powder charge vs velocity

[rscott5028]

That's the question I would like to know that answer to! They certainly were not compressed loads. I did a lot of testing with charges in the 48-48.5 grain range and never experienced any big variances in velocity like this.

Once the wind dies down up here I am going to test that same 50.5g and 51.0g again and see if I come up with the same results.

Let's say you shoot 30 of each load.
And, you alternate shots 50.5, 51, 50.5, 51, 50.5, 51... evenly distributing the effects of lighting, temperature, and fouling until you've shot all 60.

You collect each individual MV and calculate the mean and standard deviation for each load.

If the mean for each load is not separated by more than 2x the standard deviation, then you don't have much of a statistical confidence level to ascert that the mean will likely be different with future samples.

That's over-simplified, but the point is that small samples may hint at something interesting. But, it's no reason to question established principles.

You also don't have to shoot such large samples to work towards a good load. ...only to prove that the load will be consistent going forward. ...or, to statistically demonstrate some other extraordinary claim.

Either way, you've got a decent load workup started and will want to pick the best one so far and work on your seating depth before you burn out your barrel.

Good luck!
-- richard

 

[BML]

Thanks again Richard! I appreciate the advice.

 

[BML]

Thought I would share a few pics of the groups referenced in this thread.

50.0g--Average speed 2985--Group size .766
Ignore that top shot. That one was not part of the load tested here.

50.5g--Average speed 3039--Group size .799

51.0--Average speed 2861--Group size .358

Obviously, I am very happy with the 51.0g load and the first thing I will do is load some more and test again to see if I can repeat those results. I am struggling with a little internal dilemma though. I can't help but shake that something is "wrong" because of the drop in velocity. I guess as I see it now I have 2 directions to test. First try to duplicate 51.0g results. 2nd, play with seating depths on the 50.5g load and try to shrink that group as much as I can.

Again for all those that helped, I appreciate it.

 

[brentc]

This particular instance does raise flags of something going wrong with the chronograph because of the amount of declining velocity. I'd guess changing light conditions affecting the chronograph. More testing will tell you what's actually happening.

I've seen it many times that if you map your velocities with a particular powder combination, you can see a steady rise in velocity with powder increase, usually linear. As you start reaching the maximum powder charge the velocity per powder increment begins to decrease until you reach the point of diminishing returns and the velocity begins to decline as you exceed the maximum charge. Some combinations show pressure signs before the point is reached, and some combinations show a distinct velocity curve slightly before or right along with traditional pressure signs.

 

[BML]

Brentc,

I actually did test with a chrono throughout. All of my prior testing was from 48-49 grains though. Speeds steadily increased with each load, but the closer I got to 49g the more my bullets just sprayed all over so I never tested above that. I'm new to reloading and just assumed my rifle wouldn't shoot anything well above that. I ask a ton of questions on this site and a member suggested I jump up and test 50.0g and up. This is the first round of testing with charges above 50.0 grains. The pressure signs I've seen have been only very slight extractor marks on the head. They are almost unnoticeable but they are there.

 

[brentc]

Brentc,

I actually did test with a chrono throughout. All of my prior testing was from 48-49 grains though. Speeds steadily increased with each load, but the closer I got to 49g the more my bullets just sprayed all over so I never tested above that. I'm new to reloading and just assumed my rifle wouldn't shoot anything well above that. I ask a ton of questions on this site and a member suggested I jump up and test 50.0g and up. This is the first round of testing with charges above 50.0 grains. The pressure signs I've seen have been only very slight extractor marks on the head. They are almost unnoticeable but they are there.

Based on all the indicators you've given, you're at the max for your load. What are the corresponding ES numbers with each powder charge?

If it were me making a decision based on what you've provided, I'd do a seating depth test at 50.0 grains. Once you find the sweet spot for seating depth, you can bump your powder charge up or down in small increments to find your best powder charge.

 

[Lefty7mmstw]

Sounds as though you may want to alter your powder choice, as you are altering burn rate as you add fuel to the fire. This is rather common with ball type powders, and with medium cases (the '06 clan) I've actually been able to use more of a given powder with a heavier bullet of similar construction because the heavier load had slowed the powder down. I've also been able to push past medium charges that were seemingly topped out and get a good bit more out of the load. With stick powder, it is a sign that you are topped out and any more powder will just make the rifle work harder for the same result.
I'm curious as to why you are only using 1/2 grain increments on a caliber that is able to burn 50 grains.

 

[brentc]

Just checked the Hodgdon load data and they have 49.5 listed as the max with a 140 grain bullet. It also indicates that your 2900+ chrono readings may be a little out of whack.

 

[Mikecr]

I'm sure there is a rational reason.
I've never seen, or met anyone who has seen, DECREASING velocity with MORE powder.
I've taken brass all the way to single shot death. The velocities always climbed, and predictably via Quickload.
Barring barrel and/or bolt failure, AND brass so yielded it could not ever be extracted with a bolt, I know of no way this would be possible.

