Dacron fluff

[338RemUltraMag]

Ok,

I bought some low knapp sheet dacron from walmart, I am going to cut it into small squares but would like to know how big (inch by inch) a 1/2 gr square and a 3/4 gr square is?

Thanks guys!
Josh

[Larry Gibson]

I cut the batting into strips about 5/8 - 3/4" wide. I then have weighed examples of 1/3, 1/2, 3/4 gr etc. to use as an example to cut a strip into the size I want. I simply eye ball it as I cut the chunks. Trick is to use enough dacron to fill the airspace between powder and bullet. A little more than that is ok and inconsequental to internal ballistics. To little is not good and poses potential problems. It is not necessary for an exact weight, just have enough to fill the airspace.

Larry Gibson

[338RemUltraMag]

Thanks for that larry, I have never played with the stuff and am going to try it with some reduced 4350 loads and the 30-06

[Larry Gibson]

Assuming you read the sticky; http://castboolits.gunloads.com/showthread.php?109280-The-proper-use-of-fillers ?

I explain how I use the Dacron filler in post #4. Any questions be glad to help.

Larry Gibson

[338RemUltraMag]

Let me rephrase, I am shooting a start jacket load for the 220 rn I am hopeful that the use of dacron will give me a better group.

[Larry Gibson]

If the start load is pushing the 220 cast to fast to begin with I doubt the dacron filler will improve accuracy. Have you chronographed the load? If not what is the load?

Larry Gibson

[runfiverun]

the Dacron will make the load faster.
it acts like it makes the case smaller and generally is about a grain for grain replacement for the powder. [in velocity]
using the filler to position the powder for better ignition characteristics is the idea here.
back the loads down and start over with the filler.

[338RemUltraMag]

If the start load is pushing the 220 cast to fast to begin with I doubt the dacron filler will improve accuracy. Have you chronographed the load? If not what is the load?

Larry Gibson

Larry,

The load is 37 gr of IMR 4350 with a .312 sized 311331 (220 gr) in my 30-06. It is a start load in my Hornady book for a 220 gr jacketed RN and the book velocity is 2,000 FPS. I was getting a 1.5 inch group at 50 yds with water dropped WW, I was looking to see if the fluff would improve the load any. If the fluff will not work then could you suggest a load that would get me in the 2000-2100 range with that boolit?

[Larry Gibson]

You're in the correct neighborhood for it to work. However, as R%R says the Dacron with make the 37 gr ignite and burn more efficiently thus velocity will be higher. Suggest you drop back to 35 gr, use the Dacron filler and work back up. You might also add 2% tin to the WWs to add better malleability to the alloy. Do you have H4831(regular or SC) or RL22 available?

Larry Gibson

[338RemUltraMag]

Larry,

No and no for the powders, but I am headed to a shop to check on stuff. I am shooting a 1954 M70 so I am almost positive I am dealing with a 1-12 twist. Since I have gotten a good group at that speed it seems to confirm my theory..

If I am not mistaken, you use H4831 for everything right?

[runfiverun]

i'll answer for him and say no he don't.
the slower powder is to give a good launch but generate enough gas volume to accelerate the boolit to velocity.
there's a line to walk here.
enough gas volume, a clean burn, but controlling when/where the pressure peaks.
all are important.
when i'm seeking velocity I generally walk my way down the line with powder speed generating more and more gas volume but trying to maintain a pressure window where accuracy is found with the faster powder I started with.
hopefully that made sense to you.
eventually you get to a point where you need to tweak the alloy or the ignition of the powder needs help to stay in the pressure window.
you also get to a point where the powder won't work in that window and you have to step things up a notch at a time to maintain the accuracy at the new pressure window.

[338RemUltraMag]

I completely understand that, it is like the 6th grade experiment with the egg inside a "car" you built. It simulates how much cushion you create on impact hoping not to smash the egg, except we do the opposite. He is going for a slower powder that generates a longer push while fooling the powder into thinking it is in a smaller container.

That is what I got from you.

[Larry Gibson]

Larry,

No and no for the powders, but I am headed to a shop to check on stuff. I am shooting a 1954 M70 so I am almost positive I am dealing with a 1-12 twist. Since I have gotten a good group at that speed it seems to confirm my theory..

If I am not mistaken, you use H4831 for everything right?

I think all factory M70 (pre and post 64) '06s were 10" twist but I'm not that up on pre '64 M70s.

R5R give a good answer for me but in my own words; no, I do not use H4831 for "everything". I have been accused of using 4895 for "everything" though. While I do use a lot of 4895 (H4895 is a favorite if I'm buying new canister powder but I still shoot a lot of milsurp 4895) I prefer to use what works best for the cast bullet application at hand. Seldom do I like to "make do" with a powder simply because I have it or because it is cheap. I used to do that but I discovered the false economy of using powders that did not perform the way I wanted.

For HV cast bullet loads with medium to heavy for caliber cast bullets I have found 4895, Varget, RL 19, AA4350, H4831SC and RL 22 to ignite well and burn consistently in the 25,000 - 40,000 psi range atypical when pushing cast bullets to HV. As mentioned in another thread it is a balancing act to use the powder that gives the slowest time pressure/curve and lowest muzzle psi for the cartridge/load/barrel length combination......but it has to ignite and burn efficiently within that psi range. Many slower burning powders do not. Using a good slower burning powder is especially necessary if one is pushing the RPM threshold upwards.

IMR4350 many times does well, especially with the Dacron filler, with the top end loads you are attempting because the psi is in the range where IMR4350 burns efficiently. However, a slower burning powder may do better w/o the filler as load density will be greater and the time/pressure curve slower for an equal velocity with the 220 gr cast. The slower push of the slower burning powders may enable a higher velocity with equal accuracy.

Larry Gibson

[runfiverun]

josh remember that even a good push and balanced pressure you still have to have fit of the boolit to the throat.
the fit will allow things to be not quite right in other areas and still maintain accuracy, but you can't compensate the other way around.
you also have to have good boolit to barrel centerline concentricity.
starting a good boolit crooked or out of the centerline of the barrel will not help you when things get going fast.
good concentricity will allow you to back the boolit out of the throat a tick and allow a faster powder to "work" this is of course part of tuning a load for accuracy.
it works because you are not trying to make the nose of the boolit hold everything in semi-alignment.
this is what I was talking about in the "cast in the AR" thread I wrote
on Jay's sight.

[Larry Gibson]

R5R is correct. Additionally, if it was easy to push cast bullets above the RPM threshold we would not have lengthy discussions on how to do it and we'd all be shooting cast bullets at much higher velocities/RPM than we do.

Larry Gibson

[338RemUltraMag]

This is an excellent thread, once I get to the LGS I will get more powder so I can experiment. Me thinks this will take some time.