The service rifle is based on a AR-15.

The assualt carbine is based on a Colt Commando/CAR-15.

The Chinese AR is based on a Galil /Type 56 hybrid and both these guns are AK family variants.

The Service Rifle is a "mash up" of AR-15 and AR-10.

The I suppose you mean the Handmade Rifle in Nuka World is based on AK-47 yes.

Technically, the Handmade Rifle*F76 Variant*/Chinese Assault Rifle are nonsense. An AK chambered in .223/5.56x45 is a relatively new phenomenon that has taken place in the past decade or so. An AK-47 is chambered in 7.62x39 while the AK-74 is chambered in 5.45x39. The reasons for an AK chambered in .223 or 5.56x45 is due to the popularity of the AR-15 in the USA and also the sanctions that the USA has put on Russia, *The dudes who make 5.45x39 cartridges.* Acquiring 5.45x39 is expensive and harder to come by.

I'm not a fan of the "AR-15 type" weapons in New Vegas, they feel out of place with the era that Fallout is set in.

The Service Rifle and Survivalist's Rifle are fine in my opinion, but the Assault Carbine and Marksman Carbine are too modern in my opinion.