CAUTION: The following post (or a page linked to) includes or discusses loading data not covered by currently published sources of tested data for this cartridge (QuickLOAD or Gordon's Reloading Tool data is not professionally tested). USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from using this information.
Mrappe,
Your IMR4198 should work well if you are not after maximum velocity. I read somewhere that Eugene Stoner used it early in AR development, but it was dropped because its maximum load fell short of his target velocity by a couple of hundred fps. Its maximum loads are about 9% lighter than the bottom end of the usual 223 powder charge range, as Shadow9mm pointed out, but it is also about 9% bulkier than IMR4895, so the light weight does not mean unacceptable case fill. The maximum listed Hodgdon load should be over 85% case fill. That will produce a bit more velocity variation than a higher case fill. Still, many have noted in the 222 Remington, where IMR4198 is more commonly used, that despite more velocity variation than some other powders, it often produced the best accuracy. Velocity variation and accuracy don't always coincide. Lower recoil, muzzle blast, and average barrel time can sometimes be the dominant accuracy terms.
Your primer dents are pretty pronounced. It leads me to ask, how deeply are you seating your primers? Many bolt rifle shooters are in the habit of seating only until they feel the primer anvil's feet touch the floor of the primer pocket. The military, however, will typically compress the anvil into the primer pellet to about -0.003" (what they call reconsolidating the primer, aka, setting the bridge). I've seen tests reported where this improved accuracy and tests reported where it reduced accuracy. The results are not consistent. However, it does move the back end of the primer cup further from the tip of your firing pin and may reduce the chambering indentation, so it's worth trying out.
You can also measure the length of your firing pin protrusion.
This video is a good demonstration of how to do it. It should be between 0.028" and 0.036", with 0.032" right in the middle. If yours is on the long side, a different firing pin or a different bolt body can correct it.
Another path is to get a titanium firing pin, whose lower mass will mean it carries less kinetic energy when it hits the firing pin, and the pin metal has to apply less force to bring it to a stop.
This thread at Brain Enos's forum includes a post by a fellow who had slamfires and stopped them by getting a titanium firing pin. I tried going to the source recommended in the video, but my browsers all refused because it was insecure and had tracking cookies, like Google.com.