So I won 1000 of Nozzy's 77g projo's at the Crimson Trace Midnight 3 Gun match last month, and I've also been trying to figure out how to do a Mk262 clone load. The heavier 77g projos do much better on knocking down steel than the 55g pills. I noticed that CFE223 tends to show higher velocities in Hogdons data charts than the other usual powder selections. "Hmmmmm..." says I. "Higher velocities before reaching max pressure in almost any given bullet weight..."
Yes, Hodgdon only lists a 53,500 psi SAMMI load that max's out at 24.3 grains for a reported 2811 fps (apparently from a 24" bbl), but I'm not afraid to experiment with slightly "+P" loadings of the CFE223 in my mil-spec guns. If Hogdon had published NATO spec 62,500 psi loads like Ramshot does, I bet CFE223 would be prominantly displayed. If uncle sams guns can do 62,500 PSI, so can mine. Increasing .2-.3g at a time, I was able to get the following results from a 14.5" carbine, and a 20" HBAR. Both chrome lined 1/7 twist 5.56 chamberings, using LC brass and CCI "5.56 military" primers, 2.25" COL. 5 shot strings, barrel was warm to touch, ambient temp 92 degrees, chrono 10 feet from muzzle.
CMMG M4- 24.3g = 2525 fps av, 24.6g = 2580 fps av, 24.8g = 2618 fps av, 25.0g = 2654 fps av, 25.2 = 2675 fps av.
Colt AR15A2 HBAR- 24.3g = 2650 fps av, 24.6g = 2740 fps av, 24.8g = 2790 fps av, 25.0g = 2834 fps av, 25.2g = 2890 fps av.
I read, and re-read all the helpful comments here before proceeding, and appreciate all the work that you guys have done. Now obviously you are proceeding at your own risk with loads that are 4-5% above published max if you choose to follow this path. Your mileages may vary! Just to be clear, I DID NOT START WITH +P LOADS. MY STARTING LOADS WERE 5% BELOW MAX TO CONFIRM THAT NO PRESSURE SIGNS WERE PRESENT BEFORE PROCEEDING UP TO THE "+P" NATO'ISH PRESSURE LEVELS. I did not do any chrono or other data collection at the lower levels, as that was not the intent of my endeavour. I do not have a pressure transducer, but have unfortunately peirced my fair share of occasional primers in over pressure .223 service rifle / 3gun loads over the last 35 years. Not proud of it, just giving reference that I recognize the over pressure signs listed below when I exceed them. "Good judgement comes from experience, and experience usually comes from bad judgement."
As far as range notes on this session; much of what has already been discussed applies. The comments about the repeatable measured weight of CFE 223 are correct. This stuff meters like water! I never threw even a .05g variation in weight from my RCBS measure. Best accuracy was in the 1-1.5 MOA department, and was with the lower velocity loads (24.3g -24.6g = 2525-2700 fps). Groups opened to 2.5" at 25.2g. Groups were fired with 4x optics, comparable to the ACOG's in use today (so theres likely a bit better accuracy possible with a higher magnification optic used on Mk 12 clones). Not a single sign of over pressure was detected all the way up to and including the 25.2g load in either rifle. I had reached my velocity goals, and accuracy was deterriorating, so I did not persue it further. No flattend/cratered/peirced primers, no scuffed ejector marks, no incipient case head seperation ring, no split case necks. I used 3X fired LC 85 cases. I used sorted cases with a slightly heavier weight (94g deprimed) to push the limits of the smaller case capicity / higher pressure envelope. Muzzle blast and felt recoil were noticeably higher after 24.6g loadings. All rounds were magazine fed and functioned 100%, and brass was deposited on the deck at 4 o'clock about 5 feet out. It appears that in MY guns, the clone load for the M4 is going to be 24.7g of CFE223, and 25.0 for the A2 based on reported Mk262 velocitys in Jicko's OP. However, due to the lower accuracy produced there, I will be using loads in the 24.5g - 24.6g range.
Listed velocitys of spec Mk262 are:
14.5" 2576 FPS
16" 2669 FPS
18" 2769 FPS
20" 2818 FPS
So to summarize: I pushed the envelope with CFE223 by over loading by almost 5%, using heavier weight cases, shot in hot weather, and got away with it. Inventory reveals 10 fingers, 2 eyes, and all bodily fluids accounted for. Probably the most useful information I take away from this experiment is that IN MY GUNS there is going to be AT LEAST a .6g+ margin of safety before I reach over pressure loads when I shoot the 24.6g loads. I will likely load some of the 24.8 loads and try them at 300 yards to check accuracy, since the longer "VLD" type bullets (its hard for me to call a .34 BC projo "VLD") have a tendancy to not fully stabalize until the 150-200 yard mark. But given the 2"-2.5" I got at 100, I don't hold out much promise. Remember speed is fine, but accuracy is final.
Last edited by Mark I; 09-16-2012 at 8:16 PM..