The Accurate Reloading Forums THE ACCURATE RELOADING.COM FORUMS Rifles Small Calibers Metric to inchesGo | New | Find | Notify | Tools | Reply | |
| Metric to inches | Login/Join |
| One of Us |
I don’t need a full tutorial about all the different caliber naming conventions over the years, but I have a few questions about metric to inch correlation amongst several of the popular centerfire small bores: 6mm – Pretty sure I am correct in understanding that this is the same as a .243. When I run a straight math conversion I come up with .236, but the difference in .007 accounts for one measurement being between the lands, and the other the grooves. 6.5mm – When I do the math I come up with .256. Do the 6.5s shoot the same diameter bullets as a .257 Roberts, or .25-06? 7mm – The math comes out to .276. I know that these can be called .275 Rigby, (and I understand there are some differences in throating and twist rates for different weight bullets) but are they the same diameter bullets as a .270 Win? I thought I knew this stuff better! Thanks. | ||
|
| One of Us |
| |||
|
| one of us |
Its not that straight forward and simple ! The reason being two fold. First and foremost the British designated caliber by bore ( for the most ) ie the diameter of the Drilled barrel ( bore ) before the grooves are cut . So basically land to land diameter. The Europeans for the most designated caliber by groove to groove diameter. To add to this practice some simply named their cartridges to a bore diameter when it was not. The second issue is that what is designated as 7mm or say 6.5 mm is not necessary a 7mm or 6.5 mm ! There are various 7mm's which are not true 7mm's but rather 7.25 mm's and inbetween. For the most in low pressure loads using conventional cup and core bullets this was not much of an issue but when going monometal and monometal with bore riding ribs a more precise fit becomes mandatory. Then 6.5s some are smaller like the 6.5x54 Mauser or bigger like the 6.5 Carcano which is actually a 6.9mm | |||
|
| One of Us |
Um, thanks NONAGONAGIN, but doing the conversion isn't the question... ALF, thanks for your answer. I understand that there are a lot of exceptions and oddballs out there, maybe I can narrow down the questions: 1. If I bought a take-off barrel from a 6mm Remington could I rechamber it in .243? 2. If I am trying to decide between building a 6.5 x 55 or a 257 Roberts, is the only difference the extra 2mm of case length in the parent 7 x 57 case of the Roberts? (aside from slight differences in the shoulder, focus on caliber to answer the question...) 3. Does a 7mm Remington Magnum shoot the same bullets as a 270 Win? | |||
|
| One of Us |
the bore diameter for the 6mm Remington and 243 Winchester are the same but the Remington chamber is bigger so the barrel would have to be set back a bunch for that to work. some confusion comes from true bore diameter and the groove diameter. groove diameter is usually .0075 to .0080 larger than the bore diameter the head diameter of the 6.5x55 swede is actually larger than the 7x57 case head diameter. the shoulder locations are different so it is not only 2 mm in length. the 7 mm magnum shoots bullets .284 in diameter and the 270 Winchester shoots bullets .277 in diameter. | |||
|
| One of Us |
Thanks, but are the bullet diameters the same?
