I have loaded a bunch of 5.56mm over the years, both for semis and bolt guns (although most has been for semis). It is an easy cartridge to load.
First, many will tell you that small base dies are necessary for the .223 if it is to be fired in a semi... I have not found this to be the case. I use a standard Full Length resizing die (usually RCBS, but sometimes a Lee), and bottom it out against the shellholder when resizing the case.
As mentioned above by g56, you will need to get a cheap (or expensive, if you like) dial caliper and a case trimmer. I save up a bunch of cases, and then load a sizeable batch at once. I trim the cases every time that I load them (which usually means that little neck material is removed on the ones that I previously reloaded).
Actually, let me run you through my process.
First, I remove the fired primer with a Lee Decapping Die. I then run the batch of cases through a RCBS Primer Pocket Swaging Die to remove any primer pocket crimp on new military cases that haven't previously been reloaded. After removing the crimp, I clean the primer pocket with a tool made by Herter's (mentioned to show my age, I guess. But the tool still works well after 38 years of use).
I then wash the cases in a mild Palmolive Dish Washing solution with hot water. I then dry the cases on a sheet out on my back deck in the sun.
I then run the cases through the RCBS FL sizing die, using the RCBS Case Lube II (which is water soluable). Any water soluable case lube will work. Do not use too much. It doesn't take much after the first case, and you will end up with dents in the case neck if you over lube.
Then, I wash the cases again as above, since I do not remove the lube after sizing the cases. If you try to rub the lube off each case individually after resizing, 100 cases will take you forever...
I then trim the cases to length, with a powered Forester trimmer (that is cobbed up to a sewing machine motor). I then, as a separate step, debur the case neck, inside and out.
Then, I throw the cases into a Midway Vibe Polisher and make them shiny...
Next, I seat the new primer using a Lee Auto Prime (the handheld one with the primer tray), which works great... I almost always use CCI400 primers, even for the semis, although some prefer the harder CCI 41 for AR15 type rifles. I have put several thousand rounds through AR-15s, and have never had problems with the CCI400. Lee also recommends the CCI primers for their tool, citing potential problems with other primers if an accidental detonation of primers in the tool occurs... Every once in a while, I use some Win primers.
Most of what I load is M193 ball spec ammo. I use IMI M193 bullets or Win M193 bullets. The IMI ones are better.
I use a Lee Perfect Powder Measure to throw powder charges (of H335, or AA 2230C, or WC846, or WC844, or Win 748, or, sometimes a little of the newer Finnish stick powders or Varget). I have blocks made that hold 300 cases, and I drop powder charges into all cases before the next step, which allows me to check every individual case visually for the same powder level.
I then seat the bullet to the cannelure, using a RCBS or Lee bullet seating die. Then, as a separate step, I crimp the bullet using a Lee Factory Crimp Die. I believe that this last step is important for cartridges used in semis...
I then shoot them...
I use every boxer primed case that I can find anywhere... However, I do inspect them carefully before using them. If you have difficulty identifying a case displaying signs of an impending head separation, you will be wise to use newer cases... And such signs can be particularly difficult to spot in the .223. Fortunately, head separations are quite rare in this cartridge if it has been correctly reloaded.
I do not differentiate between military and commercial cases in terms of the powder charge. I have found that there is usually not enough of a difference to worry about. This is true only for the .223, however, for you must be much more careful about military versus commercial with the 7.62mm NATO/.308 Win and the .30-06. In other words, in the usage of scores of different 5.56/.223 cases, I have not found military 5.56 cases to be significantly thicker in the web than .223 commercial cases. However, this is not to say that such a problem is impossible to encounter. Be careful.
I also chronograph every powder charge/bullet combo that I load before loading in bulk.
Have fun. It's a great cartridge to load for, and it makes shooting your Bushmaster really cheap. I can shoot the .223 much cheaper than a .22WMR.
By the way, when your friend said to lube the cases, I'm sure that I don't have to mention that he meant lubing them before resizing, and didn't mean lubing the cartridges before firing them. It is also important to remove the lube after resizing the cases, which I accomplish by washing the cases. You can accomplish the same thing by using a paper towel to wipe each case off. It just takes a long time to wipe every one.
By the way again, my guess is that your Bushmaster has a 1/9 twist barrel. Most of the AR-15 type rifles produced by others than Colt over the past 15 years have a 1/9, compared to 1/7 in newer Colts. The original Colt AR-15 SP1 (and M16 and M16A1) had a 1/12 twist, which was developed to stabalize the M193 55gr FMJBT bullet. A 1/12 barrel will shoot 55gr bullets perfectly, since the twist was designed for them. Personally, I prefer 1/12 for what I shoot. It's just not very easy to get rifles with 1/12 anymore. Having said that, the 1/9 (and even 1/7) is fine for everything except the lightest .224 bullets...