View Full Version : totally confused over metric
nekshot
06-11-2018, 09:32 PM
Math was never my strong point in life but some of this metric stuff is confusing to me an ignorant old man! A 8mm mauser bore is .3106. Ok I get that. Now a 8.15x46 is bore .2992! I assumed this 8.15 would be the 8mm of .3106 plus 15. But according to the book a 8.15 is bore of .2992! I know they are right and I am confused. Any body willing to explain this to me? Go slow!
turtlezx
06-11-2018, 09:39 PM
mm = .03937" usally round to .040" so 8mm .320"
obssd1958
06-11-2018, 09:53 PM
Take a look at this thread, it might help ---
http://castboolits.gunloads.com/showthread.php?41492-8-15x46R-Schuetzen
Don
nekshot
06-12-2018, 07:09 AM
That is a very inspirational thread but I still don't get the smaller diam. I know I am slow with this metric thing but I'm a trying! Reading of these guns sure puts the wants in me to have one. Rather than using the H&R single shot I think a Remington Russian single shot center fire rifle would have nice character. Would be an easy stub fit.
sharps4590
06-12-2018, 07:34 AM
nekshot, were you taking measurements from a slugged bore as well as from a book?
GhostHawk
06-12-2018, 07:35 AM
When it comes to calibers there are no hard and fast rules IMO.
Look at .44mag. How do you get .44 out of a .429 or .430 cast bullet?
.38 special is another.
People label stuff to suit themselves. And it gets stuck there.
kungfustyle
06-12-2018, 07:51 AM
When it comes to calibers there are no hard and fast rules IMO.
Look at .44mag. How do you get .44 out of a .429 or .430 cast bullet?
.38 special is another.
People label stuff to suit themselves. And it gets stuck there.
And to add to the fun a 44 mag rifle has sammi specs to .432 what a mess
Petrol & Powder
06-12-2018, 08:16 AM
When it comes to calibers there are no hard and fast rules IMO.
Look at .44mag. How do you get .44 out of a .429 or .430 cast bullet?
.38 special is another.
People label stuff to suit themselves. And it gets stuck there.
/\ THIS /\
There's little uniformity in the naming of cartridges.
English & metric designations for cartridges have little bearing on actual dimensions in the world of firearms.
The same way a 30 caliber wound up with a bullet of .308" diameter. There is only a general relationship between stated caliber and bullet diameter, or groove or bore diameter.
Jedman
06-12-2018, 09:46 AM
Cartridges in 8 mm can vary over a wide range of diameters. Early 8 X 57 had .317 groove later .323 I have rifles in 8 X 56 and 8 X 50 that need .329-.330 diameter bullets.
You were speaking of bore diameter and that varies wildly between different 8 mm cartridges also. :confused:
Jedman
JimB..
06-12-2018, 11:48 AM
Way off topic, but I’ve heard that some of the old black powder loads (38, 44, 45) were named based on the diameter of the loaded case at the mouth. No idea if there is any truth to it.
sharps4590
06-12-2018, 02:44 PM
I have a few 8mm rifles and my experience echo's Jedman's. I believe it was in 1913 the German government took it upon themselves to "Normalize" cartridge and bullet dimensions. WWI kinda got in the way and things didn't take off until after war. Even then it was slow going as there was so many variations of popular cartridges. If I remember correctly the 9.3 X 72R and the 8.15 X 46R were among the first to be Normalized. Probably because at that time they were among, if not the most popular cartridges. Even so, .318 barrels were still being used for a lot of the 8mm sporting rifle cartridges as they weren't going to waste them. I have a post WWI sporter with a .318 groove dia. barrel. The German military changed the groove diameter of the 8 X 57 from .318 to .323 in 1905 and I believe most military rifles then in service were tooled to that diameter. Later barrels were rifled to .323 groove dia. Bore diameter remained the same. By the beginning of WWII nearly all the popular, standard cartridges were Normalized. Rifles manufactured after WWII have been pretty standard.
