If one compares SAAMI's specs for both the Weatherby and Winchester .300 Magnum chambers, they'll see that the Weatherby one has a longer freebore than the Winchester has:
http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Weatherby Magnum.pdf
http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Winchester Magnum.pdf
Then compare the SAAMI velocity and pressure specs for both in:
http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf
All of which means that if a Remington .300 Win Mag rifle's got more freebore than what's shown in those specs, they're not following the SAAMI specs they've agreed to.
There's often confusion between "throat," "freebore" and "leade" in firearms jargon. "Freebore" is often called the "throat," for example. Here's SAAMI's take on them from their glossary:
FREE BORE
A cylindrical length of bore in a firearm just forward of the chamber in which rifling is not present. Associated with bullet jump.
LEADE (LEAD)
That section of the bore of a rifled gun barrel located immediately ahead of the chamber in which the rifling is conically removed to provide clearance for the seated bullet. Also called Throat or Ball Seat.
THROAT
See Leade (Lead).
The Winchester's angled leade starts at the chamber mouth's .315" diameter tapering down to bore diameter. There seems to be no freebore at all. Weatherby's leade starts .361" forward of the chamber mouth at .3085" diameter then tapers down to bore diameter. That's clearly a .3085" diameter free bore of .361" length. With the 25' leade angle and diameter differences of the chambers as well as actual bullet diameter and jump to the lands, it's a complicated calculating conundrum. It's easy to measure.
http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Weatherby Magnum.pdf
http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Winchester Magnum.pdf
Then compare the SAAMI velocity and pressure specs for both in:
http://www.saami.org/specifications_and_information/specifications/Velocity_Pressure_CfR.pdf
All of which means that if a Remington .300 Win Mag rifle's got more freebore than what's shown in those specs, they're not following the SAAMI specs they've agreed to.
There's often confusion between "throat," "freebore" and "leade" in firearms jargon. "Freebore" is often called the "throat," for example. Here's SAAMI's take on them from their glossary:
FREE BORE
A cylindrical length of bore in a firearm just forward of the chamber in which rifling is not present. Associated with bullet jump.
LEADE (LEAD)
That section of the bore of a rifled gun barrel located immediately ahead of the chamber in which the rifling is conically removed to provide clearance for the seated bullet. Also called Throat or Ball Seat.
THROAT
See Leade (Lead).
The Winchester's angled leade starts at the chamber mouth's .315" diameter tapering down to bore diameter. There seems to be no freebore at all. Weatherby's leade starts .361" forward of the chamber mouth at .3085" diameter then tapers down to bore diameter. That's clearly a .3085" diameter free bore of .361" length. With the 25' leade angle and diameter differences of the chambers as well as actual bullet diameter and jump to the lands, it's a complicated calculating conundrum. It's easy to measure.
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