Fractions of the copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride containing 15.7 ± 0.5% of charged units are obtained by radical polymerization, fractionation, and hydrolysis. Viscous flow, velocity sedimentation, and translational diffusion of their dilute solutions are studied in 0.2 M NaCl. Viscosimetric studies are also carried out in a wide range of ionic forces: from the minimum (~10^–6 mol/L) to the maximum (6 mol/L). The hydrodynamic volumes and equilibrium rigidity of the copolymer under study are compared with the data obtained earlier for an uncharged homopolymer and a copolymer with a higher linear charge density (~44% of charged units) in solutions with different ionic strength. The correspondence of the values obtained to the theories of Odijk, Skolnik, and Fixman (OSF) as well as Dobrynin is discussed.