Hi Ryan this isn't drilled and tapped for one. You would need to take it to a gunsmith.

Gunsmithing required. If you have not bought the gun I would recommend The H&R youth pump for around the same money its drilled and tapped to make it a single shot is simple just cut a wooden dowel to replace the magazine plug. specs and link to follow UPC:
010633051218
Description:
H&R PARDNR PUMP YTH 20M/21M B
Brand:
Harrington & Richardson
Model:
Pardner Pump Compact / Youth Model
Type:
Shotgun: Pump Action
Caliber:
20 Gauge
Finish:
Blue
Action:
Pump Action
Stock:
Black Synthetic, Checkered
Sight:
Bead
Barrel Length:
21
Overall Length:
41.125
Weight:
6.5 lbs
Capacity:
5+1, 3 Shot Plug Furnished
Safety:
Cross-bolt Safety
Receiver:
Blue, Drilled & Tapped
Chamber:
3
Chokes:
Screw-In Modified
Butt Plate:
Black Vented Recoil Pad
Features:
Grooved Forend, Vent Rib;
Length of Pull 13 budsgunshop.com/catalog/product_info.php/products_id/20983/H%26R+1871+NP1-2S1+Pardner+Compact+4%2B1+3+20ga+21

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