Thanks to a Law Enforcement buddy, I scored a large haul of AK brass that I wanted to use for my Grendel build. It's nearly all PMC and it's all large primer. I wouldn't have given it anymore thought but there was a couple factory Grendel pieces as well and they're all small primer. Should I still convert it or trade it out?

With brass availability what it is for Grendel, I would strongly consider keeping maybe 20 pieces for fire and forget hunting loads, and selling the rest.

The reason is that case volume is quite different (less) with 7.62x39 brass, so all the load data out there is different, and you will hit max pressure with less charge weight.

You can also use pieces for dummy cartridges once they are fire-formed if you don't want to use Grendel brass, but I just use Grendel brass aside from one 7.62x39 piece in my dummy round assortment.

The LRPs aren't the issue.  Case volume is.  They work in a pinch, but it's pretty excessive labor-wise when there is no real need.

Grendel brass manufacturers:

Lapua
Hornady
Nosler
Norma
Federal
PPU

Part of me was hoping they would be on par with normal Grendel brass because as I understood it, the 7.62x39 that was the parent case. I did notice after forming a case, that there was a drastic reduction in powder capacity; even for the minimum case load for the bullet weight. The only problem I see with the manufacturers you provided, is the sheer cost per case and there are only a few places locally to me that carry Grendel on the shelf, and what is there is incredibly expensive. Have you had the chance to test Wolf Gold Grendel yet, LRRPF52?

Yes.  It's PPU loaded ammo.

From 18" Lilja, I was shocked at how accurate it was, but admitedly just a 3rd group.  Bughole though at 100yds.

The brass from it is pretty soft, and most people get 3-5 loads max.  Some claim longer brass life with it, but it also uses LRP for some odd reason.

I stack it up when I see it on sale for $9.99 from PSA though.  That's hard to beat.

If you use Ammoseek, you can get much better deals on factory ammo, even the Hornady 123gr AMAX and SST, which are great loads.

Lapua brass is the most cost-effective brass there is.  You will get insane numbers of loads with it, especially since 6.5 Grendel works at such a lower pressure than most other center fire rifle cartridges.

Lapua sells 7.62x39mm for 2/3 the cost of their 6.5 Grendel. It should be resized as new as opposed to once fired.

Once fired 7.2x39mm brass needs to be annealed prior to resizing to 6.5 Grendel for best results.

I reload 7.62x39mm so I need those case for the rifles they were made for. I buy Alexander Arms 6.5 Grendel brass when it's available.

Make sure you clearly mark the ammo so your heirs no what they've got. The major problem with converting cases is it increases the chance of an accident. Most people look at head stamps to ascertain what caliber ammo they have. You may know what's what, but someone else is going to have a problem.

I converted a bunch of x39 IMI brass to Grendel, my son uses them for hunting, and I am not concerned about finding or retrieving them.

My Alexander brass has a case capacity of 36gr H20, my IMI converted has 33gr H20.  That's a lot and my IMI loads use significantly less powder than my True Grendel brass.

If you are going to convert x39 brass, do yourself a huge favor and compare internal case volume of fired cases.  You and your rifle will be glad you did.