I am 5"1, 115 lbs, barely an A cup. I want to be a C cup, will 460cc HP Silicone under the muscle be too big?

You’re
absolutely right that some women look “ok” with a 460 cc implant while others
look “huge”.  Just like breast implants
come in several shapes, profiles and sizes so do women’s breasts and so the
same implant placed in one woman is not going to look exactly the same in
another woman.  This is why I recommend using your
breast base width to find an implant that will fit your body.  The width of your breast is an
important measurement to determine the range of implant sizes your body will
hold.  During a consultation, I have my
patient “try on” different implant sizes.  This allows me to visualize the additional volume that is needed to get
the desired look.  I highly recommend
meeting with your board certified plastic surgeon before surgery to confirm
your implant size.Be well and good luck!@norrisplastic

There is no way to tell other than through a personal consult.  I find cup size is not very helpful to figuring out final desired breast size.  Look at my websites at the before and after pictures and you will see many women who's  afters are a much larger bra cup size then you would have guessed based on the pictures.  I find it is better to try on implants until they feel like the correct size and then the surgeon and patient will be on the same page for expected breast volume

Unfortunately, you have not told us your bra size just your
cup size. If you are 32 or 34 each 100
cc’s of implant corresponds to 1 cup size change. If you are 36 or 38 each 200 cc’s of implant
corresponds to 1 cup size change. From
this, you can compute the volume required to achieve your desired goal. 460 cc implants are large and if placed under
the muscle will extrude inferiorly and laterally requiring revision. I always recommend small round textured
silicone gel implants placed retro-pectoral since they look and feel more
natural, are more stable, less likely to ripple or have complications needing
revision. Implant profile is irrelevant
in the retro-pectoral position since the muscle compresses it. 22% of women who undergo breast augmentation
alone require revision within 2 years because they are dissatisfied with the result. Best Wishes,Gary Horndeski, M.D.