Duplex load question

[wmitty]

In using W C 860 along with 5 grains of 4227 as a “kicker” I have obtained velocity levels in both the .30-06 and .375 H & H around 2400 f/s and would like to reduce this velocity somewhat in order to attempt to improve accuracy… is the use of an inert filler acceptable in order to reduce the 860 powder charge and still maintain compression of the .4227? Nobade’s “ filler with an attitude “ is working very very well and I think I need to slow it down a bit.

[pworley1]

Try it with out the kicker.

[MUSTANG]

^ As Stated above, try a slightly compressed load of your WC860 (Full case of WC860 to bottom of the neck of the case) with boolit/bullet seated to slightly compress the powder. By compressing, you should get a better burn and fewer unburned kernels and mummies. No filler.

[Larry Gibson]

Here's a test I did a few years back duplexing WC 860 with Turk 8mm pull down powder with a dacron filler. Might give you some insight to your question.

Duplexing Turk ’43 and WCC860 in the 375 H&H

In considering whether to test a 375 H&H duplex load (I value my M70) I gave it some thought. I had not really considered duplexing before as I've not invested in the really slow burning powders so had no need to. Also I've so many test irons in the fire it wasn't on the top of my "to do" list. However, Waksupi's thread here and on goodsteelforums.com peaked my curiosity. In thinking it over I relied on my own experience with BP duplexing and previous post on the topic by Novade. I found a duplex BP load, if done correctly, to be quite safe, useful and accurate. I saw no reason why it couldn't be done with the powders Waksupi was wanting to use. My standard 375 H&H load uses 300 gr jacketed bullets (Hornady 300 SPBT, 300 RNSP and the 300 FMJ) over 78.5 gr of AA4350 in NS'd R-P cases sparked by WLR primers. They ran 2570 fps at 57 - 58,000 psi when I developed the load in Washington 7 or 8 years ago. Thus I concluded using 5 gr of the Turk powder with 75 gr of a slower powder than AA4350 (WCC860) on top of the Turk '43 powder under a 287 gr cast bullet should be "safe".

I had the 375 H&H already with a strain gauge on it for pressure measurement, I had pulled down Turk '43 powder and all I was missing was the bullets and some WCC860. Waksupi sent the bullets and Bjorn souveniered me some WCC860. I loaded one of Waksupi's PC'd NOE 378-279-FN bullets in a split necked case to check seating depth in the test Winchester M70. Turns out they fit quite nicely in the case neck.

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Being able to see the bottom of the bullet in the case gave me the correct load density needed to prevent migration of the powders. Waksupi also said he used a small tuft of Dacron on top of the powder for the bullet to push down on as "insurance". I decided to do the same. I then loaded a round with 5 gr of the Turk '43 over the primer and then filled the case with WCC860 to the base of the bullet. I then weighed both charges and subtracted the 5 gr. That gave me a charge of 75 gr WCC860 to start with using 5 gr of Turk '43.

For the psi work up I had to figure how much to reduce the WCC860 as I increased the Turk '43 powder I then filled the same case to the same level with just WCC860 and weighed that. It came to 81.5 gr. So basically 6.5 gr WCC860 equaled 5 gr of the Turk '43 powder. I decided on increasing the Turk '43 powder 3 gr per test which meant a 2 - 4 gr reduction (I was cautious at first so went with 2-3 gr changes) of WCC860. I was hoping to work up to 2500 fps or where accuracy went erratic before pressure became an issue.

I did size Waksupi's bullets at .377 and lube them with Lar's 2500+ as my experience previously with other PC'd bullets indicates lubed PC'd bullets are more accurate and do not foul the barrel. To test Waksupi's initial load I loaded 8 rounds of 5 gr Turk '43 with 75 gr of WCC860 on top. Then a small tuft of Dacron was inserted with the bullet seated on top of that. I then loaded 14 rounds for the psi workup loading 8/72 (Turk/WCC860) through 47/27 (Turk/WCC860) gr in the increments listed on the Oehler test data sheets.

With all that done last Tuesday I loaded up all the Oehler M43 accouterments and was off to the range. It did not go well. I shot 2 rounds of Waksupi's load and knew the strain gauge had apparently cracked. So, it was load everything back up and head home......

The last couple days I double checked everything on the M70. Sure enough, the strain gauge had cracked. As it had been on for 7 -8 years and a lot of heavy recoiling rounds had been fired a couldn't really complain. Yesterday I put a new strain gauge on. It is a procedure because it is permanently affixed. The old gauge had to be completely removed down to bare metal, the barrel metal prepped, the new gauge prepped and then glued on, then the leade wires attached. After that I hooked it up to the M43 and computer and all checked out. All appeared well. However, only shooting can tell if it's really good to go.

