Increasing Pwdr Chrg Yields Lower Speed

[Prerylyon]

Bonecollector & I have been talking about this: chrono'ing a lower or stagnant velocity with more powder. 'BC shared a load work-up where he is seeing this.

I too may now be seeing this as well, and wanted to start a topic on this phenomena to see what the reloading brain trust can come up with as possible causes?

We've found threads on other forums, that are more reloading and shooting oriented, that show others have experienced this drop in velocity with increased charge. In all those threads, there are experienced folks weighing in saying that it is impossible and that they have never heard of this happening. Others talk about each barrel and gun having different max load points, that may differ from the test lab's gun's max load used to develop the recipe, and that this loss in velocity could be a pressure sign, or indicative of unburned powder. Often, the variability of the chrono is brought out as the culprit.

In the previous thread last week, I shared a great group I got using a faster powder from a 9 shot ladder test. The last 4 heaviest charges nearly cut each other in an area almost smaller than a penny at 100 yards. Fellas, that was the most accurate I have shot, or seen that gun shoot. In the joy of that experience, I may have missed a major velocity problem that I hastily attributed to changing light conditions screwing with the chrono.

Here are the velocities I recorded last week-1st number is the charge of AA4350:

51.6=2,596 51.9=2,596 52.2=ERR1 52.5=2,683 52.8=2,754 53.1=ERR 53.4=2,805 53.7=2,704(? Sun) 54.0=2,486(? Sun)

The "? Sun" were notes I jotted down to show my doubts of the validity of the measurements.

These were shot in order of lowest to highest charge. Since the last 4 cut the same hole, I figured 53.7 was a good charge out of that last set to go to print with.

Fast fwd to this past Friday at the range. My buddy was there with his chrono as well. He has a magneto model that straps to the muzzle-its non optical and we have seen it correlate well to my Shooting Chrony; when I take care to position it past the muzzle blast and align it well-which anymore I always do.

We measured 9 shots Friday loaded at 53.7 gr AA4350 that averaged ~ 2,660 on both chronos while I was tweaking the scope in. The scope and group tweaked in with no trouble. But what about that velocity? [emoji21]

I figured last week, the low speed meas at 53.7 was due to issues with strong shadows/variable sun-since up to 53.4 gr it did show an increasing trend in speed.

Chrono issues? For this past Friday, I don't think so. We have two sets of measurements with two instruments using completely different speed sensing methods. This just doesn't seem to make sense, other than it shows some similarities to last week's speed measurements. Either I misloaded the cartridges or something else is at play here.

Any ideas or shared experience with this is greatly appreciated. I will go to the range again and shoot a set of the 53.7 gr, and also now the 53.4 gr, to see what I get.
The gun was cleaned conventionally a couple of weeks ago; it has 27 rounds through it since then. I got copper fouling cleaner today and will be giving it a very thorough cleaning before hitting the range.

Regards,

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[Colorado Cowboy]

After doing a little research, the data I see is that all 3 of the 4350 powders (IMR, AA & H) have different burn rates with the AA being the slowest. To me this means that the powders are NOT interchangeable and I would stick to one Mfgr. I would tend to think that with higher charges of the AA, it could mean unburned powder could have caused the decreased velocities. There are a lot of variables, so it might be almost impossible to really find the cause. By the way the AA4350 is made in China....not that it makes any difference. I just am pretty cautious about Chinese made junk in the firearms industry.

 

[Prerylyon]

CC,

I got the AA4350 4 yrs ago because it was literally the only powder available at my local store. I have since found another source of powder near my inlaws in PA that is well stocked. I just buy whatever when I am home for a visit.

But, yes, the 4350s are NOT interchangeable to my understanding.

That being said, the load recipe I used is straight from the online Speer manual and it states "Acurate 4350" which is what I used when I changed from RL-19 a couple of weeks ago; which is also listed, amongst many other powders for this bullet in the manual.

I was not and have not been swapping 4350s through the course of this load work up. The powder is all from the same can bought in 2014.

The powder can, says 'made in Canada' [emoji38][emoji260]. But, I hear ya, maybe they re-label it.

