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Showing results for tags 'power factor'.
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I still see a lot of people wondering why they fail to meet PF at a match. If you just add a few extra power factor points, now you know what can happen. The bottom line is that velocity is random in nature and the BEST way to understand and manage it is to use statistics. You don’t need to have any special math skills. This post provides the simple steps to follow. For the why and more details, see Frontsight Magazine, Jan/Feb 2015 Edition, Pg. 70. The standard deviation (STD) measures the amount of variation (uncertainty) around the average velocity and it should always be used when reloading. The table below maps the chance of failing an official USPSA PF check to the variable Z. Use Z for reloading by simply multiplying the value of Z by your STD (measured using 8 rounds with your chronograph) and add the result to the required velocity to make major or minor PF for your bullet weight. The result is your desired load velocity. Values of Z are shown from 0 to 3 to illustrate the tradeoff between Z and the chance of failure. My guidance is to use values of Z in the 2 to 2.5 range. Note that if you use the STD (i.e., Z=1), which I’m sure some people do, the chance of failing PF is a whopping 44%. Z Chance of failing PF (per USPSA rules) 3.0 3% 2.5 5% 2.0 10% 1.5 21% 1.0 44% Assume a shooter’s standard deviation for a load with a 155 gain bullet is 15 ft/second (chronographed using 8 rounds). An average velocity of at least 1065 ft/sec is needed to make major power factor. To limit the risk of failure to no more than about 10%, use Z = 2.0 and simply add 30 ft/sec (Z*STD=2*15) to the required velocity to meet PF. Thus the desired load velocity would be 1065+30 =1095 ft/sec. It’s that easy! In our example above, if we “just add a few PF points” and loaded to say 168 PF, this is equivalent to Z=1.26 and the result is a 1 out of 3 or 33% chance of failure. If instead we use the measured extreme spread (which can typically run 60 fps or higher) and load to 1065+60 =1125 fps, it is equivalent to 4*STD or a 186 PF and we needlessly incur excessive recoil and higher cost. If you always load to say a PF=170 (1097 fps), your chance of passing is okay so long as your STD remains below 16 fps (1097-1065)/2. However, if your STD is actually 23 fps, Z drops from just above 2 down to 1.4 (i.e., 32/23) and your chance of failure more than doubles going from below 10% up to 26%. This is why you should measure and use the STD. Shoot with any comments or questions!
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In preparation for several major matches in the area, a club performed a chronograph check at a local match last weekend. About 6% of the competitors failed to meet their declared PF. This included several experienced competitors. So remember this! The average velocity (and hence PF) you measure at the range will always be better than the official USPSA chronograph results. Yes, it is true! The two measurements are like comparing apples and oranges. It has nothing to do with the small differences between chronographs and of course all the laws of physics apply equally in both cases. So how can I say that? It is strictly because of the number of rounds used to determine the average velocity in each case. To pass the official PF test the first time, only 3 rounds are used compared to 8 or more rounds we typically use at the range. The bottom line is that velocity is random in nature and the best way to understand and manage it is to use statistics. So statistically speaking, the term “better” means less uncertainty. We can quantify this uncertainty in terms of probability which can easily be determined from statistical tables. My post "Reloading to Meet PF with Confidence" located here ( http://www.brianenos...opic=229005&hl= ) illustrates the problem and provides a very simple solution. Also in this post, there is an example which compares the probability of being at or above the same average velocity in each case (at the range versus a USPSA chrono). Using 8 or more samples the result is at least 97.3%, but using 3 samples the result is only 85.2%. And it is important to note that the two results can be much farther apart. A seemingly obvious solution is to just chrono your ammo using 3 rounds. The problem is that using only 3 samples causes wild variations in the results and you will drive yourself crazy trying to get any type of consistent measurement. The good news is that the link above provides a very simple solution to avoid this problem. For a better explanation and more examples, see page 70 of the Jan/Feb 2015 edition of FrontSight Magazine.
