Here are the restrictions on firearms in Washington D.C. budsgunshop.com/catalog/feeds/state_reg/washington_dc_restrictions.pdf

The DC restrictions say no threaded barrel (not under Semi rifle) all by itself makes it Illegal

I agree with you 100%, DC is not a state - But Buds lists it under "State Restrictions" and so does every one else including the BATF as it has regulations same as any state.

But DC is not a state

Here : gunsamerica.com/blog/50-state-legal-pump-ar-troy/

what I see is that because its a pump most of those restriction do not apply but on in the restrictions near the bottom it says The following are prohibited:
Magazines exceeding 10 rounds
.50 BMG ammunition
Collapsible/adjustable stocks
Stun Guns and TASERs
Defense Sprays
Batons
***********Threaded barrels****************
Air guns (pneumatic, spring, or BB) firing projectile exceeding .18” (i.e. .22 cal. Prohibited)
budsgunshop.com/catalog/feeds/state_reg/washington_dc_restrictions.pdf

I'd be very careful, and perhaps check with the manufacturer or Bud's before ordering as there are a number of items you cannot have on a semi auto rifle in D.C. Including: telescoping stock, flash hider, detachable magazine, or pistol grip. All of which this rifle appears to have. Bud's will not modify a firearm to make legal either.

The way I read the restrictions I would say that it is NOT legal in DC I believe it would be legal because it is a pump and only 10 rounds in the Magazine but the fact that it has a threaded barrel makes it illegal. I would check with my local FFL holder to make sure of any local laws that may affect it budsgunshop.com/catalog/feeds/state_reg/washington_dc_restrictions.pdf on page 3 it says no threaded barrels

Looks Ok to me! Enjoy it! The following are prohibited:
Magazines exceeding 10 rounds
.50 BMG ammunition
Collapsible/adjustable stocks
Stun Guns and TASERs
Defense Sprays
Batons
Threaded barrels
Air guns (pneumatic, spring, or BB) firing projectile exceeding .18” (i.e. .22 cal. Prohibited)
Ammunition Qualifier: For the purchase of ammunition, the purchaser must present a valid firearms
registration card.
The following are prohibited:
Semi-automatic shotguns with one or more of the following
1. Folding or telescoping stock
2. A pistol grip that protrudes conspicuously beneath the action of the firearm
3. Thumbhole stock
4. Vertical handgrip
5. Has the ability to accept a detachable magazine
6. Shotguns with revolving cylinders:
a. Franchi SPAS 12 and LAW 12
b. Striker 12. The Streetsweeper type S/S Inc. SS/12

Hi Terrance, It is legal in DC