IMO, it's most likely the Independence Aluminum case ammo. I'm not bad mouthing Aluminum case ammo. I like inexpensive practice ammo. I have a couple cases of CCI Blazer aluminum case ammo. I expect it to be 99% problem free, and it is. Every once in a while, I'll get a short stroke of the slide. One time the aluminum extractor groove on the 9mm rimless ammo didn't hold up. Another time, whatever case treatment/coating on the aluminum case was probably missing and caused a failure to extract.
Try a hundred rounds of brass case 115gr practice ammo. I'm sure you'll have no problems.
There is one specific manufacturer and brand of inexpensive practice ammo I highly advise you never buy. Stay away from it as if it could give you contact herpes.
Tul MaxxTech ammunition. It's nickel washed, steel case, brass jacket over soft lead ammo manufactured in Bosnia and Herzegovina. I found a case for a stupidly cheap price. The price overrode my common sense. The ammo powder charge is inconsistent. Under live fire I'll get some rounds that feel like they're +P+, and others with a mouse fart charge that force me to make sure there isn't a squib in the barrel. I also think the projectiles aren't balanced, and wobble in flight. From pistols that are known to be both precise and accurate with regular brass case 115gr practice ammo, I could never achieve accuracy or precision using Tul MaxxTech ammo.
The round fires. The steel expands to the chamber, but doesn't rebound like brass. With a traditional polymer coated or lacquer coated steel case, the coating provides the lubricity needed for the slide's rearward momentum to yank the spent case from the chamber. In this nickel washed abomination, the thin nickel wash flakes off when the steel case expands. The nickel doesn't add any lubricity. The case then sticks in the chamber and I have to tap it out with a dowel.
Even more worrisome:
This is a case fired from a Springfield Range Officer 9mm. You can see the case expanded when fired, and the case failed (cracked). This case had to be tapped out with a dowel. The same thing occurs with my Glock 19, Glock 43, Sig P938, S&W SD9VE, and Styer M9-A1. I tried to give 100rd plastic cans of it away to friends. It jammed a Sig SP2022, Sig P320, Ruger P95, Taurus PT92. I average 2 to 3 failure to extracts per 15 rounds, with the case stuck in the chamber. Case failure doesn't always occur with a stuck case. Out of 30 spent cases, I counted 10 that had case wall failure.
My SD9VE will experience a failure to extract with every round of this junk ammo. Shoot, swear, dowel down muzzle end to tap out stuck case.
I have 350 rounds of it left in my ammo can that I can't give away. It's going to stay tin my ammo can as my end-of-the-world ammunition to be used when I have no other choice because my sling shot is out of rocks.
Former Taurus 709 slim owner here. Key word = former. Don't generalize issues with your 709 slim to every other pistol. The 709 slim is a gamble. Some work fine. Some (like mine) were nothing but problems even after trips back to the Taurus Miami Mothership.
IMO if your 709 Slim is problematic with brass case, copper FMJ ammo, time to get rid of it. Luck of the draw whether or not you get a problem free 709, and you weren't lucky. If you need a single stack 9mm polymer frame pistol, go get a Ruger LC9s, Glock 43, S&W Shield, or XD-S 9mm.
