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Measuring choke size.

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Measuring choke size.

Postby Bluelungbutter » Mon Jun 09, 2008 6:36 pm

Just bought a second hand semi auto shottie at the weekend. It's a multi choke but only came with one choke already in it.

Never thought to ask the guy at the shop to measure it but can anyone tell me if it's possible to measure it with a set or verniers and if so what measurements are they.

It's not a big issue as i'm knocking down the doo's better with this gun, i just want to know what it's choked by.

Cheers

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Re: Measuring choke size.

Postby Foxy » Mon Jun 09, 2008 10:33 pm

The size of a choke is detremind by the amout of resrtiction measured at the muzzel from a known bore diamiter measured 10inces from the breach.

English 12 G bore diamiter is set at 729 thou measured 10 inches from the breach end, Threfore a 10 thou resriction at the muzzel ie (719 thou ) is a 1/4 choke
a 20 thou resriction is 1/2 choke ect up to a full 40thou restriction of full choke.
So this is the princapal.

Contenental guns may be marked at 18.5mm or there abouts( incedentally these sizes are stamped at breach end by proof mark) and work in the same way, bear in mind there is 40thou to 1 mm.

Out of intrest 12g is determind by the number of equall sized balls that can be made from a 2lb block of lead ie 12 balls 729 thou in diamiter would weigh 2 lbs
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Re: Measuring choke size.

Postby Bluelungbutter » Mon Jun 09, 2008 10:53 pm

I guess 10 thous is a bit much to ask from a farmer with a set of verniers!!! :oops:

I guess i'll take it into the gun shop and get them to measure it for me.

Any idea where to get chokes for a Hatsan Escort semi-auto?

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Re: Measuring choke size.

Postby RichardH » Mon Jun 09, 2008 10:54 pm

Foxy wrote:The size of a choke is detremind by the amout of resrtiction measured at the muzzel from a known bore diamiter measured 10inces from the breach.

English 12 G bore diamiter is set at 729 thou measured 10 inches from the breach end, Threfore a 10 thou resriction at the muzzel ie (719 thou ) is a 1/4 choke
a 20 thou resriction is 1/2 choke ect up to a full 40thou restriction of full choke.
So this is the princapal.

Contenental guns may be marked at 18.5mm or there abouts( incedentally these sizes are stamped at breach end by proof mark) and work in the same way, bear in mind there is 40thou to 1 mm.

Out of intrest 12g is determind by the number of equall sized balls that can be made from a 2lb block of lead ie 12 balls 729 thou in diamiter would weigh 2 lbs


Thats an excellent summary apart from the last part, a 12 bore shotgun has a bore correctly sized to accept a ball weighing exactly 1/12 ib

So its the number of balls that can be cast from a 1ib block of lead, ie a ball weighs just over an ounce or 543 grains

Just to be pedantic ;)

Richard
Last edited by RichardH on Mon Jun 09, 2008 11:04 pm, edited 1 time in total.
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Re: Measuring choke size.

Postby Born Again » Mon Jun 09, 2008 10:54 pm

Choke is a function of bore size and choke size and many manufacturers have a different interpretation. Your best bet is to do some pattern testing, a steel plate with whitewash and a measuring tape are required. Once you have seen the pattern your gun throws you'll be a better shot too.
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Re: Measuring choke size.

Postby Bluelungbutter » Mon Jun 09, 2008 10:58 pm

Born Again wrote:Choke is a function of bore size and choke size and many manufacturers have a different interpretation. Your best bet is to do some pattern testing, a steel plate with whitewash and a measuring tape are required. Once you have seen the pattern your gun throws you'll be a better shot too.


Cheers for that advice. WIll give it a go.

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Re: Measuring choke size.

Postby Beer Hunter » Mon Jun 09, 2008 11:00 pm

If you can find a way to get the verniers in:
Cylinder = zero restriction
Imp cyl = 5 thou restriction
1/4 = 10 thou restriction
1/2 = 20 thou restriction
3/4 = 30 thou restriction
full = 40 thou restriction

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Re: Measuring choke size.

