Here is the front story....
The Rifle: AR15, Satern hand cut 16" match barrel, 1:8 twist, Wylde chamber, Young National Match BCG and the rest of a long list of fancy parts that make up this "special" rifle. It is a nice piece to say the least.
I shot a couple of boxes of Federal XM193 through this rifle after I built it. Did my own personal break in procedure, sighted in the scope and had a great day of shooting... That was a little over a month ago.
I collected all of that brass and saved it as fire-formed to that rifle.
Once I started reloading that brass, and started my load development for that rifle, I purchased QuickLoad and started in on the process.
One of the first things I did was to get an average (maximum) case volume/capacity for those particular fire-formed, once fired cases. That number is 30.9 grains of water , filled as indicated so that the meniscus just protruded over the top of the case mouth.
Here is where the problem/challenge begins:
QuickLoad's default case volume for .223 Remington (SAAMI) is 28.8 grains of water. Conversely, it shows 28.5 grains of water for 5.56x45mm (NATO) cases.
Using that data, and knowing that I have 5.56x45mm NATO cases (Lake City 11 head stamp) I select the 5.56 case from the drop down in QuickLoad and input my maximum case capacity of 30.9 grains of water. I select the bullets I was going to reload (Hornady #2266 55gr SP W/C) and select the powder (Accurate 2230).
Additionally, just prior to starting in on the loading process, I made up a dummy round seated to the top of the cannelure and did a chamber test on my rifle to determine that this particular bullet seated at this particular depth (COAL of 2.185") afforded .048" of bullet jump, and was safely off the lands. I have a home made series of tools I use to make this determination and I am completely comfortable with my methods.
QuickLoad will work up a load ladder based on powder charge number you input, so I selected a starting charge of 26.2 grains of Accurate 2230 since this charge was in the "yellow zone" and more than 15% below max indicated (NATO) chamber pressure. See the attached picture below:
Looking at the data QL provides for this load, one could expect this to be a reasonably safe load, since as indicated, it is at the maximum .223 (SAAMI) chamber pressure of 52K PSI and more than 10K PSI below the NATO max chamber pressure of 62K PSI. So I proceeded with this as my MAX load for the day, and loaded up a ladder of 20 rounds for each, decreasing the charge by .2 grains for each rung of the ladder. At 25.6 grains, QL indicates that load to be 25% BELOW the NATO max chamber pressure of 62K PSI (bottom of the "yellow zone".
Interestingly enough, at 26.2 gr. QL indicates muzzle velocity should be 2931 FPS, and is right about where I thought these Hornady's might start to get me close to an accuracy node, which is what I was going for.
So, with reasonable confidence that I should be in the hunt.... off to the range I went with my CED M2 Chrono and my new rounds. It should be noted that the rounds were loaded in the evening and it was 72*F in my shop when the cartridges were created. At the range yesterday, it was 97*F, so it was considerably warmer... Accruate 2230 temp stability is the reason I mention this... I have no real data to show me that the difference in temperature could have anything to do with my findings, nor do I know how temp unstable Accurate 2230 is.. I am just mentioning it in the spirit of full disclosure, so that you folks have all of the data I had.
The Chrono data indicated that these loads were more than 300 FPS FASTER than QL indicated they should be as seen below..
Here is a pic of a ready to fire cartridge. As you can see, I seat them to the top of the cannelure:
Needless to say, I knew these numbers indicated a potentially serious problem which is why the string is short, and I halted the testing on these particular bullets at that point for safety reasons. I promptly collected the brass from this string and inspected it carefully and the ONLY signs of high(er) pressures were that the primers (CCI #41) were slightly flatter than I like to see them. There were no other obvious signs of dangerous pressure, but I was alarmed that I was seeing velocities far in excess of what QL indicated I should be seeing.
When I got home and downloaded the chrono data, I also went back in to QL to see if I could adjust input(s) to a point that I would see these velocities, from these bullets, using this powder, and the only combinations that pushed the bullets that fast were 28.6 grains of powder (which did NOT happen) or a case (water) capacity of 26.7 grains (waaaaayyyy smaller than I measured).
A case capacity of 26.7 grains of water and the indicated powder charge would have put chamber pressure over 80,000 PSI and would have surely resulted in my gun (and possibly my face) coming apart.
A charge load of 28.6 grains would have pushed chamber pressure to 72,000 PSI and would have probably damaged something seriously as well.
Again, no pressure signs on the cases, no damage to the gun, definitely NOT a chrono malfunction because I also tested different loads with predicted results, and I also compared my chrono against my buddies new magnetic chrono that mounts to the end of the muzzle, and results were within 30-50 FPS using his ammo.
Really wondering what I am up against here because it is definitely un-nerving to say the least. I am really curious to hear what you guys have to say....?
I just can't see pushing a soft point 55 grain bullet to 3200 FPS being remotely accurate, and the 300 FPS difference in QL definitely means that something is amiss in my procedure(s).
Care to help me try and uncover the "mystery" ? The only thing I can come up with is that because this rifle has a Wylde chamber which is a bit tighter than a NATO chamber, I am seeing a pressure spike since the case cannot expand as much as it would in a NATO chamber?