Woke up at daylight this morning and the temperature was only 78 degrees and the wind seemed manageable, so I loaded everything up and headed to the range. Set up went smoothly and the new gauge checked out. The rifle is a Winchester (New Haven) stainless M70 375 H&H. Scope is a Leupold 1.5x5X with duplex reticle.

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I then set up to shoot the remaining 6 rounds of Waksupi's load. Target was at 100 yards. 1st shot out of the clean barrel went high left. The pressure was 37,500 psi at 2078 fps. The pressure trace looked fine. I then shot the remaining 5 shots which went into a nice 1.9" group. Looking good with no problems so far. Muzzle velocity averaged 2096 fps for the 6 shots with an average psi of 38,000. The SD and ES for velocity and psi were excellent. If you look at the rise of the pressure trace you can see where the pressure eased a bit as the Turk powder burned out and where the WCC picked up by itself.

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The PSI workup

I then ran the 14 shot psi workup test of increasing the Turk '43 powder while decreasing the WCC860 powder. The charges were from 8/72 (Turk/WCC860) through 47/27. All went well with relatively smooth pressure traces. Looking at the pressure rise of each increase/decrease of Turk/WCC860 we see the slight psi drop off decrease as the amount of Turk '43 is increased. Looking at the target you can see where each round hit. Six rounds, 8 through 13 hit into a very nice group right at point of aim. Rounds 11, 12 and 13 hit the magical 2500 fps. That is very equal to factory 300 gr 375 H&H performance. I will load 10 shot tests of loads 11 and 12 to test for a more complete pressure picture and for group. If either does well that would be an excellent load for anything walking this continent........

[Larry Gibson]

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It would appear that duplexing with these components is safe. Is it safe with other components......I don't know and won't conjecture. However, since the Turk powder is very close to 3031 and H4895 I will load a test string substituting H4895 for the Turk '43 powder, probably load 11.

Be safe.

Larry Gibson

[Maven]

I concur with the above, but since I've used quite a bit of WC 860 with a filler in my .30-06 with CB's of at least 175gr., let me add: Fillers allow you to reduce the main charge a bit (no duplexing), but can migrate into that charge if not stored with primers up when loaded. Additionally, they can form a solid plug if heavily compressed and that's most certainly not what you want. The two fillers I've used are bran fiber and spherical shotshell buffer once sold by Winchester as "Grex." If using the .30-06, start with 48 - 50 gr. WC 860 and enough filler to allow you to compress the load. If I recall, a 1cc Lee dipper will allow this, but you'll need to experiment with the amounts of each component. A chronograph would be very useful here, btw.

Two other suggestions: (1) With such a slow propellant, you should use LR magnum primers. (2) Coarse ground corn meal will also work as a filler, as will Cream of Wheat (COW). In fact the late Ken Mollohan* did quite a bit of experimentation with COW loads, so some of his work should be available via a Google search.

*Mollohan, Molly here, was one of the founders of the Cast Bullet Association.

[wmitty]

I am very grateful for the replies posted by you gentlemen and especially the detailed description which Larry posted. The reduced expense of duplex loads along with cast boolits allows me to shoot the .375 at near full power without feeling like I am spending my children’s inheritance on ammunition components! I too have thought about increasing the volume of the primary powder charge and reducing the amount of 860. I proceeded very cautiously in doing this; and the chronograph showed the resulting increase in velocity as the primary charge increased. Having no pressure testing equipment, I felt I was walking blind and stopped the testing. Thank you very much, Larry, for posting your results regarding this idea!

[Larry Gibson]

Follow on testing of duplex loads with WCC860 in the three six bits with 3031 and 4895;

I completed the Turk/WCC860 duplexing test a couple days ago. Based on the previously posted psi workup and projected further tests I loaded 7 rounds of 26/50 (Turk '43/WCC860), 8 rounds of 32/42 and 8 rounds of 38/36 to get a better idea of the internal ballistics and the accuracy capability. Waksupi's bullets were used and a small Dacron filler was used to assure some compression. I've no idea of the alloy Waksupi used or the PC method. He stated in a PM the bullets were "seconds".........if so they did pretty darn well.....

