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This is the Webpage for Tobias Hassel a freelancing writer.

 

Tobias Hassel a freelance writer in Swedish guns and shooting magazines.


http://www.shotguns.se/

 

tobias@shotguns.se

 

Tobias has kindley allowed me copy a couple of pages from his website

please visit his website for loads more information about

shotgun and carteidges etc


 

 

 

 

 

History

 

Three different inventors aspires to be the inventor of the choke: William Rochester Pape (UK, Newcastle), William Wellington Greener(UK, Birmingham) and Fred Kimble (US).

Pape was first with his patent 1866 that contains a constricted muzzle: patent 1866/1501. But the choke as just a minor part of that patent - mostly it's a breech loaded gun.

Kimble in US patented 1868 the same type of constriction, but that patent is just about the choke. In US that patent did have some practical use: to mechanically constrict the muzzle with a sliced muzzle and one form of the adjustable choke was invented. For obvious reasons that design can't be used on double barreled shotgun since the ribs keep the barrels together.

These two first steps on the road was primitive and one could not say that the performance was neither predictable or gave a dense pattern.

Greener that often refers to himself as the inventor of the choke developed 1874/1875 the Greener type of choke we know today: parallel section, cone, parallel section and muzzle. The question is: did he continue the work of Pape or the work of Kimble?

Most experts today lean on Kimble as the inventor, but Pape was arguable first. And anyway the choke wouldn't have been the success it became if it hadn't been for Greener who developed the concept.

And this little odd discussion about patents shows that neither Pape or Kimble was first with constrictions in the muzzle. The Manton brothers constricted the muzzles (free bored the barrel behind the muzzle more correct) on some of their guns - not for choke (adding density in the pattern) but to increase the pattern quality.

And before that some Spanish gunmakers use both muzzles that was very opened funnel shaped as well as constricted. The latter was forgotten since they were a little bit complicated to load in the era of muzzle loading.

 

 



This type of choke should prove to give a more even performance and predictable results and is more or less the one we use today in most cases. Greener experimented during 1874 a lot with the concept of choke, and 1875 he won the Fields Trials 1875.

The technique was then soon adopted by all other makers and by 1880 most guns had choked muzzles. The Fields trials had an enormous impact as it was the most important publication of its time in this field.

The result was not only that we could control the pattern density (pellet per area) but also pattern quality was enhanced from the true cylinder barrels. But should not take this fact to far - best pattern is normally achieved with 1/8 to 1/4.

    Greener is most likely also responsible for inventing the recess choke, a choke that in the beginning was developed to be able to give cylinder barrels some degree of choke - as long as there was enough barrel thickness to work with.


 

 

 

Interchangeable chokes

The modern interchangeable choke was patented earlier than most people thinks; it was patented by Sylevester Rooper in US 1866. But it would take a while before this invention was adopted generally on the market. It was put on the market by Winchester 1959, and by 1970-ties it was regarded as a common thing to find on a shotgun. Since then it has been more or less impossible to sell a shotguns without interchangeable chokes unless we are talking about very expensive guns.

When it was used by Winchester one can not by think of the reasons why they did so - but most likely it was a need for showing the market a new gizmo on the market, and it did give some manufacturing benefits: you don't need to bother about choke when making the barrel, whatever choke the buyer wants he or she can give the by changing chokes.

The backside of this is that the barrel is not properly regulated and choked from how the barrel performs. The interchangeable chokes also gives the same length of the cone and parallel section - something that Greener knew was to be a dead end. The upside is that the gun owner can buy after market chokes which normally has way better performance than the original ones that normally performs rather badly.

But as other things as ejectors and single trigger the interchangeable chokes can be a source of very complicated and strange problems. If the choke is not correctly aligned with the barrel the pattern can sometime jump around when the choke are replaced.

Definition of choke

Choke is the constriction in the last inches before the muzzle, and it is normally measured as the percentage of pellets that hits a 75cm circle at 35 meters.

 

 

 

The amount of choke is not only a question about constriction between the barrels cylindrical part and the diameter of the muzzle. The most important things are:

- the construction and material in the wad

- the cone between chamber and barrel

- the finish of the barrel

- the angle of the choke cone

- the length of the cylindrical part after the cone of the choke

The last one first: the cylindrical part after the cone of the choke. The reason for this is to give the pellets some time to "calm down" before they leave the muzzle. If it's to short the pellets distribution will be less even. If it's to long it will actually contradict the choke with a less dense pattern.

The angle of cone (for the choke) normally has the following impact on choke performance: a short cone makes the choke more efficient (at the same constriction) in terms of how much choke it will perform. A longer choke has less choke efficiency (at the same constriction), but it normally gives a more even pattern.

