Let me go a little further. You usually use more powder with lighter bullets than with heavier ones. That being true if you are using data from a heavier bullet with a lighter one you are using charge weights that are lighter than those that would be safe if you had the actual data for the lighter bullet. Like I said, the data from the 155gr bullet won't be Max with the 140gr bullet but it's a very good place to start. You couldn't safely use the Max charge from 140gr bullet data with a 155gr bullet but you are going the other way. That makes it safe as long as you don't go too light on the powder charge and stick a bullet in the barrel. (highly unlikely but possible)
You can buy a good chrono for right around $100 or just a little more on sale from most manufacturers. They work well enough for what we as reloaders do. I have had my chrono for about 5 years now and I have no idea how I got along without one. It's probably my most important tool for reloading...
