Clubs are built to a swing weight based on head weight, shaft balance, and grip weight. Replacing a shaft or trimming butt or tipping doesn’t directly determine a swing weight.

Based on the weight of the head, which all vary from manufacturing., Titleist adjusts a club to a swing weight, either D2-D3 unless otherwise specified in the order as the stock swing weight or if intended for a female set (C11?). For irons, they add weights in the hosel then recheck the sw.

All the required components are set prior to getting the sw. Any tipping or butt cutting to length of the shaft as well as the grips selected are included before the final sw check.

Shaft weights are before cutting- tipping and cutting to final length. The playing length of a club is measured from the shaft butt end to where the shaft would reach the ground if it was extended to that point. The physical length is taking that same playing length and subtracting the length from the bottom of the bore to the ground- this is called the "BBGM"- Bottom of the Bore to the Ground Measurement. Taking that physical length divided by the original length and multiplied by the uncut shaft weight will give you the aapproximate final weight. If you don't have the BBGM 1.5" is a good number to use.

The following may no longer be the case:

Based on the weight of the head, which all vary from manufacturing., Titleist adjusts a club to a swing weight, either D2-D3 unless otherwise specified in the order as the stock swing weight or if intended for a female set (C11?). For irons, they add weights in the hosel then recheck the sw.
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I just ordered custom built T250/T150 combo iron set. They swing weight at C7 and C8. I contacted Titleist customer service and they emailed me the following:

Looking into the specs for this build and the swing weight that we can achieve.

T150's target weight was C7, (range between C6-C9 is what production can achieve for this build)
T250's target weight was C6, (range between C5-C8 is what production can achieve for this build)

So, they actually components are not checked prior to the build, nor are they checked after the build!!!
My order was for Swing Weight - Standard which should be D2-D3.