The design of the semi-automatic tip-up barrel pistol Beretta 21A creates a number of redesign opportunities, according to this team of authors. As part of the ongoing research project, it has been considered feasible to create an add-on kit that takes the form of an additional barrel whose multivariate additions provide this weapon with new features. If used correctly, the kit also makes it possible to significantly enhance the operational qualities of the pistol. Enhanced with the add-on, the weapon is suitable for application both in sports and in the context of special forces. The authors have confirmed the conclusions and results of the theoretical studies in practice - by means of field tests in the firing range.