The biggest giveaway is the stock. The barrel isn't correct as well. M40A1s used Schneider rough finished barrels. The Marines like the rough finish on the barrels because it held paint.

The mount looks like the correct mount but its a repo. That mount is still worth a good bit probably $300-$400

There are a few builders that specialize in correct clones. I used Raven Rifles https://ravenrifles.wordpress.com (he is now retired) because he's well respected in the clone community and lives close by smile I had a hard time with shipping some of the parts across the country to have mine built. My M40A1 was built on one of the return stocks.
Here is a pic from the other thread discussing m40s
[Linked Image from i.imgur.com]