Quoted:
Even with gas checks, you try to shove a lead bullet down a barrel at over 1800 FPS, and your going to get some nasty leading in the bore quickly (doesn't mater what wax, or if you are tempering (water dropping) the bullets as well). If chrome lined bores, even faster leading.  No matter what speed you push the bullet down the barrel down, lead is going to shave off the bullet at the barrel gas port, and pretty much plug weld the gas system shut at the FSB in no time (read no joy having to pull the FSB and gas tube to try to dig the packed leading out). At the low speeds that you are pushing the bullet down the barrel, the rifling rate is all wrong. Plus, if you are using standard powders (not some bulk casting type gun powder), you chance a flash ignition of the powder at both ends unless you are using a filler, which could KB that barrel as well.

Simply forget the idea of casting bullets for the Ar's, and find a source for cheap 55gr FMJ bullets instead.  If you just must cast for some type of auto loader, then think SKS or AK in 7.62x39 instead with the right bulk type powder, since on these rifle, you can cast heavy bullets to keep the speeds down, and cleaning the gas system is a snap.

And for the record, lead bullets (even gas checked) will seal off faster to the bore than jacket bullets.  For this reason, you do not use jacketed loading data for lead bullet, hence if you do, your working pressures will be well over the top (read KB).  Even with a reduced load, you still want at least 90% case volume of powder in the case (so you don' get a flash burn of the powder at both ends, making working pressures spike to almost double and blowing up the gun).

Quoted:
OK, here and here only, if you find a load that suits the bill, then you can clip a full length recoil spring to achieve the lessen spring tension needed to allow the action to cycle correctly. Since you are shooting reduced load, and the math of the action is gas unlock dwell, B/C mass, and spring tension, going after the spring tension for the solution is reversible with nothing more that a new spring.

Test clip the spring cut one coil at a time but checking if the rifle will lock the bolt back after such.  When you clip the spring down to just getting the bolt to lock back, clip about 1/2 More coils and call it good.

BUT, MARK THE SPRING IN SUCH A MANNER, AND EVEN MAY BE THE RIFLE IT'S IN, SO YOU KNOW THAT YOU HAVE A REDUCED TENSION SPRING IN THE RIFLE FOR JUST THAT AMMO ALONE!!!!!!!
You try to run standard ammo with that reduced tension spring, and over function will be the least of your worries (the buffer off the back of the receiver extension is going to be so great that it will cause major damage.

Now having said that, remember that a clipped spring may cause some problem with the manual charging (spring not strong enough to strip a round out of the mag correctly).  So, although this may cause some mag recover problems if the mag spring at not up the snuff, you may want to pull the weights out of the buffer to decrease the B/C-buffer mass from the start.  This will allow you to keep a bit more spring tension when clipping, with the buffer mass reduced down to help with the the math needed to get the lower powdered lead cast loads to cycle correctly.

To add: once you have found the happy clipped/reduced mass setting, if the rig starts acting up done he line, check the gas port to see if it's clogged before clipping the spring even more.