Also, I have a 'control' round to compare against using a 140 gr Sierra bullet. It uses 52 gr of this same powder and it chronos about like the Sierra manual says it should, 2,700 fps.

That is why I find this situation baffling. I am left with either I mis-weighed the charge/have a messed up balance beam, or some of this other stuff about unburned powder/different maxes for different guns/barrels entering the fray.

Since the AA4350 is the slowest of the '4350 flavors, could it be that 53.4 gr at that 2,805 is it for my gun and I am seeing unburned powder going beyond, and that is causing the slowdown, even though the load manual has max at 54 gr?

Regards,




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[JimP]

Are the cases the same make and manufacture?

In the long run I wouldn't worry too much about it. If you find a load that is shooting how you like use it, a few fps isn't going to make that much difference and there is usually enough variance in powder scales that tenth of a grain could be off a little one way or another, and if you are using a balance beam scale it actually can be quite a bit.

All I do anymore is decided on the velocity that I want out of a load and work up to it. If I have problems getting there with one powder I'll try another. I very seldom shoot "max loads" per the reloading manuals anymore since a lot of them err on the very low side from what the manual said 15-20 years ago. A good example is a load that I have for my .340 Weatherby. A old manual that I based my loads on has hotter loads than the new manual has. The new manual doesn't even list the same load but stops a few hundred fps below what I am actually shooting.

 

[Colorado Cowboy]

JimP is right about measuring scales. I have a balance beam that is over 50 years old....it is stored in it's box. I use 2 different digital scales, they are much more accurate. The older AA stuff was made in Canada, but not today.

Jim uses the same approach that I use for developing loads. For me 3,000 fps is my threshold for my hunting rifles/calibers. I have 8 or 10 loading manuals that go back to the early 60's. Loads published in the old ones were much hotter than what are in them today...too many Lawyers! I also have 5 or 6 books by noted authors on shooting/reloading (P.O.Ackley, Philip Sharpe). Also powders are all not created equal. The 3 manufacturers of 4350 are a good example.

Best advice is the old KISS principle. (Keep It Simple Stupid) When you find the load you want to use and it performs the way you want it to, buy lots of powder & bullets that you are using and get rid of everything else. I have one load for my 25-06 (for deer & antelope), one load for my 30-06 (for deer & elk) and one load for my .300 Wby (for elk & moose). These are my main "go to" hunting rifles. When I want to play around and experiment on new stuff, I use other guns and calibers. The way I approach it (and have for 40 years or so) is that my main hunting stuff shoot to my expectations and perform exactly the way I want them too. Trying to improve something that is exactly where I want it be is a waste of time and money.

 

[rammont]

To answer the OP's post, you might want to research chambrage, gas pressure rarefaction and compression theory. The basic concept is that due to the characteristics of how the powder burns the pressure behind the bullet varies due to rarefaction (reduced pressure) and compression (higher pressure) impulses. Under the right circumstances velocities do not change in line with the powder charge weight changes.

 

[Prerylyon]

The cases are all of the same lot of 50 pieces; Norma. They were bought new in 2014 and have been shot less than a dozen times. The last few weeks is the most use they've gotten all year. I shoot 12-24 shots at each of these recent range trips, and don't go to the range often-I probably should change that! lol

I full length resize and trim/chamfer each case prior to loading.

As for speed loss, in my case its significant. These are the values quickload, a respected load software program, say I should be getting with this powder in a 22" barrel-I do get that software is not perfect and that it can predict erroneously:

52.8 =2790
53.1=2806
53.4=2823
53.7=2839
54=2855

We measured 2,660 fps consistently on Friday, with the two independent chronos, at a charge of 53.7 gr, which is 179 fps less than the program predicts. These charges are all within the Speer recipe-which has max at 54.0 gr. A week ago, I measured 2,704 at 53.7 gr; but at that time, I ignored the low reading as chrono error. After last Friday, I think it may have been correct. This is as much about safety as it is accuracy and speed-I want to understand what might be going on, and if its an issue.

