Doing my 1st (but not last) AR build.  My only real problem has been getting the roll pins (Bolt Catch, Trigger Guard, and Forward Assist) fully seated without marring.

I'm using a roll pin starter to get it in, a brass punch to drive it the length, and then a small punch (1/32) to finish it with masking tape applied to the area around the roll pin hole.  

The issue comes in getting it flush/slightly recessed without marring the receiver.  Even with the tape, it's getting (very slightly) dinged up.  Putting tape completely over the pin protects the area better but makes it hard to ensure that I hit the pin with the small punch and not the area beside it.

Any tips on how best to finish seating the roll pins?

Thanks.

Roll pin punch

The best and only way roll pin punch

Roll pin punch, or several layers of tape on both jaws of some channel-lock pliers (if it's something you can get the jaws around easily like a gas tube roll pin or the trigger guard roll pin.

plastic gunsmithing hammer

Roll pin punch.

Ideally one would do this with a properly sized roll pin punch, i.e. one that is a couple thousandths smaller in diameter than the pin being driven. Don't remember the sizes off the top of my head, but I have a dedicated set that has only the sizes needed for the AR. I chucked them into my drill press and filed them down just an RCH and they work perfectly. ymmv.

Yea, as mentioned, the right tool for the job does the job well and is first choice. 
Second choice, tapping flush with a non-marring hammer. 
Third the tape around pliers method. 

All three work, but having the right tools make life SO much easier sometimes.  

+1 on the properly sized.  I use a punch set from Tekton that works well as long as I do my part.

If you want it slightly recessed a roll pin punch.

For the trigger guard, I took a C clamp and epoxied a piece of leather on each side. No effort at all to install. I also mount all pins in a a drill and polish with fine sandpaper, taper the point, and oil pins.

I always put some oil in the hole, too, to help the pin slide in easier.  I can't say it works but it seems like it should help.

Ursus:  In addition to the other suggestions about polishing, tapering and oiling the roll pins, the key to solving your problem is to use the right tools.  There are two kinds of steel roll pin punches, and only two diameters specific to the AR-15's pins (see link below).  

First you need starter punches, those with a little orfice in the end that the pin fits into.  These hold the pin while you bang on it with your brass mallet.  Second you need driver punches.  These are not the same as ordinary drift punches, instead they have a little tit on the end to keep them centered on the roll pin.  These make it much easier to put a layer of masking tape over the almost finished pin, then put the little tit into the hole in the pin and drive it that last millimeter past flush without marring the adjoining metal surface.  

That's about it, a total of 4 punches for the AR, available from Brownells.  BTW, the pin that affixes the trigger guard is special, you need to take care not to break off the fingers on the lower that the pin fits into.  The c-clamp method described above is ideal since is doesn't place any undue impact stress on those little fingers.  Good luck - CW

pin sizes

Looking at the construction of roll pins vs. spiral pins it seems that for spiral pins you would use a regular punch? The spiral pin doesn't seem to have the proper "cavity" to admit the end of a roll pin punch.
Or have I not had enough coffee yet this morning?

Roll pin punches work fine with the spiral type roll pins.

I put a taper on rollpins to get them started easier.

I seriously doubt there are many sheared rollpins for bolt catches, forward assists and trigger guards.  They do much more than menial tasks such as these in other industries.

I use THESE most the time. They are great for the trigger guard roll pin too!

I've used this roll punch punch set. Excellent quality and customer service. I lost my 1/16 punch, somehow rolled somewhere under something in the kitchen, and Avitron sent me another one, gratis
Roll pin punch set

FPNI. Or as suggested you can use pliers in some locations. A roll pin punch set is worth it, got myself a nice Proto set. They should have a tip on them (obviously) and they work great and makes the job easier.

I used these on my last 4 80% with no marring. Pair of tweezers helps if you have sausage fingers
Can use tape on the jaws if you want to get fancy, but they are smooth and I didn't.


https://www.amazon.com/Knipex-8603180-7-Inch-Pliers-Wrench/dp/B000X4KP1C/ref=sr_1_2?s=power-hand-tools&ie=UTF8&qid=1482043152&sr=1-2&keywords=knipex&tag=vglnk-c102-20

Way easier than swinging a hammer at a punch and don't have to worry about blowing the ear off the trigger. I wouldn't do it any other way.


ETA: Beat by Bbar605, looks like he has also seen the light

+1 Spiral pins go in much, much easier!!

I have a KAK hollow end starter punch I use to start almost all my small pins.