Free float handguards will not jeopardize zero. Well I guess it can in one way, if you're shooting from a barricade and you're resting your barrel on the barricade, the pressure will cause your barrel to flex up and your poi will be off. By how far? Far enough to wonder why your not hitting ****. Rest your free float handguard on the barricade instead and then there's nothing putting pressure on the barrel, issue solved. You can test this once you get your stag. If you have a laser bore sighter that goes in the muzzle, put it in your barrel and start puttin pressure on the barrel while looking through your sights. You'll see how much pressure will move your barrel and when you take the pressure off it will return to zero. I see this mistake all the time at 3 gun matches. Sometimes it doesn't matter, and sometimes the person can't hit anything and will burn an entire mag on a few long range targets. It's a learning moment.
I have the TAD Gear Litespeed and EDC packs that I put all my gear in for matches. Of coarse they won't hold my AR, even broken down. But they hold all my ammo, eye and ear pro, some basic cleaning and maintance stuff. Then might get a lo pro case like the LaRue or spikes tactical one but pretty much everyone can tell your carrying a gun in there. And it's broken down which means you have to put it together before you can use it. But it only takes seconds to put it together. Try that with stress and zombies charging torwards you. I have a 5.11 VTAC double rifle bag and it holds my shotgun and AR. The shotgun sticks out the end a few inches but I don't care. If I'm bugging out, I'm driving. If I have to walk, then the shotgun and most of my shtuff is being stashed somewhere until I can come back to them.
The EDC is big enough it might fit a broken down SBR. It seems like my 16" barrel stuck out of the top a few inches. Expensive pack but they're built like a brick shithouse.
