I know this is a done deal for you but I'm going to parrot what many others have said... a 10k loan for a gun is not really a good idea even if you are young, have few responsibilities, and want it before you get saddled with wife and kids.
Were my son to come up and ask my opinion, I would tell him he's lost his darn mind. He would get mad and not speak to me the rest of the day. We would be fine after a few hours or the next day. Sometimes he would never mention it again, he would just go out and do it because he wants to. Sometimes he realizes I'm right and skips it. Sometimes, when it's important to him, he would ask again the next day. What I would tell him at that point goes something like this....
If it means SO MUCH, then consider saving aggressively for the first half, and then take a loan on the second half? When you commit to saving half, you may find that 6 months to a year down the road owning a .50 for long range shooting wasn't as important as you thought it was. Maybe it's more about the long range shooting, and you will realize that you can get set up with an accurate rifle in .338 Lapua, reloading components, and good glass for WAY less. You may look at the cost reward analysis and decide that a 5k rifle with basically the same capabilities (the .338 has the record for longest kill in combat, BTW) as the 10k rifle makes more sense to you. OR... you'll find that you want that Barret just as bad as when you started saving so you can be more confident in your decision to take out a loan. That plan takes the "impulse" out of it. Also, you can save money on interest and you will only make payments for 1 or 2 years instead of 3 or 4. If you save aggressively, say 500 bucks a month, you can have 1/3rd of your price in 6 months. That's not a terrible wait time for big ticket purchase such as this, but it's just long enough to make sure it isn't "impulse." Be smart about how you conduct business and you're not likely to be saddled with the prospect of house, wife, and kids in that time frame either.