# Re modifying guns & homemade guns - At what point does a modification become illegal? **URL:** \ **Category:** Factual Questions\ **Created:** [February 18, 2007, 5:41pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722 "2007-02-18T17:41:01Z")\ **Posts on this page:** 6\ **Page:** 1
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [February 18, 2007, 5:41pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/1 "2007-02-18T17:41:01Z")
[I was looking at this thread on high powered air guns](http://boards.straightdope.com/sdmb/showthread.php?t=408884), and wondered what the legal status of an airgun would be that was modified to shoot larger 22 caliber pellets vs the no-license required .177 pellet ammo. It’s still an airgun, but it’s shooting 22 caliber sized pellets now. What about a BB gun that’s souped up to spray BB’s at very high velocities? What governs how far you can tweak a gun out of spec before it becomes illegal? Also, what about entirely homemade weapons. Let’s say you made an air powered blunderbuss that shot pea gravel at deadly velocities. Who’s going to tell you that you can’t carry that gun in your car? It’s not a gunpowder based firearm, and it doesn’t use bullets. ---
**Author:** ![Unregistered\_Bull](https://avatars.discourse-cdn.com/v4/letter/u/3da27b/32.png) [@Unregistered\_Bull](https://boards.straightdope.com/u/Unregistered_Bull)\ **Post date:** [February 18, 2007, 8:46pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/2 "2007-02-18T20:46:19Z")
[QUOTE=astro] [I was looking at this thread on high powered air guns](http://boards.straightdope.com/sdmb/showthread.php?t=408884), and wondered what the legal status of an airgun would be that was modified to shoot larger 22 caliber pellets vs the no-license required .177 pellet ammo. It’s still an airgun, but it’s shooting 22 caliber sized pellets now. What about a BB gun that’s souped up to spray BB’s at very high velocities? What governs how far you can tweak a gun out of spec before it becomes illegal? Also, what about entirely homemade weapons. Let’s say you made an air powered blunderbuss that shot pea gravel at deadly velocities. Who’s going to tell you that you can’t carry that gun in your car? It’s not a gunpowder based firearm, and it doesn’t use bullets. [/QUOTE] Airguns are not a firearm in the US. US Federal firearms laws don’t apply to them. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [February 18, 2007, 8:50pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/3 "2007-02-18T20:50:59Z")
[QUOTE=Unregistered Bull] Airguns are not a firearm in the US. US Federal firearms laws don’t apply to them. [/QUOTE] Interesting. Thanks. ---
**Author:** ![Unregistered\_Bull](https://avatars.discourse-cdn.com/v4/letter/u/3da27b/32.png) [@Unregistered\_Bull](https://boards.straightdope.com/u/Unregistered_Bull)\ **Post date:** [February 18, 2007, 9:26pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/4 "2007-02-18T21:26:26Z")
[QUOTE=astro] Interesting. Thanks. [/QUOTE] You’re welcome. Keep in mind that making a moderator for one that would also work on a real firearm would be illegal. Some states and other localities might also have different laws regarding airguns as well. Here is a link to some airgun forums. [AirgunForums](http://airgunartisans.com/AirgunForums.htm) The Crosman forum will have a lot of cool custom work. ---
**Author:** ![Kevbo](https://avatars.discourse-cdn.com/v4/letter/k/e47774/32.png) [@Kevbo](https://boards.straightdope.com/u/Kevbo)\ **Post date:** [February 18, 2007, 9:40pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/5 "2007-02-18T21:40:51Z")
[QUOTE=astro] [I was looking at this thread on high powered air guns](http://boards.straightdope.com/sdmb/showthread.php?t=408884), and wondered what the legal status of an airgun would be that was modified to shoot larger 22 caliber pellets vs the no-license required .177 pellet ammo. It’s still an airgun, but it’s shooting 22 caliber sized pellets now. [/QUOTE] In the US, an airgun is an airgun. Canada has some limits on muzzle energy if I recall correctly. Changing the bore diameter doesn’t change the muzzle energy. The spring section of an air rifle is referred to as the “powerplant” To increase the power, the spring has to change. As far as firearm modifications, quite a lot can be done. There are minimum barrel length limits and overall length limits that must be observed. It is, for example, illegal to add a shoulder stock to most pistols…it then becomes an illegal short-barreled rifle. One case where this was done legally, a longer barrel was also added, and the stock attached to that barrel only. ---
**Author:** ![St\_Ides](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@St\_Ides](https://boards.straightdope.com/u/St_Ides)\ **Post date:** [February 18, 2007, 10:23pm UTC](https://boards.straightdope.com/t/re-modifying-guns-homemade-guns-at-what-point-does-a-modification-become-illegal/392722/6 "2007-02-18T22:23:41Z")
[QUOTE=Kevbo] Canada has some limits on muzzle energy if I recall correctly. [/QUOTE] Not muzzle energy. Muzzle velocity, 500 feet per second max. It’s a European country that has the muzzle velocity limit (I think Germany, but I’m not entirely sure.) I seem to recall there were issues with paintball guns there… They only fired at 300fps, but the weight of the ball was great enough that it exceeded the muzzle energy laws. I believe an exemption was created. This does cause some issues for airsoft as well. It’s still a grey area here. Many airsoft guns can easily be upgraded beyond 500fps, not to mention that the whole “replica firearm” thing is not-strictly legal either.