzle, in relation to the bore diameter! I think the barrel with no choke constriction, would still be termed cylinder! Irrespective of bore diameter. Edited February 5, 2018 by panoma1 Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 5, 2018 Author Report Share Posted February 5, 2018 I see,,,so you don't think that as the shot column is restricted to .719 that it is not same as a 10thou choke on a .730 barrel. Is it simply the fact that the shot is "compressed" by a choke which created the effect. I know this is a little like how many angels can stand on the head of a pin question but it just won't give me any peace ! Quote Link to comment Share on other sites More sharing options...
panoma1 Posted February 5, 2018 Report Share Posted February 5, 2018 Choke was invented for a specific effect, i.e. tightening the pattern......if making the Bore tighter had the same effect, there would be no purpose in putting choke in a barrel! Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 5, 2018 Author Report Share Posted February 5, 2018 Its the actual mechanics of focussing the shot by the choke that gives the tighter pattern,,not just the size of the hole it comes out of which matters then. I can see how that would work. Quote Link to comment Share on other sites More sharing options...
Stonepark Posted February 5, 2018 Report Share Posted February 5, 2018 Choke is measured by the percentage of pellets in a 30 inch circle at 40 yards, muzzle diameter in relation to bore diameter is only an indication. The only sure fire way to know is to test it on a pattern plate. Quote Link to comment Share on other sites More sharing options...
JohnfromUK Posted February 6, 2018 Report Share Posted February 6, 2018 7 hours ago, Stonepark said: Choke is measured by the percentage of pellets in a 30 inch circle at 40 yards, muzzle diameter in relation to bore diameter is only an indication. The only sure fire way to know is to test it on a pattern plate. This is the correct answer. However, with no constriction near the muzzle, you will get very open patterns - probably similar to 'true cylinder'. There will be some variation between cartridge makes/brands. The bore diameter of .719 is possibly measured with 'plug gauges' in 10 thou increments. This is how proof size was measured for many years. 0.719 does fit, 0.729 doesn't, hence a 'nominal' 0.719. The actual diameter will be greater than 0.719, but less than 0.729. Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 6, 2018 Author Report Share Posted February 6, 2018 Thanks for all that,,it seems clearer now,,,and the pattern plate will get some stick this weekend. I'll post the results afterwards. Quote Link to comment Share on other sites More sharing options...
Fil Posted February 7, 2018 Report Share Posted February 7, 2018 On 05/02/2018 at 20:16, panoma1 said: Choke is determined by the amount of constriction at the muzzle, in relation to the bore diameter! I think the barrel with no choke constriction, would still be termed cylinder! Irrespective of bore diameter. Yupp Quote Link to comment Share on other sites More sharing options...
lancer425 Posted February 7, 2018 Report Share Posted February 7, 2018 On 05/02/2018 at 23:09, Stonepark said: Choke is measured by the percentage of pellets in a 30 inch circle at 40 yards, muzzle diameter in relation to bore diameter is only an indication. The only sure fire way to know is to test it on a pattern plate. The correct answer. Quote Link to comment Share on other sites More sharing options...
geordieh Posted February 7, 2018 Report Share Posted February 7, 2018 On 06/02/2018 at 10:24, Velocette said: Thanks for all that,,it seems clearer now,,,and the pattern plate will get some stick this weekend. I'll post the results afterwards. Does it matter.Just shoot it Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 7, 2018 Author Report Share Posted February 7, 2018 I had a go with the patterning today and so far its not too good. Using Fiocchi Pigeon 32g No.6,Fibre at 25 and 30 yards I could only get very loose patterns with substantial gaps which I have yet to count and do the percentages. I fired 20 shots out of the same barrel to get these results. Looks like I need to try some different carts and perhaps try plastic wads to see if things tighten up a little. One thing I did notice was that it shot a little high. Could this be anything to do with the short,26" barrels or just the mount? Quote Link to comment Share on other sites More sharing options...
