It supplies a formidable variety of guns, ammo, and armor. Eldridge pays Jules on Virgin street to send newcomers his way and also pays for an advertising slot during boxing matches at the Jungle Gym. It can be inferred that Eldridge is a supporter of the NCR by the numerous NCR posters and the promotional NCR History Holodisk found in his shop. Also, the New Reno Arms is the only independant store in New Reno, not affiliated to any of the Mafia families.
All retrofitting of weapons provided by Eldridge is performed by the munitions savant Algernon. Algernon lives in the basement of New Reno Arms tinkering amid the squalor and scattered parts surrounding him. The basement includes a fair array of tools, ammo, and even a howitzer. If you can break through the store's back door and get past Eldridge's three dogs (Packard, Buck, and Missy) down to Algernon, he can upgrade any weapon for free.
Eldridge also reserves a special stock of heavy weapons offered at discount prices exclusively to a Made Man of any family. If you want to avoid confrontation with Eldridge, make sure you sneak in during day time and only come upstairs during day time.