As several others have already said, there is no rhyme nor reason to the naming of cartridges and in the early years no standardization. Many early 9.3's, (.366), can easily, accurately and effectively shoot bullets of .358. I have been told by those who should know that a lot of the old German makers believed a tight bore was conducive to accuracy and, according to some of my rifles, they definitely were not afraid to do so!!!!
nekshot
06-12-2018, 04:05 PM
nekshot, were you taking measurements from a slugged bore as well as from a book?
No, I am trying to educate myself what barrel I have that would also give the legit 8.15x46 name and what molds do I have that fit in that caliber. I was at first thinking this cartridge is close to .300 and would also give me reason to get 7.? carcano barrel. Then it seemed like I ran into information putting it around .321 and I like that as it can give company to the 32 winny. I would be happy if it was .318. Boy, can I confuse myself!
Char-Gar
06-12-2018, 05:01 PM
Always remember Dear Ones, that the "bore" diameter and the "groove" diameter are different.
Texas by God
06-12-2018, 06:38 PM
My high school algebra teacher told me in 1974 that by 1980 the United States would be totally converted to the metric system. I told him I did not think so. I guess I won that argument!
Sent from my SAMSUNG-SM-G930A using Tapatalk
My high school algebra teacher told me in 1974 that by 1980 the United States would be totally converted to the metric system. I told him I did not think so. I guess I won that argument!
Sent from my SAMSUNG-SM-G930A using Tapatalk
Unfortunately you did. Just think how simple it would be if we were totally metric. Changing from mm to cm to meters is just moving a decimal point. Remember, out money system is metric in nature.
bdicki
06-13-2018, 10:26 AM
My high school algebra teacher told me in 1974 that by 1980 the United States would be totally converted to the metric system. I told him I did not think so. I guess I won that argument!
Sent from my SAMSUNG-SM-G930A using Tapatalk
The United States is moving to the metric system inch by inch.
obssd1958
06-13-2018, 05:01 PM
The United States is moving to the metric system inch by inch.
Hahahahahaha!!!!!
I see what you did there!!!:D
Just think how simple it would be if we were totally metric.
...but a 7.62x54R, a 7.65x53 Mauser, and 7.7 Arisaka all shoot the same size bullet...
Back in the day there were differences in sizes because some standards measured bore diameter, some the lands, and some the actual bullet.
The name of a cartridge is just that; a name. Sometimes the name is chosen to make sure someone doesn't try to put the wrong cartridge in the wrong gun; .38 Colt Auto and .38 Super, or 9mm Largo and 9x23 Winchester, for examples. Sometimes "just because."
In its early form the 38 Special was a heeled bullet-- so it really was 0.38-- which matched the outside diameter of the case. As the cartridge evolved the brass stayed the same but the heeled bullets went out of use-- so we're left with a bullet that fits the inside of the case. So the name originally was really the size of the bullet, but the design changed later. Also, keep in mind that caliber often refers to the bore at the top of the lands. 30 caliber is 0.30 but the bullet has to be 0.308 to engrave in the rifling. Similarly, 0.303 British describes the bore, not the bullet. Of course, there is also the problem of describing a cartridge that fits the same bore as another one where you want to distinguish between them (for example-- all the different 30 caliber bullets). As noted in the posts above, this takes some imagination.
john.k
07-23-2018, 03:07 AM
Years ago I was given a very nice tape measure......one of the big 100 yard ones in a leather case with a brass folding handle.I used it for a few setouts.......and lots of snide comments...........finally figured it out.........the tape is in yards and feet........and what look like inches are actually 1/10 of a foot........So you can have metric in feet as well,as millimeters etc.
Jeff Michel
07-23-2018, 04:34 AM
Spend some time in a machine shop that works in both systems, you'll have it figured out in about a day.
William Yanda
07-23-2018, 05:32 AM
My high school algebra teacher told me in 1974 that by 1980 the United States would be totally converted to the metric system. I told him I did not think so. I guess I won that argument!
Sent from my SAMSUNG-SM-G930A using Tapatalk
Even then the whole country was using the metric system for time-hours and minutes.
.the tape is in yards and feet........and what look like inches are actually 1/10 of a foot........So you can have metric in feet as well,as millimeters etc.
