. Appendix D4 Production Division (effective 01January 2010) 19.2 Base plates and/or any other devices which provide additional ammunition capacity (e.g. “+2” magazine extensions), are prohibited. Magazines accessible to a competitor during a COF must not contain more than 15 rounds at the Start Signal. 20.1 Aftermarket magazines which match the external dimensions of standard magazines offered by the OFM for the approved handgun are permitted. Aftermarket magazines are permitted, subject to 19.2 above. . Wanna kill these ads? We can help!