Sig double stack problem (what am I doing wrong ?)

My favorite is my Sig 239 .40 (single stack)
Several years ago I added a Sig 229 .40 double stack. The 229 gets a trip to the range every 6 months or so just to be sure it gets some sunlight.

Anyway, I don't recall ever fully loading the mag at the range but I'm sure I did at one time without anything but thumbs.

Today on loading, it gets real stiff after 9 or 10 rounds. I did buy a loader / helper (fits around the mag and has a metal tab to push the rounds down), but the fancy loader got its first use today since I can not load more than 10 rounds unassisted.

Here's my problem: I have two mags for the 229 and both do the same thing with and without the helper loader. The rounds don't double stack, they pile up on each other limiting the capacity to 9 or 10 rounds. They pile up on the right side as you face the primer side of the rounds. Since they both have the same bad behavior I figure this is operator error. Help !

This is going to sound like a dumb question, but do you have 10 rd mags?! I mean, they do make double stack 10 rounders.

Hmm, I can see that one side is empty (after the half load). Good to know, I'll investigate a little closer.
I can load my, all three, double stack 9mm's for my sig 2022 with no problems.

40 cal is a different beast.

I own Sigs but don't know enough about their 40s to know if they make a flush fit mag > 10 rds.

Good luck

Currently SIG only offers 10 & 12 round mags for the 229 in 40 S&W on their website. The site only shows the 229 Nitro Compact in 40 S&W and there are two versions of that available; one with SKU: 229R-40-BSS. and the other with SKU: E29R-40-BSS.

So which mags do you have 10 or 12 round mags? If you're loading 10 rounds into a 10 round mag, what's the problem? If only 9 sometimes go into a 10 round magazine, it seems like stiff springs. If loading only 9-10 into a 12 round mag, possibly the same issue. As per what you wrote above, that you have taken to the range only twice per year for a few to several years, that few range trips may not have been enough of a break-in period for the springs.

Of course, if they are double stack mags and the rounds are not stacking onto alternate sides, there is an issue and it might be best to contact Sig about that.

Well it does partly sound like you have the ten round mags but if the rounds are only going to one side of the mag and not double stacking then that's weird. Have you taken out the spring and follower to check maybe the follower is in wrong. Most of the guns I own are Sigs and I have never had any issue like that nor have I ever had really stiff mags even when new. All my mags have always loaded to full capacity with no problem. Check the springs and follower and if nothing funny inside mags, then contact Sig.

Yes, mine are 10 rounders. Operator error ! They indeed are double stacking properly.
Thanks guys for pointing me in the right direction.