How does one properly measure choke in the little guns? I have a good, long bore mike for 12s and 16s, but lack a good means of measuring down past the choke, into the true bore diameter, of a .410 in order to get the true constriction.

I don't believe I have ever seen anything like a Skeet's Bore Gauge for sale for a .410, and now that I am getting more serious about the little guns I'd like to be able to properly measure them. Skeet's doesn't make them and neither does John Hosford, as near as I can tell.

Thanks, SRH

You may try to find one of the now out of production Stan Baker multi-gauge bore micrometer sets. I have one and a Skeets as well. The Skeets does a better job on 16 ga. guns. I do not think I have ever used my .410 bore micrometer.

This is what I use.
http://www.100straight.com/products/index.htm#top

I use a small inside caliper and a micrometer.

Steve

I use the one Mark cites above, the CSP. It is pricey, but works easily and accurately. I have also used inside calipers and a mike, and inside dial calipers. If using inside calipers, you need the spring type with round legs. The flat leg ones won't reach far enough into the bore. My CSP set is the short version, and reaches 9" into the bore, which is more than adequate for checking chokes.

A patterning board. Minimum of ten rounds of ammunition, 20 rounds is better, count the hits inside the circle, average the count and determine the degree of choke.

Do not assume the percentage will be the same with different ammunition. Do not mix ammunition brands or lots for the same reason. Do not assume a choke measured and marked to a certain degree of choke will actually throw that pattern with a particular brand of ammunition.

Works with all gauges.



Best,
Ted

Once when I was getting desperate to measure the chokes on a .410 SxS I forced a bar of hard soap into the muzzle then carefully pushed it out from behind with a dowel. I then measured the resulting plug with a mike. It was pretty crude but worked. Pete

Stan, there is a machinist's tool called a "small hole gauge". It is an expanding ball that will tighten up inside the bore or the choke by turning a knob. When it tightens up, drive it out the breech end and measure it with a micrometer or vernier caliper. My small hole gauge will go about 3 1/2" into the muzzle, so it will measure the bore and the choke. I assume these gauges are available on ebay. Mine was in Linda's late husband's tool cabinet. Lucky me.

To add to what 8-bore said these small hole gauges once you learn them are extremely accurate. I believe a good way here would be to take a dowel of the largest size which would pass through the choke (3/8" should work) & drill a hole centered in the end just large enough to take the handle & deep enough so the dowel would seat against the head. It could then be easily pushed on through unless there was a tight spot in the bore in which case you would have to push it back to the muzzle.
Also even better & I will have to check on this, but I believe a Starrett telescoping gauge set has a head mall enough to enter a .410 bore. With these & one of their long handles you can reach in beyond the forcing cone & measure the bore from the breech, then measure the choke. I was thinking mine had a 9" handle but checked it after I mentioned it recently on another thread & it actually has a 12" handle. Other brands are available but Starrett is the one I have. This is what I use to measure bore & choke diameters with for all the gauges, I just don't happen to have a .410 to measure but am almost certain it has a head which will go down to 3/8".
To use you simply insert it in the bore with to measuring surfaces tipped a bit, snug up the clamp on the end of the handle then pull it across center "Once", remove & measure across the contact points. This can be done either with calipers or a micrometer & is also very accurate. More so than will ever be necessary in measuring a shotgun bore or choke.
Both of these tools are I believe still being produced new today, but if you can find a good used one it will save some dollars. Most machinists I ever knew, including me, would not pay over half of new price for a used tool regardless of how good a condition or how little used.

Stan, they are all over ebay, search "small hole gauge". However, most of the sellers neglect to tell you what size they are, how deep the probe is, and whether the body of the gauge will fit in a .410 bore. Some have fat ends that won't go in the barrel. The good news is that they are very cheap if you shop through the listings, some as little as ten bucks. I like Miller's idea of pressing a dowel onto the handle so the gauge can be pushed through the breech and you get a longer measuring area.

I do not know if this is universal among other makes or not, but my starrett set of small hole gages is a 4 piece set with sizes A, B, C & D. A measures from .125-.00, B .200-.300, C .300-.400 & D .400-.500. To measure any bore & choke or the .410 you would thus need sizes C & D. To measure the bore on a tight choked gun you would likely have to make sure the measuring ball was set small enough to pass through the bore & slide it in from the breech handle first & let it go through till the handle extended from the muzzle. You could then tighten it, being sure you were beyond the choke & push it back out the breech.
I checked the Starrett telescoping gages & the two smallest sizes, again A & B, cover from 5/16" to 3/4" (.3125" to .750"). A 4 piece set goes up to 3½ with a 6 piece going to 6". The thing I like about the Starrett's in the telescoping gages is they telescope from both sides so the handle remains centered, most other brands only telescope from one side so near the smallest size for a gage the handle is close to one wall.

