It’s amazing how many archers do not understand the nature of the Berger Button/Cushion Plunger and the center-shot setting.
If you are a recurve archer, have you ever taken the time and trouble to explore the effect on tune and arrow behavior which changing your center shot has? Perhaps you should experiment so you understand cause-and-effect and can tune better.
Start by measuring exactly how “deep” your plunger is so you can put it back to it’s current location if you want to return there quickly and easily (iow, when you panic).
Now, whatever its depth was, unscrew the plunger and set it to be about HALF as deep as it was. This’ll be the starting point and you’ll gradually move it deeper (past its original position most likely). If it is designed like the Beiter Plunger you can tighten the spring by rotating the shroud until there is NO give in the button. KEEP TRACK OF HOW MANY 360 DEGREE TURNS AND CLICKS YOU HAVE TO GO TO LOCK THE BUTTON DOWN. Again, so that you can put it back where it was at any time. If another brand, just use the matchstick trick, insert a matchstick or a toothpick, something that eliminates the action of the spring for this exercise.
I like to do this shooting exercise with bare shafts. Fletchings/vanes only serve to disguise the effects you seek to understand. Be sure you are close enough to keep the arrows on the bale! Put up a blank sheet of butcher paper with a dot to aim at, or use a fresh target so you can circle each end of arrows. Assuming you can shoot 3 arrows and get a group, well… do so. Note how the arrows fly (how much they skew sideways) and where they go relative to your aiming point. After each three arrows, rotate the plunger IN 1/2 turn pushing the centershot deeper away from the riser, and watch the arrows “march” across the target bale.
At some point the arrows will fly better than they have been and keep getting better, cleaner in flight. Then as you continue changing the center shot, they will start to fly worse. Keep going for a few ends and simply educate yourself on how the arrows fly, how they look in the bale (esp. if a foam bale – if a straw bale the angle of the dangle is not so diagnostic). Ultimately you want to return to that plunger setting of “best behavior”. You then might wish to check this “center shot” position in the traditional, arrow-on-the-bow-and-look-down-the-center-of-the-limbs method just to see how far off it is from the “accepted perfect center shot” (where the edge of the string away from the riser is just touching the junction of the shaft and arrow point joint). If there is a difference between the “ideal” and your empiric center shot I would suggest it is due to the spine of the arrows and most importantly your release technique.
So which is better? The one that give you the best groups, of course.
Incidentally, you did the center shot first because it has the more profound, basic influence on the arrow compared to the spring tension, but the spring can have a huge effect on the shape and size of your grouping pattern.
SO, how about the plunger tension now? same thing. You will not know until you try all the settings, using the same “little bit at a time” method keeping track as you make half-turns on the tension. Notice how certain areas of adjustment actually make big changes in the left-right arrow groups, and as you get close to the sweet spot, you get better groups. But you have to decrease the number of clicks per change as you near the sweet spot or you might go right past it. Again, this exercise is simply to learn what effect the plunger tension has on the flight of the arrows as well as the grouping.
There is no more commonly used, less understood, hardware on the olympic recurve bow than the plunger. You can study the engineering and physics of it all day long, and never really understand what it’s good for. Till you experiment a little…