I made a new post because I didn't want to take from King's.

I thought I would ask this because a lot can change if one does not know bore size of gun, am I correct? Also we take for granted what the bores are supposed to be and then have someone put a Skeet's or Brownell's dial indicator in and say we have a .015 and .025 readings, compared to what?

In my opinion unless you know bore size how can you know choke size. Example early 16 ga L.C. Smiths, bore was .650 and changed I believe in 1936 to .662 so there is .012 difference in size of bore.
Also an early 1899 L.C. Grade 2 12 ga. the bores start out at .724 and in the right barrel go in 13 5/8", left barrel 17". Bore gage of .722 goes in right barrel 26 9/16" to start of choke taper. Left barrel goes in 27 3/8" to choke taper. Barrels are 30" long. Muzzle end choke area mikes up right barrel. 686 and left barrel .683. Skeet's gage going in 11" from muzzle, zeroing indicator and withdrawing gets .015 in right and .017 in left. Which would mean to me, light modified. Bore readings and choke readings make this .037 & .040 difference.

To me anyway, too many people put too much emphasis on what kind of chokes their guns have. The only things that have changed in 100 years are the ammunition that it fires. The only real way to tell is shoot the gun with the shells you use most often and see how it patterns at different yards. All will be different.
The only good thing about getting bore readings and choke readings is to see if your gun's barrels were honed or bored out.

The short answer is "No". The definition of choke is the constriction at the muzzle subtracted from the bore diameter. I.E. Bore = .729", muzzle = .699", then the constriction, or "choke" = .030", which is called Improved Modified, Light Full or Full, depending on whom you're talking to.

You can also pattern the gun at 40 yards and count the holes within a 30" circle and check the choke charts to see what your pattern gives you. Not only will different guns with the same constriction pattern differently, but the same gun with diffent ammo will also pattern differently.

Actually, yes, as noted by BPGuy you can pattern the gun, which will tell you the choke size or more importantly how it patterns.

Patterning is the way to go, to know how a given constriction will work with the loads you have picked.
I too have been playing with a bore meter, and found a unexpected choke on a 28 gauge.
It has 1mm or .039 of constriction, which should be considered an extreme case of over choke. Another 28 gauge measured for comparison has a lot less ( I don't remember exactly) and both are marked the same (Full)
The thing is, the tighter one patterns way better. Obviously it's a tight pattern but very well distributed and perfectly shaped.

Interesting question - and a bit of a semantic dilemma.

IMO, the real answer to the question as asked is 'no', there is no way to determine "choke size" w/o knowing bore size. By "size", I'm assuming you mean a decimal figure that could then be compared to a choke chart to see where your figure falls.

However, as pointed out correctly above by Gregsy, you can take a gun and a load and head out to a patterning board. There, if all is done correctly, you can determine the pattern percentages for such load(s) @ whatever range you choose to test for.

Is such a % figure the "choke size" for the barrel(s) tested? IMO, no, though you've learned a lot more about that gun w/ that load than any bore minus muzzle decimal figure alone could ever tell you...

Choke "size", if you mean amount of constriction, can not be determined without knowing the bore inside diameter. The "size", meaning ID at the choke end of the barrel can be measured with any precision measuring device but will mean nothing without knowing the bore ID.
Patterning in the traditional way will show you how your chokes perform with the ammunition you are using.

You answered your own question in para 3. If you set the bezel of your dial indicator to zero with the mike in the bore and withdraw toward the muzzle, you get the constriction in thousandths as the mike leaves the choke by counting the multiples of 10, 5, and 1 thousandths that the needle moves All you have to do is watch the needle. No remembering the bore ID number and subtracting the choke exit number. Doesn't matter if one bore is .723" and the other .725" you still know the constriction in each. If you want to do the arithmetic, you use the gauge ring (which I believe is .700" for 12 ga.) to calibrate the dial bezel, and then actually measure bore and choke and do the subtraction to get points of constriction. So yes, you absolutely can measure constriction without knowing bore size. The problem arises when folks use step gauges. These don't account for under-over boring from the "nominal" gauge ID (say .729" for 12 ga.).

jack

Jack,
I pretty much new what the answer was, just didn't know how many people referred just to what a chart tells.
In going to gun dealers they put the gage in, most of the times I have seen without the .700 ring for 12 ga. and read the pointer coming out and look at their chart and say mod/full, etc. Which to me just shows me that the barrels have not been honed.

I decided to make bore gages out of aluminum starting at .729, nominal bore size, didn't fit in one of my L.C.s', .727 fit in some down to .724 on the circa 1899 with Crown Steel barrels. (I added .001 to the final readings because as you know size to size will not fit.) Setting the bezel to .700 and inserting it all the way gave me +.022 (which is what I got with the bore gage .722) and withdrawing it gave me -.017, so a total reading of .039.
The indicator reading is nice and fast but I like the bore gages and telescoping gages to see if there is taper in the bores, which there was. Is this is what they called "Multiplied Choke Boring"?

M. Lapin,

After your description of measuring you may not know the bore, but the contraption
you are using to measure does, that is why you set it to zero and then measure the
difference. So what you say is accurate as far as the operator, but...

I've always thought these gadgets not very practical and can only give you an estimate
of actual choke:


JMTC.

JC

Great post where we're all right. JC. Dang, it's hard to be humble but no doubt an opportunity will come along soon. I like to KISS those numbers as some can be confusin, such as why .38 cal bullet is .357" diameter but .36 cal. ball is .375". Yeh I know it has to do with swaging a round object with not much bearing surface otherwise but still. . . Lots of fellow shooters think I'm stupid when I won't let them stick their turned brass choke gauge in the end of my gun. Actually, I don't wish them to loose the damn thing down the barrel of my overbore Barnes aftermarket 12 ga. m12 barrel (bored .779";screw-in choked to .774" most of the time; must be a 12 ga. as they see me usin them 12 ga. shells, right?)

jack

A most educational thread.

You really think so? I'm not sure David really gets it yet. His explanation of what he gets left me mostly confused.
No offense, David.