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QuestionableMaynard8130
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Measuring Bore/groove diameters
Nov 29th, 2013 at 8:09am
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Now I need to know how to measure bore and groove diameters properly?   I know that some of my questions are basics, but I'm trying to phrase them is such a way that future searchers can find the info with a simple search of the site data base.
    
Specifically I having trouble because this particular 8.15x??? has rather narrow and shallow lands.  On the chamber throat casts I have made the slots they leave are not much wider than the thickness of my thumb nail.  Because of the curve of the rifling I have a hard time getting the knife edges of the vernier into the slots.

Perhaps actually slugging the bore, by carefully driving a well lubed bullet through the bore, might be more productive than working from the chamber throat casts.
  

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Fred Boulton
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Re: Measuring Bore/groove diameters
Reply #1 - Nov 29th, 2013 at 8:55am
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It depends what equipment you have. A lathe makes it easy. Drive a slug through the bore so that you are sure that it fills the grooves. Centre up a piece of scrap and drill an undersized hole, which you then carefully enlarge with a boring bar until the slug will just enter it. measure the hole and you have your groove diameter. Turn down the outside of your piece of scrap until it is thin enough for you to hacksaw through one side of it longitudinally. This is now a split sleeve with which you can hold the slug in the lathe chuck. Turn of the lands of the slug until smooth, then measure it. This is your bore diameter.
Fred
  
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Lefty38-55
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Re: Measuring Bore/groove diameters
Reply #2 - Nov 29th, 2013 at 8:58am
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The OD of the slug is easiest. If you had access to a lathe, you can put a slug (driven through the bore previously) into the chuck, carefully trued. Then use a dial indicator to get a reading from the groove measurement, which will be the most proud. Carefully machine or file away the groove and pick a reading from the land measurement, then subtract that from the initial reading, as that height is the height of the step between the land and groove.

Your ID or bore diameter is the OD minus twice the step diameter. I hope I write this to be easily understood, as it works slick w/ odd numbered groove barrels!
  

All of my single shots shoot one tiny ragged hole with cast bullets ... it's just the following shots that tend to open up my groups Wink ...
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QuestionableMaynard8130
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Re: Measuring Bore/groove diameters
Reply #3 - Nov 29th, 2013 at 9:37am
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Really good tips, thanks to both of you; if a guy had a lathe, and had it set up. and knew how to use it.   
  I've got one, but fail so far on points 2 & 3 Sad.  just not had time to rewire the basement for workshop yet-----or time to learn how to use it.
  

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KAF
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Re: Measuring Bore/groove diameters
Reply #4 - Nov 29th, 2013 at 10:54am
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Pin Gauge, can easily measure the bore.

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Groove dia, a good set of mics, and a gentle feel.
  
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QuestionableMaynard8130
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Re: Measuring Bore/groove diameters
Reply #5 - Nov 29th, 2013 at 12:57pm
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have a set of 4 Brown & SHarpe expandable ball gauges up to about .50 that do well measuring bores  as long as they are not rodded out  they'll reach about 2 "  into the muzzle end and are small enough to drop into most chambers to get the other end
  

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Lefty38-55
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Re: Measuring Bore/groove diameters
Reply #6 - Nov 29th, 2013 at 6:36pm
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Quote:
Groove dia, a good set of mics, and a gentle feel.

... but only works if the # of grooves is an even number Wink

But here is a method using shim stock, instead of a lathe, to get the groove measurement if an odd-numbered groove.

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« Last Edit: Nov 29th, 2013 at 6:42pm by Lefty38-55 »  

All of my single shots shoot one tiny ragged hole with cast bullets ... it's just the following shots that tend to open up my groups Wink ...
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craigd
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Re: Measuring Bore/groove diameters
Reply #7 - Nov 29th, 2013 at 8:41pm
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I've done a low tech (cheap) bore and groove measure that seems to work for odd number grooves, but may not be accurate enough for some folks.

