Compressed load anomaly

[Buzz]

I worked up a new hunting load this year with 39.4g of H4350 and 129ABLRs jumping about .060 (they like to jump). I use a Wilson in-line seater and notice that some cartridges are lightly compressed, while others are not and I can hear the powder moving around when I shake the case.

At first I didn't think much of it, but I was seeing 80fps swings in velocity on my Labradar, so I decided to mark the cases that were compressed on the next loading. My ASSumption was that the compressed loads were the high velocity loads, but on two different trips I have confirmed that the compressed loads are actually the low velocity loads. The high velocity loads are consistent 2770-2780fps and the low velocity are 2700-2720fps.

I have tried different lots of Lapua brass, formed 22-250 brass, and formed 6.5 creed brass. No matter the brass, all have some loads that are compressed and some that aren't. This last time I checked the loads on 3 different scales, and while there was a .1g variation between the scales, the loads always read consistent (i.e. if a scale read 39.5 vs 39.4, all loads on that scale read 39.5). Tapping or vibrating the brass doesn't seem to make much difference. To make things even more perplexing, I dropped the load to 39.2 and still had some compressed charges and velocity swings.

My questions are:
1. What is going on that's causing some charges to be compressed?
2. Why is there such a big downward swing in velocity with the compressed charges?

I'm going to just keep the cases segregated and only bring the non-compressed cartridges on the hunt, but my curiosity is through the roof on this one.

 

[MagnumManiac]

The simple answer is called ‘packing scheme’.
As you dump the powder, due to HOW it is dumped, a different height column is made causing some lower and some higher in the case.
To eliminate this completely, there is a technique where you pour the powder by ‘swirling’ it around a powder funnel...it looks just like a tornado as it spins around the funnel and should never clump up. It will drastically lower your powder charges in the case and will also change your ES/SD for the better. It allows more time and space for the powder to settle...only drawback is that it slows the process, but I live with that.
Give it a go, there are YouTube vids that show the technique.

Cheers.

 

[Texas10]

Whereas it has been my experience that certain packing schemes work very well, you seem to say you've tried them and that it doesn't make a difference. From that I would have to conclude that your scale is varying the load considerably, but again you seem to have covered that possibility. Have you verified and sorted the internal capacity of your cartridge brass via H2O method?

Some other possibilities: Unburnt powder remaining in the brass, how do you clean or inspect? Is there media remaining after cleaning? Is your bullet seating held to within a couple thou?

Your ES/SD indicates to me that your combustion efficiency is a bit lacking. Are your primers old? Have you tried others? Are you loading in a humid environment?

Is it possible that you are confusing excessive neck tension with a compressed load? Is your seating depth varying due to incorrect seating stem? Some push against the tip instead of the ogive of very long and slender bullets.

Just trying to imagine all the things that would cause the effects you are seeing. You seem to be very experienced at the craft, so I'm writing this in such a way to inform the less experienced who may also be tuning in.

 

[Buzz]

Thanks for the suggestions. I can feel/hear the crunch and using the highly scientific shake test I don't hear any powder rattling around, so I think they're compressed. Neck tension seems consistent throughout.

The scale was the first thing I questioned but it looks like it's working. Also, the compressed being so much slower would make me think it wasn't more powder.

Admittedly I have not done any brass sorting and it would pain me to have to do it for this rifle. You bring up a good point with brass cleaning though. I just give the outside of the neck a couple turns in 000 steel wool, run a brush on the inside of the neck, and then just tumble in dry media long enough to knock out the big stuff. It would surprise me if there was enough build up in there to cause an issue, but definitely something I hadn't considered. I'll put a few pieces through a couple cycles in my wife's sonic jewelry cleaner and see if that makes a difference.

My cartridge OAL is consistent, but I haven't measured out the bullets to see how consistent they are. I'll add that to the list.

Primers are Wolf SRM and the same I use in other rifles and don't see the same issues. The 22-250 and creed brass is large primer and I use Winchester for those. I use them in my 6XC and they seem to be fine as well. The powder is the only thing I don't use in any other rifle, so maybe that's the culprit here. I'm in Phoenix so it's about as dry as you can get.

This might be dumb but your point about combustion made me think that maybe that's why I'm seeing slower speeds with the compressed load. If I'm borderline on combustion for whatever reason, would having less air in the case cause even poorer combustion?

 

[PigButtons]

One thing to think about is the non-compressed load has an instant where there is compression of the small amount of air before it will expand the neck and release the bullet. A compressed load may start that process a tiny fraction of a second earlier and therefore not build quite the same pressure inside the case before releasing the bullet. Small things matter at 50K+ PSI.

 

[DirtySteve]

Compressed charges can give you higher velocity but at the expense of ES. Want a lower ES go to uncompressed charges...

 

[338 dude]

Thanks for the suggestions. I can feel/hear the crunch and using the highly scientific shake test I don't hear any powder rattling around, so I think they're compressed. Neck tension seems consistent throughout.

