For BR gunsmiths: While I can use reamer spec sheet dimensions to estimate corresponding reamed chamber dimensions, is there a way to directly accurately measure resulting chamber dimensions in a freshly reamed chamber. I understand that chamber castings have been used for this purpose, but I am unsure whether this method provides accurate measurements. How can I directly accurately directly measure chamber key dimensions. All comments are welcome.
How to Precisely Measure Chamber dimensions after reaming
- Thread starter Cassidy
- Start date
Two of your key dimensions, headspace and chamber length are easily measured with the appropriate gauges, which are either purchased or made. Neck diameter, diameter at the shoulder, and base diameter are best measured with hole mikes. Throat length and diameter can be measured but with some difficulty (especially with regard to diameter. WH
DaveTooley
Gold $$ Contributor
By precise what tolerances are you looking for?
.001" fairly easy at times
.0001" gets much more difficult.
An assortment of gage balls can help measuring tapered surfaces.
A CMM is the only way to get realy precise measurements.
.001" fairly easy at times
.0001" gets much more difficult.
An assortment of gage balls can help measuring tapered surfaces.
A CMM is the only way to get realy precise measurements.
How much money do you want to spend? There are machines available to give you dimensions to .00001 on diameters, lengths, surface finish, and roundness. Might need 500k to a million to get that.
Besides the cost of a renishaw probe for our company's cmm that's long enough I estimate 2 hours minimum plus overhead.
Jonnyofalltrades
Silver $$ Contributor
Yes, CNC shops do this sort of thing all the time. Run off a milling fixture full of parts, then probe some of them to be sure a tool didn't break during the cycle. Renishaw is the only brand of probe I've worked with, they're sort of the industry standard. Accuracy depends a lot on how carefully they were calibrated.
If you wanted to measure a one-off, and you can find a shop willing and able to do it, expect to pay! Most probe styluses are 6mm(at least in my experience), so they would likely need a new stylus, which would then need to be calibrated. Time is money.
If you wanted to measure a one-off, and you can find a shop willing and able to do it, expect to pay! Most probe styluses are 6mm(at least in my experience), so they would likely need a new stylus, which would then need to be calibrated. Time is money.
jackieschmidt
Gold $$ Contributor
You asked how to light a fire cracker and posters give you details on how to make a atomic fusion bomb.
Exactly what are you wishing to measure? I do barrels to a high level of precision with just a few simple home made tools, a depth mic and OD mic.
If you use proper machining practice, the reamed chamber will be as noted on the reamer print. Of course, that term “proper machining practice” does allude many.
you have at your disposal a precision gage, the reamer. If properly done, the reamer should fit the finished reamed chamber with absolutely no play. That means if you remove the live pilot and insert the reamer to the sholder, it should feel snug. If not, you need to critique your setup.
I do all of my measurements such as diameters, headspace, and cone depth using these simple tools.
Exactly what are you wishing to measure? I do barrels to a high level of precision with just a few simple home made tools, a depth mic and OD mic.
If you use proper machining practice, the reamed chamber will be as noted on the reamer print. Of course, that term “proper machining practice” does allude many.
you have at your disposal a precision gage, the reamer. If properly done, the reamer should fit the finished reamed chamber with absolutely no play. That means if you remove the live pilot and insert the reamer to the sholder, it should feel snug. If not, you need to critique your setup.
I do all of my measurements such as diameters, headspace, and cone depth using these simple tools.
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Jonnyofalltrades
Silver $$ Contributor
Haha! But Jackie, atomic fusion bombs are so much fun!
You are very correct in what you say, I didn't think of using the reamer for a measuring reference.
In my own shop, that's likely what I would end up doing, keep it simple.
Because of my dayjob repairing CNC equipment, I also see the amazing measuring potential these machines have. If they can be set up with a probe, they can very quickly measure even more precisely than they can cut.
If you want hard numbers, that's the way to go. Massive overkill, I agree.
Here is the kind of straight forward answer, applicable to the real world, that you need. As the saying goes, it isn't rocket surgery! WH
Sniperhandle
Silver $$ Contributor
Do a chamber cast, You can get very close measurements, And also see the throat etc.
