Issues with my 22 Hornet

The .22 Hornet is a rimmed cartridge and head spaces off the rim. If the cases are stretching so as to cause case separations, than I would also suspect excessive head space. Either the chamber is cut to deep or the rims are to thin. I'd measure the case rims and if they are within specs, I'd suspect the chamber was cut to deep. Buy a head space gauge or take it to a gun smith and have it checked. If it's excessive, than the barrel would have to be set back and rechambered. If it was my rifle, I'd would probably go the K-Hornet route.
 
Prior to firing, the diameter just forward of the rim is:
Hornady - 0.2916"
Remington - 0.2928"

After firing - 0.2956" - in both cases.
The spec calls out 0.299"

Since I purchased 3 boxes of the Hornady ammo, I now need to go out and try shooting rounds from the other two boxes.

If the Remington works, then that is what I will use from here on. I need to find some Winchester brass and see about it. They had some a week ago (1 box), but apparently it has now been sold.
Out of curiosity I pulled out my 22 Hornet ammo and cases to see how they compared to your figures. I only measured the cases just in front of the rims. Here are the results from RWS, S&B (Sellier & Bellot) and Winchester cases. These were shot through a Weihrauch HW 60 J BA rifle.

RWS Factory Loads 0.2958"
RWS Twice Fired Cases 0.2958"
S&B Twice Fired Cases 0.2957"
Win Unfired Cases 0.2935"
Win Twice Fired Cases 0.2953"

I also weighed a sample of each brand and these are the averages,
RWS 56.3 gr, S&B 57.4 gr and Win 51.5 gr.

The Winchester cases were very disappointing, the necks were cut on an angle to the point that they wouldn't stand upside down on a level glass topped table. Added to that the low side of the angle was shorter than the SAAMI recommended trim to length. I shan't buy any more!

Your fired case web area measurements are very similar to mine but the Hornady factory measurement seems small to me.
 

Check this out. More info than you could ever want to know about the 22 Hornet. Long and short, Hornady has had issues over the years with their 22H and 17HH ammo and brass. Go buy some loaded Privi Partisan ammo, also known as PPU. Way cheaper, shoots great and makes great brass for reloading. Otherwise, the WW ammo is generally good stuff and makes good brass.

Courtesy of Tillyman from Saubier. Click on the image to enlarge it.

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