If you don't handload, factory ammo available for the .450 Marlin is very limited....on the other hand, factory ammo available for the 45-70 is abundant...This list is a couple years old, so there are some changes....
$41.54 250g @ 2200fps, 2687fpe, Barnes X Flat Nose (Conley)
$??.?? 300g @ 1810fps, 2182fpe (Remington @ Remington web site)
$20.39 300g @ 1880fps, 2355fpe (Winchester JHP, Natchez)
$20.60 300g @ 1880fps, 2355fpe (Federal, Natchez)
$29.81 300g @ 1880fps, 2355fpe (Winchester Partition Gold, Natchez)
$22.84 300g @ 2100fps, 2938fpe, HP (Conley)
$44.66 300g @ 2100fps, 2938fpe, Barnes Original Flat Point (Conley)
$32.50 300g @ 2100fps, 2938fpe, Nosler Partition (Protected Point) (Conley)
$41.54 300g @ 2100fps, 2938fpe, Barnes X Flat Nose (Conley)
$25.08 350g @ 1970fps, 3017fpe, Hornady JFP (Conley)
$34.89 350g @ 1800fps, 2519fpe, BCSP (Corbon @ Corbon web site)
$19.47 350g @ 2025fps, 3188fpe, PMC @CheaperThanDirt.com)
$39.99 350g @ 2150fps, 3593fpe (Buffalo Bore Ammo @ Cabelas)
$24.99 400g @ 1250fps, 1388fpe (Black Hills @ Cabelas)
$44.66 400g @ 1900fps, 3207fpe, Barnes Original Flat Point (Conley)
$54.46 400g @ 1900fps, 3207fpe, Swift A-Frame Flat Point (Conley)
$12.99 405g @ 1350fps, 1639fpe (PMC @ Cabelas)
$18.99 405g @ 1100fps, 1088fpe (Ultramax @ Cabelas)
$22.50 405g @ 1325fps, 1579fpe, RNFP (Conley)
$18.99 405g @ 1330fps, 1590fpe (Remington @ Cabelas)
$24.50 405g @
(Winchester @ Cascade Ammunition web site)
$35.57 405g @ 1700fps, 2600fpe, FPPE (Corbon @ Corbon web site)
$22.99 405g @ 1900fps, 3247fpe, JSP (Conley)
$39.99 405g @ 2000fps, 3597fpe (Buffalo Bore Ammo @ Cabelas)
$41.99 405g @
(Obsolete Ammunition @ Cabelas)
$50.00 420g @ 1850fps, 3200fpe (Garrett)
$39.99 430g @ 1925fps, 3537fpe (Buffalo Bore Ammo @ Cabelas)
$34.50 460g @ 1650fps, 2780fpe, HC (Corbon @ Corbon web site)
$41.99 500g @
(Obsolete Ammunition @ Cabelas)
$52.99 500g @ 1625fps, 2931fpe (Buffalo Bore Ammo @ Cabelas)
$50.00 540g @ 1550fps, 2880fpe (Garrett)
$180.00 500g @ 1530fps, 2600fpe (Speer AGS Tungsten, Garrett)