Shear strength is 50-60% of tensile, not 10%. And grade 8 bolts using the lower # are 120,000psi. So each bolt will have ~5800# shear nominal. But the design of your setup it sheared at the threaded portion. So the diameter of the bolt is far less than 1/4". the minor diameter of a 1/4-20 bolt is 3/16" Which gives you ~3300# shear per bolt. With 10 bolts thats only 33k of shear. And if I recall correctly, you are using a rather large cylinder arent you?
I used 6 grade 8, 1/2" FHCS when I did mine. Using the minor diameter of 1/2-20 bolts, thats about 18k shear per bolt. With 6 bolts I am close to 100k for shear. So far no issues. Even 10 3/8" bolts wont be as strong as the 6 1/2" bolts I have.