drop tubes, how do they work?

slimjim · Posted: Wed Nov 13, 2013 4:02 am Post subject: drop tubes, how do they work?

I would like to learn about drop tubes to get more powder in my .270 and 6.8 cases but I'm not finding much information on them. What is a good internal diameter? How long should it be? Metal or plastic? Thanks for any knowledge you can share.

Aloysius · Posted: Wed Nov 13, 2013 5:36 am Post subject: Re: drop tubes, how do they work?

Is it not easier to go for a 7 mm RM, a 300 WM or even a .375 H&H. When you still want more powder in then the .50 BMG comes in my mind...

Just to say that some things I will never understand. For me instead of going to AI, I would go to the next caliber on the line up.

By the way, is there a .270 Win Ackley Improved? Just thinking...

SingleShotLover · Posted: Wed Nov 13, 2013 6:51 am Post subject: Re: drop tubes, how do they work?

In my experience (though I haven't used one all that much) I used a piece of rubber tubing that made a snug fit over my measure's spout and used that to dump into the funnel over each case. Mine was maybe 12" long. Too me the theory is that by dumping into the tube, the length allows the powder to separate and travel in a loose stream rather than being clumped up by the sudden drop from the measure directly into the constriction of the funnel and causing it to "bridge". The powder also tends to swirl slightly which helps to more evenly distribute it into the case.

As to the AI cartridges...if velocity is the goal, most only offer about as much gain over the parent cartridge as a couple of additional inches of barrel with the original cartridge.

One of the brutal truths related to cartridge design is that when increasing the capacity of any particular case, velocity increases at the rate of one quarter (25%) the percentage of increase in case capacity while pressure rises at a rate of 2% for each 1% of velocity increase. In other words an improvement to a case that increases capacity 10% only increases velocity by 2.5% over the parent design but increases pressure by 5%. Taking this further, a case that develops a velocity of 2,800 fps that is modified to gain 10% in capacity now turns in a velocity of 2,870 fps…only 70 fps gain. In most cartridges an additional 2” of barrel length would very nearly add that much. Put another way, 70 fps is not an inconceivable deviation within a string of shots using the same load! In terms of trajectory the gain would be far less than .25” difference (assuming the same bullet design and weight) in favor of the improved version regardless of the distance. All of this would be at the cost of the improvement plus the additional powder and recoil required for the increase. In addition, assuming a cartridge that generates 60,000 psi of pressure at that 2,800 fps, pressure would rise by 3,000 psi. This would certainly not be worth the effort. The hottest rounds at the highest velocities seldom gain more than 3” in realistic range trajectory over more sedate offerings. When shooting at most game animals, 3” is insignificant if range is known.

Aloysius · Posted: Wed Nov 13, 2013 7:07 am Post subject: Re: drop tubes, how do they work?

SSL, thanks for the theory behind this stuff. I only had feelings about it + an attitude of taking a round too big for the purpose and loading it down till it fits. That's the opposite. But I do understand SJ's requirements and they are not the same as mine. Some of us here call 100 yards a great distance, most of us here would call you insane when you try a 300 yards shot (unless you're trying for a fox or a crow). So when I see the distances you all are getting your game, I just feel myself very small.

Just another question: when you use such a tube on your powder dispenser, is the profit you get high enough that you do so instead of weighing each load separately?

Suzanne · Posted: Wed Nov 13, 2013 7:49 am Post subject: Re: drop tubes, how do they work?

Black powder guys use a copper drop tube about 3 feet long, diameter is equal to the case they're filling. Don't know if that relates to smokeless. There might be a few YouTube videos on it (not that they know much but some of those guys do).

Suz

SingleShotLover · Posted: Wed Nov 13, 2013 7:58 am Post subject: Re: drop tubes, how do they work?

Actually, I never used it to try to get more powder into a case than any manual would recommend (since I still believe that if you want a "hotter" cartridge, buy one - don't try to make your .30/06 perform at .300 magnum pressure levels) but to make it easier to use "stick" or IMR type powders in small diameter cases, such as the various .224" calibers. Anymore, I tend to lean toward spherical powders and don't have such issues except in my .22/250, and then only because I have a considerable supply of IMR 4064 and it has given me the best accuracy in this particular cartridge/rifle combination. I also use it in my .30/06 and .280 Remington for the same reasons.

