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I was previously loading a 68 grain hornady for my rock river AR15. I switched to a nosler 60 grain ballistic tip. The c.o.l for the 68 grain is 2.250 according to my hornady book. My nosler book says to go with a Max c.o.l of 2.260. Will a c.o.l of 2.250 work for my 60 grains?
Welcome to the Guide.
I'm assuming you don't want to bother resetting your seating die.
However, you will find that the two bullets have slightly different profiles and you will not get the same OAL without readjusting anyway.
That said, there is a reason why Nosler suggested increasing the length. The longer the OAL, the lower the chamber pressure. How much will pressure increase with the shorter round? I don't know, but I would want to see if I could increase my OAL as long as it did not interfere with functioning rather that shortening it for the sake of convenience. It will probably work just fine at the shorter OAL, but any semi auto works best within a specific envelope of pressure curve. Go too hot and you risk damage to the rifle, too mild and you have function issues. When the maker of any bullet suggests a specific OAL, that's where you keep it while working up the load. Then if you want you can increase it to see if you can get the groups any smaller as the bullet approaches the lands. Sometimes you get a pleasant surprise, sometimes not. Decreasing the OAL unless necessary to fit in the magazine or to feed without hanging up is usually asking for trouble.