My Sig 226 mags from AIM surplus came in Sig boxes but the mags are stamped Mecgar. Are they as good as Sig stamped mags.

Mec-Gar are great mags.

They are OEM for a couple companies.

Most US OEM sig mags are made by Mec Gar

I have the same set up - they all work fine.   As the previous post mentioned, Mecgar is the "OEM mag manufacturer" in some cases.

Mec gar are gtg

Probably a bit better than most companies can do in house.

If given the choice
Mecgar over OEM marked

Usually mecgar made the OEM mags and stamp Sig, CZ, etc

Mecgar are cheaper and are the exact same

yes

Sig has been using checkmate as a manufacture for magazines for their classic P series, the P320, and P365. The checkmate mags are not that great from my experience. The springs wear out faster the finish sucks and the tolerances are not consistent. The Mec-Gar mags are better in every way. Med-Gar mags were all Sig used until around 2020 or so when they started using CM. If you get an Sig marked mag that says made in Italy it is a mec-gar mag.

I ordered 15 rd P226 Sig brand mags recently.  They are actually made by Mec-Gar.

Mec-Gar in general has always made good quality mags. Like somebody above already pointed out they are the OEM provider for a lot of different manufacturers. I've been using Beretta 92fs and CZ 75b Mec-Gar mags for years.

Very few companies make their own magazines.

Only time they let me down were some Ruger 22/45 mark III mags. Didn't function all compared to factory Ruger ones. Bodys didn't match the factory Ruger either. I scavenged the internals and trashed the mag bodies.

Never had any problem with the p226 mags.

+1 on MecGar which is OEM.
When I bought my last Sig, a p320 in .45, there were complaints of mag problems with OEM Sig mags NOT marked 'Made in Italy'.
Not sure who made the USA mags but as mentioned above, MecGar is as good as or better than factory OEM.

Checkmate is making the USA marked Sig mags. They are trash compared to the Sig marked Mecgars and the non Sig marked Mecgars. Sig knows the checkmate mags are subpar because their LE guns only ship with the Mecgar mags. This is across the board for the P320, P365, and P226/229 series. The Checkmate mags have a crappy finish that rusts pretty easily, the springs wear out significantly faster, the followers are often rough with flashing that hasn’t been removed and the tolerances for the mag body, follower, and floor plates are all over the place. For most people the checkmate mags are probably fine but if you carry your gun expect the mags to rust and if you shoot more than a couple thousand rounds a year, expect the springs to wear out. I avoid the checkmate mags as much as I can. When I can’t I will often replace the springs and followers from those from Grams Engineering. Mecgar also sells their spring, follower and floor plate kit so you can retrofit the CM mags. It is less expensive than the grams kit. I use the GE kit because I have lots of experience with that kit. I’ve uses the GE kit in various pistols for years but the Mecgar kit is also typical Mecgar quality which is to say, outstanding.

https://gregcotellc.com/cart/mecgarcz-plus-1234-adapters-c-107/mecgar-sig-sauer-p226-plus-1-set-p1setsig-p-2211.html

It's been a long time since I actively shot a lot but all I ran were Mecgars in my 226 and never had a single issue. When they came out with the 18's I bought a pile of them because they were significantly cheaper than factory mags and held more rounds. I need to order some of the X5 mags too talk about price difference.

I sold guns for years at a couple levels and have sold thousands of Mecgar mags with basically no issues. I would have no issue trusting them at any level of usage.

MecGar are Sig OEM mags. Every Sig OEM mag is made by MecGar.

This isn’t accurate. Sig has mags made by Mecgar and Checkmate. The mags marked “Made in Italy” are Mecgar mags. Their mags marked “Made in USA” are Checkmate mags.

What’s the going rate for P226 9mm?

I'd prefer MecGar stamped over OEM stamped.

I have a couple of mags that are stamped MecGar and have OEM stamping too.

MecGar knows mags like Bo knows football.

Not just a couple..
I’d say most of the OEM pistol mags out there are made by MEC Gar