The autopsy is a matter of record. Pictures and all...the coroner who performed the autopsy was widely considered to be the best in the business, Thomas Naguchi.
This is what you are basing your allegation on:
After listening to the recording, some acoustic experts say Van Praag misidentified some sound impulses as gun shots and that only seven or eight shots could be heard on the low-fidelity tape. Forensic acoustics engineer Philip Harrison said, “I can’t find any more than the seven shots that are there.” In 2013, comments by Harrison and others helped convince U.S. Magistrate Judge Andrew J. Wistrich that the tape was no smoking gun. “Van Praag’s opinion is far from ‘conclusive’ evidence of a second gunman,” Wistrich wrote, “because other experts analyzing the Pruszynski recording have reached contrary conclusions.”
But Van Praag hadn’t stopped with simply counting the gunshot sounds. Then Van Praag revealed two additional findings: That two pairs of shots occurred so closely together that they couldn’t have been fired from the same gun, and then the finding that two guns were involved firing in opposite directions — one facing Pruszynski, presumably Sirhan, and one facing away from Pruszynski
Here's the thing...if 7 more shots were fired, in that small enclosed area, where did the bullets go? 8 rounds were recovered. I don't know if you actually have the discipline to read the whole article, but if you do--you come away with the clear idea that while the number of shots is in dispute, with most of the extra shots not passing the sniff test--the idea of a 2nd hidden shooter delivering the killing shot--is bolstered just a bit..not definitively though.