Just purchased an Orion 2s battery. It has 4 4mm bulet holes in it plus the pin hole for the balancer. My question is do I have to have a balance plug that has 4 leads on it for all 4 holes or can I juts use a regular one that has two?

The extra 2 bullet holes were to deal with the amperage this battery is able output. It's more than a 4mm bullet can handle. That's why most of the industry has moved to 5mm bullets. For charging you don't need a special cable because your charge amps is well within the 4mm bullet rating. Just connect one bullet on both - and + side.

I always thought the extra holes were a matter of convenience to let you charge the pack without having to disconnect from the ESC... pretty sure 4mm bullets is more than sufficient to handle any 2S load.

The dual bullet batteries I've seen have battery leads that come with them that have 2 bullets per side. The 4mm bullet is limited to about 70-75A. While it's debatable if you need more than this with high C batteries, most high end batteries now come with 5mm bullets.

I agree that 5mm bullet is the new industry standard, however I've never had a problem using 4mm bullets on my 4WD SCT which tends to average around 30A over a typical discharge cycle where I have used a 30A bulb discharger which drains my packs at roughly the same rate as a typical 10 min main for the class.

Also worth noting that many 40A chargers come with 4mm bullets as well, only have to wonder when they will make the shift to 5mm bullets too?

When there's a battery that can be safely charged at 80a and there's a charger that will allow that, then maybe they will move to 5mm bullets on the charger. 40A is well within the limits of decent 4mm bullets.

I haven't been able to find anything from a trustworthy source on short current bursts. Based off my motor dyno tests, most of my 17.5 motors on acceleration are pulling ~130amps, but after a second it's under 50 amps. Guessing a SCT would have similar inertia to the flywheel.

yeah there's a YUGE difference in Burst vs Continuous draw, not complaining that 5mm bullets are here to stay, but I feel they are overkill, regardless I would prefer having just 1 connector style to mess with, switching back and forth between 4mm charge leads with 5mm ends is just "stoopid"

Easy problem to solve, charge leads with stepped 4/5mm bullets.

Been there done that, seriously an excellent suggestion! However, there are 2 fundamental problems I have with the charge leads you pictured:
1) Cage style bullets tend to crush and can't be spread back out leading to poor connection issues
2) Stepped bullets also can't be spread back out like traditional slotted bullets, I have attempted to do this once and broke the stepped bullet, you can spread the 4mm step, but not the 5mm step... now they are dead to me

I do realize that folks should replace their connectors as they all wear over time, but I have grown to trust slotted 90° angle bullets to work best for my needs as I choose to charge my packs in my cars where I need to get the charge leads in at a tight angle.

4mm to 5mm leads are acceptable (for now) but when it's time to replace connectors, I would much rather have a tray full of 5mm bullets than having to fish around between 4mm and 5mm bullets, just my personal preference

Zero issues with these charge leads. Having really good tension is only important on the ESC connectors to the battery. I would never put either of these bullet styles on the ESC for the reasons you stated, but charge leads no problem.

I have helped 2 different racers at our track with troubleshooting intermittent problems with their chargers using almost identical charge leads you are using... first thing I did was have them swap out with my Trinity charge lead which is the perfect design for my needs... and in both cases we discovered their charge leads had failed... I helped them solder on fresh "slotted" bullets and they were back in business, I also showed them how to spread the slots to improve connectivity when they get bad voltage errors again in the future

Note that the 2mm cage bullets (for the balance lead) will go bad over time too, I've had to replace those from time to time as well, I haven't seen any slotted 2mm bullets around yet