My quest for the "perfect" cast .223 load for my AR-15
Final update and summary, as of 3/10/19: While there are still plenty of things I think could improve my results (better bullet design, using an alloy with higher tin/antimony content than pure COWW, experimenting with more powders, and using a nicer barrel), I have concluded my .223 through AR-15 tests for the foreseeable future. I achieved just north of 3 MOA with heat-treated 28-30 BHN COWW bullets, from the Lee C225-55-RF mold. This was at around 2600 FPS, using 19.6 grains of H335. The bullets are powder coated using Smoke's Clear PC, and copper Gator Checks brand gas checks. They are sized to .225" after powder coating. For plinking on steel out to 100 yards, these bullets are great. If you want to win competitions, you're going to have to put in more work.
For anyone wanting to shoot cast .223 through an AR-15 rifle, I can suggest ~19.0 grains of H335, using very high BHN 55gr bullets, as an excellent starting point. I have zero cycling issues with this load in my standard 16" barrel and carbine-length gas system. With my less-than-stellar barrel, I'm getting about 3 MOA.
For those who want to do better than 3 MOA, I can suggest the following measures to improve on my results: try mixing in some Linotype alloy with your COWW alloy. If it was me, I'd start by experimenting with a 1:3 ratio of Linotype to COWW, and playing with heat treating to find the optimal BHN for accuracy. Others who are having more success here than I have recommend a BHN in the 18-22 range with this alloy, and IMR 4895 powder to make near-full velocity loads that shoot with excellent accuracy (2700+ FPS).
One last word of caution; it's a really good idea to establish the accuracy potential of your rifle by working up a jacketed load first. I could have saved literally months of testing had I done this first. It turns out my muzzle break was either faulty or incorrectly installed, and was limiting my barrel's accuracy to around 3 MOA regardless of projectile type. After removing the muzzle break, accuracy improved.
Thanks again to everyone who helped me out as I spent the last year or so really learning a ton about how to make cast bullets work in difficult situations. If you have stumbled upon this thread and are trying to do cast .223 in an AR-15, I assure you it's possible, and I'm happy to answer any questions you may have. Feel free to send me a PM.
-Andrew
Original Post:
Hey everyone--
I've spent lots of time reading here and gotten lots of great info. Now that I've joined the ranks of the AR-15 crowd, I'm tackling my most ambitious casting goal yet: an inexpensive cast .223 load that cycles my "M4 clone" reliably, and is accurate out to at least 100 yards, preferably 200.
I'm doing a short video series to carefully document my "somewhat-scientific" approach to chasing down this unicorn load. The documentation is more for myself than anyone else, but if it helps a brother out who is as overwhelmed with information as I was when researching for this, all the better.
This first video is mostly just an introduction and the culmination of my research into the different factors that go into a successful cast load in an AR-15. About 10 minutes of talking and reading off of a paper so I could remember everything I wanted to cover... haha.
https://www.youtube.com/watch?v=EriLIM-_e-A
But this weekend or next, barring a life-changing event (my wife is due to give birth to our first child any day now :D), I'll be testing out my first set of loads to see where they get me. I will be carefully recording my tests, and documenting my findings for the next video.
All testing will be done on my rifle with the following specs, so anyone looking to develop a load for their own rifle will have mine as a starting point:
Anderson Lower
Bear Creek Arsenal Upper
16" chrome-moly barrel with 1:9 twist
Carbine-length gas system
Standard carbine buffer and buffer spring
Standard 8620 steel BCG