No he wouldn't know the exact length without measuring it.
He was willing to say that he could have been mistaken about how Oswald carried the rifle into the depository (The Trial of L.H. Oswald. Dir. Ian Hamilton. Showtime Entertainment, 1986.
We could be mistaken about anything. I saw him say he was positive the bag fit entirely between his arm and his palm.
This is from the link I posted earlier. Funny, he doesn't sound so sure.
He sounded sure on the History Channel. I guess he's just another liar or someone who doesn't know what he's talking about to you guys though. Let's see, the witnesses near the knoll were liars or inept, the doctors at Parklnd were liars or inept, the driver co-worker is a liar or inept, the fingerprint experts are liars or inept. The only truth-teller in 1963 was Hoover, huh? lol
The following is a selection of the testimony of Wes Frazier, Oswald's coworker who drove him to the Depository on the morning of November 22, 1963. This is at 2H228-229. ------------------------------------------------------ Mr. BALL. Did it look to you as if there was something heavy in the package? Mr. FRAZIER. Well, I will be frank with you, I didn't pay much attention to the package because like I say before and after he told me that it was curtain rods and I didn't pay any attention to it, and he never had lied to me before so I never did have any reason to doubt his word. Mr. BALL. Well, from the way he carried it, the way he walked did it appear he was carrying something that had more than the weight of a paper? Mr. FRAZIER. Well, I say, you know like I say, I didn't pay much attention to the package other than I knew he had it under his arm and I didn't pay too much attention the way he was walking because I was walking along there looking at the railroad cars and watching the men on the diesel switch them cars and I didn't pay too much attention on how he carried the package at all.