# Why the use of strange calibers like 5.56mm, 7.62mm, 155mm, 203mm? **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2022, 6:42am UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311 "2022-09-10T06:42:16Z")\ **Posts on this page:** 5\ **Page:** 2
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [September 11, 2022, 6:03pm UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311/21 "2022-09-11T18:03:25Z")
Its a tragedy thats the .280 British never saw service. It had much more ooomoph than the 5.56mm but less of the full auto controllability issues the 7.62mm did. ---
**Author:** ![AK84](https://avatars.discourse-cdn.com/v4/letter/a/85e7bf/32.png) [@AK84](https://boards.straightdope.com/u/AK84)\ **Post date:** [September 11, 2022, 6:06pm UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311/22 "2022-09-11T18:06:23Z")
I just want to point out that the the two most popular 7.62mm rounds, the 7.62x51 NATO and the 7.62x39 Kalashnikov bullets are actually 0.308 and 0.311 inches in diameter. ---
**Author:** ![JRDelirious](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jrdelirious/32/9531_2.png) [@JRDelirious](https://boards.straightdope.com/u/JRDelirious)\ **Post date:** [September 11, 2022, 6:11pm UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311/23 "2022-09-11T18:11:42Z")
And now the US is moving towards adopting 6.8x51mm/.277Fury. ---
**Author:** ![Alessan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/alessan/32/465_2.png) [@Alessan](https://boards.straightdope.com/u/Alessan)\ **Post date:** [September 11, 2022, 9:59pm UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311/24 "2022-09-11T21:59:00Z")
You know, I Googled that round, and while I found plenty of information about PSI and other ballistic data, I can’t fine anywhere that says how much it _weighs_. How many rounds fit in a magazine? How many mags can you carry? You know, the important stuff. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [September 11, 2022, 10:32pm UTC](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311/25 "2022-09-11T22:32:16Z")
> [@Alessan](#): > > You know, I Googled that round, and while I found plenty of information about PSI and other ballistic data, I can’t fine anywhere that says how much it _weighs_. How many rounds fit in a magazine? How many mags can you carry? You know, the important stuff. > [@](#): > > The XM5, which weighs about two pounds heavier than the M4, and the XM250, which is about four pounds lighter, are still in their prototype phase and may change slightly by the time it is out for mass production. The XM5 weighs 8.38 pounds and 9.84 with the suppressor. The XM250 weighs 13 pounds with a bipod and 14.5 with the suppressor. > > Currently the XM5 basic combat load is seven, 20-round magazines, which weighs 9.8 pounds. For the XM250 the basic combat load is four 100-round pouches, at 27.1 pounds. For comparison: the M4 carbine combat load, which is seven 30-round magazines, weighs 7.4 pounds, and the M249 light machine gun combat load, which is three 200-round pouches, weighs 20.8 pounds. > > The overall length of the weapons with suppressors attached are 36 inches long for the XM5 and 41.87 inches long for the XM250. The barrel of the XM5 is 15.3 inches long and the XM250 is 17.5 inches long. The barrel on the XM250 is also not considered a quick-change barrel like the M249. > **[NGSW signifies an evolution in Soldier lethality](https://www.army.mil/article/256697/ngsw_signifies_an_evolution_in_soldier_lethality)** > > WASHINGTON –- The future Soldier will soon be significantly more lethal. The Army recently announced that the Next Generation Squad Weapon, the XM5 rif... [Previous page](https://boards.straightdope.com/t/why-the-use-of-strange-calibers-like-5-56mm-7-62mm-155mm-203mm/971311.md?page=1)