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Why do they call it 28mm

Posted: 19 Jan 2017, 00:31
by celtic88
Anyone know which projectile is 28mm?
Of the 6 or 7 different bullets I have range from 13mm to 20mm
I did a little bit of looking earlier and 20mm is as long as I can find.
My 7.62x39's are 39mm long and my 7.62x51 are 51mm long,
Why are the 5.7x28 not 28mm long?
Not that it really matters though

Re: Why do they call it 28mm

Posted: 19 Jan 2017, 04:52
by DoubleJ
It's the case length...but not exactly.

Re: Why do they call it 28mm

Posted: 19 Jan 2017, 09:15
by celtic88
Yeah definitely not exactly. 28mm is 1.105in
I get 1.137 on fnh brass and 1.135 on ae brass.
But I guess that's splitting hairs talking hundredths of an inch.

Re: Why do they call it 28mm

Posted: 19 Jan 2017, 17:10
by DoubleJ
Yup, welcome to FN world, where no one else lives. It's also not a .224 bore, saw one slugged recently at .221. I measured a fired case, came up with 29.xx mm without trimming, but no way am I knocking a mm off during trimming, so it's all make believe, just like the .38 and .380.

Re: Why do they call it 28mm

Posted: 16 Mar 2017, 15:52
by Grocerius Maximus
.224" (5.7mm) is NOT the bore size, its the nominal bullet diameter. In 22 centerfire nominal bore diameter will be .005"-.006" under bullet diameter depending on rifling geometry, .218"-.219".