I�m shooting fox with a Rem 22/250 using 55 gr Blitzking and N140 powder and it�s accurate and fast.
Can I get 60 to 70 grs bullets with same accuracy and speed.

The twist rate might prevent it. However, the best way is to try it. That's part of the fun of reloading to experiment-but stay within the bounds.

Garp,
If it ain't broke, don't fix it! If your rifle has a factory barrel it's 1-14" and it's not likely it'll handle longer bullets.
I use Sierra #1360 in mine for everything up to and including deer.
Stepchild

garp,

As you can see in your loading manual the heavier a bullet goes the slower it can be shot. As to accuracy it depends upon the rifle as mentioned above. Many 22-250's have a 1-14" twist. This rate of twist limits how long a bullet can be. The 55 gr Blitz King is near or over that limit in my experiance. Some heavier bullets are shorter than the very sleek Sierra so they may be accurate but not as "fast".

I am not positive what you want to optimize. Is it trajectory, striking power or wind drift? If you use the free program "PointBlank" at www.huntingnut.com and enter the ballistic coeficient of each bullet your considering then compare them.

Same speed with 60-70 grain bullets as with 55 grainers? Sure, if you load the 55 grain ones down.

My 12" twist Savage will shoot 60 grain spitzers fine, but I believe that's about the practical limit. (55's probably the practical limit for 14" twist in cold weather when the air's dense.) The old semispitzer 70 grain Speers should work fine, and they're potentially quite accurate, but they don't offer a big gain in ballistic coefficient over the 55 grains, the muzzle velocities achievable with them will be lower, and they're heavier jacketed bullets that I really think were made for those who want to hunt deer with .22 centerfires.