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 Post subject: Using simple bore gauge as a go/no-go gauge to measure choke
PostPosted: Fri Jul 31, 2020 9:57 am 
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Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
With so much time on my hands due to the "Rona" I have been wanting to measure the constrictions of my chokes. I needed a bore gauge to do that, and thought I could get a dial or digital type. But what I found at just about any reasonable price were only very large ones with minimum width of about 2 inches. Of course that is a deal breaker for shotgun chokes. So I opted for the simpler telescopic "T" kind that you have to measure in a separate step after locking the width/diameter into them and which come in smaller sizes.

Unfortunately I found that I was too ham fisted to get good measurements. Everything went smoothly until I tried to measure the gauge width in my digital micrometer caliper. From trying to make sure I had a snug fit between the caliper and the telescoping gauge, I kept smashing the telescoping part hard enough with the caliper jaws to squeeze it smaller and propduce low readings. Not matter how tightly I locked in the gauge width, I couldn't keep it from being reduced when measuring it with the caliper.

After thinking about it for a while, I came up with an iterative method that avoids the problem I was having and uses the telescoping gauge like a go/no-go gauge.

I set the micrometer caliper for the nominal ID of the choke or the expected ID and lock that measurement in with the set screw. Then I place the telescoping gauge squarely between the caliper jaws and lock that width into the gauge with its set screw. Then I take the telescoping gauge and insert in squarely into the choke. It either just barely fits (bingo) or is too loose or too tight. If just right, I will check 1/2 thousadth wider and narrower just to be sure. If it is too loose or tight, I do the whole thing over with the caliper set a 1/2 a thousandth of an inch larger or smaller and repeat this until I get the desired snug fit. Then I go one 1/2 thousandth further just to check my result. The last measurement should be too tight or too loose because of overdoing it, showing that the previous measurement was just right.

This may seem a little tedious, but for me it is a big improvement. I was going around in circles trying to use the standard technique and getting nowhere.

I am pretty confident in the results since my I can measure to +/- 0.0005" and chokes are usually only specified to +/- 0.001".

The other benefit of the method is you don't really need expensive telescoping gauges. As long as the gauge expands, contracts and locks up, it is fine. The measurement precision and accuracy are all in the micormeter caliper. So my $20 set of gauges is just fine for this.

I hope this helps you all.



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Morris


Last edited by moishepipick on Fri Jul 31, 2020 1:41 pm, edited 1 time in total.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 11:12 am 
Tournament Grade

Joined: Wed Nov 12, 2014 1:49 pm
Posts: 257
Put the telescoping gauge in loose with the shaft touching the side of the choke. Tighten it very tight, now move the shaft to the other side of the choke and touch and remove the gauge. You should be able to measure the gauge without collapsing it. That is what I do.


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 11:57 am 
Tournament Grade

Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
fecmech wrote:
Put the telescoping gauge in loose with the shaft touching the side of the choke. Tighten it very tight, now move the shaft to the other side of the choke and touch and remove the gauge. You should be able to measure the gauge without collapsing it. That is what I do.

You would think, huh? I was just having trouble with it and found the method I described simplified things for me. Thanks for the input.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 12:26 pm 
Crown Grade
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Joined: Mon Feb 09, 2009 10:59 am
Posts: 6347
Location: Neosho, MO
As a gunsmith with a college degree in machining, I hate to tell you, but fechmech is correct on using the telescoping bore gauges. Also, a micrometer is the preferred measuring tool on the telescoping gauges. The broader anvils on the micrometer allows the telescoping gauge to be maneuvered to where you are absolutely sure you are measuring the widest part.

Personally, I have the CSP bore gauge set that allows measuring the bores and chokes in one simple step. Knowing the choke diameter without knowing the bore diameter only gives half the info needed.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 12:46 pm 
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Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
Riflemeister wrote:
As a gunsmith with a college degree in machining, I hate to tell you, but fechmech is correct on using the telescoping bore gauges. Also, a micrometer is the preferred measuring tool on the telescoping gauges. The broader anvils on the micrometer allows the telescoping gauge to be maneuvered to where you are absolutely sure you are measuring the widest part.