Does the 7mm Mag and 7x57 shoot the same diameter? | |||
|
| One of Us |
yes. | |||
|
| One of Us |
If you are confused about the relationship between cartridge nomenclature and actual bore and groove diameter of the barrel used, I suggest you simply Google the caliber. There is usually a detailed, informative and largely accurate Wikipedia article on a given cartridge, giving most of the pertinent details. Usually on a separate site there is also a sketch of the cartridge, giving the case dimensions. | |||
|
| one of us |
Modern US based bullets and bores are pretty standard where 7mm is given as . 284 inches but mathematically this is not correct because .284 is 7.21mm  Confused yet ? The problem is when one is shooting and loading older Euro metrics and British versions of euro's that issues of mismatch crop up especially when loading with US based bullets. A simple example is the 7mm Mauser aka .275 Rigby. The US the caliber 7mm is a .284 bullet. Which in metric is not a 7mm but a 7.21mm but in Europe a 7mm as in 7mm Mauser is given as anything 7.23mm to 7.25 mm (.285 inch) Original Hirtenberg bullets were 7.23mm and RWS bullets were .285 inches Now we have the 275 Holland and Holland which was their solution to the 7mm Rem Mag. This shot a .287 inch bullet and bullet makers like Kynoch and Woodleigh still make bullets specially for it! Woodleigh actually designates this bullet specifically for the H&H So then we have this screamer. the 7mm x 66 Vom Hofe Super Express with it's 7.7mm bullet ie .303 bullet....... but you cant shoot 303 British bullets in it because that is a .311 bullet  Model 66 Mauser ( Gehmann Rifle) in 7x66 HSE Vom Hofe Super express.  | |||
|
| one of us |
Does a 7mm Rem Mag and 7x57 shoot the same bullet ? No ! if you are shooting a modern US spec 7x57 in say a Ruger and a 7mm Rem mag yes ie .284 inch bullet if however you are shooting a original Euro spec 7x57 you are shooting a 7.25mm bullet and not the 7.21mm bullet ! | |||
|
One of Us |
The 6.5 and .257 are not the same diameter. 6.5 is .264. | |||
|
One of Us |
.224 = 5.56mm .243 = 6mm .257 = no common metric cartridge .264 = 6.5mm .277 = 6.8mm .284 = 7mm .308 = 7.62mm .323 = 8mm .338 = no common metric cartridge .366 = 9.3mm | |||
|
One of Us |
And Dave get's the ATFQ award. Mike Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue.  What I have learned on AR, since 2001: 1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken. 2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps. 3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges. 4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down. 5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine. 6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle. 7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions. 8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA. 9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not. 10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact. 11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores. 12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence. 13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances. | |||
|
| One of Us |
Montea6b, One exception is for Russian cartridges 7.62 refers to .311 as in 7.62x54r and 7.62x39 Mike Never under estimate the internet community's ability to reply to your post with their personal rant about their tangentially related, single occurrence issue. What I have learned on AR, since 2001: 1. The proper answer to: Where is the best place in town to get a steak dinner? is…You should go to Mel's Diner and get the fried chicken. 2. Big game animals can tell the difference between .015 of an inch in diameter, 15 grains of bullet weight, and 150 fps. 3. There is a difference in the performance of two identical projectiles launched at the same velocity if they came from different cartridges. 4. While a double rifle is the perfect DGR, every 375HH bolt gun needs to be modified to carry at least 5 down. 5. While a floor plate and detachable box magazine both use a mechanical latch, only the floor plate latch is reliable. Disregard the fact that every modern military rifle uses a detachable box magazine. 6. The Remington 700 is unreliable regardless of the fact it is the basis of the USMC M40 sniper rifle for 40+ years with no changes to the receiver or extractor and is the choice of more military and law enforcement sniper units than any other rifle. 7. PF actions are not suitable for a DGR and it is irrelevant that the M1, M14, M16, & AK47 which were designed for hunting men that can shoot back are all PF actions. 8. 