CUP dimple pressure gauge

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jbunny

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i have thinking about a need for some way to measure chamber pressure
for my antique revolvers. u can get the OEHLER chrono with the pressure
transducer. the price don,t look to bad until u figure in the grand for training and the cost of going to texas. my first thought was to make some pliers
to dimple the brass and sticking on a strip or disc of known width or diam
and then measure the wider strip or disc after fireing. i,m now thinking in another direction. take cheap pliers, grind, file one jaw the same
radius as the inside of your brass u are useing. the top jaw would have
3 or 4 holes to accept small pins of varrying size and shape. theses
pins would mate in the bottom jaw that has radius. insert the radius
jaw in the brass and squeeze. the bigger shallow dimple would become
smooth at a lower pressure. u get the drift. lyman lists the pressure
for the 38 spl, trial and error and recording the results. the finger is capable
of feeling 1/2 thou imperfection. crude but it should work.
thoughts, ideas???
 
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I looked into the pressure trace when I wanted to test my .41 Colt loads. The thing is they only work on chambers that are perfectly rounded, meaning they won't work on a revolver's cylinder, and on octagonal barrels you need to calibrate the system with a known PSI load. I figured my only option was to get a T/C Contender or some type of single shot and get a barrel custom made.
 
about the same basic price as the OEHLER. $785. then u need a laptop
ect ect. the Oehler will do revolvers and i just got an email from Jim Ristow
of RSI and theres will not do revolvers. u would have to take the barrell of
and build a test rig to put rhe strain gauge over the chamber. back to the cannary song, cheap-cheap-cheap. i,ll be picking up a pair of cheap pliers
next time i,m in town and going to give this a whirl. thanks for the link. no harm in looking.
 
I am thinking that any and all dimples regarding size or depth would be totally flattened out even with a minimum load... By placing a disc in one of the dimples to measure its crush may work, but then again the disc would have nowhere to flow, so the results may be rather inconclusive...
 
The dimple sounds interesting. You would have to figure out a way to calibrate each piece of brass or at least each batch.

But I'm guessing that everything will be flattened right out even with a light load. Brass is made soft so it will expand to fit the chamber. If it can't expand it usually splits.
 
wellllllll; right now, we are all reloading for these antiques by keeping our fingers crossed. the chrono is our only tool or load with BP. the lyman
46th edition lists the vel and pressure for the 38 spl. that will give me something to calibrate my findings. might have to use real small center
punch type dimples or wide shallow pointed and use the Lee microscope that is used for there lead hardness tester. the scale wolud tell u how much
the pointed crater has filled in. the cup material in pistol primers is thinner
and softer the rifle primers. i have had some pistols the barrely fire the primer
and that dimple staysas punched. true the fireing pin probly has a lot to do with it. this is not going to cost a bunndle to try. keep thinking guys, there has to be a way foy the DIY. the last resort would be to put a lead pellet
on the back off the bullet . that means recouvery of the bullet. time will tell.
cheers
 
Yes it would be nice to KNOW the chamber pressure instead of making edumacated guesses. I use Quickload program and a chrono but it's still ballpark-ish estimates at best.

You must be gray haired if you're using the Lyman 46th edition - that's close to 30 yrs old. ;) It was my first manual and i still refer to it often.
 
I think the main problem with using changes in dimple size is standarizing the hardness of the brass shell casing. Possibly all cases in a batch of unfired brass might have the same or similar hardness but I would suspect there might be differences between batches made months or years apart. I am in the process of fire forming annealed cases and getting considerable differences from case to case there and definitely think used brass would be a questionable source of data

cheers mooncoon
 
dimple CUP indicator

well boys and girls; this dimple pressure indicator is going to work. the first
two rnds with a blunt point, the dimples are still there. i then rounded the
point into a ball and with a full hose load left just a faint trace of a dimple.
i have taken some pics but can,t get them on to photo bucket . i click on
up load and then get the next page but there is no green bar to click
on to get the pics.
 
here are some pics of my proof of concept . in this pic was my first test
with a blunt point. the edge of the dimple was a bit flater.
cpudimples.jpg

By mouich at 2012-02-05
in this pic i put 2 dimples, diff size , rounded end. the one that u can still see the dimple was 3.4 gr unique , supposed to be 8,900 cup.
the case on the left was 5.4 gr unique, supposed to be 18000 cup. the dimples are gone. now the real work begins. i wiil aneal a bunch of brass
tomorrow useing my lead pot and the wait foe warmer weather for range
work with the chrono.
cupdimplepressureindica.jpg

By mouich at 2012-02-05
 
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This dimple method is certainly fascinating, and perhaps it can give useful information within reasonable error-bars. However, I think that the idea of estimating breech pressures from known - i.e. tabulated - values is not such a bad one. The problem is trying to develop safe loads for which no tabulated (and reliable!) values can be found

I recently borrowed a copy of Handloaders Digest (3rd ed.), from the 1960's and in it a very interesting technical article by Edward M. Yard: "Handloaders - Know Your Breech Pressures!" Essentially, one uses a chronograph, loading tables, and the charts in the article, to arrive at estimated chamber pressures.

Because this article dates from the era of log-tables and slide-rules - i.e. the days of my youth :D - many people might be bored and/or confused by the calculations that one is required to perform. But the basic concepts seem pretty sound to me. In addition, the method is explained, step-by-step, and is not a "black-box" in which the user is obliged to rely on programmed software.
 
Metman old buddy old friend. would it be posible to scan, take digitle pics
of that article. i would be realy interested in haveing a copy. i just got done
reading diff articles on interior balistics. very interesting. talking about slide
rules, i still have mine but don,t ask me how to use it.LOL
regards
 
It may take a few days but I can get scans and post them. Stay tuned...

Jpegs of the ten-page article now at:

http://s1093.photobucket.com/albums/i433/nilsek/Pressure/

jbunny said:
Metman old buddy old friend. would it be posible to scan, take digitle pics
of that article. i would be realy interested in haveing a copy. i just got done
reading diff articles on interior balistics. very interesting. talking about slide
rules, i still have mine but don,t ask me how to use it.LOL
regards
Click to expand...
 
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Sorry for the mixup (I pushed "Edit" button and not "Reply"

Jpegs of the ten-page "Pressure Article" article now at:

http://s1093.photobucket.com/albums/...lsek/Pressure/

jbunny said:
Metman old buddy old friend. would it be posible to scan, take digitle pics
of that article. i would be realy interested in haveing a copy. i just got done
reading diff articles on interior balistics. very interesting. talking about slide
rules, i still have mine but don,t ask me how to use it.LOL
regards
Click to expand...
 
Metman2; a big thank u. very nicely done. i opened each page, click on it once
for full sized, i then copy and paste in my documents. i then sent all this to a flash drive for backup. i only read the first 2 pages so far, realy interesting.

update on the dimples , i annealed a bunch of brass and
the brass is noticibly softer. a shalow dimple stays at 8000 cup and dissapears
11,000 cup. now for some weather to put this all together.
regards
jb
 
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