By a very respected Gent named Van that was in the MMB series.
Here is a long read by Van on plunger tuning;
Talking Re: plunger springs First I am assuming that you are shooting right handed.
One must remember that the spring tension and plunger depth are interconnected when tuning. Or perhaps I should say that results can overlap.
A bow tuned with the shaft point set closer to the center of the shaft will shoot a wider range of shaft spine. The better release one has the closer to center one can go. The closer to center one tunes the less forgiving the bow becomes. If set to close everything can go to hell in a hand basket real fast.
By changing the brace height one can move the center of rotation of the arrow, thusly moving the impact point right or left. Try lowering the brace height.
Also any interference of any kind, from flitching making contact to nock misalignment or to tight or loose will mask bare shaft results.
Ok, now how I start out tuning a new bow.
First I set the shaft center shot with the plunger spring turned in all the way in at the strongest spring tension. (I don’t use a match stick) I set the shaft/string alignment too slightly inside the shaft point, somewhere between the point and the right side of the shaft. That is, not on the out side the right edge of the shaft. (best guess)
Go to 10-15 yards from the target and let fly a bare shaft. If you are really off in spine retrieve the broken carbon shaft and replace it with a better guess depending which way it hit.
What I am looking for here is an impact just to the left (within one or two inches) of the aim point. With not a lot of soft or stiff shaft flight. Now the juggling act starts.
Adjust the shaft to string alignment with the plunger depth adjustment so as to bring the point of aim to the slightly to the left of center spot on the target. Then adjust the spring tension to bring the point of aim to the center.
Now the plunger tension, plunger depth, point weight, arrow length, and brace height juggling truly starts. At this point if you think anything went wrong with your shooting don’t count the results. Shoot a new bare shaft.
Adjust plunger spring tension for the best shaft flight. Readjust plunger depth to center of target if necessary. Now comes the feel part. You don’t want to adjust the plunger depth so as to be close to the center of the shaft. (What’s to close, is when the shaft goes wild).
At this point you should have an idea if you need to go stiffer or softer in spine. Or add/remove point weight.
Now adjust point weight You should be within one inch of paper tune rip. Re-adjust plunger spring tension to center of target if necessary.
We are at the point that the interaction of plunger spring tension and plunger depth becomes very apparent. And one may go back and forth with adjusting both before one achieves perfect shaft flight. Less then 1/8 turn of ether plunger depth or spring tension turn can cause a large shaft reaction. At any point here one may see the need to change point weight or shaft spine.
Now the fun part.
Go to 20 yards. – Resist the temptation to shoot a fletched shaft. It will just mess up your mind.
Reset plunger spring for best bare shaft flight. And aim point centering. Readjust plunger depth if necessary but be forewarned if you feel the depth setting ring move you most likely have changed it to much. Ha ha- Reset spring tension after.
By now you should have good shaft flight but you may not be at the exact aim point that you want, and you find that if you change plunger spring pressure to center the aim point that the shaft flight is slightly off. And you have readjusted from the beginning at least five times. Well all is not lost.
By adjusting brace height and plunger tension you should find the correct point.
Go about it by only changing no more then two twists of the string at any time. And readjust plunger tension. And be advised by changing the string tension tighter the nock point will move toward the Stronger limb at full draw, and conversely when going to a lower brace height.
Now go to 30 and repeat the fun part. You now may shoot a fletched shaft Now go to 60 yards with bare shafts and flabbergast your shooting buddy’s
