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Strange 9 Major Results

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Experts, I have a strange issue with my 9 Major loads that perhaps you can help with. I picked my Open gun backup after 2 years, a stock STI Trubor, and was using the pile of loaded ammo I still had. I was getting low so I refered to my log book and set the press back up to create the same load; 124 MG FMJ, 9.5 grains of AA#7, CCI500. The new load prints about an inch higher, but chrono's slower (1438 vs. 1385). I have the same crimp, same chrono, same box of bullets, same OAL, same gun, etc. Any idea what could be causing the different results? And for what it's worth, I pulled 4 old rounds and measured the powder and 4 rounds of the new load, and the charge is almost identical. In fact, the old load was a wee bit lighter than the new load. 

I'm stumped.

 

Old Load 2015 - 9.5 - STI TruBor
High: 1470
Low: 1410
AVG: 1438
ES: 60
SD: 17
PF: 178.3
 
New Load 2018 - 9.5 - STI TruBor
High: 1409
Low: 1340
AVG: 1385
ES: 69
SD: 22
PF: 171.7

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Is it the same lot # of powder if it's a newer can of powder the lot# you have could be a little slower then your original load.

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Are you using the same jug of powder from 2015 and if so how has it been stored? Also if it’s a different lot of powder from what you were loading in 2015 you will get variation and have to rework a load. 

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Different production lots of primers, powder, bullets, and cases will all play a part.

 

Slower bullets will be in the bore longer, allowing the muzzle to rise more before the bullet exits, resulting in higher impact point compared to the faster load.  Not knowing the range, it's hard to say if the 1" difference is reasonable.  For a 45 fps difference, it seems more than expected at handgun ranges.

 

 

 

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1 hour ago, Guy Neill said:

Different production lots of primers, powder, bullets, and cases will all play a part.

 

Slower bullets will be in the bore longer, allowing the muzzle to rise more before the bullet exits, resulting in higher impact point compared to the faster load.  Not knowing the range, it's hard to say if the 1" difference is reasonable.  For a 45 fps difference, it seems more than expected at handgun ranges.

 

 

 

Ahhh. That makes sense, never thought of that! 
And for what it's worth, I sight in my Open gun at 15 yards.
Thanks for the post! 

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1 hour ago, 36873687 said:

They say aa7 is temp sensity

I was wondering about that. Do you know if it gets faster or slower when it gets cold?

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2 hours ago, Wvaughn7 said:

Are you using the same jug of powder from 2015 and if so how has it been stored? Also if it’s a different lot of powder from what you were loading in 2015 you will get variation and have to rework a load. 

I "think" it was from the same jug, but not absolutely sure. It was a couple of years ago.
:)

It was in a cabinet in the garage the entire time. Not sure if that is a good/bad place to store powder.

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5 hours ago, saibot said:

I was wondering about that. Do you know if it gets faster or slower when it gets cold?

My buddy put rounds in the freezer. 4 degree then went to range. FPS dropped a ton. I said we never going to shoot in Alaska. I’ve tested all this yr. in all temps I didn’t get the drop butnhe would know shoots over 50 k a yr

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13 hours ago, Guy Neill said:

Different production lots of primers, powder, bullets, and cases will all play a part.

 

Slower bullets will be in the bore longer, allowing the muzzle to rise more before the bullet exits, resulting in higher impact point compared to the faster load.  Not knowing the range, it's hard to say if the 1" difference is reasonable.  For a 45 fps difference, it seems more than expected at handgun ranges.

 

 

 

The gun doesn't even start to move until the bullet lets go of the rifling and all of the gas pressure behind it uncorks. 

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3 hours ago, chevrofreak said:

The gun doesn't even start to move until the bullet lets go of the rifling and all of the gas pressure behind it uncorks. 

Not true.  The gun begins to move at the same time the bullet does.

 

In a 1911 45 Auto, the slide - barrel has moved about an eighth of an inch at the time the bullet exits the 5" barrel.

 

That's why the barrel points down compared to the line of sight.

 

Guy

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Sounds like you've solved the problem, but sample size could also play a part, here.

 

How many rounds did you send over the chrono ?

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6 hours ago, Guy Neill said:

Not true.  The gun begins to move at the same time the bullet does.

 

In a 1911 45 Auto, the slide - barrel has moved about an eighth of an inch at the time the bullet exits the 5" barrel.

 

That's why the barrel points down compared to the line of sight.

 

Guy

 

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1 hour ago, chevrofreak said:

 

 

And there it is. Movement of the slide before the bullet exits.

 

This has been brought up before, but it's simple physics - Newton's third Law.

 

The gun starts to move as soon as the bullet starts to move. No way around it.

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On ‎10‎/‎12‎/‎2018 at 5:48 AM, 36873687 said:

My buddy put rounds in the freezer. 4 degree then went to range. FPS dropped a ton. I said we never going to shoot in Alaska. I’ve tested all this yr. in all temps I didn’t get the drop butnhe would know shoots over 50 k a yr

 

I have not experienced temp sensitivity with AA7.

 

My 9 major 115 load has consistently averaged just under 1500fps between 37 and 110F.

5 shot ES is around 20, and has never been a detriment for accuracy.

Most of my chrono sessions have been in the 50-100F range though. The one 37F session was looking for temp sensitivity and the bullets were in the open for over an hour before being tested. That's just one cold test and I haven't tested AA7 any colder than that yet.

 

I've heard that AA7 was reformulated many years back. Maybe you have the old stuff?

Any number of things could have occurred to your powder in that time. Water content from humidity when the jugs were opened could have changed powder density and potentially burn characteristics. Just speculating.

 

AA#7 is a great powder for 9Major. Slowest powder that easily makes major with 115's with a charge that easily fits in the case.

 

 

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4 minutes ago, racer-x said:

 

I have not experienced temp sensitivity with AA7.

 

My 9 major 115 load has consistently averaged just under 1500fps between 37 and 110F.

5 shot ES is around 20, and has never been a detriment for accuracy.

Most of my chrono sessions have been in the 50-100F range though. The one 37F session was looking for temp sensitivity and the bullets were in the open for over an hour before being tested. That's just one cold test and I haven't tested AA7 any colder than that yet.

 

I've heard that AA7 was reformulated many years back. Maybe you have the old stuff?

Any number of things could have occurred to your powder in that time. Water content from humidity when the jugs were opened could have changed powder density and potentially burn characteristics. Just speculating.

 

AA#7 is a great powder for 9Major. Slowest powder that easily makes major with 115's with a charge that easily fits in the case.

 

 

I’m same I have tested super Comp an 9 major in 14 degrees to 100 degrees. An I’m running 115 grain pills also. 

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On 10/13/2018 at 12:31 PM, racer-x said:

 

I have not experienced temp sensitivity with AA7.

 

My 9 major 115 load has consistently averaged just under 1500fps between 37 and 110F.

5 shot ES is around 20, and has never been a detriment for accuracy.

Most of my chrono sessions have been in the 50-100F range though. The one 37F session was looking for temp sensitivity and the bullets were in the open for over an hour before being tested. That's just one cold test and I haven't tested AA7 any colder than that yet.

 

I've heard that AA7 was reformulated many years back. Maybe you have the old stuff?

Any number of things could have occurred to your powder in that time. Water content from humidity when the jugs were opened could have changed powder density and potentially burn characteristics. Just speculating.

 

AA#7 is a great powder for 9Major. Slowest powder that easily makes major with 115's with a charge that easily fits in the case.

 

 

That's great to know!

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Thanks all for the info! Great links and videos.

I bumped up the charge a bit and will get out soon to chrono. Fingers crossed.

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