How can I convince my mom to let me buy an airgun/pellet gun?

I'm 13 and really want a pellet gun just for target shooting in my backyard. I have had airsoft guns for a couple of years and have never gotten into any trouble with them. My mom just thinks its a waste of money because I already have airsoft to shoot targets with. The pellet gun that I want is on sale for 25%... show more I'm 13 and really want a pellet gun just for target shooting in my backyard. I have had airsoft guns for a couple of years and have never gotten into any trouble with them. My mom just thinks its a waste of money because I already have airsoft to shoot targets with. The pellet gun that I want is on sale for 25% off this week only, so I want to buy it while its still on sale.

This is the gun I want: http://www.canadiantire.ca/AST/browse/5/SportsRec/1/Hunting/Airguns/PRD~0755031P/Dual%252BCalibre%252BAir%252BRifle.jsp?locale=en

She just keeps saying she's not sure it if's a good idea or not.

So pleeeaseee How can I convince my mom to let me buy a pellet gun?
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