300$ gaming pc?

You can't get anything better than this:

PCPartPicker part list / Price breakdown by merchant

CPU: Intel Pentium G4400 3.3GHz Dual-Core Processor ($57.33 @ OutletPC)
Motherboard: ASRock H110M-HDS Micro ATX LGA1151 Motherboard ($44.99 @ SuperBiiz)
Memory: Patriot Viper 4 8GB (1 x 8GB) DDR4-2400 Memory ($52.79 @ Newegg)
Storage: Western Digital AV-GP 500GB 3.5" 5400RPM Internal Hard Drive ($28.35 @ Amazon)
Video Card: Asus Radeon RX 460 2GB Dual OC Video Card ($89.99 @ SuperBiiz)
Case: Rosewill FBM-01 MicroATX Mini Tower Case ($19.35 @ Amazon)
Power Supply: EVGA 450W 80+ Bronze Certified ATX Power Supply ($37.49 @ OutletPC)
Total: $330.29
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2017-03-29 05:38 EDT-0400

Although I'd highly recommend you to make a used parts build if you can't go more than 300$.
 
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