To answer DaveTooley's question about what tolerances and measurements I am looking for, the reason I asked the original question above is I was looking over a reamer spec sheet that showed a lengths tolerance of +.005", body tolerances of +.0005, and an angle tolerance of +/- 15 min, and bolt face to chamber mouth tolerance of +.0005". I suppose if I had the gunsmith use my own reamer and I had the right tools I could take these measurements on the reamer to identify the actual dimensions on the reamer. But this would not tell me if there is much a difference in these measures between the reamer and the actual reamed chamber; I do not know if the process of reaming confers measurements somewhat different in the chamber, so I'm interested in learning how to measure these dimensions directly in the reamer. To further answer Dave's question, chamber dimensions I might be interested in are neck ODs, the bolt face to neck mouth distance, and the lead angle (if this is the correct term). Others might be interested in other chamber measures. I don't know how accurate chamber castings area compared to actual direct chamber measures. These are questions I am interested in learning more about to more ably determine the case body/neck chamber gap, how to more precisely neck turn, and trim case OAL from base to mouth to allow adequate room for carbon buildup. All comments are welcome.
Triming case and neck, Try inserting a teslong bore scope down the front of barrel and take a look with chambered non loaded case. Check reamer print and fired cartridge dimensions and I’m sure you should get close enough. If you shoot a lot without cleaning immediately it’s almost impossible to not get some form of carbon ring. Whether or not it will affect your group or pressure? If all else fails, I use a drill and copper brush with cleaner and carbon ring gone rather quickly ( for real stubborn carbon ring). Just my 2 cents, cause thats all I got
Enrique - I lightly clean the bore/chamber after about every 12-30 shots and later borescope the bore and chamber to be sure it's all clean. I once used a drill with a nylon brush with some bore cleaner on it and spun the brush in the first 3-4 inches of the bore to remove stubborn carbon there. Later, my gunsmith (hof br shooter) noticed via his borescope that the bore rifling surface in the first few inches was slightly shiny and advised that I never (he used more emphatic language) use a drill to spin anything anywhere in the bore. Later, another hof gunsmith more than strongly advised similarly and was worried that the rifling edges in the first few inches might have been worn a little by the drill spinning. It was hard to tell using my borescope but the edges there looked a little rougher than farther down the bore. The rifle then shot 3s and 4s instead of 0s to 1s before. Presently I'm waiting for a new barrel (which is why I'm asking here about how to check/measure newly reamed chambers). Just some info I've recently learned re use of drills to clean bores. To clean the accumulated carbon ring at the end of the neck in the chamber, I use a brass brush with the shaft marked so I know exactly when it touches the end of the neck in the chamber, and I turn it slowly by hand with some (a little) bore cleaner on it maybe 10-15 rotations or so. I then place a clean patch over a different bore brush and turn it by hand a few times at the same location to clean up the loosened carbon, and this removes the carbon ring at the mouth of the chamber in my rifle. I got my hands slapped by two hof shooter gunsmiths for using a drill to spin bore brushes in the bore. In this sport which I am relatively new at, sometimes I've had to learn the hard way. I hope this explanation is helpful. All comments are welcome!
Measuring from the bolt face can be a problem. I agree with using a bore scope to look at the clearance at the end of the neck, but that will not get you a number. The neck diameter is easiest to measure from a fired case. Compare to a loaded round and adjust accordingly.
Like Jackie said, with proper set up and technique, the reamer will cut on size. Chamber length is easily measured with a home made gauge. In fact, if you want to get fancy, you can make a gauge which allows you to check headspace and length at the same time. WH
Tim Singleton
Gold $$ Contributor
gauge pins for the neck diameter
Jonnyofalltrades
Silver $$ Contributor
Well, the thread title asks, "How to precisely measure chamber dimensions after reaming?".
I'm a literalist, when I see "precisely measure", I just assumed that the OP wanted real, hard numbers to the fourth decimal place. I'm NOT knocking comparative guesstimates or go/nogo measurements with pin gages. That's likely what I would do under the circumstances.
I'm a literalist, when I see "precisely measure", I just assumed that the OP wanted real, hard numbers to the fourth decimal place. I'm NOT knocking comparative guesstimates or go/nogo measurements with pin gages. That's likely what I would do under the circumstances.
Except when there is 1 or two high flutes.
Don't see that much anymore, but it does happen.
I measure new reamers with a 50 power lense on- a J &L
Once it's chambered Is there any point in measuring. Your stuck with what you got. A long time ago I read they sell chucks to 3 runout spec class grades.
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