Another means of accurately measuring bores and chokes is with a set of plug or pin gauges of the correct diameter. In the case of .410, you would need a set that ranges from .251" to .500" or .276" to .500". A set ranging from .626" to .750" covers 12 and 16 gauges nicely.

These gauge sets are precision ground steel dowels in .001" increments. I bought mine on e-bay. They are a bit more tedious than using my Stan Baker gauge which only covers 12 and 16 gauges. You start with one slightly under nominal bore size and push it through the bore with a long wooden dowel. Then go up in size a step or two at a time until you reach a size that will not push through the bore. Here, a second wooden dowel rod is handy to use from the muzzle end to push it back out. You can use them to measure choke diameters from the front, but they won't give an accurate measurement if the muzzles are out of round. Naturally, you cannot use plug gauges to measure a bore if there are any dents that stop a correct diameter gauge plug from passing through.

Another advantage to having a set of plug gauges is that they make perfect incremental plugs or mandrels to use for raising dents in barrels. Just mark your dowel to make sure you push the plug gauge directly under the dent and find a plug gauge that is a snug fit under the dent. Then go to work with your plastic tipped dent removal hammer, tapping around the dent to relieve stresses and raise it. When the dent comes up a bit, switch to the next larger size plug gauge and continue until the dent is completely raised and a bore size plug gauge passes through. This one paragraph is not intended to be a complete instruction for properly removing barrels dents, but once you learn how, it ain't rocket science.

My first job out of high school was as a final inspector at a large machine shop that made a lot of proprietary one-of-a-kind gears for the government. I got to be pretty good at accurately taking measurements with things such as calipers and micrometers or whatever it took. However, it does take practice.

Steve

My bore mic was initially a typical four-gauge (12-, 20- & 28-ga and .410-bore) set from Custom Shooting Products in Omaha. I bought it a Jaqua's. I got the extra 10- and 16-gauge spades for it from Brownells. If I was to do things over I might go for the Hosford and forego .410-bore. As it is my .410-bore spade won't go in the full choke barrel of my Winchester Model 23 Classic.

Eightbore clued me about small hole sets. I have the Brown and Sharpe; it would take a very long choke section to want a push stick.

There is no need to push the gauge out the chamber. Use a sharp tip marker to scribe the collar, then withdraw through the choke section. Return to marked bore diameter and get a mic reading. Easy and reliable - even for a klutz like me.

The gages on the left are telescoping gages, to use them you turn the knurled handle to the left to open, insert on an angle and lightly tighten handle, straighten gage parallel and retract from choke at an angle to make sure you don't compress it anymore and then measure with a micrometer.
They will measure about 2 3/4" into bore doing the same BUT you have to then angle them to get out from choke area without them compressing. Not so easy.

The gages on the right are small hole gages, but work better. Open gage by turning knurled handle, insert into choke, turn handle to left until snug and retract. The good thing about these is that they expand as an oval and if you are not perfectly parallel they still will give you a good reading with a mic.
If is always best to take a few measurements to see if you get the same reading.

The only way to go from the breech with the small hole gage on a dowel would be to open it fully, lightly tightened and insert it at least 5-6 inches for bore and then retract, or as long as you want to make it.

Can't use the small hole gage shown here as it will compress to the smaller diameter.

I use a Fowler inside dial caliper. It measures .375" to 1.375" and will go into the 410 bore about 2 1/2". Very easy to work.

We shoot a lot of skeet and have found that .002 throws a great pattern a skeet range (22 yards) The best thing that has happened is we put 25 more BB in the pattern by polishing the forcing cone. We have been using 400, 600 , 2000 paper followed with chrome rouge

bill

Thanks for the good advice on measuring tools. Sounds like the small hole gauges are what I need. If I didn't already have a really good 12/16 bore gauge I might be tempted to spring for the 100Straight set Mark posted the link to.

No thanks, Ted. I just can't figure a way that patterning can measure how many points of constriction is in the choke of a gun. I already know how to pattern, and what patterns can tell me.

SRH

Are you looking to see exactly what you have or just trying to see if both bores are the same diameter and have the expected constriction? Measuring gives you a number but a pattern sheet will give you the real picture. There is just no substitute to shooting patterns with the .410.

If I had it to do in large numbers I would use white lithium paste or latex paint to coat a steel plate and either count the pellet strikes on the plate or take photos to blow up on the computer later. Use a circle to find the defined pattern area, 20", 25", 30". I used a cardboard with a circle cut of of it and moved it over the pattern to find the best concentration of pellets. You are looking for the pattern not the poi. 30" might be the norm for most but when patterning the .410 I drop down to 25" or 21-20". 30" might "catch" all the pellets but the effective pattern is much smaller.

After a few dozen patterns you almost can go by first impression just looking at them. Is the pattern even? Is there a lot of clumping or holes in the pattern? Does the point of impact look about right?