The scale was the first thing I questioned but it looks like it's working. Also, the compressed being so much slower would make me think it wasn't more powder.

Admittedly I have not done any brass sorting and it would pain me to have to do it for this rifle. You bring up a good point with brass cleaning though. I just give the outside of the neck a couple turns in 000 steel wool, run a brush on the inside of the neck, and then just tumble in dry media long enough to knock out the big stuff. It would surprise me if there was enough build up in there to cause an issue, but definitely something I hadn't considered. I'll put a few pieces through a couple cycles in my wife's sonic jewelry cleaner and see if that makes a difference.

My cartridge OAL is consistent, but I haven't measured out the bullets to see how consistent they are. I'll add that to the list.

Primers are Wolf SRM and the same I use in other rifles and don't see the same issues. The 22-250 and creed brass is large primer and I use Winchester for those. I use them in my 6XC and they seem to be fine as well. The powder is the only thing I don't use in any other rifle, so maybe that's the culprit here. I'm in Phoenix so it's about as dry as you can get.

This might be dumb but your point about combustion made me think that maybe that's why I'm seeing slower speeds with the compressed load. If I'm borderline on combustion for whatever reason, would having less air in the case cause even poorer combustion?

IF you think of it like an engine when you dump in too much fuel or gas and it runs rich you have less performance

 

[Tokay444]

Have you checked consistency of base to ogive on your bullets?

 

[Buzz]

Compressed charges can give you higher velocity but at the expense of ES. Want a lower ES go to uncompressed charges...

That was part of, or actually the main, question I had. I'm seeing higher ES and lower velocity with the compressed loads. Definitely backwards from what I was expecting.

 

[Buzz]

IF you think of it like an engine when you dump in too much fuel or gas and it runs rich you have less performance

Got it. Thanks. That makes sense.

 

[Tokay444]

IF you think of it like an engine when you dump in too much fuel or gas and it runs rich you have less performance

An engine requires many things to run. An appropriate air:fuel ratio being one important one. Internal ballistics are nothing like internal combustion engines.

 

[1shot]

The simple answer is called ‘packing scheme’.
As you dump the powder, due to HOW it is dumped, a different height column is made causing some lower and some higher in the case.
To eliminate this completely, there is a technique where you pour the powder by ‘swirling’ it around a powder funnel...it looks just like a tornado as it spins around the funnel and should never clump up. It will drastically lower your powder charges in the case and will also change your ES/SD for the better. It allows more time and space for the powder to settle...only drawback is that it slows the process, but I live with that.
Give it a go, there are YouTube vids that show the technique.

Cheers.

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is good advice. I do the same thing and incorporate a 6" drop tube. If the load is still overly compressed I look for a different powder.
I hope this helps,
Lloyd

 

[Homerange]

Compressed charges can give you higher velocity but at the expense of ES. Want a lower ES go to uncompressed charges...

Yet that hasn't been my experience with a max load of well compressed Varget behind a 130gr in a 308.
3000fps and 6fps ES....a load taken straight from the ADI loading manual !
Lowest ES load of any I've found.

 

[DirtySteve]

Yet that hasn't been my experience with a max load of well compressed Varget behind a 130gr in a 308.
3000fps and 6fps ES....a load taken straight from the ADI loading manual !
Lowest ES load of any I've found.

My statement was a result of reading testing done by Litz. Of course his testing was done using components used in long range shooting applications. This also coincides with what I have experienced.

 

[DirtySteve]

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is good advice. I do the same thing and incorporate a 6" drop tube. If the load is still overly compressed I look for a different powder.
I hope this helps,
Lloyd

6 inch drop tube! That’s cute, I use a 40 for my black powder. ...!!!! Lol

 

[TheOtherZilla]

I gave upon drop tubes. I now use a cheap vibrating tool marker.. Just turn it on and touch it to the side of the case with your finger over the case mouth.. Settles the powder right down. Consistently.

 

[Buzz]

I've been using an old electric toothbrush but I'll try something with a higher frequency vibration and see if that works. Thanks.

 

[Tokay444]

Generally, and I think most people's experience will align with this, as you move further away from the lands, velocity will be reduced, until such time that you start to compress the powder column, where initial pressure will begin to spike dramatically.

 

[Straightshooter1]

Generally, and I think most people's experience will align with this, as you move further away from the lands, velocity will be reduced, until such time that you start to compress the powder column, where initial pressure will begin to spike dramatically.

Actually, "as you move further away from the lands" you're decreasing the volume inside the case. As volume decreases pressure increases resulting in higher velocities. When powder is compressed, volume is also reduced and the powder becomes more dense in that volume, which results in a significant spike in pressure also resulting in more velocity.

 

[Tokay444]

Actually, "as you move further away from the lands" you're decreasing the volume inside the case. As volume decreases pressure increases resulting in higher velocities. When powder is compressed, volume is also reduced and the powder becomes more dense in that volume, which results in a significant spike in pressure also resulting in more velocity.

Air is highly compressible. The slight compression in air volume isn’t enough to make up for the running start at the lands, and velocity is reduced.