Caliber and Actual Measurements

[rwm]

Are 38 and 357 really the exact same projectile? Or just very close? I measured a 7.62 x 51 and it is .308". Is a 300 WM really .300? I don't have one to measure.

 

[verbotenwhisky]

The idea that .223 and 5.56 cannot be interchanged is a myth.
They have different pressure because the use different units.
One is PSI and the other is CUP.
They are the same round.

That is incorrect. The difference between the .223 and 5.56 Nato is the Thickness of the brass the size of the load, when fired the 5.56 dose not expand the same. You can fire both cartridges from the same chamber; however over time firing the 5.56 from the .223 chamber will cause the chamber to wash out. additionally, due to the difference in the expansion of the brass you'll loose accuracy firing the .223 through the standard 5.56 chamber. the recommendations are not to fire the 5.56 through a standard .223 chamber, either round can be fired in the 5.56 chamber but you'll be less accurate using a .223 and then there is the .223 wylde which is chambered in such a manner as the take advantage of both .223 and 5.56, it is not awesome for either round but is good for both.

 

[verbotenwhisky]

Are 38 and 357 really the exact same projectile? Or just very close? I measured a 7.62 x 51 and it is .308". Is a 300 WM really .300? I don't have one to measure.

I believe, I need to check this as it has been a while since I last read up on it but, the .300 is the barrel bore and the projectile is .308 which create a tight fit. Many believe that a heavy load makes these perform better but it is my experience that a less than max load is best because the heavier load will channel around the bullet and keep it from seating properly in the rifling which reduces the spin/stability and thus accuracy.

The 38 Special and the 357 are the same projectile and both can be shot through the same weapon.

 

[rwm]

Seems weird to me that the 5.56 barrel will take either round but when you get to the AR-10 its the converse. The 308 barrel will take either round. The 7.62 will not, at least theoretically it's not recommended.

 

[rabler]

My vague recollection is that to some extent, the third digit (.308, or .223, or ...) has gotten corrupted in use to differentiate between similar diameter rounds, rather than being the precise diameter which is found in the detailed specs.

 

[rwm]

Module 10 :: Caliber/Diameter

projects.nfstc.org

 

[verbotenwhisky]

Seems weird to me that the 5.56 barrel will take either round but when you get to the AR-10 its the converse. The 308 barrel will take either round. The 7.62 will not, at least theoretically it's not recommended.

That is correct, the 7.62 NATO is not as hot as the .308, primary difference again is the brass thickness but in the case of the 7.62 the cartridge will not fit as much powder, I think the brass is thicker relatively speaking. I had a 7.62 that I had to put an adjustable gas block on to get it to cycle properly, prior to doing so a .308 cartridge would cycle the gun but a 7.62 would not. I can tell you for a fact that the gas port on a DSME pastern gun is larger for the 7.62 and smaller on the .#)* version.

 

[pdentrem]

And I always thought a thirty ought six was a 0.3006 OD round! Thanks all for the education. Feel free to keep going.

The 30-03 Springfield had a round nose 225 grain projectile which the 1903 Springfield was originally chambered for. Due to advances in powder and other considerations was reworked to a Spitzer point 150 grain bullet and a small change in the cartridge dimensions and called the 30-06 For the year 1906.

 

[verbotenwhisky]

The 30-03 Springfield had a round nose 225 grain projectile which the 1903 Springfield was originally chambered for. Due to advances in powder and other considerations was reworked to a Spitzer point 150 grain bullet and a small change in the cartridge dimensions and called the 30-06 For the year 1906.

other than the projectile diameter those are completely different rounds....

 

[Eyerelief]

Are 38 and 357 really the exact same projectile? Or just very close? I measured a 7.62 x 51 and it is .308". Is a 300 WM really .300? I don't have one to measure.

Yes, 38 and 357 use the same projectile. A 30-06, 300 WM, 300 WSM, 300 WBY, yada yada yada are all .308 bullets.