I'm wanting to replace the upper and lower hand gaurds on my SAR-1, I am looking at some the black polymer style, like you find over at KVAR. My question is how likely are they to melt under under rapid fire. Back around 2003 I had a set of Tapco polymer upper and lower hand gaurds melt right of after I had put approximately 4 to 6 30 round clips through as fast as I could pull the trigger. And is a heat shield insert needed to prevent the melt down. Thanks!