Personally, I have the CSP bore gauge set that allows measuring the bores and chokes in one simple step. Knowing the choke diameter without knowing the bore diameter only gives half the info needed.

I’m certain you and he are both correct regarding a well accepted way of performing the measurement. I just ask you do you have any reason to believe either of you would get a different result than I do? I mean if a gauge preset to 0.7145 is too small, and a gauge preset to 0.7155 is too large, can the correct result be anything but 0.715 given the practice of rounding to the nearest whole thousandth of an inch?

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 2:28 pm 
Crown Grade
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Joined: Tue Mar 06, 2007 5:21 pm
Posts: 5149
Location: UK
If you just want to measure choke constriction a low cost digital caliper works perfectly. At least it does on my chokes. I paid about £15 on a well known auction site.

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“when Muslims are in the minority they are very concerned with minority rights, when they are in the majority there are no minority rights.”


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 3:01 pm 
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Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
Trickster wrote:
If you just want to measure choke constriction a low cost digital caliper works perfectly. At least it does on my chokes. I paid about £15 on a well known auction site.

Crazy how cheaply you can get a decent digital caliper these days. I paid about $20 on Amazon. Works great.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 3:16 pm 
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Calipers have a tolerance from tip to neck. Close the caliper, hold it up to the light, see light between the faces, that's the tolerance. You should be using a micrometer. Or buy a used Mitutoyo 209-111 (that's what I use) or one of the Chinese clones (SPI), that's the minimum level of gauge that would accurately and repeatably determine ID and constriction, and even that requires finesse. A real shotgun bore gauge would be the best item with the least amount of "touch" required.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 3:30 pm 
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Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
Skeet_Man wrote:
Calipers have a tolerance from tip to neck. Close the caliper, hold it up to the light, see light between the faces, that's the tolerance. You should be using a micrometer. Or buy a used Mitutoyo 209-111 (that's what I use) or one of the Chinese clones (SPI), that's the minimum level of gauge that would accurately and repeatably determine ID and constriction, and even that requires finesse. A real shotgun bore gauge would be the best item with the least amount of "touch" required.

Good point about the variation along the length of the jaws. Mine are pretty good, but I do understand what you are saying. I will look into a micrometer.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 3:46 pm 
Crown Grade

Joined: Sun Jan 17, 2016 3:34 pm
Posts: 5337
Riflemeister wrote:
As a gunsmith with a college degree in machining, I hate to tell you, but fechmech is correct on using the telescoping bore gauges. Also, a micrometer is the preferred measuring tool on the telescoping gauges. The broader anvils on the micrometer allows the telescoping gauge to be maneuvered to where you are absolutely sure you are measuring the widest part.

Personally, I have the CSP bore gauge set that allows measuring the bores and chokes in one simple step. Knowing the choke diameter without knowing the bore diameter only gives half the info needed.



This^

I realize not many have a real bore gauge.....but it’s really the only true and consistent method of getting accurate readings.


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 4:51 pm 
Tournament Grade

Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
Rooster booster wrote:
Riflemeister wrote:
As a gunsmith with a college degree in machining, I hate to tell you, but fechmech is correct on using the telescoping bore gauges. Also, a micrometer is the preferred measuring tool on the telescoping gauges. The broader anvils on the micrometer allows the telescoping gauge to be maneuvered to where you are absolutely sure you are measuring the widest part.

Personally, I have the CSP bore gauge set that allows measuring the bores and chokes in one simple step. Knowing the choke diameter without knowing the bore diameter only gives half the info needed.



This^

I realize not many have a real bore gauge.....but it’s really the only true and consistent method of getting accurate readings.