Decimal feet. American industry used to run in fractions, mostly, as did government contracts. During WWI a coalition of Detroit manufacturers petitioned the War Department to be able to use decimal inches instead of fractional inches when filling government contracts. (decimal inches were something that Thomas Jefferson had advocated, long before...)
Companies like Ford held on to fractions for decades, which is why pre-WWII Ford service manuals specify dimensions in 1/128ths and such.
Then there are peculiarities like metric micrometers which read in 1/4 mm increments...
john.k
07-28-2018, 06:34 PM
it took me a while to figure it out...just so unexpected..............finally the penny dropped when I couldnt find 11 inches on the tape......who d a thunk it?...........You lay out a $5000 concrete slab,and when poured its noticeably cockeyed.
Larry Gibson
07-28-2018, 07:12 PM
The metric system is a communist conspiracy to corrupt the moral fiber of America's youth.
Note the attempted adoption of the metric system coincides with the beginning of the downfall of the American society.......just kidding...... but.......:-?
leebuilder
07-28-2018, 07:40 PM
I like the metrics, but when you build stuff that is 39,000mm long it's good to have a second set of eyes. I have come across fractional metric threads, never seen a lathe that would cut it. So time to get out goes-into-ta-matic and make due. I seen an Indian made mill that was graduated in 1/128ths.
I am sure there are many other unique items around ie Whitworth and BA.
Be well
Kenstone
07-29-2018, 12:11 PM
Here's a useful online converter, it's free, down load it and create a shortcut on your desktop or task bar:
https://joshmadison.com/convert-for-windows/
Click on the yellow/orange download button, NOT the green one :coffeecom
Did I mention it's FREE :shock:
Edit: Use 25.4 for metric/inch conversions it's way more accurate than .03937.
The same way a cap and ball 44 is really a 45. Or as Winchester put it, "All our 44's are really 43's except for the 38, which is a 40". Depends if you are calling it by bore or groove.
7.35 Carcno is much closer to 0.30 cal than the 7.62 we call 30 cal. 357Sig = 0.355" while 38 special = 0.357" 460Rowland=0.451" ...
:roll::roll::roll:
ANick57
08-04-2018, 01:59 PM
Here's a useful online converter, it's free, down load it and create a shortcut on your desktop or task bar:
https://joshmadison.com/convert-for-windows/
Click on the yellow/orange download button, NOT the green one :coffeecom
Did I mention it's FREE :shock:
Edit: Use 25.4 for metric/inch conversions it's way more accurate than .03937.
While 25.4 is indeed accurate, using .03937" per mm results in an error of .0000787 inches at one meter. Kinda tough to measure methinks. :)
25.4 came from the US Department of Commerce, to simplify conversion between systems in international trade.
It has had far-reaching consequences in chemistry and physics, where the rounding error invalidated much experimental data collected by people who should have known better...
Dieselhorses
09-30-2018, 10:45 PM
I own a 12.7 mm S&W Magnum revolver. Believe me, it confuses me too.
RED BEAR
09-30-2018, 11:13 PM
and the British have there own thread system for bolts and nuts.
fast ronnie
10-01-2018, 12:23 AM
and the British have there own thread system for bolts and nuts.
Mauser large ring has a 1.1 thread that is 12 pitch 55 degree which is Whitworth. I had a very well known gun maker try to tell me it was metric. The machinery to build the original Mausers was purchased from England.
nekshot
10-01-2018, 05:50 AM
Ok, ok, now i am really getting confused! I kinda think Larry might have a point, you know the globalization and all that was jammed down our throat. I really would like to open up a 7.2 x39 in a ar to 9mm but should it be a .356 or .366 diameter?
nekshot
10-01-2018, 05:51 AM
dang meds!! 7.62x39 is what I meant in last post.
Willbird
10-04-2018, 11:36 AM
Well some cartridge names are bore and others are caliber. .218" is the minor dia of many .224" barrels, hence the 218 bee and the 224 Valkrie can share the same bullets :-). Then some stuff is rounded up or down too. The 6.8SPC and the 270 both use .277 bullets. 6.8/25.4 = 0.26771".
