More powder = less speed????

[jsthntn247]

Logically one would think the higher the powder charge, the higher the velocity would be right? After doing some more testing last night I have found that's not the case all the time and I'm not exactly sure why.

Here's my ingredients: 6.5x284-H4831SC-Fed 210-Norma brass-AMAX 140g

Here's my numbers from yesterday.

50.0g shot an average of 2983
50.5g shot an average of 3039
51.0g shot an average of 2861
51.5g shot an average of 2879

Why such a drop in velocities above 50.5 grains of powder? Is it because there's more powder, which takes longer to burn, which in turn will affect velocity?

51.0g shot the best group at .358 but if I can achieve similar results with 50.5 I will drop down to achieve that speed. I will always take accuracy over speed but I do like to test other loads thoroughly until I can prove they will or won't work.

 

[normbal]

Re: More powder = less speed????

Velocity isn't the whole picture. What's the standard deviation doing?

What's probably happening is you're not getting complete ignition of the compressed powder charge. I've seen blue dot come out of 9mm and .45 loads unburned.

A hotter primer might do it, but you might need a different powder for the purpose.

Try reading this article from Ed Shell (Central Virginia Tactical), it'll help make some sense out of what's happening.

http://www.shell-central.com/Powder1.html

 

[Boomholzer]

Re: More powder = less speed????

In the step function certain small charge windows will show little increase in MV before powder compression. I would first question the chronograph or any changes during these tests.
Track record with chrono? Virgin brass?

 

[Trevor300wsm]

Re: More powder = less speed????

Ive expericaned this same thing during load development while doing OCW tests. I've never known what caused it, and never asked either. My ES & SD was usually not too good at or during the velocity drop so i never focused on those charges.

I will tell you that for 6.5-284 the "go to" powder is 4831SC and the "go to load" is usually always right around 50.5-51.5 grains. I know several people who have been shooting the 6.5-284 for 5+ years and have shot out several barrels, but the load never changes by more than .1-.2 grains. You might try a different primer, but I would stay with the 4831SC.

 

[Paladin2147]

Re: More powder = less speed????

What's the bbl. length?

 

[Greg Langelius *]

Re: More powder = less speed????

As a general rule, disproportionately diminishing velocity increases are usually thought to be a symptom of max and beyond max loads.

Since I have no experience with the 6.5-284, I can't say whether that applies in this case. But I also believe that the 6.5-284 has no lack of speed, so backing down to a lower node, as you have done, would seem a wise choice.

Greg

 

[ChadTRG42]

Re: More powder = less speed????

One of two things is happening. My first guess is a chrono error. Was the sun at a steep angle to the side when testing the last loads? Are you running a shooting Chrony chrono? If yes to either of these, it's your chrono. Test them when the sun won't be at such an angle. Also, if the chrono is too close to the muzzle, you will get muzzle flash across the sensors, and cause error readings. Make sure it's at least 12 feet or more away from the muzzle. I set mine as far away as the cables will let me.

Next, like Greg said, when you get to max pressure or slightly above, you reach the point where you can no longer get more speed, only more pressure. You will often see velocity go down and reduce some from the loads at max, but didn't show any pressure signs. Usually you only lose 10 to 40 fps when you go beyond your max. So, the large drop over 100 fps is leading me to a chronoy error.

 

[MMAJunkie]

Re: More powder = less speed????

Try a hotter ie magnum primer.

 

[boltgunluvr]

Re: More powder = less speed????

Its like the law of diminishing returns. An old gunsmith told me about this years ago. I had a difficult time believing him, but I've witnessed it too. Basically, as we increase the powder charge, we are decreasing the amount of oxygen inside the cartridge. And what does combustion need to burn hotter....oxygen (air). The simplest way I can state it. Just food for thought.

I am with you. Accuracy over anything else. I don't like folks getting focused on speed. So why do most of us get better results with higher powder charges with an appropriate powder? A tech told me its better to give a projectile a good hard constant shove rather than something screaming out from an fast explosion. Meaning....letting a powder burn nice smooth evenly.

