What is the difference between these 2 m1 carbine scope mounts?

[Grouch]

Other than price.

http://www.sportsmansguide.com/net/cb/cb.aspx?a=408056

http://www.cheaperthandirt.com/SKM1070-63653-2871.html

[Draven]

The groove down the middle.

I had one (the Sportsman's Guide one) on my Universal carbine. Note, you may have to trim the mounting bolt in order to be able to tighten down the mount against the receiver.

In order to mount these, you have to hammer out your old rear sight- they both completely replace the rear sight.

If you have a Universal Carbine as opposed to a milsurp one, there is a dedicated scope mount you can (still) get for it that leaves your irons intact.

If you're mounting a red dot on a milsurp, there is a mount available that fits onto the barrel and replaces the upper handguard. Removal is easier and it leaves your irons intact.