95 deg F in Africa is different than 95 deg F in TX or CA and that is why you must worry about ammunition temperature in Africa (even though most safaris take place in winter) but not in TX or in CA. 9. The size of a ding in a gun's finish doesn't matter, what matters is whether it’s a safe ding or not. 10. 1 in a row is a trend, 2 in a row is statistically significant, and 3 in a row is an irrefutable fact. 11. Never buy a WSM or RCM cartridge for a safari rifle or your go to rifle in the USA because if they lose your ammo you can't find replacement ammo but don't worry 280 Rem, 338-06, 35 Whelen, and all Weatherby cartridges abound in Africa and back country stores. 12. A well hit animal can run 75 yds. in the open and suddenly drop with no initial blood trail, but the one I shot from 200 yds. away that ran 10 yds. and disappeared into a thicket and was not found was lost because the bullet penciled thru. I am 100% certain of this even though I have no physical evidence. 13. A 300 Win Mag is a 500 yard elk cartridge but a 308 Win is not a 300 yard elk cartridge even though the same bullet is travelling at the same velocity at those respective distances. | |||
|
| One of Us |
Mike you are, as always correct, I thought about that discussion but thought it would muddy the waters.... | |||
|
| One of Us |
The "Euro spec" 7x57 ammo I have must be out of spec. The bullets measure .284". How many angels can dance on the head of pin ? | |||
|
| one of us |
Craigster: The original specification for the 7x57 as per the Mauser Patents for the rifle and cartridge did not call for a .284 bullet ! This is the rare complete collection of early Mauser patents by Korn  GS Custom knowing this actually make their bullets for the two versions. Here is a picture of a original "boer war" DMK 7x57 bullet on the left and a modern US spec Hornady .284 on the right. The difference in diameter is obvious. The most complete (to my knowledge) list of original 7mm ammo and examples can be found in Bester's two books on the small arms of the Boer War and can be seen at the Museum of the Boer War in Bloemfontein South Africa.  Some years ago just after the STW was released I did a article on the loading for the STW with Somchem powders in Man Magnum and actually measured various "available at the time" 7mm bullets. Many were Euro bullets not commonly seen in the USA. As for rifles in 7x57 and 275 the earliest models in my collection go back to 1893.    1895 Plezier Mauser  Early English translation of the Mauser spec sheet sold with the first Rigby 275's  | |||
|
| One of Us |
The simple answer is that the metric sizes are measuring the bore while the Imperial units are groove. Not all follow this form, but most do. | |||
|
| one of us |
Cartridge names are like Bob, Mike and John, they are just names and no technical spec can be derived from the name. For instance, a 260 Remington and a 264 Win Mag are the same caliber and a 308 Win, 300 Win Mag and a 30-06 Springfield are all the same bore and groove but not the same twist. A 325 WSM is neither bore or groove diameter and 7 mm of any description is not 7 mm. If you want to know the bore/groove/twist of a cartridge, go to the CIP or SAAMI spec for that cartridge. | |||
|
| One of Us |
"The 6.5 and .257 are not the same diameter. 6.5 is .264." Exept .25-35 win who are called 6,5*51r in metric. | |||
|
| one of us |
When a strong man armed keepeth his palace, his goods are in peace - Luke 11:21 Suppose you were an idiot... And suppose you were a member of Congress...But I repeat myself. - Mark Twain | |||
|
One of Us |
You can look up these cartridges in most any reloading manual. In the cartridge specs, they list bullet diameter. Leo The only way to know if you can do a thing is to do it. | |||
|
| one of us |
Let's not forget the.340 Weatherby, which shoots a .338 bullet, or the .460 , which is actually a .458. Grizz Indeed, no human being has yet lived under conditions which, considering the prevailing climates of the past, can be regarded as normal. John E Pfeiffer, The Emergence of Man Those who can't skin, can hold a leg. Abraham Lincoln Only one war at a time. Abe Again. | |||
|
one of us |
7.25mmm = .2854".You must have a pretty good eye if .0014" diameter difference (.5% difference) is obvious. GOOGLE HOTLINK FIX FOR BLOCKED PHOTOBUCKET IMAGES https://chrome.google.com/webs...inkfix=1516144253810 | |||
|
| One of Us |
Then there are the various 6.5mm: 6.5mm x 50mm (Ariska) 0.264" bullet dia. 6.5mm x 52mm (Carcano) 0.268" bullet 6.5mm x 53mm (Dutch) 0.262" bullet 6.5mm x 54mm (Mannlicher) 0.263" bullet (originally) Cartridges and bullets are a confusing mess. | |||
|
| one of us |
GOOGLE HOTLINK FIX FOR BLOCKED PHOTOBUCKET IMAGES https://chrome.google.com/webs...inkfix=1516144253810 | |||
|
| Powered by Social Strata |
 | Please Wait. Your request is being processed... |
|
Visit our on-line store for AR Memorabilia