OK;
For the most part, pretty much everything that salesman told you is in line with the exhaustive test and report linked below.
I scanned the report for this post several times and could neither confirm nor refute any data on whether the necks and/or cases failed to expand conventionally during firing.
On my own part, I did some pretty intensive experimentation with TulAmmo Boxer Primed 55gr steel case ammo, going so far as to reload several hundred of the ones that were Boxer primed, and even developing a 75gr Match handload using the cases.
During the project fired case necks and primer pockets were carefully measured after every firing for diameter and case neck thickness. I was unable to detect any measurable dimensional deviations using my basic reloading dial caliper.
I reloaded mine 5 times and stopped at that point because the cases were not really .223/5/56 cases; their volume was considerably smaller, almost as small as a 222.
Because of this I abandoned a fairly extensive report I had been accumulating, because I did not think it wise to write something about reloading a deceptively small case that someone else may gloss over reading and try to load with regular brass case loads.
It was a liability case just begging to happen.
For the record, never attempt to reload steel .223/5.56 cartridge cases. It's dangerous way beyond any normal reloading project.
Brass vs Steel Case torture test report
I read that report when it came out. What the salesman tried telling was incorrect. That report dose not agree with the salesman. It confirms everything I said.
Per that report you linked, copper plated steel projectiles do accelerate wear on the barrel. “ Brown Bear and Wolf carbines exhibited significant accuracy loss by the 6,000 round mark. It is quite possible that this first started occurring earlier than 6,000 rounds, because groups at 4,000 were well within standards of 5MOA or less, while some shots at 6,000 “keyholed,” or impacted the target sideways“
“As indicated by accuracy testing, the steel cased/bimetal jacketed ammunition caused accelerated wear to the inside of their respective bores.”
The cheaper ammunition had multiple cycling issues. “Brown Bear carbine’s gas tube and gas key were so fouled with carbon after 5,000 rounds that it would no longer function reliably. Nearly the same level of buildup was found on the replacement key and tube after they had seen just short of 5000 rounds”
The cheaper ammunition produced more fouling. Not going to copy quote more paragraphs, see above.
My first experiences with Wolf ammunition goes back to 06. Wolf had lots of problems back then. Some very serious, like very over pressure rounds. I never had a case rupture from it, but I had friends that did. The steel case cheap stuff has gotten much much better since then, I just don’t care for it.
Anyway that’s not the dumb thing the salesman pitched. He’s stated that when a steel case is fired it does not expand. As in remains the exact same dimension as a new unfired case during the firing process and because it does not expand the combustion gasses go past the case into the receiver.
This is simply not true. The steel case of a steel case 5.56 round expands exactly the same as a brass case to seal the chamber while under pressure. Also confirmed from a simple call to Hornady who also has steel case 5.56. The barrel around the chamber will distort some during firing. This is what a piezo electric pressure trace strain gauge reads. So given how thick the steel is around the case and it still moves some 0.0005” under 60,000 psi. There is absolutely no way the wall of steel case 5.56 round that measures 0.013-0.015” thickness is not going to expand till it hits a immovable object, the chamber wall.
Further more if the case did not expand to grip the chamber walls when fired it is possible to damage the rifle by excessive bolt thrust. Also confirmed from speaking to the tech department of FN rifles, (yes I know about their “gas lubricated chambers to aid extraction”. That’s a entirely different topic). It’s why manufactures place a 600ish grit finish on the inside of the chamber and not a super polished finish. To grip the case under firing.
You can also read about this effect in most rifle owners manuals where they mention wet ammunition may increase bolt thrust due to the case not adhering to the chamber walls. If you want to see the phenomenon yourself. Take a round and coat the case in some Imperial wax, chamber and fire. Bet it comes out looking like a hot loaded round. Now I have never felt the urge to test this, so I’ll just take the manufactures word on it.