Barrel finish: the finish of the barrel has been and still is questioned, but normally a barrel with a very smooth surface works against the choke, that is less choke performance given the same choke (cone angle and length). But a barrel that has been lapped wrongly (a good smooth finish) but with variations in diameter can give very poor quality in pallet distribution since the pellet body is not given a stable state.

And finally the cone between the barrel and chamber: one might wonder how this can affect the choke, and the reason is probably more indirect than directly. A sharp angle (short cone) increases the force needed to press the load and the wad over the cone, hence a higher pressure behind which in the next step gives a faster acceleration in the first inches of the barrel. And this effect in some way affects how the choke cone performs: the coke increases.
Short cones was normally used in the old days to compensate for poor quality in the wad, a wad that leaks gives extremely poor performance. And for the same reason very long cones and over bore barrels can perform very poorly if the fiber wads is of poor quality.

The type of wad is rather easily understood: plastic wad (formed as a cup) normally gives one step more choke than if fiber wad is used. But how hard the wad material also have inpact om choke performance. A very hard fiber wad has the same effect on the choke as poor barrel finish or very sharp angles in the cones.

Choke performance

The other side of pellet percentage is the area of the load, the higher the grade of choek the smaller the area the pellets are distributed over.

 

 

 

That the roundness of the pellets, the pellet size size and type/quality of the wad affects the pellet distribution I have mentioned earlier. But even choke has its limitations. According to new research done by BASC in Britain suggests that it has a max% pellets in a 75cm circle that hardly goes above 80%. To increased choke further is in the best case useless, in the worst case the % of pellets decreases, although it should actually rise.

 

 

 

 

 

By choosing the smallest area that represents a target, usually a circle of 125 mm with an area of ​0.6 dm2, you can define how good the pellet distribution over the circle is whatever shot size, choke or the number of pellets when this surface corresponds to a grouse or woodcock, which we can assume is our smallest game.

Distribute pellets optimally; you need only 69 pellets to cover the 75cm circle.

 

 

 

 

 

 

 

In reality, however, 70 pellets is too little to cover the entire surface. 28gram US3 in half choked barrel that add up to ½ choke with this cartridge. But to what can this hit picture be used? And how good is it?

To achieve full coverage, ie no holes greater than 125mm requires just below 70 pellets distributed quite evenly over the 75 cm circle. The holes must not be touching each other or extend outside the outer circle. Usually the bulk of pellets ends up inside the 50 cm circle. For the same reason is likely that the majority of the circles centers that fall between the outer and the inner circle.

If one calculates the number of pellets in the inner circle and the number in the outer one can calculate: the number of pellets in the inner circle divided by the number of pellets in the outer circle which gives us a value on how well the pellet distribution fills the 75 cm circle. The area is fairly equally between the two circles, about 20 dm2.

The assessment of the pellet distribution is based on the chart below. This has been compensated for pellet size size and number of pellets in the pattern. If one uses 36 grams US7 which has about 416 pellets in the cartridge that gives with 1/2 choke approx. 60% within 75 cm circle, it will be about 250 pellets in the 75cm the circle. Obviously there will be fewer gaps in the hit picture than if you shoot with 32 grams of US3. This allows us to compare different patterns with each other even if they themselves contain different number of pellets in the cartridges.

 

 

Practical test

So how do you do in practice? Well you measure out the distance to exactly 35 m, looking up sufficiently large cardboard (at least 1.2 x 1.2 m) and shoots. The analysis of the shots requires a 75cm circle of plywood with a 50cm circle sawn out inside. As a measure of the 125mm circle can be suitably used plastic disc that lies at the bottom of a CD spindle, or an old CD. The CD gives a slightly smaller circle than 125mm (a CD is 122mm), but the small difference is usually not more than max one circle in the hit picture, and we are now dealing with a total average of three to five rounds so one or two odd mm does not do much difference. However, it is important that the distance between weapon and board is exactly 35 meters.

 

 

 

 

 

How to choose shotgun cartridge

In a book from the time around when the primer was invented gives an old forester good advice to a young hunter: if you hit with more than five pellets have you shot too close to or loaded with too much pellets, if the pellets pass thru - you have used to big pellets.
A simple and fairly concise advice, we are now 150 years later probably should give some thought about.

Most people choose rifle ammo very carefully, they test firing range and sometimes in different media to see how the bullet behaves at impact. From this they then make their choice. But when it comes to shotgun cartridges are often routinely chosen from what the dealer has in stock for a reasonable price.

In the case of shotgun hunting there are three parameters to take into account, the weapon (especially its choke), ammunition design and construction and ammunition charge load. Our predecessors in the field who were hunting on flintlock or percussion time had really only two parameters: pellet size and weight of the charge. So holds the rule above even today?

