Home Forums Hunting & Shooting Ask The Gunwriters Question about metric conversion

The other day, someone had a thread about a 8mm rifle. Having never heard of such, I googled up a conversion site and looked it up. Then as a fluke, I checked some others that I thought I knew. Such as 6mm = .244, nope = .236...... What about 6.8 = .277, wrong again = .268. One more try, 5.56 = .223, nada = .219

My reloading stuff is all boxed up, while I'm remodeling a house, so I cant go grab a bullet and check it out with the calipers. So what am I missing?

You are confusing the groove diameter with the bore diameter.

Looks like the metric designation is referring to bore diameter whereas our imperial designations are typically groove diameter.

Except when they are not. 218 Bee, 250 Savage, 256 Newton, 300 Savage, 30/30, 30/40/ 30/06, 350 Rem, to name a few. In the end, it's all pretty meaningless. GD

Yeah, you're right!

The numbers are all over the place. The 8x57 was also called 7.92x57. The 325WSM is an 8mm (0.323"). They all need "-ish" added to the end of their names.

Too funny! Except for my wife who is from Minnesota, to her "ish" means" Yuck!"

Then there are the two different 7.9x57 groove diameters, .318" and .323"--though the bore diameter is the same.

Plus, 7.9mm and 8mm....

There's 25.4 MM to an inch, but simply doing the math doesn't always work. For instance, if we multiply 25.4 by .308, the calculator spits out 7.823 - - - - -not the 7.62 that we usually associate with ".30 caliber". Inch/MM conversions are a SWAG at best!
Jerry

7.62 / 25.4 = 0.3 the .300" bore size associated with 30 cal

The world needs to come to grips with the fact that the inch/foot/yard measuring system is far better than the damned metric system!

I could agree with you but then we would both be wrong!


Jerry

I would agree with you so then we could both be right!

Nope, you'd both be still wrong.

The metric system is perfect;

10mm = 1cm - 100cm = 1 metre - 1000 metres = a kilometre

10ml = 1cl - 100cl = 1 litre - 1000l = 1 kiloletre

Water boils @ 100*C & freezes at 0*C (roughly)

JOC wrote a good chapter on it in the Rifle Book titled "how Cartridges are Named" I think. Some for bore diameter and some for groove diameter. I've never understood the rant about metric. metric is what it is. We here in the US have grown up with the imperial system so we're comfortable with it. Europe has the metric system and our autos are a mix of the two. You can convert and machine just as precise either way. Threading metric with an inch lead screw lathe that's geared for it isn't as easy as cutting imperial threads. Cutting metric threads on a metric geared lathe isn't so easy either. The thread dial is a mass of gears. Then there's British Whitworth.

I had forgotten about British Whitworth, glad you mentioned it. Several years ago, I was working for a company that made machinery, thus there was a machine shop. Once in a while, they would take in machines, not made by them, for repair. Usually machines that no one else would touch. One day, one of the foreman came by my office and asked if I would come look at a machine they were having problems with. None of our bolts would fit. A machinist helper had disassembled the machine and thrown away the old bolts. Gonna replace them during reassembly, but nothing we had would fit, different threads. Found one of the old bolts and none of our thread gauges matched the bolt. Didn't know what we had.

I was told they took the bolt, to the the place where they bought bolts, and they figured out it was Whitworth. Guess the machine had been made somewhere in the UK, but that's just a guess. Last I knew, they were trying to find the correct bolts, instead of having to tap out the holes. Never did find out what they did.

The bullet does the job, so I don't really care about land or groove diameters. This confusion should have been avoided from the beginning.

Ok wise guy divide a meter by 3, divide the meter by 4, What is the metric equal of .001? Notice anything here?

The metric system, being invented by the French, cannot be perfect. At least we can never let them think that it is, they're arrogant enough already.

1 Metre = 100cm/3 = 33.3cm or 333mm

1 Metre - 100cm/4 = 25cm or 250mm

1" = 2.54cm/1000 = 0.00254mm

Don't see your problem