Postby Bluelungbutter » Mon Jun 09, 2008 11:30 pm

Cheers kev.

I think this ham fisted farmer will let the gunshop measure it. :grin:

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Re: Measuring choke size.

Postby Born Again » Mon Jun 09, 2008 11:43 pm

Bluelungbutter wrote:Cheers kev.

I think this ham fisted farmer will let the gunshop measure it. :grin:

DunK


You're better off looking at patterns, different wads make different patterns, whatever your choke. When I reloaded, fibre wads were more open than plaswads, a choke size different .
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Re: Measuring choke size.

Postby Foxy » Tue Jun 10, 2008 1:21 am

Born Again wrote:Choke is a function of bore size and choke size and many manufacturers have a different interpretation. Your best bet is to do some pattern testing, a steel plate with whitewash and a measuring tape are required. Once you have seen the pattern your gun throws you'll be a better shot too.


Pattern is determind in a diffrent way.
If i remember correctly the 30 yards and 30inch circle and you are lookinf for 90 % of the shot fired to within the 30inch circle to give a set choke size but i cannot remember the size but i think it was 1/2choke.
For testing perposes English trade uses Eley GPrix 7shot as the standard.
Over and above the density you are looking for holes in the pattern and this can be ajusted by reaming the lenght of forcing cones ect.
Having establishing the best pattern at this standard trap cartridges are worth and exrta 1/4 choke approx
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Re: Measuring choke size.

Postby Rowley Birkin » Tue Jun 10, 2008 9:51 am

If you are having problems measuring them, find a precision engineering company, they will have the tools, just a thought and they might do it for free.
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Re: Measuring choke size.

Postby David » Tue Jun 10, 2008 4:13 pm

You need to remember that .729 at proof ( 9" from the breech and not 10" methinks)is a nominal measurement and an older English gun would be marked as 729 but could actually measure anything from 729 to 739 so to ascertain the degree of choke you must first know the actual measurement at the proof point. Measuring at the muzzle only will tell you nothing.
I suppose at the end of the day the pattern plate with various cartridges is the final arbiter.
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Re: Measuring choke size.

Postby Foxy » Tue Jun 10, 2008 9:42 pm

RichardH wrote:
Foxy wrote:The size of a choke is detremind by the amout of resrtiction measured at the muzzel from a known bore diamiter measured 10inces from the breach.

English 12 G bore diamiter is set at 729 thou measured 10 inches from the breach end, Threfore a 10 thou resriction at the muzzel ie (719 thou ) is a 1/4 choke
a 20 thou resriction is 1/2 choke ect up to a full 40thou restriction of full choke.
So this is the princapal.

Contenental guns may be marked at 18.5mm or there abouts( incedentally these sizes are stamped at breach end by proof mark) and work in the same way, bear in mind there is 40thou to 1 mm.

Out of intrest 12g is determind by the number of equall sized balls that can be made from a 2lb block of lead ie 12 balls 729 thou in diamiter would weigh 2 lbs


Thats an excellent summary apart from the last part, a 12 bore shotgun has a bore correctly sized to accept a ball weighing exactly 1/12 ib

So its the number of balls that can be cast from a 1ib block of lead, ie a ball weighs just over an ounce or 543 grains

Just to be pedantic ;)

Richard

Ok no one is perfect and my brain now hurts :shock:
You may well be correct it was quoted of the top of my head
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Re: Measuring choke size.

Postby Deker » Sun Jun 22, 2008 6:46 pm

Guys

The principle of what you say may well be true but 1/4, 1/2 etc, etc are dictated by individual manaufacturers, ie not everyones 1/4 is the came size for the same guage...check a few manufacturers site yourselves! :)
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Re: Measuring choke size.

Postby Foxy » Mon Jun 23, 2008 12:35 am

Deker wrote:Guys

The principle of what you say may well be true but 1/4, 1/2 etc, etc are dictated by individual manaufacturers, ie not everyones 1/4 is the came size for the same guage...check a few manufacturers site yourselves! :)

Yes i agree but if you look at my comments i stated on English guns and gave the resriction for them and suggested this was a guide
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