This is too funny...
At some percent(I'll just say 60%), if Bowser does nothing after being B-thrown, Ike's grab misses. If he shields as soon as he is able, Ike can grab him. Silly frame perfect-ness...
This alone would make this NOT a chaingrab at this percent(since it depends on the action of the throwee, regardless if your inputs are perfect).
Example:
Counting frames after the hitstun from the Bthrow ends, Ike has 12 frames before he can act and Bowser has 34 frames before he can act.
For the distance Bowser is thrown, a running shield grab is the most desirable(it comes out faster and has more range than the Dash grab).
So, you need running frames, plus 3 frames of shielding, plus 7 frames for grabbing. You can't perform a standing grab until 3 frames of shield have passed...otherwise you will dash grab instead.
Also keep in mind, Bowser's fastest action is spotdodging...which his first invincibility frame comes out on frame 3, which makes his first invulnerable frame to be on frame 37(34 frames of lag, 2 frames of spotdodge startup, invincible the next frame).
Also keep in mind, these are assuming FRAME PERFECT inputs for BOTH characters.
Test 1:
13 frames of running were used. So Ike's total frames are 12 + 13 + 3 + 7. This comes out to 35 frames...meaning Ike's grab hitbox comes out on frame 35.
If Bowser...
--Does nothing: NOT Grabbed!
--Shields: Grabbed!
--Spotdodges: Grabbed!
--Rolls Away from you: NOT Grabbed!
--Rolls Towards you: NOT Grabbed!
--Jumps: Grabbed!
Test 2:
14 Frames of running instead of 13. Total frames for Ike are 36.
If Bowser...
--Does nothing: Grabbed! (Frame 37, not 36)
--Shields: Grabbed!
--Spotdodges: NOT Grabbed!
--Rolls Away from you: NOT Grabbed!
--Rolls Towards you: NOT Grabbed!
--Jumps: Grabbed! (Frame 37, not 36)
If you look closely, you may notice the spotdodge situation. "He's not invincible until frame 37, yet Ike grabs on frame 36! What gives!?" Simple: Bowser moves his massive bulk out of your range with his spotdodge animation. Instead of his standing animation(his head sticking out for you to grab), the animation of the spotdodge has him moving his hurtbox out of your grab range. This is also the reason for various Grabbed/Not Grabbed situations(i.e. Standing/Shielding/Jumping has Bowser's head out front, while his landing lag from doing nothing[crouched down to the ground], spot dodge, and roll dodge animations all have his hurtbox shifted elsewhere).
Another note, at lower percents it is better to dash grab instead of a running shield grab. Reasoning: Ike cannot cancel his run into a shield until frame 11. At lower percents(for this example, 0% - Bowser can act after 30 frames), Ike can run 6 frames then do a dash grab(12 frames), grabbing Bowser on frame 18(plus 12 frames from the lag from Bthrow). If you did a running shield grab, it would be 10 frames for running, 3 for shielding, and 7 for the grab...20 frames(. You're too sloooowwww!
Yeah...how's that? Confusing enough for everyone? xD
EDIT:
Another look is needed methinks.
Oh, and does this work on Snake? Or D3? Both of them are heavy....
Boost grab gives NO range bonus for Ike. So sorry.
Snake and D3 aren't fat enough for this to work. Also, so sorry.
EDIT2: I don't see this working on Zard. How did you test Yagami?