Larry Vickers always recommends one to two rounds under on the 30s

He doesn't exactly say that, and what he does say isn't exactly this post's topic. And I don't happen to even agree with him even on GI mags. Not needed to download pmags IMO.
Reproduced below:
On tough to seat mags, download at least 1 round. If a fully loaded mag is difficult to seat with the slide or bolt assembly in battery, then download the mag by at least 1 round as a matter of habit. USGI aluminum M16 magazines are a good example of this as they are really only properly designed to take 28 rounds, not 30 as advertised

Our duty mags were always loaded to 30 rounds. Policy requires it, and that’s where we are starting from if we have to count down your magazine after an incident. I never had an issue in training that I would attribute to the magazine being fully loaded. We got some cheap training ammo once that caused issues, but that’s about it.

My personal magazines are all loaded to 30 rounds and I’ve never had one that needed more than a gentle tap to make sure it was seated.

I slightly prefer Lancers because I like the feed lips better, but I’m fine with Pmags.

Now my CZ Micro, on the other hand. That one I download as there is ZERO slack in the springs when fully loaded.

End of the day though it’s YOUR gun. Load it how you see fit.

Good grief, guys.

Know your weapon, know your magazines.

There is no hard and fast rule.

If you haven't run your gun enough to know how to feed it, you best get going.

Put as many rounds as possible in, and get shooting, and pay attention to performance.

It's not about the Pmag. Don't assume that it is.

Load 30, shoot. Adjust if needed. Pmag or no.

I load 28. Always have. Always will.

I have noticed I have to insert my 30-round Lancer mags "with authority." It never occurred to me to try down-loading them by one or two.

I will test this. With my two P-Mags, as well.

Glad the OP brought it up!

Yeah, and I guess that Lancer has corrected it now, but used to be, their 30 round AR mags had a follower with a long leg, and users were unable to get 30 in the mags, or were barely able to get that 30th round in the mag. So, what you had was a column of rounds that could not move farther down into the mag body. Well, what happens when you lock a loaded magazine into an AR15? The column needs to be able to move down a bit, because the top round in the mag contacts the underside of the bolt carrier as the magazine is locked into place.

Say, here's an idea- load no more than 28 rounds in your AR mags. But, what do I know? And that Vickers guy, too. He's nothing but talk and has no experience with such things, right?

I usually load all my mags w/28 rds, regardless of Mfr. I seem to recall reading somewhere that the lips of the Gen 2 Pmags could be "damaged" or weakened over time if left fully loaded for long periods of time. Especially when not using the little thingy from MagPul that pushes the top round down a little to take pressure off the lips. I have them for some of my Pmags but not all of them.

I either do 25 if I’m storing them, or 28 for when I shoot them

quote:

Originally posted by parabellum:
Yeah, and I guess that Lancer has corrected it now, but used to be, their 30 round AR mags had a follower with a long leg, and users were unable to get 30 in the mags, or were barely able to get that 30th round in the mag. So, what you had was a column of rounds that could not move farther down into the mag body. Well, what happens when you lock a loaded magazine into an AR15? The column needs to be able to move down a bit, because the top round in the mag contacts the underside of the bolt carrier as the magazine is locked into place.

I've had no problem loading 30 into my Lancer mags, but, as I wrote, they have to be inserted quite forcefully to latch.

quote:

Originally posted by parabellum:
Say, here's an idea- load no more than 28 rounds in your AR mags. But, what do I know? And that Vickers guy, too. He's nothing but talk and has no experience with such things, right?

Honestly, it never occurred to me to do that. They are 30-round mags so I loaded 'em to 30. I'll try 'em at 29. If that does it: Fine. If not: Down to 28 they'll go.

ETA: And 28 it is. The difference in getting a mag to lock in between 30 and 29 rounds was imperceptible. At 28 rounds it definitely became easier.

quote:

Originally posted by parabellum:
I load 28. Always have. Always will.

Yup....may or may not be an issue but loading 28 has never created an issue....since I keep 50+ loaded mags stashed in separate kits it is just easier.

These are all GI mags, I have Pmags but they are still wrapped in the spare mag tub

As to Lancer 30 rd mags, they designed them so that you could barely get 30 rds into them. They have a limiter tab built into the bottom lockplate that must be ground down. Lancer posted about this perhaps 5 years ago on one of the internet boards and advised folks to just grind off the limiter if they didn't live in a location that mandated 30/20 rd mags only.

I have ground down the limiters on every Lancer mag I own and they are MUCH easier to insert on a closed bolt. Of course be careful loading as you can now fit 31 or 32 rounds, but this extra space makes it much easier to lock into the gun on a closed bolt.

This is a mandatory upgrade for Lancer mags, in my opinion.

quote:

Originally posted by arcwelder76:
Know your weapon, know your magazines.

There is no hard and fast rule.

If you haven't run your gun enough to know how to feed it, you best get going.

Bingo.

From my experience, virtually every magazine -- regardless of brand or capacity -- requires additional effort to properly seat on a closed bolt. On an open bolt, I have no seating issues with any brand of any capacity.

Because of this, I will download 30-round magazines a round or two in competitions, as sometimes I don't perform at my best when the clock is ticking a bit too quickly.

Ive not had an issue loading to 30 in Pmags or USGI personally but I agree with Arc, know your equipment and know that it runs with 30 if you do so. I also dont think people who load 29 or 28 are wrong and it may be good insurance if you are unsure.

quote:

Originally posted by bubbatime:
As to Lancer 30 rd mags, they designed them so that you could barely get 30 rds into them. They have a limiter tab built into the bottom lockplate that must be ground down.
...

This is a mandatory upgrade for Lancer mags, in my opinion.

Interesting factoid. I will definitely look into that. Thanks, BT!

quote:

Originally posted by fritz:
... I will download 30-round magazines a round or two in competitions, as sometimes I don't perform at my best when the clock is ticking a bit too quickly.

One imagines the same would obtain under self-defense/combat conditions. Thus Para's policy.

All the solid ground guys I have ever talked to said -2 in 30s and -1/2 in 20s.

So I load them all that way, with the exception of the PMAG D-60, I only have one of those and it would be the first one in a weapon on an open bolt.