doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Choke Measurements

Through my perusing for information on shotguns I have noticed quite a variety of ways to measure/describe chokes. I have heard references of half and full, 5/8 and 3/4, .693 and .709, 15 thou and 18 thou, and perhaps there are more. Some of these I understand and others only guess at what they mean in trying to interpret them.

My problem arises when the bores are not in proof and have been bored out. If in proof with a bore of .729 and a choke measurement of .693 I understand to be a full choke. However if the bore measures .735 and the choke .693 then what do I have in terminology of full, modified, etc? I also infer that to subtract these 2 numbers would be .036 and that by itself doesn't compute for me with out a common reference.

Has anyone compiled a reference chart of the different systems that reference back to a common denominator and/or a good description of how each system is measured?

Thanks,
David

You have opened a can of worms, and most everyone has their own opinions about what degree of choke does what on the pattern board. Understand you're entering an area of study that suggests "imprecision"....absolutes do not exist here.
A number of companies have their versions of truth - Google is yer friend.
Several problems arise when checking printed references. Books from pre-c.1970, for the most part do not take into account the change in patterns when using the (then new) one piece shotcup/wad. The printed or computer reference likely will not tell you the complete information on the particulars of the test shotgun and the test shot load make-up. Different size shot pellets apparently may change the "degree of choke" as interpreted fom the pattern board. Hard pellets apparently may pattern differently than soft pellets. Gross changes in shot charge velocity may affect pattern percentages.
Regardless of what information you find and how you think it applies to your particular shotgun, the proof of the pudding is the patterns it fires with YOUR ammo - and judging the patterns correctly. There are no shortcuts here, although the measurements of your barrel compared to the "charts" should give you a general guide, which is better than no guide at all.
Older shotguns with fixed chokes, will usually give notice of the degree choke either with the printed word visible on the barrel (eg. FULL) or by choke code symbols beside or under the barrel chamber(s), these codes or symbols vary depending on the manufacturer.
I suggest - http://www.choketube.com/patterning-shotgun.php
To answer your last sentence - I am away from my library for several months, so I'm running on memory. Several books will answer your questions, but the best IMHO is Shotgun Technicana - by David Trevellion (aka Crossed Chissels) and (the late) Michael McIntosh.
Hope this helps....my $0.02 and you're welcome to take it FWIW.

Kreighoff publishes the amount of constriction for each of their chokes. I use an internal dial bore to check choke but the ultimate test is on paper.
bill

In the above two posts you cannot add much more to what they said. It is true that in order to find constriction you need to know the bore diameter.
The slip in choke tools are only good for a reference that the barrels have not been cut.
As Ian stated in his post, patterning with the shell you use most will tell you what the choke is, another manufacturers shell could and most likely will be different.

OK, I'll put my neck on the block.

Speaking 12ga. only & in points of constriction:

.010" = IC

.015" = LM

.020" = M

.025~.030 = IM

.030+ = F

Used as a rule of thumb, you won't be too far off the mark w/today's target ammunition.

If the barrels are over or underbored, the nominal constrictions that TW presented are not governing. Best results go to those willing to pattern choke boring. Don't think there is a "desk" manner of predicting choke boring results.

True, and exactly why thousandths of constriction is so important. It is a point of reference that all can agree upon, regardless of what load they use. If a .020" constriction patterns as a modified choke with a particular load then it is a modified choke ....... with that load. If it patterns as an improved modified choke with another load, it is still a gun with .020" constriction.

There's too much arguing over semantics, IMO. One says choke and really means constriction. Another says choke and means patterns. Who is right and who is wrong?
What does it really matter? Just ask what the constriction from bore diameter is and you will have a very good starting point to guess how it will pattern.

SRH

Stan, I have to agree with you because when some one tells me the choke of a gun they almost always mean constriction. I've yet to come across anyone with a pattern in their back pocket who can pull it out and provide an explanation of choke.

My understanding is choke is defined as the amount of constriction between the 'bore' measurement and the amount of constriction of the choke. That can be done with a pen and paper and some gauges. What if I were to use percentage change. .693/.729 over x/100 = 95%, a 5% constriction. So anytime I could measure the bores and chokes and get a 5% constriction I could say I had a full choke?

What shot I use or what pattern I obtain is irrelevant because that 5% constriction is really my only constant and what I am trying to determine is some reference for the amounts of constriction. When a seller tells me that the chokes are 5/8 and 3/4 I have no idea what that means.

My question is not to understand how a certain type of shell performs in a particular shotgun. I don't look at it the way Ian has described. I would turn it around and say that I have a 5% constriction, a full choke, and in this gun with this wad, shot size, pressure, velocity is how that shell performs with a 5% constriction. And is should perform somewhat similarly in any gun with a 5% constriction. I realize that may be somewhat simplistic as there are many more variables from barrel to barrel.

Perhaps I am way off the mark in my understanding. If I follow Ian's description then my first question would be what pattern describes what choke?

Bore sizes from small to big don't matter enough that what tw says won't get you in the ballpark. The question you really need to ask is does the choke I have do what I need it to do?

Fixating on some mythical number is meaningless - what do you get for knowing it? A maybe. There is a big enough range of numbers attached to any designation that you will have a seizure trying to rationalize them. If you look at something like Perazzi choke stamps for fixed choke barrels you'll not be happy. And just WTF practical difference is there in 3/8 - 1/2 - 5/8? Go on, take a guess.

Worry about how the gun performs not what it measures

JMO of course

have another day
Dr.WtS

Here's a practical reason that the numbers matter. If I am looking at a gun I like, there are things I want to know about it. Numbers quantify those things. I wouldn't buy a Fox HE if the ad said: chokes - .000"/.000" (no choke at all), neither would I want a 20 ga. for preserve quail that was choked .025"/.035". I'll bet you a dollar to a doughnut that many of the same people who decry speaking of choke in points of constriction would go into apoplexy if they didn't have the exact measurements for length of pull, drop at come and heel, and cast. Why? Do all guns with the exact same stock dimensions shoot exactly the same for all people? No, of course not. Neither do all barrels with the same choke constrictions shoot the same with all loads. But, you don't throw the baby out with the bathwater.

Sure, there is a learning curve for understanding how barrel choke (constriction) affects patterns. It takes less constriction to effect change in patterns as the bore size gets smaller. Two thousandths constriction in a .410 may result in a 65% pattern, whereas it might take .006" to do that in a 12 gauge. The takeaway is that "The amount of constriction does not mandate the EXACT amount of pattern percentage, but it is the most influential factor in determining it". I, for one, want to know what the amount of constriction is, and I have gauges to determine it. And just because I want to know does not mean I worry about it.

SRH