I got a regular push pin for a note board and flattened the point. Glued the handle of the pin to the spindle of a mic. I forget, but used just a spot of glue that came off easy later with just some solvent. Then zero the mic or take a reading for what zero would be.

Anyway, a bore slug, or maybe cerrosafe of just the bore part should sit on the anvil at the groove depth. If needed, I don't think so, a v block or half circle can be rigged up for the anvil side to steady the slug. Then, rotate the slug and take readings, with the small flat on the pin, down on the lands and up on the grooves. Subtract double that difference should give the bore measurement.

It's been a while since I did it that way, hope it makes sense or even helps a bit. Just one way to get a reading down in some tight spot. Probably could rig up something similar on a caliper. I can't remember where I picked up the idea, but I'd give credit if I could. Might be an option for some folks.
  
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KAF
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Re: Measuring Bore/groove diameters
Reply #8 - Nov 30th, 2013 at 8:21am
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Real Way to measure odd grooved bullet.
  
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QuestionableMaynard8130
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Re: Measuring Bore/groove diameters
Reply #9 - Nov 30th, 2013 at 8:31am
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Oh, god my head is hurting,   a mathematical formula,  HELP. Cheesy
  

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Fred Boulton
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Re: Measuring Bore/groove diameters
Reply #10 - Nov 30th, 2013 at 9:03am
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I have a friend who owns a large engineering business and wanted to be able to do this. I worked out the maths, as shown above and pointed out to him that the vee block angle is unique to each number of grooves. His tool room manager told him that to make a set of vee blocks with sufficient accuracy would cost rather a lot and he gave up.
Fred
  
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Fred Boulton
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Re: Measuring Bore/groove diameters
Reply #11 - Nov 30th, 2013 at 9:03am
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I have a friend who owns a large engineering business and wanted to be able to do this. I worked out the maths, as shown above and pointed out to him that the vee block angle is unique to each number of grooves. His tool room manager told him that to make a set of vee blocks with sufficient accuracy would cost rather a lot and he gave up.
Fred
  
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JonT
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Re: Measuring Bore/groove diameters
Reply #12 - Dec 1st, 2013 at 7:51pm
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SmileyI am retire now, but I was a tool and die maker, machinist and oil field mechanic for years, and if you want to find out how to do something, don't ask an Engineer.
The easiest way to find what you want, is to use a depth mike to find out how deep the grooves in the slug are and then if you can feel the high spot on the round, just using either pin mikes or calipers, from the end, get the size and for the groove diameter of the bullet, subtract the depth of the groove, and for the land diameter, of the bullet, add the depth of the groove. If you are not sure of your feel on the high spot, just make a shim, to fit in the groove and measure with regular mikes over the shim and land opposite it. If you cannot get a shim the exact size, get one a little bigger and subtract the difference of the groove depth and the shim, for the land and for the groove subtract that and 2 times the groove depth for the groove diameter.
  
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JonT
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Re: Measuring Bore/groove diameters
Reply #13 - Dec 1st, 2013 at 8:17pm
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For the original post, I would slug the barrel and then use regular mikes to get the land diameter, and the groove diameters. Easy if it is a even number of grooves, and not to hard if odd, because with the lands of the bullet being so narrow, you should be able to get pretty close using calipers or just make a shim for the depth, the same as in the first post I did for checking it. I would think that using cast bullets just using calipers would be fine.
  
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frnkeore
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Re: Measuring Bore/groove diameters
Reply #14 - Dec 1st, 2013 at 8:54pm
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The bore diameter is of less importance than the groove diameter but, if it's is of importance for your purpose (i e bore ride nose) then use pin gauges. If you have a lathe you can also turn steps on a piece of rod to see what fits.

For even grooves the best way is to simply slug the barrel and mic it. For odd grooves, my way takes pin gauges and a blade micrometer. Mine has .030 wide blades. You can sometimes find these used at machinery dealers or pawn shops. Measure the slug and subtract the bore size from it. That will give you the depth of the groove. Mulitiply that by two and add to the bore size and you will have a accurate groove diameter.

Frank
  

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