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9mm 147 Grain Bullet Load Anomaly - Input Appreciated

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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.  

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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. 

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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    

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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.

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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.

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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.

post-3162-0-67888700-1440885385_thumb.jpg

post-3162-0-78643000-1440885404_thumb.jpg

post-3162-0-50914800-1440885419_thumb.jpg

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<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.

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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"

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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.

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