Understood. Just trying to get some use out of more general purpose stuff

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Fri Jul 31, 2020 6:05 pm 
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Joined: Sat Apr 20, 2013 7:43 am
Posts: 530
According to what is standard these days it only takes 2.5 thousands to change patterns !
The industry offers .005 as standard but the barrels we get are +or- .004 ! Maybe it would
benefit most if everyone knew what their "True" bore was , first ?


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 8:28 am 
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Joined: Fri Jul 24, 2020 2:22 pm
Posts: 10
I like this idea. Just tried it, and it works. I don't have a jig to hold chokes and I sometimes feel like I need three hands to do it right the normal way, one to hold the choke, one to hold the gauge, and one to tighten the screw. Sometimes I avoid that problem by mounting the chokes in a gun, which helps. But Morris's suggestion is really simple. Thanks, man.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 12:08 pm 
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Joined: Tue Mar 06, 2007 5:21 pm
Posts: 5149
Location: UK
When I referenced the digital calipers I should have said I don't use anything else. The only measurement that matters with chokes is the exit diameter and my calipers can measure ID or OD.

I wanted to measure mine because I'd acquired various additional chokes, including a set of flush, to add to the 8 originals supplied with the gun so I had chokes from about 5 different manufacturing runs and in 2 styles. My barrels are both stamped 18.6mm (0.1mm less than specs), all the chokes measured to within a thou or so of the makers specs and all were correctly marked. Hats of to CG for that!

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 1:24 pm 
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Joined: Fri Jul 10, 2020 4:20 pm
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Trickster wrote:
When I referenced the digital calipers I should have said I don't use anything else. The only measurement that matters with chokes is the exit diameter and my calipers can measure ID or OD.

I wanted to measure mine because I'd acquired various additional chokes, including a set of flush, to add to the 8 originals supplied with the gun so I had chokes from about 5 different manufacturing runs and in 2 styles. My barrels are both stamped 18.6mm (0.1mm less than specs), all the chokes measured to within a thou or so of the makers specs and all were correctly marked. Hats of to CG for that!

Good news! I would just add that what you are identifying as the specification is actually the center of a specification tolerance range or ideally the average value of all production of a certain SKU. It is normal for individual examples of an SKU to differ in a dimension, etc. from the average value. It is common in specification setting for the actual tolerance limits for a dimension to be the average +/- 3 standard deviations. I imagine 0.1 mm less than the center of the spec (0.5%) would meet this criterion. I suspect chokes are cut to a tighter tolerance with a smaller standard deviation.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 1:31 pm 
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Joined: Wed Nov 12, 2014 1:49 pm
Posts: 257
A poor mans bore gauge is a soft lead egg sinker slightly larger than the bore. Oil the bore lightly and drive the sinker through with a metal rod. Mic the diameter of the of the sinker, voila, you have bore diameter. Obviously take the choke out or in the case of fixed choke guns drive the slug back to the chamber. If the sinker is too small flatten it till it's large enough.


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 3:39 pm 
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Joined: Mon Apr 27, 2015 8:11 pm
Posts: 953
And what is the expectation from this knowledge other than constriction ?


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 4:27 pm 
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Joined: Fri Jul 10, 2020 4:20 pm
Posts: 137
captjsjr wrote:
And what is the expectation from this knowledge other than constriction ?

That’s how hobbies are. No particular need for what you do except to be doing something.

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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sat Aug 01, 2020 8:23 pm 
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Joined: Sat Apr 20, 2013 7:43 am
Posts: 530
Without a proper Bore Reader it would be hard to ask or expect a choke to work for you !
You would be better off just using the patterning board at the distance you expect the choke
to work but don't forget , using good ammo is half the battle !


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 Post subject: Re: Using simple bore gauge as a go/no-go gauge to measure c
PostPosted: Sun Aug 02, 2020 1:44 am 
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Joined: Mon Apr 27, 2015 8:11 pm
Posts: 953
moishepipick wrote:
captjsjr wrote:
And what is the expectation from this knowledge other than constriction ?

That’s how hobbies are. No particular need for what you do except to be doing something.



Fair enough !




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