I just recently received some quad rails from a friend of mine to install on my Sport 1 and 556. They fit very good and look very nice as well. But, I need some rail covers. Can anyone suggest an online gun store as to where I can buy some? Thanks.

Google "quad rail covers" and you'll get a ton of hits. You have rail ladder covers which fit between the grooves and are low profile. You also have curved panel covers that bulk out a little bit. With the above search you can see pictures of both types. Magpul is the most known but there are many other brands that are the same. You're local gun or big box outdoor stores will have them.

Check out Scar333's thread on where to buy accessories for AR15, most of the online retailers listed there will carry some form of rail covers. You can get the low profile ladder type covers or the thick ones that make the grip round, just depends on what you want.

LOL, jagular typed faster than I did.

Here is a set that popped up on Amazon. I am not sure f it is exactly what you are looking for, but here you go.

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S&W M&P 15 Sport II