Pellet size and impact energy

Jan Åkerman states in his excellent book Jägarens vapen ( The shooters waepons) the following values; for the one pellet: 0.11 kgm (1.08 Joule) for birds and smaller game, 0.22 kgm (2.16 Joule) for larger birds and larger game. Gerald Burrard use approximately the same values in his book; The modern shotgun, vol III the gun and the cartridge.
They are both based their conclusions on the same survey. So one should not be surprised that they came to the same conclusion.
If we make the assumption that most of Shotgun cartridges for lead or bismuth has a muzzle velocity around 400 m / s we get the following table.

 

 

 

 

 

This is the rather dry facts. Never mind that the information itself comes from the evaluation of several thousand shots in the game, but what does that say? I have shot several hundred hares during my 25 years of shooting, and done so with everything from US3 to US8. My experience is that US6 is sufficient to game of size and weight of hare over 30 yards by a wide margin. The same goes for goose. For Pheasant, partridge, wood pigeon, it is sufficient with a good margin with US7 the normal shot distance, up to approximately 30 meters. Further out you can go up to US6. If you have even pattern and pattern density over 35 meters that is. The motto is simple:

 Pellet pattern quality is unusable long before the individual pellet energy is too low

The British have a saying that you must have at least 100 pellets in a 30 "(76cm) circle to have a relatively high probability of dropping the pheasant dead in the shoot. And they use as a rule English size 6 to the pheasant, which is a cartridge with a 2.6 mm pellets i.e. between one and a US6 US7. Recent evidence shows that you get better results with English size 5, i.e. almost the same as a US6, at the longest shooting distance. And if you look at the table above gives US6 adequate performance up to about 40 meters in terms of energy for all small game. US7 is on the limit, but if you hold back a bit on the shooting distance is sufficient even US7.

But how to test striking energy? Energy for the pellet depends on two factors: speed and pellet weight. The problem with measuring the chronograph is that measurement results are quite varied. Measured in series of five shots of the same cartridge, it can turn at 25 m / s or more in speed between shots. Then comes the risk that you shoot chronograph, the one who measures the speed of pellets must live with the fact that it is not a question if but when you can add the chronograph in the list of game you have shoot. And to measure the speed and then draw conclusions one need to compare the cartridge to another with the exact same pellet size of exactly the same material.

And you can also not rely on the size of a pellet in a given US numbers are. In addition; the weight of the pellet of lead depends on volume and density, see also the size of pellet.

And you can also not rely on the size of a pellet in a given US numbers are. In addition; the weight of the pellet of lead depends on volume and density, see also the size of pellet.

Different manufacturers use different materials to alloy with lead in order to get desirable characteristics. Pure lead is generally too soft to work well as pellet. So even if you measure the pellet diameter, the weight may vary some.

Then there was another method that was used before the electronics era: setting up a number of cardboards (with a minimum distance of 5mm between each slice, otherwise the cardboard sheets are packed together and then you get uneven test results) and see how many of these the pellets can penetrate . If you have access to an almost infinite number of cardboard, this is a safe and accurate method that provides an answer regardless of pellet size, weight or speed. But now they have generally no access to an infinite number of cardboard the exact same material. And we usually have much less opportunity to measure the exact temperature, wind or humidity.

So if the chronograph gives a little uncertain answers and the traditional method is tedious and difficult, what do you do? Well it always wise to start from a reference cartridge that you should opt for maximum even performance. I use Eley Impax / Grand Prix, but that choice is free as long as the cartridge in question is performing consistent results in the current weapons. And then you start to shoot one or two shots to the reference cartridge in the test media you have access to for the day, then you only need to count the number of penetrated pages for each shot, and divide each cartridge results with the results for the reference cartridge. The ratio greater than one penetrates it more, it becomes less penetrating the smaller. And choose reference cartridge pellet size at about the same size as most cartridges you should test and you can see pretty quickly in which way it leans.

I have tried this a few years now and it gives very consistent results, much, much smoother than the chronograph. And regardless of the cardboard I get hold of, no matter the weather. Given that each test sequence is performed by exactly the same paper for all the shots in the test. An old CD rack from IKEA works well to put cardboard squares in, they will then be quite small (125 xx125 mm) so you have to be very careful that you get the rack straight down shooting direction. The ambitious makes a similar device for the larger cardboard disks.

 

 

 

 


 

 

And now we see that 32 grams of US6 contains about 230 pellets and with ¼ choke gives pattern with about 130 pellets. In theory, for we know now that there are many factors that affect the grade of choke. That the manufacturer of the weapon states ¼ choke should only be seen as suggestion of what we can expect. A cartridge with 32 grams of US6 is sufficient for to the pheasant / duck and the upwards given that the choke rate for the combination of weapon and cartridge is ¼ choke. With full choke we'll get about 160 pellet within 75 cm circle and it would cover everything from wild pigeon and up.