After you get that all done then get out your chrono and check you velocity. Speed kills and no more so than when you are talking about pellets. With increased speed you get better penetration. But I found out that you also get blown patterns and a different poi with too much speed. I guess it came down to a point of diminishing returns that after so fast anything above that just give you less results than its worth.

For sporting clays I find that the 1300 plus fps loads are fine but have yet to find a good load to hunt with going that fast in the .410. The patterns all seem a little patchy. Wounded clays are all marked dead.

A number, .0??". I just want to know exactly how many points of constriction I have in my guns. I want to be able to measure the choke in a potential purchase, and I want to be able to describe it accurately if I decide to sell. I have already patterned the guns, and know what they throw. I like to know what I've got in the gun, then I can see by patterning if it the patterns are consistent with the constriction.

I have patterned many guns in my life ........ on plates, on paper, on the side of abandoned cinder block buildings, even on the doors of junked cars. I like a grease plate the best. I used to think it important to save the patterns, so I used paper. No more. If it's important enough to save I snap a digital pic of it. I have also chronographed many loads. One interesting thing is how close the velocity always was to published load data, and to the velocity printed on the box of factory loads.

SRH

That's for sure. There are as many measured velocity contradictions (vs factory specs) as you will see with actual constrictions vs what's stamped on the barrel. 3" .410 shells are exhibit A - all over the place.

You can't have too much data. The old line of "patterns are all that matter" falls short when buying and selling. If there is little choke, and the gun throws a tight pattern with someone else's pet skeet load, it may or may not be acceptably tight for a hunting load.

CHOKE MATTERS.

I can work with metal that is there. If it isn't there, you are limited in what can be done to tighten patterns. How many of you would buy a gun for pass shooting geese that wasn't tightly choked, but the owner said "my pet load is incredible in this gun for geese at great distances"?

Like Stan, I want to know what I have and what I'm buying.

The line about patterning and not worrying about choke has been parroted so many times, people have lost touch with reality. There actually is a direct correlation between choke and pattern with a given load.

Well said, Chuck. Thank you.

SRH

You are very right about needing to know what constriction a gun has. A lot of guns have had choke work, both good and bad, done to them over the years. I had to have a few gun back bored behind the chokes to try to get some choke back into a gun someone else reamed out.

Saddest case was a mint condition high grade Smith 32" barrels, 3" chambers some previous owner had opened to cylinder and cylinder to shoot steel shot in. It went from a great waterfowl to a collector closet queen. The patterns were just awful. I sent it down the road. Not enough metal for thin walls, not enough metal to back bore a little choke into it. And when I start thinking about thin walls in a high grade double I am desperate. Had I know how and had the tools to measure it I never would have bought it in the first place. From that one gun I learned how and why I need to measure things better

I have the CSP set for 5 gauges - 12 through .410. I have found several .410s that were choked so tight I could not get the bore gauge in them. I measure the bore from the chamber end in as far as I can, about 17", and then ASSUME that the bore diameter is the same all the way to the choke. Then I measure the diameter of the choke with a dial caliper. This does not allow me to measure the length of the choke or its profile. Not perfect, but close. These barrels that the gauge would not fit in all had over 0.020" of choke when measured indirectly as above and threw very tight patterns with small shot (8s and 9s). Not so good with #6 shot.
Regards,
Jeff

Chuck,
With all due respect, He isn't buying. He isn't selling. I'm going to guess he isn't pass shooting at geese, because, he said he wanted to measure constriction on a .410, but, I guess you never know. You can measure all you want, but, the direct correlation between choke, pattern, and given loads gets fuzzy in a .410. If anyone is parroting anything, it is the guys with a spiffy new micrometer, who measure a gun and declare it to be such and such choke, and head out with a variety of ammunition they have never, ever patterned said gun with said loads.

Choke matters, when you have done the homework. If you haven't patterned, you haven't even started.


Best,
Ted

I am most definitely not one of the technical guys here, but Ted's take on this problem rings true with me...Geo

Ted, no disrespect and none taken. Patterning IS important too. Choke is the equipment to facilitate the desired pattern. Sometimes more or less choke for the load at hand to get desired results. Some loads just don't pattern well, etc..

But if we know the internal configuration and dimensions of a barrel, Most of us have a good idea of its performance with loads we have experience with. We can buy a P-gun with a skeet choke and toss in some AA skeet loads and we are not likely to be surprised.

Do telescoping gages have radiused ends so that they will give a true reading of the inside diameter of a bore?

SRH

Yes.

Yes

Definitely, & radiused enough for the smallest diameter they will measure. While working as a machinist on several occasions just for the info I would measure a bore with them & then with a very expensive dial bore gage & was never off with the telesoping gage by more than .0005" (½ thousandths).

Thank you all.

SRH