August 27, 201511 yr Tested 147 grain bullet loads today and had some very unusual results that I would like to understand. N320 3.2 gr - 884 fps 3.4 gr - 818 fps 3.6 gr - 861 fps Bullseye 3.1 gr - 884 fps 3.3 gr - 816 fps 3.5 gr - 849 fps TiteGroup 3.1 gr - 818 fps 3.3 gr - 834 fps 3.5 gr - 871 fps Before we start the discussion, here's what I did with each load First string n=5 Second string n=3 just to get a gut check cause it was so weird Looked through each string to get rid of any outliers, there were none Went home and pulled 2 bullets of each weight and confirmed the powder charges weren't mislabeled and they weighed perfectly WHY WOULD THE LOWEST GRAIN LOAD GIVE ME THE HIGHEST VELOCITY with two different powders????????? FYI - TG @ 3.3 was most accurate, N320 @3.2 gr second most accurate and Bullseye @3.1 third most accurate. Unfortunately 3.3 TG load doesn't make IDPA power factor.
August 28, 201511 yr I would say the powder is too fast for the load and is reaching the peak of the burn curve way too soon causing erratic results. 9MM prefers a fuller case capacity and a slower burning powder especially with heavy pills.
August 28, 201511 yr I would have to say that it is merely inaccurate chrono results. My pet load is 3.4gr of N320 under a jacketed 147gr bullet at 1.142" OAL. This, for me, results in a very accurate and soft shooting round. The powder fills the case very nicely. From a G34: 3.4 gr N320, 147 gr Zero JHP, 1.142 OAL 874 896 876 877 870 875 891 876 883 860 AVG 878 SD 10 PF 129066
August 28, 201511 yr Why do many cartridges "flat-line" or drop velocity with increasing powder charge after max load is reached? How does a cartridge know what arbitrary "pressure" was established? In my .44 Mag, after max pressure, the next charges would show a "significant" drop in velocity. Where was the powder in the case? Did you make sure the powder was always down near the primer? Did all loads use the exact same lot numbers of components and the same cases? Should make very little difference, but you are "worrying" about very little difference. How did the recoil feel? Many powders produce pressure spikes and, I would guess, velocity variations. Maybe this is part of what you are seeing. N320: 3.2gn 864fps 3.3gn 884fps 3.3gn 910 fps 3.5gn 936fps Thus, there is even variation when repeating a test.
August 29, 201511 yr Author I'm not "worrying" but I do need to make power factor with the loads. While I understand that measurements vary, the results you posted as an example show an expected trend of higher powder weight with increasing velocity. My results were clearly not an expected result and not even close to maximum pressures. I did not raise the muzzle of the pistol before each shot but will on the next go around, however I have never done this before and the trends were as expected with 100+ other loads that I have tested. I do appreciate all the input so far. I expected the chrono had a glitch and that's why I repeated with a second n=3 and the results mimicked the first run of 5 so while I won't rule a glitch the results were repeated two separate times.
August 29, 201511 yr Author Reshot the suspect loads and repeated the same exact results. BE 3.1 grains, n=10, 871 fps N320 3.2 grains, n=10, 878 fps I'm just going to go with these loads and call it a day. By the way, here's two targets at 25yards from a G34. I like how soft they are and they seem very accurate so far.
September 3, 201511 yr <the results you posted as an example show an expected trend of higher powder weight with increasing velocity. My results were clearly not an expected result and not even close to maximum pressures. No, I was showing that repeating a test can give different results--note TWO data points for 3.3gn. I was simply mentioning max loads as "somehow" the round knows the man-made max pressure and responds--Simply pointing out that these things happen and life isn't simple. Didn't imply you were any where near max. PF: make sure you are OK by being at least 5 points over min.
January 26, 201610 yr Author Tested 147 grain bullet loads today and had some very unusual results that I would like to understand. N320 3.2 gr - 884 fps 3.4 gr - 818 fps 3.6 gr - 861 fps Bullseye 3.1 gr - 884 fps 3.3 gr - 816 fps 3.5 gr - 849 fps TiteGroup 3.1 gr - 818 fps 3.3 gr - 834 fps 3.5 gr - 871 fps Before we start the discussion, here's what I did with each load First string n=5 Second string n=3 just to get a gut check cause it was so weird Looked through each string to get rid of any outliers, there were none Went home and pulled 2 bullets of each weight and confirmed the powder charges weren't mislabeled and they weighed perfectly WHY WOULD THE LOWEST GRAIN LOAD GIVE ME THE HIGHEST VELOCITY with two different powders????????? FYI - TG @ 3.3 was most accurate, N320 @3.2 gr second most accurate and Bullseye @3.1 third most accurate. Unfortunately 3.3 TG load doesn't make IDPA power factor. So I'm back at it before I load up 4k rounds, wanted to double check once again. Here's what happened with similar results from the Glock 34, however the Sig 226 Legion gave results that were expected. I do not think there's anything wrong with the choro as I've confirmed my other loads were in the 10fps ballpark with a different chrony. 3.2gr n320 w/CCI SPP Glock 34 - 874 fps Sig 226 - 827 fps 3.4gr n320 w/Fed SPP Glock 34 - 817 fps Sig 226 - 871 fps 3.4gr n320 w/Fed Magnum SPP Glock 34 - 819 fps Sig 226 - 882 fps 3.4gr n320 w/ CCI SPP Glock 34 - 813 fps Sig 226 - 869 This is almost exactly what I saw with the last batch in August. All done with 10 round strings and temp was 35 degrees, although ammo was still almost room temp. Sig is showing appropriate trend, G34 still shows a dip which is killing me. Sig barrel - 4.4" G34 barrel - 5.3"
January 26, 201610 yr I wonder if the higher load is causing the Glock to cycle the slide out of battery faster resulting in less pressure being applied to the bullet, or if the barrel rifling is such that the higher pressure actually causes more pressure leakage past the bullet. It seems clear, confirmed by the Sig results, that the higher load is indeed creating more pressure but something in the Glock is causing that pressure to be lost somewhere other than the bullet. Something is acting like a pressure relief valve with the hotter loads.
January 26, 201610 yr Author Going to try the g17 and put original recoil spring in the 34 and see what happens tomorrow.
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