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Charge weights are noted to the hundreths because I drop ten charges on the scale and take an average. Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 45 degrees F Bullet: 130 gr BBI Powder: 4.0 gr Solo1000 OAL: 1.110" Primer: Wolf 968,946,948,971,944,961,948,967,992,945 Average = 959 fps PF = 124.6 ES = 48 fps SD = 15.68 Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 45 degrees F Bullet: 130 gr BBI Powder: 4.23 gr Solo1000 OAL: 1.110" Primer: Wolf 994,1004,1029,983,996,976,984,994,1013,1024 Average = 999.7 fps PF = 129.9 ES = 53 fps SD = 17.67 Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 45 degrees F Bullet: 130 gr BBI Powder: 3.20 gr Clays OAL: 1.110" Primer: Wolf 976,989,992,968,997,976,977,986,967,992 Average = 982 fps PF = 127.6 ES = 48 fps SD = 10.58 Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 60 degrees F (indoors) Bullet: 130 gr BBI Powder: 3.35 gr Clays OAL: 1.105" Primer: Federal 987,1012,985,998,993,996,984,962,995,996 Average = 990.8 fps PF = 128.8 ES = 28 fps SD = 12.92 (I tested 3.5gr clays in between the 3.2 and 3.35 charges, and it showed pressure signs on the primers that matched the sudden jump from 129PF to 135.5! I'd estimate that 3.35 - 3.40 would be the fastest I'd go with that powder under a 130gr lead or coated. Clays showed very little smoke under a moly-coated bullet, almost as clean as Solo and certainly less smoky than WST.) Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 65 degrees F (indoors) Bullet: 130 gr BBI Powder: 4.10 gr WST OAL: 1.110" Primer: Winchester 1027,1033,1032,1053,1048,1020,1013,1063,1036,1041 Average = 1036.6 fps PF = 134.75 ES = 36 fps SD = 15.18 (Same load as above. Glock 34 factory barrel, back to back:) 1006,1014,1051,1043,977,1054,1054,1036,1034 Average = 1029.88 fps PF = 133.88 ES = 48 fps SD = 26.11 Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 65 degrees F (indoors) Bullet: 135 gr BBI Powder: 3.60 gr WST OAL: 1.130" Primer: Winchester 928,932,913,921,948,937,935,929,919,949 Average = 931.1 fps PF = 125.7 ES = 36 fps SD = 11.77 Barrel: 5" M&P 9L / Apex SDI fitted barrel Temperature: 65 degrees F (indoors) Bullet: 135 gr BBI Powder: 3.80 gr WST OAL: 1.130" Primer: Winchester 983,974,994,957,1000,993,998,989,966,988,975,976 Average = 982.75 fps PF = 132.67 ES = 26 fps SD = 13.33 I hope that helps a few of you. The 135gr BBI coated RN bullet and 3.8gr of WST is going to be my new match load, once I test it to see if it's accurate through my barrel, and my girl's stock M&P barrel. Now that Solo1000 is scarce and I don't want to burn through my stash of it without very good reason, I'm pretty happy with WST and plan to use it until my 8 pound jug is done. That said... stay tuned for a side-by-side comparison with Ramshot Competition. I have 8 pounds of that which arrived last night. My plan is to work a load up that shoots to the same power factor as the WST load, and compare them side by side for accuracy, felt recoil, and cleanliness (lack of smoke).
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Hello, I will start my new season of IPSC. I am a newbie on reloading. I shot in minor production. I would like some informations on reloading. My goal is to be a minimum factor not more. Because like this, there will be less recoil, best gun control, faster return to target, so less time which is important for ipsc. (my wife shoot with me, and less recoil is better for her too) Im scared to load my cartridges for 125 PF. 1) because if there is a difference between my chrono record and the one on the competition, I may not pass and not being classed. 2) I was told that according to weather conditions, atmospheric pressure from one place to another, that can change the power factor? is it true ? how many this can change the power factor? In the end, I'd really like to know the smallest value of factor that I can take, without taking the risk of not passing the chrono on a competition. Finally, last question, the power factor influences really much the accuracy ? The research for the reduced recoil with light load will not going to influence so much on accuracy ? I heard that for the 9mm 124gr best power factor was 133, someone would already heard that and have some sources to prove it? sorry for my bad english, I try to do my best. Thank you for your reply. PS if needed : i shoot with cz75 sp01 shadow. bullet : 124gr LOS powder : n320 primer : sellier & bellot brass : wincester / magtech
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Developing a .45 ACP Major PF load using Berry's 230gr TMJ-RN bullets. Trying to keep the PF right at 168 out of a 5" barrel. Currently use Titegroup for 9mm and .40, but was wondering if others found a softer shooting/less smoky powder for .45.
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I am trying to develop some reduced recoil loads for 3 gun. Unfortunately it’s still hard to come buy some of the more popular pistol powders so my selection is limited. I have on hand Silhouette, Accurate No. 5, Power Pistol, and CFE Pistol. I would love to find some NV320 or 231. I am using 180 JHP Montana gold bullets. Looking through several different loading manuals all of the minimum loads are still close to major PF velocities. I see several threads on here where people are loading up to 1 grain under the minimum recommended level. Is this safe? Can i start a minimum and back it of .1 to .2 grains and see where that puts me for PF and reliability. My goal is to get closer to minor PF but I would be happy with a power factor around 150 and good accuracy. I found one thread on CFE Pistol, Hodgdon list min at 5.9 for 180 JHP and he had loaded it down the 5.1, AVG 877 PF 158, with 180 HP. What is the general consensus on loading below the minimum recommended charge levels? What’s the safe way to do it, if it is safe?