I cleaned the bore last night with "Hoppes Benchrest 9", the only copper fouling cleaner at my local store. It was nasty stuff. It took 25 pairs of patches (soaked and dry) until I got a patch come thru that was mostly clean. I have never seen the bore so shiny. I don't think I have ever cleaned it with a copper fouling cleaner-this was the 1st time. I always just used the regular Hoppes #9. We'll see what happens with this squeaky clean bore.

Regards,

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[Bonecollector]

Like the OP stated, I too am seeing this issue. This is my first usage with a copper bullet.
My variables are very straight-forward.
The cases were once-fired brass from Hornady. I've reloaded the same 12 cases 5x from the same 1lb powder jug of RL-26. All bullets have come from the same box (weighted them) with the same box of primers (Winchester). The only difference has been the powder charge amount, with the exception of one 3 shot group that was neck sized only.

All this said, I too noticed a lower velocity with a higher charge. This does not make sense to me as it is consistently erratic and trending down.
I agree with the KISS principle, but when you can't verify a velocity, thus verifying yardage drop, it is no longer simple. Do not blow off this phenomenon as there is an issue at hand.
Can it be the bullet composition (copper) itself? Perhaps something different in the material makeup? Perhaps others are using old stock from years past when they could load up on what worked then.
I'm grasping at straws, but that's how the real solutions are found.

Additionally, I would think a fouled barrel would produce more pressure than a clean barrel. Would this translate to a decrease in velocity because of where the pressure is generated (along the bullet path and not behind it)?

 

[Colorado Cowboy]

I really don't have an answer, as I havn't experienced this situation. In the example above, RL26 is an extremely slow burning powder. I use it in my .300 Wby and have had no problems with slower velocities.

I need to do a little thinking on this and will get back later today.

 

[Tim McCoy]

Odds are one of the issues already raised is the answer. But I’d look for another person with a chrono, lab radar or magneto speed and check that.

 

[Bonecollector]

I've been using a bud's new Caldwell chrono. I plan to suggest a magneto to the wife for Christmas.
Part of my issue may have been shot angle going through the chrono. I'm looking further into this.
1% angle can change 100 f/s according to an article I read.

Based on prelims: I should have 145 gr Barnes LRX @ 3200 f/s. This load is 0.80 (68.2 of 69.0) below max charge of RL26.
I put 8 of 9 into 6" target at 400 yards Sunday. There's always 1 flyer in the group. This one was 2" right. If hunting, it was still dead.

That said, I still like to understand all the numbers.

 

[Prerylyon]

Odds are one of the issues already raised is the answer. But I?d look for another person with a chrono, lab radar or magneto speed and check that.

Like a third Chrono?

We used a shooting Chrony and a Magneto Speed last Friday, and for all intents and purposes, the two agreed. Another machine would add a third vote.

I guess my ultimate question is if this velocity foldover can be a real phenomena -is it even theoretically possible?

Rammont provides some theories that might explain it. I'm still very new at this stuff, so I am trying to get solid info from those with more experience. Other threads that delve into this phenomena point to the excess powder, esp slower powders, not burning to generate the velocity-being further aggravated by a short barrel. At the same time, experienced voices in those same threads will say that is pure baloney - who is right, who is wrong? (Somewhat rhetorical)

Regards,

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[Bonecollector]

I'll add the fact I'm using a 26" barrel and below a lower than max charge suggested in a 24" barrel.....

 

[Colorado Cowboy]

Like I stated before...too many variables. It is hard to zero in on one thing that is causing the velocity changes.

Yes definitely get another data set from another chrono. Look at burn rate charts vs barrel length. Another thing is that the all copper bullets tend to be longer with a different ogive than traditional copper lead bullets.I have found big differences using all the same components and just changing bullets (staying with the same weight, just changing bullet material).

The burn rate charts I saw suggest unburned powder in the shorter 22" barrel.

 

[rammont]

A quote from a military study

When the projectile in a gun begins to move, expansion (also termed rarefaction) disturbances or impulses are sent back to the breech. These rarefaction impulses are characterized by the fact that they decrease the pressure and density of the gas through which they pass (in contrast to compression impulses which increase the pressure and density of the gas through which they pass). This pressure drop results from the fact that gas is accelerated by the rarefactions "shed" from the accelerating projectile; hence, this pressure drop is designated here as the "pressure drop from the accelerating projectile motion".

