I just bought a H&R single shot rifle in 25.06 caliber. Today i started working up a load and using a Stoney Point OAL gage i got the OAL for my bullets. I am loading Speer 120 SP. When i got my reading from the gage and seated them .020 off the lands my OAL is 3.306 . My Speer and Hornady manual says that 3.250 is the Max cartridge OAL for this bullet. I shot three groups of three and they shot ok. If i seat them deeper i will be to far off the lands. I shot 10 rounds of factory loaded Rem core loks just to see how they would shoot and they were flying everywhere, they measured 3.212 and were seated way to deep for this rifle. Is it ok to load and shoot bullets that are longer than the manual suggest?

What are you talking about here? O/A CARTRIDGE length, or bullet length? You can't do much about bullet length, because they come from the maker at a specific length!! If your question is about CARTRIDGE length, then yes, you can MAYBE use a cartridge length greater than the "standard" length you see in the manuals. This depends on two things: a., the length of the leade or throat in your rifle's chamber, and b., the shape of the ogive on the bullet you chose to use. With a single-shot rifle, the way I determine O/A cartridge loaded length is by dropping a bullet into the chamber, letting it slide up into the throat, then putting a sized empty case in behind it. I then use a dial caliper to measure the amount of case left sticking out of the chamber when the case mouth is touching the bullet base. I then add 2mm to this measurement. That is the seating depth I use with that particular bullet. With a single-shot, using this method, no extraneous fancy bullet seating gauges are needed at all.

As to your question, there is NOTHING WRONG OR DANGEROUS about using a cartridge length greater than what the manual gives. In fact, doing so probably causes LOWER pressures, as long as the bullet is not touching the rifling. In your particular rifle, it sounds like you NEED to have a longer O/A length so the bullets don't have too far to travel before engaging the rifling!!

Keep yore powder dry!!