Beat me to it. Good eye. We can see where the slide was when the BBQ paint went on too.
If the DP is only on the bolt then AFAIK and not on the receiver as well it is almost certainly not a service job, but just a No4 that was lacking a bolt and that was the one someone stuck in there.
Obviously if the bolt had been re-used in service the DP mark would have been struck out, unless done in one of those hot, dusty and divided little countries.![]()