As said, GB doesn't set the rate. It's the actual vendor shipping from his location to your zip code. One guy across the country could be cheaper but his shipping at $35, compared to another at a higher price with flat rate across the state might be cheaper.
This is entirely normal across all vendors across the internet.
I bought a pistol based on my "front door cost," the vendor was $10 more than everyone else, but he also offered "free shipping." Which it was, and that was the overall lowest cost to my "front door," ie the FFL.
This is the same thing I discuss with customers who state their internet vendor offers a lower price than my auto parts store. Ok, it is - the most common mentioned is Rock Auto - which is really a "server farm in strip mall," no storefronts, compared to the 5,000 stores in my company, most of who stock the part on the shelf nationwide ready to pick up, the shipping is part of the price. The customer never wants to include his shipping, making it an unfair comparison, and often never considers that a used part installed cannot be returned. I will accept your mistake in not describing your vehicle correctly, and I will warranty said part next year even if you installed it incorrectly. The internet won't.
I say all that to provide an example of how people look at things and think the brick and mortar store is "too darn high!" Ignoring the cost of shipping and the protection of addon service is usually ignored when it comes up. In the OP's case not finding one in stock is a bummer, but finding the best online price is still a matter of due diligence. Don't fool yourself when it comes down to price, include all the charges, to get to a front door price. That is what you will really pay, so it goes to including shipping to see who has the better deal.
I bought my Kahr .380 from a local dealer, a Taurus UL from the internet. The Kahr was no more expensive, but the local guys wanted $100 more for the Taurus "front door priced." Okay, I will have it my way and eat Burger King today. Next time? Who knows. It's always a spin the price and see what you get. No guarantees in life.
BTW I have shopped out of store for my auto needs, I can get synthetic oil $1 a quart cheaper than my employee price from the ag stores. A trailer hitch, not so much. Shipped to my store. You gotta shop it.