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Old July 19, 2010, 10:27 AM   #1
Brian Pfleuger
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Different Powder RESIDUE Change POI?

So, I tried 3 test rounds using Win748 in my 204 yesterday. They were: 2" high and dead center (normal), 2" out at about 10 o'clock (not unusual in itself), and 2" left at zero height (very strange). All shots fired allowed for adequate barrel cooling time and the barrel was already fouled with Benchmark.

Here's the interesting part...

This is, admittedly, a theory to fit the data, but no other idea makes any sense to me.... the order of only two impact points was unconfirmed.

The gun had Benchmark residue in it prior to that first shot of 748. The first shot, passing through Benchmark residue was 2" high and dead center (visually confirmed), the next two, each passing through more 748 and less Benchmark, shifted down and left. These were fired at a separate target from subsequent shots, so the only unknown is which was #2 and #3.

After shooting these 3, I changed targets and went back to my proven 1/2 MOA load of Benchmark.....

The first shot was at 9 o'clock 3" left (confirmed), the second shot was about 1/2 inch higher and less than one diameter right of the first shot.... the third shot was within the margin of error of where it would be expected to be under normal conditions, dead center and 1" high.


So, it seems that passing through more and more 748 residue in the barrel shifted the POI 2" down and 3" left.... and switching back to Benchmark, shifted the POI back where it belongs after 3 rounds.

Am I crazy?
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Old July 19, 2010, 01:24 PM   #2
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No
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Old July 19, 2010, 01:53 PM   #3
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No, it will change, or no, I'm crazy?
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Old July 19, 2010, 02:32 PM   #4
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Am I crazy?
Quite possibly, but please open a different thread to discuss that subject.

The bullets I am aware of that are currently produced and available on the market cannot distinguish between different powders and their fouling residues yet.

Sounds to me like you haven't sorted out the load to dampen harmonics, allow for proper depth of seating, or played around with different bullets yet.

W748 works best close to max loads. Everyone I know who has played around with mid-range loads with W748 was disappointed.
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Old July 19, 2010, 02:43 PM   #5
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Originally Posted by Scorch
Sounds to me like you haven't sorted out the load to dampen harmonics, allow for proper depth of seating, or played around with different bullets yet.

W748 works best close to max loads. Everyone I know who has played around with mid-range loads with W748 was disappointed.

Why, though, would the first shot of 748 hit right where the Benchmark loads hit, and after three shots of 748 the Benchmark loads hit right where the 748 hits?

There is no doubt about the accuracy of the Benchmark load, I have fired several groups at 175 yards that are under 1". In fact, ALL the groups I've fired with this load at 175 have been 1" or less.

The groups are DRASTICALLY different in location.... one is dead center 2" high, the other dead LEFT 3".

It wouldn't have surprised me that the 748 grouped poorly, it was a low load, just 3770 fps with the 32gr bullet, but the group was actually fair, except that it seemed to be "walking" left as there was more and more 748 residue in the barrel, and then the Benchmark made it's way back to center after 3 shots....
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Old July 19, 2010, 04:58 PM   #6
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I have seen points of impact change going from AA2520 (a ball powder) to stick powders at 600 yards.

I have loaded a bunch of .223 ammo with AA2520. The stuff was cheap at $64.00 a keg. I will shoot a 69 SMK 24 to 24.5 grains AA2520 out to 300 yards. The load shoots well. However at 600 yards, I get "settling" when I switch to my stick powders. It takes about 2 to 3 rounds before the barrel starts grouping consistently. I have had radical, like 8 ring shots, with first rounds at 600 yards, second round is barely more predictable, somewhere around the 3rd or fourth round the rifle shoots to previous elevation and windage.

I have never noticed this issue when shooting stick powders, even if the stick powders are different. In this one rifle, I use AA4064 to 300 yards, N140 at 600 yards. I have never had “settling” issues with these powders.
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Old July 19, 2010, 07:01 PM   #7
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Here is a very un-scientific guess. I could see that happening only if there was unburnt powder in the barrel ignighted on the second and third shot.

More likely it is barrel harmonics with the 748 producing different travel times down the barrel and different pressures on the bullets.

Put your chrony up and check the fps.

Jim


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Old July 20, 2010, 03:54 AM   #8
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I long ago decided you may perhaps be crazy,P,but publications such as Precision Shooting will tell you transitioning from one powder to another is an issue and it ios about the fouling.In part,it is the transition,mixing fouling.Clean the bore a bit,shoot a few,then try
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Old July 20, 2010, 06:15 AM   #9
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I think it's my Sierra manual that goes into it, then again maybe it's not. IMR 4895 and IMR 4064 were the two examples, as pertaining to switching from a short load to a 600 yard load, but anyway it's one of them that says: you might be able to switch between certian powders, and other powders not so much. At that point I bought a couple bore snakes and relegated the location of the info to "something I read once that changed my method and now I don't need to remember where I read it cause I don't do it anymore."

It was profound stuff not easily argued.
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Old July 20, 2010, 06:19 AM   #10
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I hope you are crazy enough

to do some experimentation on this issue.

