Prompt lepton production in proton beam dump experiments has been critically analysed within the general frame work of $$A_c \bar D$$ and $$D\bar D$$ production and their subsequent semileptonic decays. Realistic decay modes based on recent experiments are used. We have investigated the effect of using differentx dependences for the charm particles obtained either from simple quark counting rules or as inferred from strange particle production data. The $$D\bar D$$ production is assumed to have a linearA dependence and for the $$A_c \bar D$$ process bothA 1 andA 2/3 dependence is used. We show that by a simultaneous fit to the energy and angular distributions of prompt leptons in all the experiments the ratio of $$A_c \bar D$$ to $$D\bar D$$ production cross section can be determined. A comparison of this fit with these experimental distributions indicates that thex dependences based on strange particle data are strongly favoured. AnA 2/3 dependence for $$A_c \bar D$$ production, which corresponds to a quasi-diffractive process, is favoured although within existing errorsA 1 dependence cannot be ruled out. Putting together the cross section results from our analysis with other results at similar energies (p 1ab ∼400GeV/c) the production cross sections ( $$A_c \bar D$$ ) and ( $$D\bar D$$ ) are estimated to be ∼25 and ∼20 μb/nucleon respectively leading to a total inclusive charm cross section of ∼90 μb/nucleon.