If you could drive the bullet fast enough in a short barrel to cause an excess amount of slow powder to blow out unburned, you still had to burn enough powder to get it there. Adding more powder would only cause more of the same while increasing pressure AND velocity with it(even though diminished). Using less powder would slow the bullet down but no more powder is burning still, as the velocity IS lower(that's why it's lower).

No,, BML's velocity DID NOT go from 3039fps to 2861fps due to adding 0.5gr of powder.....

 

[BML]

I'll have to check on the ES. I don't have the numbers in front of me.

When I tested these loads it was the last 90 minutes of shooting light so it is possible that lighting conditions caused false readings. In any case if I'm at max load I don't want to re test those loads anyway.

Brentc,
I was always under the impression that every rifle will have its own distinct "max load". There's many guys here on this site that shoot the 6.5x284 using 52-53g of H4831SC with no pressure signs at all. Plus lawyers always have a say in published max loads so I never really went by the book.

 

[Lefty7mmstw]

I'll have to check on the ES. I don't have the numbers in front of me.

When I tested these loads it was the last 90 minutes of shooting light so it is possible that lighting conditions caused false readings. In any case if I'm at max load I don't want to re test those loads anyway.

Brentc,
I was always under the impression that every rifle will have its own distinct "max load". There's many guys here on this site that shoot the 6.5x284 using 52-53g of H4831SC with no pressure signs at all. Plus lawyers always have a say in published max loads so I never really went by the book.

I've seen charges in my last 7stw that were below book max that were actually over-pressure. I had a strain guage on that rifle, and it really hit home how hard things were really being pushed when stuff got "warm". If a load was stiff on the bolt or chewed on the brass, it was over pressure. The 6.5x284 is one of those calibers what have some chamber variances, so you may be able go get away with pushing charge weight a bit, but you NEED to use your velocities as a speed limit.
An oehler chronograph wouldn't hurt either, as it measures twice. I don't think that my model 35 is in production any longer, though.

 

[brentc]

Brentc,
I was always under the impression that every rifle will have its own distinct "max load". There's many guys here on this site that shoot the 6.5x284 using 52-53g of H4831SC with no pressure signs at all. Plus lawyers always have a say in published max loads so I never really went by the book.

You're right. Every rifle is different. Some of the rifles you may be speaking may have differing chamber dimensions that allow for different load specifications. The best advice is to let your rifle tell you how much is too much, don't rely on other's rifles. I also agree that conservative load data is out there, but IMO Hodgdon data is about as reliable as any out there and with a standard chamber it will usually land your actual max within .5 grain of published max.

 

[brentc]

I'm sure there is a rational reason.
I've never seen, or met anyone who has seen, DECREASING velocity with MORE powder.
I've taken brass all the way to single shot death. The velocities always climbed, and predictably via Quickload.
Barring barrel and/or bolt failure, AND brass so yielded it could not ever be extracted with a bolt, I know of no way this would be possible.

If you could drive the bullet fast enough in a short barrel to cause an excess amount of slow powder to blow out unburned, you still had to burn enough powder to get it there. Adding more powder would only cause more of the same while increasing pressure AND velocity with it(even though diminished). Using less powder would slow the bullet down but no more powder is burning still, as the velocity IS lower(that's why it's lower).

No,, BML's velocity DID NOT go from 3039fps to 2861fps due to adding 0.5gr of powder.....

I agree it's questionable data regarding velocity, and I also agree that more powder will cause increased pressure, but there is a point where average velocity hits a plateau despite increased powder charges and can show an average velocity decrease when all of the data is analyzed. I commonly see it manifest when averaging erratic extreme spread.

 

[rscott5028]

I'm sure there is a rational reason.
I've never seen, or met anyone who has seen, DECREASING velocity with MORE powder.
I've taken brass all the way to single shot death. The velocities always climbed, and predictably via Quickload.
Barring barrel and/or bolt failure, AND brass so yielded it could not ever be extracted with a bolt, I know of no way this would be possible.

If you could drive the bullet fast enough in a short barrel to cause an excess amount of slow powder to blow out unburned, you still had to burn enough powder to get it there. Adding more powder would only cause more of the same while increasing pressure AND velocity with it(even though diminished). Using less powder would slow the bullet down but no more powder is burning still, as the velocity IS lower(that's why it's lower).

No,, BML's velocity DID NOT go from 3039fps to 2861fps due to adding 0.5gr of powder.....

Mikecr,

I agree with you. And if that phenomenon was plausible, it would be authoritatively documented. ...something I'll be eager to learn about if someone will cite those sources.

Until then, here's some food for thought...

Little Johnny flipped a nickle 3 times and got heads all three times.
Then, he flipped a dime 3 times and got tails all three times.
Why do nickles come up heads and dimes come up tails?

thanks,
richard