doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Measuring .410 choke

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 3� 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.