The Rifle: AR15, Satern hand cut 16" match barrel, 1:8 twist, Wylde chamber, Young National Match BCG and the rest of a long list of fancy parts that make up this "special" rifle. It is a nice piece to say the least.
I shot a couple of boxes of Federal XM193 through this rifle after I built it. Did my own personal break in procedure, sighted in the scope and had a great day of shooting... That was a little over a month ago.
I collected all of that brass and saved it as fire-formed to that rifle.
Once I started reloading that brass, and started my load development for that rifle, I purchased QuickLoad and started in on the process.
One of the first things I did was to get an average (maximum) case volume/capacity for those particular fire-formed, once fired cases. That number is 30.9 grains of water , filled as indicated so that the meniscus just protruded over the top of the case mouth.
Here is where the problem/challenge begins:
QuickLoad's default case volume for .223 Remington (SAAMI) is 28.8 grains of water. Conversely, it shows 28.5 grains of water for 5.56x45mm (NATO) cases.
Using that data, and knowing that I have 5.56x45mm NATO cases (Lake City 11 head stamp) I select the 5.56 case from the drop down in QuickLoad and input my maximum case capacity of 30.9 grains of water. I select the bullets I was going to reload (Hornady #2266 55gr SP W/C) and select the powder (Accurate 2230).
Additionally, just prior to starting in on the loading process, I made up a dummy round seated to the top of the cannelure and did a chamber test on my rifle to determine that this particular bullet seated at this particular depth (COAL of 2.185") afforded .048" of bullet jump, and was safely off the lands. I have a home made series of tools I use to make this determination and I am completely comfortable with my methods.
QuickLoad will work up a load ladder based on powder charge number you input, so I selected a starting charge of 26.2 grains of Accurate 2230 since this charge was in the "yellow zone" and more than 15% below max indicated (NATO) chamber pressure. See the attached picture below:
Looking at the data QL provides for this load, one could expect this to be a reasonably safe load, since as indicated, it is at the maximum .223 (SAAMI) chamber pressure of 52K PSI and more than 10K PSI below the NATO max chamber pressure of 62K PSI. So I proceeded with this as my MAX load for the day, and loaded up a ladder of 20 rounds for each, decreasing the charge by .2 grains for each rung of the ladder. At 25.6 grains, QL indicates that load to be 25% BELOW the NATO max chamber pressure of 62K PSI (bottom of the "yellow zone".
Interestingly enough, at 26.2 gr. QL indicates muzzle velocity should be 2931 FPS, and is right about where I thought these Hornady's might start to get me close to an accuracy node, which is what I was going for.
So, with reasonable confidence that I should be in the hunt.... off to the range I went with my CED M2 Chrono and my new rounds. It should be noted that the rounds were loaded in the evening and it was 72*F in my shop when the cartridges were created. At the range yesterday, it was 97*F, so it was considerably warmer... Accruate 2230 temp stability is the reason I mention this... I have no real data to show me that the difference in temperature could have anything to do with my findings, nor do I know how temp unstable Accurate 2230 is.. I am just mentioning it in the spirit of full disclosure, so that you folks have all of the data I had.
The Chrono data indicated that these loads were more than 300 FPS FASTER than QL indicated they should be as seen below..
Here is a pic of a ready to fire cartridge. As you can see, I seat them to the top of the cannelure:
Needless to say, I knew these numbers indicated a potentially serious problem which is why the string is short, and I halted the testing on these particular bullets at that point for safety reasons. I promptly collected the brass from this string and inspected it carefully and the ONLY signs of high(er) pressures were that the primers (CCI #41) were slightly flatter than I like to see them. There were no other obvious signs of dangerous pressure, but I was alarmed that I was seeing velocities far in excess of what QL indicated I should be seeing.
When I got home and downloaded the chrono data, I also went back in to QL to see if I could adjust input(s) to a point that I would see these velocities, from these bullets, using this powder, and the only combinations that pushed the bullets that fast were 28.6 grains of powder (which did NOT happen) or a case (water) capacity of 26.7 grains (waaaaayyyy smaller than I measured).
A case capacity of 26.7 grains of water and the indicated powder charge would have put chamber pressure over 80,000 PSI and would have surely resulted in my gun (and possibly my face) coming apart.
A charge load of 28.6 grains would have pushed chamber pressure to 72,000 PSI and would have probably damaged something seriously as well.
Again, no pressure signs on the cases, no damage to the gun, definitely NOT a chrono malfunction because I also tested different loads with predicted results, and I also compared my chrono against my buddies new magnetic chrono that mounts to the end of the muzzle, and results were within 30-50 FPS using his ammo.
Really wondering what I am up against here because it is definitely un-nerving to say the least. I am really curious to hear what you guys have to say....?
I just can't see pushing a soft point 55 grain bullet to 3200 FPS being remotely accurate, and the 300 FPS difference in QL definitely means that something is amiss in my procedure(s).
Care to help me try and uncover the "mystery" ? The only thing I can come up with is that because this rifle has a Wylde chamber which is a bit tighter than a NATO chamber, I am seeing a pressure spike since the case cannot expand as much as it would in a NATO chamber?
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