SAAMI and CIP have a bit of tolerance variance for .22 LR between go and no go headspace gages. That is to allow feeding of ammo from various sources that have variable tolerances. Without using caliper gages on your cases and closeups , I would suspect that bulge may be from that tolerance if you measured headspace using headspace gages and it was ok. Or, it could be from out of spec ammunition that has a too thin case rim.
If not, you may want to use a no-go gauge to determine if your firearm has headspace that is a bit long (too much) which could case that bulging from the back of the case not being supported by the chamber. Another cause could be a chamber that is too wide (usually from improper cleaning or manufacturing error) at the rear.
If the firearm's headspace exceeds a field gage for .22 LR, then you might want to have the barrel recertified which generally requires lathe/chamber work or relining the barrel/chamber work. Or you can get a new barrel but that might require reaming for top performance. If you don't you could have a case/head separation.
If it passes with the bolt not closing on a field gage, it is not so much an issue if you use new factory ammo. Be sure to wear eye and hand protection and have a case extractor though to pull out a headless case. Bulk rimfire ammo is not always of the best quality and does vary in its rim thickness.
Excess headspace may or may not actually affect accuracy in a given rifle so you really cannot use that as a measure of whether your rifle has proper headspace. The risk is getting hot gases @24000 psi near where your eyes, face, and fingers are from a case head separation. Under the right conditions, it can damage a firearm from the hot gases. .22 LR's do have a case rim that helps seal a chamber and deflect gases compared with headless cases but it is a safety risk.