 

[shootist2004]

Re: More powder = less speed????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">One of two things is happening. My first guess is a chrono error. Was the sun at a steep angle to the side when testing the last loads? Are you running a shooting Chrony chrono? If yes to either of these, it's your chrono. Test them when the sun won't be at such an angle. Also, if the chrono is too close to the muzzle, you will get muzzle flash across the sensors, and cause error readings. Make sure it's at least 12 feet or more away from the muzzle. I set mine as far away as the cables will let me.

Next, like Greg said, when you get to max pressure or slightly above, you reach the point where you can no longer get more speed, only more pressure. You will often see velocity go down and reduce some from the loads at max, but didn't show any pressure signs. Usually you only lose 10 to 40 fps when you go beyond your max. So, the large drop over 100 fps is leading me to a chronoy error. </div></div>

ok...whats a chrony chrono?

 

[mavrick10_2000]

Re: More powder = less speed????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jsthntn247</div><div class="ubbcode-body">Logically one would think the higher the powder charge, the higher the velocity would be right? After doing some more testing last night I have found that's not the case all the time and I'm not exactly sure why.

Here's my ingredients: 6.5x284-H4831SC-Fed 210-Norma brass-AMAX 140g

Here's my numbers from yesterday.

50.0g shot an average of 2983
50.5g shot an average of 3039
51.0g shot an average of 2861
51.5g shot an average of 2879

Why such a drop in velocities above 50.5 grains of powder? Is it because there's more powder, which takes longer to burn, which in turn will affect velocity?

51.0g shot the best group at .358 but if I can achieve similar results with 50.5 I will drop down to achieve that speed. I will always take accuracy over speed but I do like to test other loads thoroughly until I can prove they will or won't work. </div></div>

Adding more powder getting near max book charge weight and a lower increase in FPS or a decrease indicates that you are increasing pressure near or approaching dangerous levels.

Back off the charge weight and find the node if you want more speed you're probably going to have to choose a different powder.

 

[ChadTRG42]

Re: More powder = less speed????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: boltgunluvr</div><div class="ubbcode-body">Its like the law of diminishing returns. An old gunsmith told me about this years ago. I had a difficult time believing him, but I've witnessed it too. Basically, as we increase the powder charge, we are decreasing the amount of oxygen inside the cartridge. And what does combustion need to burn hotter....oxygen (air). The simplest way I can state it. Just food for thought. </div></div>
The oxygen needed for powder to burn is already in the powder.

 

[ChadTRG42]

Re: More powder = less speed????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: shootist2004</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ChadTRG42</div><div class="ubbcode-body">One of two things is happening. My first guess is a chrono error. Was the sun at a steep angle to the side when testing the last loads? Are you running a shooting Chrony chrono? If yes to either of these, it's your chrono. Test them when the sun won't be at such an angle. Also, if the chrono is too close to the muzzle, you will get muzzle flash across the sensors, and cause error readings. Make sure it's at least 12 feet or more away from the muzzle. I set mine as far away as the cables will let me.

Next, like Greg said, when you get to max pressure or slightly above, you reach the point where you can no longer get more speed, only more pressure. You will often see velocity go down and reduce some from the loads at max, but didn't show any pressure signs. Usually you only lose 10 to 40 fps when you go beyond your max. So, the large drop over 100 fps is leading me to a chronoy error. </div></div>

ok...whats a chrony chrono? </div></div>
It needs to be a "Shooting Chrono". It's a brand of chrono's that are very sensitive to light angles sun light.

 

[alice]

Re: More powder = less speed????

Try reading this article from Ed Shell (Central Virginia Tactical), it'll help make some sense out of what's happening.

 

[jsthntn247]

Re: More powder = less speed????

Thanks guys for all the responses. I have seen this in my 7mag also with 24" tube and the 162 amax. Book max says 70 grains but I see no speed increases after 68. In circumstances, I was thinking it was because I was getting inconsistent powder burn from the shorter barrel causing my velocities to be all over the place. The shots were fired round robin style so that should take chrony errors out of the picture.

Alice what article are you referring to? There's no link.

 

[normbal]

Re: More powder = less speed????

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jsthntn247</div><div class="ubbcode-body">Alice what article are you referring to? There's no link. </div></div>

Um, This one, from a page ago.

http://www.shell-central.com/Powder1.html

 

[antagonist]

Re: More powder = less speed????

There's no link because "alice" is a bot.