Why does it even matter if he knew the correct terminology? Brennan (supposedly) saw a 30-30 Winchester. Marina didn't know the difference between a rifle and a shotgun.
It became a pattern with Rowland, how he would start a story and then embelish it. There is no way to judge a persons testimonies other than by what is stated. He went into great detail about the man with a rifle and his description of him framed in the window. It proved to be wrong.
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It shows you Brennan was not an expert nor claimed to be knowledgeable.
Mr. BRENNAN. I am not an expert on guns. It was, as I could observe, some type of a high-powered rifle.
Now contrast that to Rowland.
Mr. SPECTER - How did you know that?
Mr. ROWLAND - I have been around guns quite a bit in my lifetime.
By Arnold's own statements he proves that was not true.
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Marina? In Russia they were not allowed to own a gun other than a shotgun. Oswald hunted with a shotgun in Russia. Given her upbringing she would have no way of knowing.