When the gas pressure drops the velocity of the bullet drops. The powder charge weight and the burn rate of the powder have a direct effect on this event. Ambient conditions will also have a direct effect on rarefaction so weather changes will cause slight changes in regards to the powder charge that is required to see the velocity drop.

If you read the study that I linked to you will also see that this rarefaction is affected by the chamber dimensions so different calibers will react differently.

And yes, I've seen the same issue with my .30 caliber rifles.

 

[Tim McCoy]

Like a third Chrono?

We used a shooting Chrony and a Magneto Speed last Friday, and for all intents and purposes, the two agreed. Another machine would add a third vote.

I guess my ultimate question is if this velocity foldover can be a real phenomena -is it even theoretically possible?

Rammont provides some theories that might explain it. I'm still very new at this stuff, so I am trying to get solid info from those with more experience. Other threads that delve into this phenomena point to the excess powder, esp slower powders, not burning to generate the velocity-being further aggravated by a short barrel. At the same time, experienced voices in those same threads will say that is pure baloney - who is right, who is wrong? (Somewhat rhetorical)

Regards,

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No need for a third. Missed you saying you tried a magneto speed.

 

[Prerylyon]

'Rammont,

That study is intense; but readable. Kudos for sharing it! [emoji106]

I am actually an engineer (I can sense the reader's eyes rolling lol) so I deal with trying to mathematically model stuff all day long to put food on the table.

I will hopefully be going to the range tomorrow to chrono this same load, and one 0.3 grs less, to see if the previous results are replicated a third time.

The variables aren't perfect. I did clean the bore, better than its ever been, with copper fouling cleaner. So, the trial is rigged in that sense when compared to previous tests.

Well see what happens. If the results replicate, and taking the ordnance lab paper into account, the view that each gun/barrel/caliber design could behave, and can operate differently, than well established typical norms-within the laws of physics- starts to hold water in my view.

Regards,

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[Colorado Cowboy]

I too am an engineer (Systems Eng) retired from 40 years in aerospace. I realized a long time ago that no two firearms are exactly alike, even ones that are of the same model and manufacture.....too many +/- 's allowed from nominal dimension in manufacturing of each gun. Thru trial and error, we have to find the right combination of components that each gun likes best.

The journey begins................

 

[Prerylyon]

CC,

I've got 25 yrs down in aerospace 'stuff', on paper as an electrical engineer, but started in school as an aero engineer before changing majors. Mostly on the black boxes that keep the planes and rockets in the air or other electronic support measures. My gig is radio/microwave electronics.

Anyhow, I got into reloading late in life. So, for those of us new to the hobby, the learning curve can be steep; being able to sit at a table of experienced reloaders for advice is very much appreciated.

I am learning to be more open to interpreting some of these reloading rules. I won't recklessly exceed published max loads or other safety data, more that I must let each load work up - the actual observation with me at the wheel-guide its development. Which, at the end of the day is kinda like work-but probably less stressful and usually more fun. lol [emoji23]

I'm headed out on my hunting trip tmrw. If I have time and actually make it to the range today, I'll post my results; otherwise it might be next week.

Regards,



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[rammont]

I was an Avionics tech in the military for over 20 years (fixed and rotary wing) and I have over 130 credit hours toward my degree but bouncing around in the military made it impossible to actually get my diploma at any one University. I guess it's in the nature of people like us to ask why things happen and experiment rather than just accept somebody's response without any evidence.

The interesting thing about these velocity plateaus is that they seem to be an indication of a limit of some kind. I've noticed that when my load hits one of these flat spots increasing the powder charge doesn't seem to be of much benefit. I've always wondered if they are the real mechanism that drives accuracy nodes rather than the theory of barrel harmonics. I could easily believe that barrel harmonics are a result of the rarefaction/compression waves being timed in such a way to create a perfect response between the between the barrel/bullet precision.

Unfortunately I haven't found any real world way of predicting these flat spots or how they affect my groups.