panoma1 Posted February 7, 2018 Report Share Posted February 7, 2018 So what choke is the percentage of pellets in a 30" circle @ 40 yards indicating? and does this choke calculation differ from the measurement of the amount of constriction in the choke area of the barrel, when compared to the bore diameter? Surely there are too many variables in the components loaded into the many different modern cartridges available, to accurately indicate, much less determine the degree of choke in a given barrel, via the percentage of pellets in a 30" circle @ 40yards? It may however, be possible in a gun barrel regulated to a specific cartridge? Quote Link to comment Share on other sites More sharing options...
motty Posted February 7, 2018 Report Share Posted February 7, 2018 Patchy patterns at that range is not good! Shooting high should have nowt to do with barrel length. Quote Link to comment Share on other sites More sharing options...
lancer425 Posted February 7, 2018 Report Share Posted February 7, 2018 8 minutes ago, panoma1 said: So what choke is the percentage of pellets in a 30" circle @ 40 yards indicating? and does this choke calculation differ from the measurement of the amount of constriction in the choke area of the barrel, when compared to the bore diameter? Surely there are too many variables in the components loaded into the many different modern cartridges available, to accurately indicate, much less determine the degree of choke in a given barrel, via the percentage of pellets in a 30" circle @ 40yards? It may however, be possible in a gun barrel regulated to a specific cartridge? Mere constriction is only part of it each barrel can throw variable patterns to its twin brother, i have a nikko 5000 fixed choke skeet gun its got very little choke yet it with most ammo throws at least 50%. Pattern it at the range you want see if the % is something you are happy with. Try several different shell types for comparison. Quote Link to comment Share on other sites More sharing options...
panoma1 Posted February 7, 2018 Report Share Posted February 7, 2018 (edited) 21 minutes ago, motty said: Patchy patterns at that range is not good! Shooting high should have nowt to do with barrel length. With a shotgun shooting at a static target, you should always shoot low! If you shoot at the centre of a static target it will always shoot high! A crow sitting on a branch in a tree.......shoot at its feet!! Edited February 7, 2018 by panoma1 Quote Link to comment Share on other sites More sharing options...
JohnfromUK Posted February 7, 2018 Report Share Posted February 7, 2018 When calculating patterns from a pattern plate, you should draw your 30" circle around the densest part of the pattern, NOT the aiming mark. This is important as many guns (especially game guns predominantly intended for incoming shots) place the pattern centre above the aiming mark. (Often about 6 - 12 inches above at 40 yards) Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 13, 2018 Author Report Share Posted February 13, 2018 The story continues! After trying several different cartridges and still getting loose and patchy patterns I'm trying a different gun of the same model. The barrel is marked up as the pictures show and although patterning is at an early stage the results seem to indicate 1/4" and 1/2" choke with 32g of Fiocchi No.6. which is promising. One field visit yielded a very satisfying dozen birds off a nice flightline. Quote Link to comment Share on other sites More sharing options...
JohnfromUK Posted February 13, 2018 Report Share Posted February 13, 2018 Re your first picture: My guess is that F stands for full and M stands for modified. 'Modified' is what Americans call half. These would be nominally 40 thousandths (thou) of an inch constriction for full (= approx 1.0 mm and 20 thou for half (= approx 0.5mm) - which also ties up with the picture. 18.2 is a metric measurement (millimetres) and is a 12 bore (and tightly bored 12 bore, similar to the old 13/1 size, which was very common in the early 20th century). I would therefore suggest that those barrels would be nominally full and half. What they actually pattern may be different - not least because they may have been enlarged at some point - they can easily be measured with a bore micrometer which any gunsmith will have. I'm sorry to have to say this but be aware that many gun shops (as opposed to gunsmiths) often either don't have a proper bore micrometer, or don't know how to use it. You CANNOT measure choke just from a gauge that pokes in the muzzle because it is all about constriction - not absolute diameter. Re your second picture: This shows proof marks for a gun proofed at 717 thou. That is 18.2 mm. Quote Link to comment Share on other sites More sharing options...
Velocette Posted February 13, 2018 Author Report Share Posted February 13, 2018 Thanks for that,,I am waiting for the gunsmith to get his bore micrometer back from re-calibrating when we will be able to get a definitive measurement though I take your point that the actual pattern may be at variance to the indicated choke. Quote Link to comment Share on other sites More sharing options...
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