I too ordered Silicone Trivets from Amazon. Found that the Hexagon's listed all seem to be too small for 30's, but as NYBushBro identified above, they will probably be OK for .223's.
(1) I ordered and received two different products that were too small (DO NOT ORDER THESE FOR 30's):
Silicone Pot Holders Set of 4, Ankway Heat Resistant to 450 °F, Non-slip, Insulation, Durable, Flexible Hot Pads (7" x 7", Blue & Green)
OR
PratiPad PLUS 4-in-1 Multipurpose Silicone Pot Holders, Trivets, Jar Openers, & Spoon Rests - Extra Thick Protection - Set of 2 - Purple/Grey
(2) I ordered a set that has Square Holes which seem to accept the 30's and should holed them up with gas checks on (ORDER THESE FOR USE WITH 30's). Have not used these yet so we will see how they actually perform; hopefully next week.
HULLR 4 piece premium silicone trivet mats flexible pot holders durable non-slip pads, multicolor spoon rest and pan lid holder coasters all in 1 non-stick food-grade silicone heat resistant to 500 f
Looking forward to trying these for standing 30's up when baking. I use Shake & Bake, will place them into square holes with angled forceps - I gas check before Shake & Bake so we will see how it works out. Will place the Trivets on a flat pan that I can slide into the oven for backing so there will be a stable bottom after loading.