.277 x 25.4 = 0.26771"
270 reamer pilot Nominal Pilot Size: 0.2692...dunno where they got the 6.8 from :-)....well some combloc stuff made for steel jacket bullets runs a bigger minor dia than typical USA designed stuff for gilding metal bullets.
indian joe
10-04-2018, 07:10 PM
Mauser large ring has a 1.1 thread that is 12 pitch 55 degree which is Whitworth. I had a very well known gun maker try to tell me it was metric. The machinery to build the original Mausers was purchased from England.
That one has caused a lot of grief !!!! Whitworth threads are same TPI as National coarse all the way from quarter inch up to inch bolts EXCEPT for the 1/2 inch whitworth is 12 TPI and 1/2 inch NC is 13 TPI ----------why is that a problem ? Aussie system is based on English due to our colonial history - but most of our AG machinery imports last century came from north america - my first lesson came pulling the brake drums on a massey harris tractor - two 1/2 inch bolt holes in the machine to do it - easy deal - grab a couple 1/2 inch bolts -----------ooooops! 12 thread ina 13 hole they go about 6 or maybe 7 threads in before they seize up good - so a simple job those days ends with a trip to town to buy a couple of bolts or (as we did) NC tap and die ------later years we added metric machinery to the mix - more confusion !! Had a International 986 tractor once with a German Neuss motor (metric fittings) US made transmissions (National standard threads) Aussie built peripherals (half whitworth and half metric) to top that off you could not buy a bearing from the bearing supplies because International Harvester had a deal where they used special order bearings with metric outer and inch size inners (or vice versa)
William Yanda
10-04-2018, 08:33 PM
My high school algebra teacher told me in 1974 that by 1980 the United States would be totally converted to the metric system. I told him I did not think so. I guess I won that argument!
Sent from my SAMSUNG-SM-G930A using Tapatalk
I remember that argument, and I chuckle every time I look through a catalog of mechanics tools and see the metric sockets offered in........wait for it...........1/2, 3/8 and 1/4 I N C H drive!
bob208
10-06-2018, 07:54 PM
metric is for people that have to count on their fingers. you think it is bad for linear measurement. try volume a 301 307 and 302 engine are all 5.0 liters and not one part interchanges
The nomenclature is rarely exact. You are taking the designations too literally.
They are no different than most US calibers. You have to know the details because the nomenclature or names are not usually exact.
So the 7.62X54R Russian round is basically the same round as the 7.62X53R Finn round.
And the 7.65 Mauser uses the same bullet diameter as the 7.7 Jap and the 7.62 Russian.
So your issue is expecting different rounds to match literally to the nomenclature and they don't.
How about a .35 Whelen and a .358 Win? They use the same bullets. So does a .350 Rem Mag.
Some rounds are named for the hole that is drilled before the barrel is rifled. Some are named for the groove diameter after rifling or after the bullet diameter.
The .357 Mag pistol round uses the same bullets as a .38 Special which are .357. However the .38 Special case does measure .38. The bullet does not.
Math was never my strong point in life but some of this metric stuff is confusing to me an ignorant old man! A 8mm mauser bore is .3106. Ok I get that. Now a 8.15x46 is bore
.2992! I assumed this 8.15 would be the 8mm of .3106 plus 15. But according to the book a 8.15 is bore of .2992! I know they are right and I am confused. Any body willing to explain this to me? Go slow!
Winger Ed.
02-14-2019, 02:08 AM
Way off topic, but I’ve heard that some of the old black powder loads (38, 44, 45) were named based on the diameter of the loaded case at the mouth. No idea if there is any truth to it.
I think it actually does go back to the cap & ball days and the industrial revolution.
For example: The 36cal. Navy Colt that had sort of a .357 inch dia. bore.
When cartridges came along, they called them .38s, then the 38. spec. just for sales and advertising purposes.
Then the .357Mag--for the same reason. .357Mag sounds more cool than 'longer and more powerful .38Spec.'
In each case, as the new cartridges came along, they could make the weapons for them with a minimum of retooling.
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