Now you do not need experiment only with the choke, but what counts is of course number of pellet within the 75cm circle, and then you can increase/decrease the amount of pellet in charge of and get the same results, or choose a different cartridge with another type of wad. 36 grams of US6 contains approximately 300 pellets, with a ¼ choke it provides, in theory, at around 160 pellets in a 75cm circle that is enough for pigeon / partridge. So the person who has a vintage gun and are looking to replace it with a modern with replaceble choke tubes, do not do it. Choose the right cartridge instead. And you should have as much chance of hitting as possible even in the shorter distances, it is better to increase pellet load and reduce choke.

From this you can choose some different types of cartridges as needed - and to test them as above - the bright person then select the ammunition that gives the most even hit the picture (even pellet distribution).

The motto is:

PATTERN ENDS LONG BEFORE PELLET ENERGY ENDS!

Since there's no need to throw away pellets after a target if the pattern is full of holes that will make the probability uncertain even if the pattern is place as a hit over the target. You can hit with a shotgun without hitting the bird....

For those who are considering performance at any distance - and you should keep in mind that a shotgun is fully operational out to 70-80 meter in the most extreme cases - should first look for ammunition that performs maximum regular pattern, and other hand look at striking energy.

But a standard gun with standard chokes loaded with what you get your hand on might be worthless as early as at 30 meters seen to pattern quality.

Summary

We have now seen that we can settle with 32 grams of US6 and ¼ choke for most shotgun hunting, except maybe the pure pursuit of pigeon / woodcock. In the former case, one can advantageously use US7, U.S. 7.5 or even less, for larger game you may chose much larger pellets if you want a decrease the number of pellets in the body. Are we going to compensate a little miss in the distance assessment, variations in muzzle velocity and low temperatures, we can just in case go up to 36 grams US5 at the same choke at the end of the season if they intend to shoot mostly fur game, but basically suffice to say 32gram U.S. 6 and ¼ choke.

And now we can see that the old game-keeper was not so wrong in all cases: five pellets US6 is sufficient for most of what we legally can shoot with the shotgun. Already in Victorian Britain knew this. A bit strange that this knowledge does not become more entrenched in almost 200 years.

And even if they do not shoot deer with buckshot in the UK the rule applies for deer.

So you need to test preferably 5 different brands of US6 and US5 and with different loads. And on 20 shots, we can fire five shots with each cartridge in order to get some more statistically stable data. And now we've really done everything except the actual test, we have the tool to evaluate and we minimized the number of shots we need to shoot.

And if you when testing are to discover just your own gun moves the center of the pattern when using different loads it is, if not desirable, rather normal. If it is so much that it affects the hit probability each and one of us must each determine, but a movement of one dm in some direction for each barrel will probably not be that bad. But it may be considerably more.

 

 

2 1/2" chambers, 65mm cartridges, 65mm chambers and 67mm cartridges....

To make a long story short: there are 2 1/2" (65mm) cartridges and 2 5/8" (67,5mm) (or 2 9/16" 68mm) cartridges, there are also 2 1/2" (65mm) and 2 5/8" (67,5mm) (or 2 9/16" 68mm) chambers.

But we normally only speak about 2 1/2" (65mm) chambers and cartridges (shells).

Chamber

Most guns are marked with a chamber length as 2 1/2" or 65mm, but that is not true. Normally the gun has a 2 5/8" or 2 9/16" chambers but there are guns that is a true 2 1/2". The reason for doing this was that in the god old days reloading wasn't that uncommon, and since the shell normally lengthen somewhat in every reloading the makers added a few mm in the chamber length.

So what the cartridge makers did was to use the fact that most guns have longer chambers than what they actually are marked with - and the longer 65mm shell was born with the length of 67-68mm.

So if there the gun is a true 2 1/2" gun, then you should not fire any cases that are longer than that.

Shell

The shell is as above somewhere between 65mm to 68mm long when fired. So you can normally never see what length a loaded cartridge is just by looking on the cartridge. One must measure the fired shell to be sure. All cartridges that misses markings or have lost the print should be regarded as 70mm (2 3/4").

Historical background

The turn over crimp was standardized in the last year before the second world war. 1947 a major part of the US ammunition manufacturer had swaped to turnover crimp instead of the crimp with over wad. The reason for this was manufacturing benefits.

There are other advantages but the mean reason for the longer shell is that a turnover crimp in 12 gauge expands approx. 11 mm when fired, a crimp with the over wad expands approx. 5 to 6mm. So the shorter shell has the same volume when using lose over wad as the longer shell has with turnover crimp.

Risk

The risk with a shell that is to long is that if the mouth of the shell reaches in to the cone the wad must pass thru the cone squeezed with high pressure as a result.