I'm still learning and I've ran into a few questions that I can't seem to answer myself.

1. I am reloading for an AR-15 and a SCAR 17S, should the bullets I'm using to reload have a cannelure?

2. For the AR and SCAR should I taper crimping the brass? I know that taper crimp is usually used when there is heavy recoil but I've had people tell me both yes and no so I would like a definitive answer. If so can someone point me in a direction of where to find a good how-to video or something along those lines, the process is confusing me

3. I've ran across some brass that is shorter than the "trim-to length" provided in my reloading manual. Should I discard these cases or are they still Ok to use?

Thank you in advance.

1 not necessary unless your crimping.
2 if your neck is sized right no need for a crimp and a crimp won't hold a bullet nearly as good as a properly sized neck.
Most regular dies err on the overly tight neck spectrum.
If you do still want to crimp I recommend a lee collet crimper which works separate from the seater and has a good reputation.
The instructions that come with it are easy to follow.
3 short necks are not a big issue especially for blaster ammo.

Thank you for the input!!!

I did read the FAQs but I couldn't find it. There's a lot to look through. I'll have to be more thorough with my research next time.

I don't crimp for the AR15s, M1A, M1 Garands, FAL, etc., etc.  Neck tension alone should hold the bullets.  When you're seating the bullet you can feel it if you have a loose/split neck as that one is suddenly very much easier to seat.

Eventually you'll need to be able to trim your cases so they are all the same length.  I adjust my seater die down on an empty case till it just touches the case mouth, then turn the die back up a 1/2 turn so that there is no way it will touch the case mouth or crimp the case mouth on the bullet.  Then I lock it in place with the lock ring.  Then I put a case with powder in it and set a bullet on it and start adjusting the seater stem till I get the over all length I want.

I only crimp handgun bullets (the semi autos just enough to remove the bell on the case mouth and the magnum revolver rounds enough to keep the bullets from moving forward in the cylinder under recoil of the previously fired rounds).

No need to crimp and you should check out the super sub moa SCAR 17 on the FN forum.  I've been burning through some 150gr with a cannalure and I'm a good MM below, so you can see the whole slot.  I'd use the short cases.

Do you by chance have a link for the thread on the FN forum?

Most of my bullets don't have cannelures. I get great results and haven't had setback issues.

The crimps I use most often are minimal.

I've used short brass from time to time.  It's okay in my experience if it'll hold the bullet.