Despite gun sales declining in 2017 from previous record levels, millions of firearms still fly off the shelves each year, and personal preferences make it difficult to pin down which model is anyone's favorite. It's even harder to determine which offerings are best-sellers, because only Smith & Wesson owner American Outdoor Brands (NASDAQ:SWBI) and Sturm, Ruger (NYSE:RGR) are publicly traded.

In order to find out what firearms are most popular these days, I turned to, the world's largest online auction site for firearms and accessories, which every month publishes the five best-selling firearms on its Gun Genius site.

Sig Sauer interchangeable grip configurations

Image source: Sig Sauer.

While Gun Genius lists the leaders in every major category of firearms sold, breaking them down between new and used, I limited the selection to the five best-selling new, semi-automatic pistols. However, doesn't list specific numbers for the guns sold -- no raw unit totals or total dollar values. I compiled all of the monthly lists from this year and tallied the results for the best-selling guns of 2017 based on a rough scoring system. There were 13 different models from seven separate manufacturers that made the overall list -- here are the top 5 (with a tie for fifth place).

A Kel-Tec PMR-30 against a white background.

Image source: Kel-Tec Weapons.

5. Kel-Tec PMR-30 and Sig Sauer P320 (tie)

The Kel-Tec PMR-30 continues to be a popular firearm for gun buyers thanks to its light weight and durability. The 30-round, .22 magnum semi-auto reportedly had Kel-Tec running at full capacity earlier this year to try and keep up with demand, so it's not surprising it landed on this list.

While the popularity of the Sig Sauer P320 seemed to grow as the year progressed, even reaching the top spot in August, it disappeared from the list in September, which may have had to do with numerous reports that the firearm could accidentally discharge when dropped at a certain angle. Several videos of the discharge were recreated, leading Sig Sauer to issue free upgraded parts to correct the problem.

Two Glock 19's against a black background.

Image source: Glock.

4. Glock 19

The Glock 19 is one of the most popular handguns of all time and has gone through several generations of changes. However, the handgun barely registered on the best-selling lists until late summer when Glock introduced the fifth generation of the firearm that included upgrades to nearly two dozen features with some of the more important ones, including new barrel rifling, ambidextrous slide stops, and a flared magazine well. It's clear the gun buying public approved of the upgrades.

A Sig Sauer P938 and holster on top of a jacket.

Image source: Sig Sauer.

3. Sig Sauer P938

Another handgun built for concealability, this lightweight, hammer-fired, single-action semi-auto, with aluminum alloy frame and steel slide is one of a number of variants on the micro 1911 platform. At under six inches in length, it is one of the smallest on the market and makes for a good all-around concealed carry weapon in virtually any situation, which is probably why it ranks so highly year after year.

A Smith & Wesson M&P 9 Shield 2.0 with a box of ammunition on top of a target.

Image source: Smith & Wesson.

2. Smith & Wesson M&P 9 Shield

Even though Smith & Wesson's parent, American Outdoor Brands, looks like it's stuck in a downward spiral as gun demand weakens, its M&P 9 Shield model remains one of the most popular guns in its line-up. The company even upgraded the firearm at the start of the year with the 2.0, a feature-rich offering that was offered first in full-sized 9 mm, 40S&W, and .45 Auto versions, with the promise of future additions and extensions coming. The M&P 9 Shield had more monthly first place finishes than any other handgun on the list.

A Sturm, Ruger LCP II against a white background.

Image source: Sturm, Ruger.

1. Ruger LCP

But it Sturm, Ruger's LCP that came out as the overall winner, and it continues to drive the company's top line. Sales of the LCP II, the Mark VI pistol, and Precision Rifle all helped keep new product sales at 30% of Ruger's total revenue across the first nine months of the year. With a lower price than other similar handguns in Ruger's arsenal, it rightly earned its place atop this list.

Industry demand has normalized after years of record sales, and firearms companies are hoping that new models, features, and other upgrades will set their products apart in this highly competitive environment. But momentum appears to be building this holiday season with background checks hitting a new high on Black Friday. The handguns on this list have proven incredibly popular, and they'll likely make up a significant portion of firearms sales in the coming weeks and months.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.