Jacketed bullets are made using a different process in 2 parts; the lead core and the copper "Cup" (jacket). The jacket is punched and the jacket encapsulates the lead core. These jackets are much thicker than the coating used on copper coated bullets. Copper coated bullets are made by swaging a lead core followed by the application of a thin coating of highly ductile copper over the lead by an electroplating process.
Over-crimping coated bullets (non jacketed) will lead to poor accuracy as the relatively thin coating can be partially scrapped off the bullet during its exit from the case during firing causing the bullet to lose its integrity and perfectly spherical shape. Further, now that the coating cannot protect the lead core, lead will be deposited in the barrel during firing with successive shots stripping more coating and building up the lead fouling even further.
To properly seat your bullets turn down your crimp die so that it just straightens out the bell/flare and if you really feel the need to, give it only a light 'kiss' of crimp.
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