I have used plenty of 4198 to cycle both cast and jacketed loads. However, this was with a midlength AR for jacketed and cast and a carbine length for only cast.
There are a couple of tricks you can do to try to get your rifle length AR to cycle, if you cannot build up enough standard pressure to the port with 4198. It really depends on how much effort and/or modifications you want to put into it.
- Create a decent load that you find is acceptable for your preferences. If you have two loads within acceptable pressures, pick the hotter load. These would be developed in single shot mode.
- Assuming the lower has a rifle buffer and tube... First, remove all the weights and the spacer. Try your developed load with the empty buffer. If it cycles reliably, try adding 1 weight back at a time with the appropriate # of spacers until you fail to cycle. Then pick the heaviest sum buffer weight that cycles reliably.
- If you have a carbine buffer system this should be even easier.
- Try a carbine gas system and remove weights as explained above.
- For that carbine gas system you should be able to buy a lighter weight buffer spring. I'm not sure if there are reduced power rifle length springs. If so, that's an option too.
- Light weight BCGs can be purchased.
- Measure the gas block gas port. Ensure it is bigger than the gas port in your barrel. You want every bit of gas you can going into the gas tube.
- The most permanent change would be to open up the gas port in small increments and see if you can get it to cycle. Then when you find a spot you like, add an adjustable gas block. Something with easy click adjustment and one that will not be gunked up by fouling.
Sounds like alot of effort. Some or all of this may not be something you are interested in if you are just trying to use up the 4198, but I enjoy having a cast only AR and enjoyed the process of learning and getting it to work. My standard load is a NOE 225-61-FN GC & PC sized 225. 62.1 gr total weight. Using Shooters World Buffalo Rifle, a powder very similar to 4198. With 4198 being a touch slower of a powder. My load is going at 2425 fps. 1.5" 10 shot groups at 100 yards.
In short:
You can customize the AR lower to cycle lesser pressure loads, or customize the upper... or both. For my carbine gas system, it's a dedicated cast bullet setup. I customized both the upper and lower. The gas port is slightly opened up, I think it was something like 0.09" with standard gas block. Regular BCG. Lower has the buffer with weights removed and a reduced spring. I tried a light weight BCG, but it didn't need it.
