From the source:
http://www.archives.gov/research/jfk/warren-commission-report/chapter-3.html#testimony
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Warren Commission Report
Chapter 3.
"The Shots from the Texas School Book Depository"
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Description of Rifle
The bolt-action, clip-fed rifle found on the sixth floor of the Depository, described more fully in appendix X, is inscribed with various markings, including "MADE ITALY," "CAL. 6.5," "1940" and the number C2766.126 (See Commission Exhibit Nos. 1303, 541(2) and 541 (3), pp. 82-83.) These markings have been explained as follows: "MADE ITALY" refers to its origin; "CAL. 6.5" refers to the rifle's caliber; "1940" refers to the year of manufacture; and the number C2766 is the serial number. This rifle is the only one of its type bearing that serial number.127 After review of standard reference works and the markings on the rifle, it was identified by the FBI as a 6.5-millimeter model 91/38 Mannlicher-Carcano rifle.128 Experts from the FBI made an independent determination of the caliber by inserting a Mannlicher-Carcano 6.5-millimeter cartridge into the weapon for fit, and by making a sulfur cast of the inside of the weapon's barrel and measuring
the cast with a micrometer.129 From outward appearance, the weapon would appear to be a 7.35-millimeter rifle, but its mechanism had been rebarreled with a 6.5-millimeter barrel.
130 Constable Deputy Sheriff Weitzman, who only saw the rifle at a glance and did not handle it, thought the weapon looked like a 7.65 Mauser bolt-action rifle.131
(See chapter V, p. 235.)
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After making independent examinations, both Frazier and Nicol positively identified the nearly whole bullet from the stretcher and the two larger bullet fragments found in the Presidential limousine as having been fired in the C2766 Mannlicher-Carcano rifle found in the Depository to the exclusion of all other weapons.142 Each of the two bullet fragments had sufficient unmutilated area to provide the basis for an identification.
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Easy, innit?

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I visited two local gun shops looking for a Mauser today.
Found 4.
None were the 1896 carbine that had the below-stock magazine, but also, none of them had the name "MAUSER" nor the caliber visible on any part of the action.