AFAIK Bushie offers M4 style handguards with single liners, unless they recently changed

Colt handguards use double liners for two reasons:

1) it was something they could patent and talk up as better

2) They actually need them, as they use an older inferior molding process called thermoset.  Thermoset is cold material going into a hot tool.  It has some structural disadvantages over more modern molding techniques.

The type of molding we (Cavalry Arms) do is injection molding with heat stabilized glass filled nylon 6.  Injection molding is hot material going into a cold tool....this offers structural and material advantages over thermoset.  On our handguards heatshields are totally unneccessary, the only reason our handguards have them is people [b]expect[/b] them to be there.  Many of our full autos here at the shop don't have heat shields in the handguards at all.

This is what it takes to get our handgaurds to melt even somewhat:

[img]http://www.cavalryarms.com/shooting/meltedtube0.JPG[/img]

[img]http://www.cavalryarms.com/shooting/meltedtube2.JPG[/img]

Multiple beta-mags fired full-auto...your gas tube will fail before the handguards do.