It would be interesting to see if you can repeat the effect a second time. And, if you can, then it would be interesting to see if you can get rid of the "transition" shots by cleaning the barrel between loads with the different powders.

In other words, if you start with Benchmark and a clean bore, where do the shots hit, sequentially? Is the first one out of a clean bore in the same group as the rest, or do they start somewhere else and "walk" to the final point of impact?

Same question for 748, starting with a clean bore.

Then, starting with a bore fouled by Benchmark, do you see that the first shot with 748 hit in the same group as the Benchmark, or in the same place that a first shot with a clean bore lands with 748, or somewhere else? And, do they "walk" the same way as the 748 residue replaces the Benchmark residue (compared to the way they "walked" when starting with a clean bore)?

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Old July 20, 2010, 07:03 AM   #11
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Quote:
Originally Posted by SL1
I hope you are crazy enough to do some experimentation on this issue.
You obviously have not noticed how hard it is to find components lately!

I may do that, I'll have to see what I've got time for.



This whole concept is strange to me. I don't understand why the powder residue in the barrel would so drastically change POI.

Could it be as simple as the amount of unburned powder changing the friction of the bullet? I can't understand how that would make such a HUGE difference. I could see 1/2 MOA or maybe 1, but 2 or 3?

With the loads I was shooting, QuickLoad predicts 90.37% powder burn for 748 (2.64gr unburned) and 95.49% for Benchmark (1.26gr unburned) at the time the bullet exits. That doesn't seem like such a drastic difference, especially when most of it is blasted out of the barrel or burns after bullet exit. There certainly is not 2gr of powder left in the barrel.
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Old July 20, 2010, 10:13 AM   #12
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Quote:
Could it be as simple as the amount of unburned powder changing the friction of the bullet? I can't understand how that would make such a HUGE difference. I could see 1/2 MOA or maybe 1, but 2 or 3?
I think it is due to residue. And it does make 2 to 3 MOA changes.

In 308, when I have switched from IMR 4064/IMR 4895/AA2495/Varget, I don't see settling issues at all.

Don't recall switching from AA2520 to stick in the 308.

I did clean my .223 barrel when moving from 300 to 600 yards, and that also made a difference in POI for the first couple of shots.
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Old July 20, 2010, 10:32 AM   #13
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What is so drastically different between the residues that would account for this?
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Old July 20, 2010, 12:21 PM   #14
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It is the weight of the fouling layers and the composition of the solids left behind and their distribution in the bore. Guns constantly remove and deposit new residue as they shoot. Match shooters have long known not to change powders between short and long range loads unless you are in a match with unlimited sighters. You have to shoot enough of the new powder for the fouling pattern to adjust to it. One that, for example, leaves more graphite unburned in the bore will tend to lubricate the bore slightly more. When you switch to a load that leaves less unburned graphite behind, until it burns or blows out or simply covers up the extra graphite from the previous load, its barrel time won't settle.
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Old July 20, 2010, 05:23 PM   #15
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Umm, what does your cleaning regimen entail? Sounds to me like a heavily fouled bore chucking them all over the place.
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Old July 20, 2010, 05:30 PM   #16
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Umm, what does your cleaning regimen entail? Sounds to me like a heavily fouled bore chucking them all over the place.
Yeah, except that the Benchmark load groups less than 1" all day long at 175 yards.


Sounds to me like the issue is solved and is simply a phenomenon that was well known to "shootists" but one which I had never encountered and never imagined.

Thanks for the info, yet again, gentlemen.
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Old July 23, 2010, 07:24 AM   #17
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From a Sierra chapter:

Quote:
Powder residue sometimes reacts very badly to a second powder being fired in the same barrel without cleaning.............................
..........................it frequently takes several shots before the second load will settle down and begin shooting accurately. If the powders were dissimilar, such as a double-based ball powder followed by a single-based tubular powder(or visa versa), this settling problem will be even more pronounced.
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Old July 23, 2010, 08:48 AM   #18
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POI change

Ball powders use a larger amt of burn retardant, modifiers surface lubes(graphite), and Im not sure what else. If you run a string 25 or 30 shots with ballpowder downrange and run a wet tight fitting patch down the bore youll probably feel resistance to the passage of the patch, even a "sticky" feel. The more rounds the greater the effect. Sometimes the sticky feel may persist evenafter a thoro solvent cleaning , Then JB or one of other mild abrasives wil be needed to completelt remove the residue. The deposit will vary w /temp, humidty, "hotness" of the load, rate of fire and most likely abt 10000 other variables. 2520 was one of the worst in my experience, but Ive used more 2520 than other ball powders, so cant speak from as much experience. Also found that 2520 could give unbelievable groups one day then degrade horribly the next, groups 5-6 times larger. There seems to be lttle or at least much less of an effect with extruded powders.
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Old July 23, 2010, 11:21 AM   #19
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I've experienced the same phenomena changing powders but I had no clue as to the specifics of it. It also works when changing 22 ammo. I won't change 22 ammo before a match or try to shoot for any group until the barrel has had at least 50 rounds thru it. But changing a centerfire powder has always changed POI. Now I know why.
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