Altered Time - your #1 World of Warcraft Mage resource!

As the title suggests, I seem to be having mana issues while running shard/class ring. Not too sure exactly whats going wrong. Stats are 38% crit, 25% haste, 9% vers, 30% mastery. Don't have logs since it's all dummy testing where this occurs since I'm hesitant to play it in raid if I'm not playing it correctly. Are there any common issues with this or am I just stupid?

You're inherently going to run into mana issues with double ring. Arcane's rotation is mana negative; Once you add in the fact that soul increases how fast you burn through mana, you can see why you're having issues. Double ring is best used for shorter fights where lust is used on pull or where there are clear instances for cd usage. i.e Maiden. Some top loggers go as low as 20-21% haste which helps when using soul but you should also always clear at 4 charges outside of your burn phases.

When I run double ring I use t19 2s.
Normally when you run double ring you go oom hella fast so the extra missles help massively (it also sims as a resonable increase over high iLvl off pieces for single target.
Using it for kj prog since there is a lot of downtime to regen mana and a lot of needing to hold CDs for burst.

For sure, thanks guys

Double ring is perfect combo but you should adjust your playstyle to the mana challenge. Barrage more (though only at 4 stacks) during conserve phase, use MoA on CD to regain some mana. You can also gain 4th charge by using AM proc instead of AB if you are below 40% of mana and evo/AP are still on large CD.
Also try to use it on some farm bosses, e.g. Goroth. It's a good excercise and you will be able to compare your logs to other players with double ring and see what's wrong with your rotation if any.

You certainly aren't going to be going to 4 stacks in conserve running double ring unless you get solid missle procs.
If you lust on the pull by the time your CDs are done depending on procs you can just Evo and start another mini burn with rune/pom.
Depending obviously on how hard you go in mini burn mark is normally coming up right after your mini burn is done. Then you just sling that bad boy out and start conserving.
Probably around 60-70% mana after all of that.
Since you're mana negative with the ring most of the time I would just arcane blast x2 then spend missle procs to get higher charges for less mana.
But casting blast till 4 with double ring is next to impossible.

I simmed again last night and my optimal gear set includes both rings. It sims about 5K dps higher than shard/kilt. Given that, I will stick with Shard/Kilt.

A bit late answer but still, I have to say that I tried double ring and had similar problems.
I came there from using Kilt+Shard and hence I had low Mastery. For double ring to work, you need to stack mastery way higher.
But that is not useful for when you actually don't want to run double rings, such as AoE fights or M+ - mastery is a complete waste there.

So while Simcraft and other tools will likely show you that it's DPS increase, I suggest you back off from that. The gain is so minimal that it's not worth the hassle unless you want to gear swap half of your items on every encounter. Besides people as incapable as myself have problems performing the double ring rotation without making a mistake which punishes you quite harshly as the mana is really tight there. So at least I did go back to my beloved flexible Kilt with which you can do anything and everything while still having more than decent DPS.

Problem with kilt is that takes up a tier slot and you can't go 4t21-2t20 that looks pretty good to me