# What's the bulge in the Abrams cannon barrel?

**URL:** <https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705>\
**Category:** Factual Questions\
**Created:** [April 10, 2003, 2:27am UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705 "2003-04-10T02:27:31Z")\
**Posts on this page:** 5\
**Page:** 1

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**Author:** ![Rockmotteller](https://avatars.discourse-cdn.com/v4/letter/r/51bf81/32.png) [@Rockmotteller](https://boards.straightdope.com/u/Rockmotteller)\
**Post date:** [April 10, 2003, 2:27am UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705/1 "2003-04-10T02:27:31Z")

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Roughly half way along the length of the 120mm cannon barrel of the M1 Abrams tank there is an oblong bulge. What is it?

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**Author:** ![Turbo\_Dog](https://avatars.discourse-cdn.com/v4/letter/t/ce73a5/32.png) [@Turbo\_Dog](https://boards.straightdope.com/u/Turbo_Dog)\
**Post date:** [April 10, 2003, 2:41am UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705/2 "2003-04-10T02:41:40Z")

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It’s a bore evacuator. It keeps the gun gases moving forward and out instead of moving back into the tank after firing/during reloading.

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**Author:** ![peepthis](https://avatars.discourse-cdn.com/v4/letter/p/9d8465/32.png) [@peepthis](https://boards.straightdope.com/u/peepthis)\
**Post date:** [April 10, 2003, 2:49am UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705/3 "2003-04-10T02:49:46Z")

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This was just asked and answered recently [in this thread](http://boards.straightdope.com/sdmb/showthread.php?s=&threadid=171779).

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<div class="post-metadata">

**Author:** ![Rockmotteller](https://avatars.discourse-cdn.com/v4/letter/r/51bf81/32.png) [@Rockmotteller](https://boards.straightdope.com/u/Rockmotteller)\
**Post date:** [April 10, 2003, 3:05am UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705/4 "2003-04-10T03:05:12Z")

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Ah, thanks. Sorry I missed the earlier thread. Did a search, but…oh well.

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**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\
**Post date:** [April 10, 2003, 2:03pm UTC](https://boards.straightdope.com/t/whats-the-bulge-in-the-abrams-cannon-barrel/167705/5 "2003-04-10T14:03:48Z")

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“What’s the bulge in the Abrams cannon barrel?”

It’s glad to see you. 😃