Jessica Davis (Alisha Boe) shows off her father's Glock 19 to Bryce Walker (Justin Prentice) and pressures him into handling it in "Tape 5, Side B" (S1E10). She says it's a Glock 19 and it's her "favorite gun" and that it "holds 15 rounds" which she is correct about, but since the show takes place in California, 15-round mags are officially illegal due to California's strict laws regarding so-called "high-capacity" magazines.
When Jessica sneaks into her father's gun safe, more guns are shown in "Tape 5, Side B" (S1E10).
Tyler's Gun Cache
In season 1's finale "Tape 7, Side A" (S1E13), Tyler Down (Devin Druid) adjusts his cache of illegally purchased firearms, ammunition, and homemade pipe bombs. Note: in "Tape 6, Side B" (S1E12), Tyler illegally purchased a handgun covered with a cloth (heavily implied to be the Kimber Ultra Raptor) and it is mentioned that it "has a bit of a kick". Since it is not clearly shown enough for an ID, it's not in one of entries above.