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As before the fouling shot with the 26/50 duplex load was a wide flyer, exhibited the lowest velocity and the lowest psi. The other 6 gave an ES of only 16 fps and only 1,700 psi ES. The smooth pressure traces show it is an excellent load though we can readily see where the WWC860 "kicked in". Accuracy was excellent for the 6 shots; right at 2". Considering the muzzle velocity was 2339 fps right at the RPM Threshold for a 12" twist I'd be confident hunting with this load.

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The 32/42 duplex load demonstrated excellent internals with and ES of 24 fps, and SD of 8 fps and a psi ES of only 2,600 psi. However, exceeding the RPM Threshold at 2400 fps muzzle velocity was evident because even though the internal ballistics were excellent on the external ballistic side accuracy began to suffer. The group size increased to 3".

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With the 38/36 duplex load again the internals were excellent; ES of 20 fps, SD of 7 fps and a psi ES of 1,900 psi ES. The accuracy again suffered at 2.6" group given a muzzle velocity of 2481 fps but one of those shots should have been much further out to the left as I called the shot. As it was it went to the middle of the group.....that happens sometimes with ammo that produces larger groups.

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Obviously many if not most of you with WCC860 probably don't have pulled down Turk '43 powder. So I ran another test using IMR 3031 and 4895 instead of the Turk '43 powder. I used a duplex load of 32/43 with each of them. The IMR3031/WCC860 duplex load performed the best accuracy wise as 9 of the ten shots stayed in 2.75" at 2395 fps which is just over the RPM Threshold. The 4895/WCC860 duplex load rand 2422 fps and the over 3" group showed it exceeded the RPM Threshold also. Neither of these 2 tests using 3031 or 4895 had the excellent internals as did the duplex loads when the Turk '43 powder was used. Their internals weren't "bad", just not excellent.

That used up all the bullets Waksupi sent me to test and all the WCC860 Bjorn gave me.

I flinched one off to the left with each of these last test loads as after 43 such 375 H&H loads off the bench I was a little "punch drunk"....felt like I'd been tag teamed by Ali and Frazier........

None the less I finished with one more test string just to test my own shooting ability, the instrumentation and the rifle's (M70) accuracy capability. Thus I let the barrel cool, cleaned it and then shot a 9 shot string of my Hornady 300 gr hunting load. This was loaded in Winchester NS'd cases, WLR primers, 78.5 gr AA4350 with the bullet seated to the canelure groove and a crimp applied with a Lee FCD. At 2612 fps it definitely lets you know you've pulled a trigger when shooting off a bench. The 9 shots went into 1.6".....not too bad for being that punch drunk.........

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Larry Gibson

[rockrat]

Thanks for the info,especially the part about lubed p/c boolits. I have noticed the same with a few different calibers and planning more testing once it warms up

[BLAHUT]

Ever thought about just trying a mag primer verses duplex loads ?

[Maven]

With such a slow propellant, you should use LR magnum primers. ....Maven

From post #6 above

[Loudenboomer]

Good data Larry. I've done a fair amount of careful WC860 duplexing. With only a chronograph you never Really know. Thank you (and your shoulder) for the time and effort with your pressure test equipment.

[rbuck351]

I don't have w860 but do have a large jug of 5010 and been loading it in a 416 Rem. I started with a full( slightly compressed) load of 5010 which gave low velocity and lots of unburned powder. I picked aa9 as a primer booster and started with 3 grs under a 3 gr less 5010. This cleaned up the burn some so I continued to increase the booster and decrease the 5010 until the burn cleaned up. I stopped at this point.

I would try a case full of W860 and check velocity. If to high then add filler with less 860. If to low add a bit of booster until the velocity rises to where you want it.

[Loudenboomer]

Be careful with the #9 booster it's very fine and could migrate way into the 5010. My thought is to get the powder burn started quicker without blending the powder. I usually use 4198 but have used a surplus pulldown similar to 3031. My 2 cents. Be cautious.

[Messy bear]

This is a very interesting thread!
Having quite a bit of 860 and having done a small amount of duplexing in 45/70, I read with great interest the testing done by Larry G.
Question Larry if I may?- Is the Turk 43 that stuff that looks like black rectangular flakes? Similar in shape to the old Alcan powders? In my ammo it seems rather dirty. But performance is good. Corrosive primed and hard primers at that. I need to check the numbers on mine.
Also you say we see the 860 kick in or however you put it. Is that the little rumble at the beginning of the trace?
Most impressive was low es in pressure. I see what you mean by being internally excellent.
Thanks for posting these tests! The learning continues.