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Old 09-15-2019, 15:01   #1
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Playing with numbers

How many people who reload like to know what pressures they are running on their ammo choices ?? I have become somewhat personally trapped on staying below the .223 pressure of 55,000 PSI for reloads for my bolt action and Mini 14 .223 loads.


I have even gone as far as figuring out a mathematical process for calculating pressure and loads to keep the 55,000 PSI number in check and reach the test barrel target speed of 3250 fps. (or more) (24 inch barrel 1/12 twist)


Keep in mind I am ONLY talking about .223 loads. SAAMI lists max pressure as 52,000 as per this article. Understanding SAAMI Pressure Standards Shooters Notes.)


I am not a math genius and in reality I really never have been good at it at all. But, it seems I have found a need for some simple algebra.


I also found a formula that I use for converting Copper Units of Pressure to PSI. I can't tell you SAAMI has given it any official blessings but it seems to be reasonable.
https://en.wikipedia.org/wiki/Copper_units_of_pressure


IMR, Winchester and Hogden still list some of their loads in CUP.
Take Aim at Rifle Reloading Data | Hodgdon Reloading


Anyway, It's my goal to stay under the "magic number" of 55,000 PSI for .223 loads to keep them safe in all chambers .223 while shooting for the velocity of 3250 as shot out of a 24 inch test barrel.


My preferred powders are Western brand powders which includes Accurate, and Ramshot. Like I referred to, Hogden, Winchester and IMR also list their powder pressures in all of their loads on their web site. Accurate (Western) lists their loads with specific bullets that includes velocities and pressures. Western also divides out and separates the .223 loads from the 5.56 NATO loads.
Load Data Accurate Powders
Take Aim at Rifle Reloading Data | Hodgdon Reloading


So, am I over thinking this or are there others that think like I do ??


kwg
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Old 09-15-2019, 18:28   #2
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Yes, I think the same. Have to keep things from going kaboom and keep things accurate as well. There are conversion programs out there somewhere that will do that. Other you can do this:

PSI = (1.516 x CUP) - 17,902

You could easily build this into a spreadsheet.
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Old 09-15-2019, 18:42   #3
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Originally Posted by dh1633pm View Post
Yes, I think the same. Have to keep things from going kaboom and keep things accurate as well. There are conversion programs out there somewhere that will do that. Other you can do this:

PSI = (1.516 x CUP) - 17,902

You could easily build this into a spreadsheet.
I use 1.52 x cup - 18000. It's in the wikapedia link I put in my original post. I have been using 62350 PSI as my NATO max pressure. My Mini seems to be more accurate with faster burning powders so it's easy to get to 55,000 before I know it.

I wish all powder makers would post pressures. As per one customer service person, there are too many variables. I translate that into, there are too many un employed attorneys.

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Old 09-16-2019, 16:10   #4
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I did load up 5 different powders with 6 different loads for this test. 5 of the 6 loads were all at 24.8 grains. One separate load of AA2460 I loaded at 25 grains. I was shooting Hornady 55 grain FMJ bullets. I know FMJ's are not the most accurate bullet but it was what I had a bunch of that I wanted to send down range. The goal was to get the best velocity and accuracy while staying under the .223 threshold of 55,000 PSI.

All of theses were shot out of a Remington 700 with a 24" sporter barrel and 1/12 twist. The loading manuals all indicated the test loads were shot out of a standard test barrel of 24" and a 1/12 twist so my numbers should be close to factory numbers. I do not have a chrono to confirm speeds. I did notice that as the barrel warmed up I started to get some stringing. This meant I had to spend a lot of time letting the barrel cool between 3 shot groups. It was 85 degrees under a direct sun while I was shooting today.

AA2230 24.8 g. v=3264 fps and PSI calculated at 54248 lbs
Hogden Benchmark 24.8g. V=3235 fps and PSI calculated at 55167 lbs.
AA2460 24.8 g. V=3253 fps and PSI calculated at 53900 lbs
Hogden Varget 24.8g. V=3238 fps and PSI calculated at 52080 lbs
Hogden 335 24.8 g. V=3239 and PSI calculated at 54965 lbs
AA2460 25.0 g. V=3278 and PSI calculated 54333 lbs

There was no noticeable difference in recoil between any of the 24.8 grain loads.

All of the powders that were at 24.8 grains had pretty much the same POI at 50 yards. The AA2460 at 25 grains had a POI of approximately 3/4 of an inch lower than the 24.8 loads. I tried some 25 grain loads of H335 that was not originally in my test loads and they had the same POI as the 25 grains of AA2460. Approximately 3/4 of an inch below the 24.8 grain loads. The difference in PSI has to be minimal considering it is only 2/10th of a grain of powder but it was noticeable on the target.

I did not calculate the PSI of the 25 grains of H335 but I'm going to assume they were very slightly over 55,000 PSI. I also thought that since the 2 powder weights were very close to each other I would get the same POI but that was not the case.

Here again it's a case of pick a weight of powder and bullet and stick with it for consistent results. The H335, Benchmark and AA2460 appeared to be the most accurate with one group of AA2460 all touching each other in a left to right string with H335 right behind with 2 almost touching and the third 1/4 inch away.

This is a new rifle with a factory trigger. A better trigger might get some better groups. Keep in mind these are all 50 yard shots. For some reason the Varget and the AA2230 got me the worst groups with about 1 inch or slightly better at 50 yards shooting the FMJ's.

ON a cooler day I will try some 55 grain soft points. The soft points tend to give me slightly better groups.
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