I seldom weigh each charge unless I am developing a particular load. My measures all are capable of throwing weights within .1 or .2 grains with specific powders and religious attention to throwing each charge the exact same way each time. I even have found that once set up properly, IMR 4064 can be measured very accurately using the inexpensive Lee Perfect Measures. Since they don't "cut" the powder, charges are remarkable consistent, and in the above mentioned cartridges, one or two tenths really doesn't matter...even in the accuracy department.

I do not trust any measure to throw accurately enough for the small-case cartridges that operate at high pressures (.17 Remington for example) since even tiny differences in weight can make a considerable difference in pressures. Those are all weighed, but since the powders I use for them are all spherical, just dumping from the weighing pan into the funnel works just fine.

As to the distance I am comfortable shooting...it depends on the quarry. Groundhogs and coyotes I will shoot at considerably longer distances than I would attempt on game animals. The longest shot I have ever taken on a whitetail deer was 187 yards (measured). Most of my deer have been at considerably less yardage, including a nice 8-point buck at a distance of 30 feet. I simply haven't seen anything in the line of a game animal that I needed to shoot extreme distances at, though I understand that regions, conditions and etc. can warrant such shots.

Aloysius

Suz, that's something different. In a frontloader I use such a tube just to get the powder down in the barrel without being mixed with all dirt of the previous shot. I don't think someone is using such a tube when he is loading cartridges for a breechloader.

Ominivision1 · Posted: Wed Nov 13, 2013 2:51 pm Post subject: Re: drop tubes, how do they work?

I have tried the drop tube method a few years back, whats wrong with taking a case and gently taping the base after you load the powder to settle it?

Suzanne · Posted: Wed Nov 13, 2013 7:06 pm Post subject: Re: drop tubes, how do they work?

Here's a YouTube video of loading black powder cartridges and a drop tube. Here's another and both of these videos sort of explain the method and reasons.

Suz

slimjim · Posted: Wed Nov 13, 2013 8:50 pm Post subject: Re: drop tubes, how do they work?

I'm working with some loads that I'm developing on my own. I wold rather try a drop tube then try to compress the loads much. I'm still not getting pressure signs from them so wanted to be able to try a few more grains of powder. Thanks for the discussion. Keep it coming.

dhc4ever

Whats the calibre, powder amount and type and bullet weight?

gelandangan

All the above plus the COL.
COL would determine the final case capacity for a given projectile.

Slim, what are you trying to achieve?
Maybe I could help by trying to calculate its internal ballistic?

slimjim

6.8mm, 37.0 grains of CFE223, 120gr Federal Fusion
.270 Win, 61.5 grains of MagPro, 150gr Accubond Long Range

Aloysius · Posted: Thu Nov 14, 2013 2:34 am Post subject: Re: drop tubes, how do they work?

Suz, thanks for that. I've learned some new tricks. I never put a paper wad on top of my primer and I've never used a PE-wad on top of the powder. And the part where he puts something between the PE-wad and the bullet I didn't understand. Never too old to learn new tricks.
I'm using a waxed beercard between powder and conical and I do have a friend here loading the 45-120 with about 0,5 cm (1/4") of bullet fat, just to keep all dirt soft and to be able to shoot a match (30 shot) without cleaning.

All very interesting, but using black powder is not going to help SJ for his 6,8 mm or his .270 Smile

(though some tricks might)

What might help: the Lyman Powder Measure has such a hammer in front to knock 3 times to get the powder settled. So when you put the powder in the case, hold the case in the outlet-funnel of the Lyman Powder Measure and knock a few times with that hammer... when you knock each time the same amount, it might just help the filling density inside your cartridge, as it does when filling the measure.
So you don't use the powder measure to measure but just to shake a well-known amount.

easier done than explained Smile

Pumpkinslinger · Posted: Thu Nov 14, 2013 9:19 am Post subject: Re: drop tubes, how do they work?

I remember using a drop tube made from a broken aluminum arrow. I just can't remember what cartridge I did that with, or why...