I do it all the time, and have been doing so since they added the "free shipping" category last year.
Recent examples:
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$84.87 - Cast bullets and some miscellaneous muzzle loader supplies.
$16.90 - Shipping.
$101.77 - Total.
Added a crappy pair of 'free shipping' gloves to the order for $2...
$86.87 - Cart contents.
$2.80 - Shipping.
$89.67 - Total.
I knocked $14.10 off the total,
and got crappy gloves for free.
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$61.98 - Ear protection and a holster.
$12.00 - Shipping.
$73.98 - Total.
Added a "free shipping" clearance trimmer pilot (that I needed anyway!
) for $4.15...
$66.13 - Cart contents.
$1.00 - Shipping.
$67.13 - Total.
I got a pilot that I already needed for free,
plus another $7.85 off of shipping.
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$18.27 - Clearance cast bullet mold for an experiment, and a some bore brushes.
$16.00 - Shipping!!
$34.27 - Total.
Added a "free shipping" accessory for my Havalon knife for $8.99...
$27.26 - Cart contents.
$0.00 - Shipping (free).
$27.26 - Total
Two ways to look at it:
1. I got the $9 knife accessory for free, and paid $9 for shipping.
2. I paid $9 for the accessory, and got free shipping.
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And another one...
$60.48 - Muzzle loader nipple, hearing protection, and a tap.
$12.00 - Shipping.
$72.48 - Total.
Added one of the nearly worthless "free shipping" 5ive Star Gear multi tools for $3.69...
$64.17 - Cart contents.
$0.00 - Shipping (free).
$64.17 - Total.
Again, this is a "glass half full or half empty" deal: Either I got the tool for free with $3.69 shipping, or I got the tool for $3.69 and free shipping.
Either way... still cheaper than standard shipping costs.
Oh... and don't bother telling me that Midway's shipping is ridiculous. They aren't the only place I buy from online. EVERYONE has ridiculous shipping costs now.