imr4198

Matt_G said:
Do you happen to have the approx. time frame that IMR 4198 changed and the characteristics of said change?
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Approximately 1976-77 after the fire at the Kearney's Point, NJ plant, after which nitrocelulose base material was sourced from Expro Energetics, Valley Field, PQ, Canada. Important difference was change in process to using wood linters instead of cotton linters used formerly. This effected efficiency of nitration and changed burning rate slightly.
 
I've not tried IMR-4198 in either 5.56 x 45 or 223 Remington. I have run it in a couple 222 Remingtons, and it was LIGHTS-OUT ACCURATE. It meters OK in my RCBS powder measures, but hitches a bit when I turn the drum to pour, so I scale-check my pours. I do this with all of my rod-type IMR powders, though 4198 is still pretty consistent--T.I.R about 0.2 grains. That wouldn't mean much in a 338 Win Mag, but in a 222 Rem with 19.0-20.0 grain charge weights.....well, I'm picky.
 
4198 meters through my old LEE dump like a champion.
i haven't touched the dial since i set it 30 sum years back and it's never wavered the weight in all that time.
 
I haven't found anything an auto-drum will meter. Both of mine short-stroked so bad only half the hole was exposed on the drop end.
Advance it one gear tooth and it won't pick up a full load on the return stroke. Also the Mack valve spring they use for a return spring spreads the casting at the bottom where the thumbwheel is and lets it pop off to one side. I gave them both away to someone else with some mechanical aptitude with full disclosure to see if he could make them work. I'm just glad they're gone and will stick to my B&M, Uniflows, and Auto-Disk measures.
 
Mine work perfect other than they leak with ball powders. Thats the thing with Lee stuff in general. They either work or they are junk.
 
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.

  1. 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.
  2. 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.
    1. If you have a carbine buffer system this should be even easier.
  3. Try a carbine gas system and remove weights as explained above.
  4. 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.
  5. Light weight BCGs can be purchased.
  6. 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.
  7. 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.
 
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I got talked out of my last jug of 4198 by a friend who told me, "Oh you live close to Recob's, you can pick up another one." Yeah yeah, well I dithered and look what happened. I'm not worried about gas and cycling and ports lowers, uppers or any of that. I believe 11 grains under a gas checked 70 grain .25 caliber flat nose delivers 1,635 fps in a .25-20. A good friend runs close to a case full in his Model 73 Musket as an every day alternative to BP. Should translate into the .38 w.c.f. as well. And there are a bunch of other candidates so......I'm thinking if I keep the 9.3x57 it'll work in that.
 
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