The Firing Line Forums

Go Back   The Firing Line Forums > The Skunkworks > Handloading, Reloading, and Bullet Casting

Reply
 
Thread Tools
Old July 22, 2012, 09:56 AM   #1
mohr308
Senior Member
 
Join Date: January 15, 2012
Location: Western New York
Posts: 423
Compressed loads question

I had been working on a load for my AR (.223) using IMR4064 and Nosler Varmageddon bullets (55gr). Last night I up my powder to 24.7 grain, it seems I had to tap the cases to get the powder to settle far enough down so I could seat the bullet. Is this considered a compressed load? I was previously at 24.5 grain. Also when I shake my loaded rounds you cannot hear any powder shake.
mohr308 is offline  
Old July 22, 2012, 10:26 AM   #2
mrawesome22
Senior Member
 
Join Date: November 9, 2005
Location: Ohio, Appalachia's foothills.
Posts: 3,779
That is a good thing. Compressed loads result in a very consistent burn which results in lower sd and es.

The more consistent things get, the groups get smaller.

Sent from HenseMod6.
mrawesome22 is offline  
Old July 22, 2012, 10:51 AM   #3
snuffy
Senior Member
 
Join Date: May 20, 2001
Location: Oshkosh wi.
Posts: 2,774
It's not a compressed load until you hear the powder crunch when you seat a bullet. Perfectly normal. Compressed loads using ball powder is another story entirely. It doesn't compress very much, if over compressed, it can actually push the bullet back out of the case a bit. Messes with your OAL, making it very inconsistent. Might even result in moving the bullet out to contact the throat.

Ball powder is less likely to NEED to be compressed, it usually come right up to 100% load density with max charges.

A trick that I use to get extruded/stick powder to settle is to use a long drop tube when manually charging cases. Another trick is to pour the powder in a funnel on the side of the funnel,(ya know the tapered side), it causes the powder to swirl into the drop tube. Seems to line up the sticks of powder so they stack tighter.
__________________
The more people I meet, the more I love my dog

They're going to get their butts kicked over there this election. How come people can't spell and use words correctly?
snuffy is offline  
Old July 22, 2012, 12:04 PM   #4
Jimro
Senior Member
 
Join Date: October 18, 2006
Posts: 5,478
No, it is not compressed. IMR4064 is what I use for 308, and I've used it some for 223. I flick the charged brass with my finger once or twice to make the powder settle before seating the bullet. If I don't settle the powder sometimes I'll hear a "crunch" even though I'll be two grains under a max load.

Jimro
__________________
"Gorsh" said Goofy as secondary explosions racked the beaten zone, "Did I do that?"

http://randomthoughtsandguns.blogspot.com/
Jimro is online now  
Old July 22, 2012, 01:02 PM   #5
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,256
Snuffy gave you good advice on the drop tube. Below is a photo of the same charge of IMR 4064 in a .30-06 case, but with the first dispensed through a powder weighing pan lip, the second through a four inch drop tube, and the last through a three foot long drop tube. Note what happens to the powder level.

Attached Images
File Type: jpg drop tube.JPG (50.8 KB, 382 views)
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old July 22, 2012, 04:22 PM   #6
mohr308
Senior Member
 
Join Date: January 15, 2012
Location: Western New York
Posts: 423
Thanks guys, I was just getting a little concerned I did hear a few crush on one of the loads when I didn't tap it. I also use Imr4064 with my .308 and have been finding it performs very well with my AR. It has actually been performing better than Varget and CFE223.
mohr308 is offline  
Old July 22, 2012, 10:49 PM   #7
frumious
Senior Member
 
Join Date: May 13, 2009
Location: Carrollton TX
Posts: 521
May be a little OT but...why does a drop tube work? I mean, I use one and all...but to me it is just magic.

-cls
frumious is offline  
Old July 25, 2012, 09:49 AM   #8
Unclenick
Staff
 
Join Date: March 4, 2005
Location: Ohio
Posts: 10,256
For a time in the late 19th century, billiard balls were made from solidified nitrocellulose (liquified by ether and built up in layers by dipping, I suspect), because the elastic bounce was good when the balls collided. I read they stopped using the material because these balls would occasionally have small surface explosions on contact like a cap going, but that it caused alarm where gambling was taking place. But I also heard the material just tended to age badly and crack. So choose your explanation. In any case, the stuff has hard elasticity that bounces well on contact with anything else hard.

My surmise has been that the drop tube simply lets the powder grains gain velocity so they have more propensity to bounce on impact with the case or the building powder column in it. Thus, they fly around in the case short distances, perhaps bouncing off each other a number of times before settling. That's the same thing vibration does to them, and vibrating granulations tends to settle them in more tightly packed orientations. That happens because gaps between grains have to be formed by bridging the same way a house of cards has each card bridge a span. A collection of such bridges is precarious compared to a stacked deck. The spaces give the elements room to fall into more tightly packed positions if bounce or vibration dislodges them, whereas a tightly packed element has nowhere to fall if loosened. Therefore, bounce and vibration are much more successful at eliminating bridging than at eliminating tight packing, and a bouncing or vibrating mass of elements tend toward tightly packed orientation (provided the bounce or vibration isn't great enough to toss the whole mass into the air, starting the packing process over).

Another way to look at it is a collection of grain bridges, forming a taller structure having more room to fall, have higher potential energy than tightly packed grains do, and randomly excited systems tend toward their lowest potential energy. It's the fourth law of thermodynamics in action.

Setting charged cases on the lid of your vibratory tumbler will also pack them down, though it takes extra time and you risk a few grains at the top bouncing out if the case is very full. But try it out. Put some charged cases in a loading tray and hold the tray against the tumbler lid and watch what happens. You can start your bullets in at the case mouths before packing to prevent bounce-out.

One fellow in the Precision Shooting Reloading Guide, (IIRC) found that a load that worked fine when assembled at home was giving him high pressure signs if loaded at the bench at the range. He finally figured out the vibration of transporting the loads was settling the powder enough to reduce its starting burn rate. That happens because the flame front has a harder time moving through tight spaces, so it propagates more slowly. This is why compressed loads don't always add as much velocity as expected.

By the way, spherical propellants don't pack nearly as much as stick powders do. I found WC852 (bulk grade H380) dropped through a 3 ft tube does not pack any more tightly than 4064 does dropped through a 4 inch tube. The spheres are less able to make bridges than the long grains are and they are like little ball bearings and tend to flow into tight spaces on their own, with the smaller spheres packing the spaces between the large ones. This low propensity to bridge and change bulk density is a primary reason it is much easier to meter uniform charge weights of spherical propellants with a volumetric dispenser (e.g., a powder measure or a scoop).
__________________
Gunsite Orange Hat Family Member
CMP Certified GSM Master Instructor
NRA Certified Rifle Instructor
NRA Benefactor Member
Unclenick is offline  
Old July 25, 2012, 09:41 PM   #9
frumious
Senior Member
 
Join Date: May 13, 2009
Location: Carrollton TX
Posts: 521
Thanks, UncleNick. That makes sense.

-cls
frumious is offline  
Old July 27, 2012, 06:24 PM   #10
flashhole
Senior Member
 
Join Date: February 9, 2005
Location: Owego, NY
Posts: 1,298
When I need a bit more room in the case I use an electric toothbrush (minus the brush) and run the vibrating flat on the shaft up and down the length of the case. Powder settles down nicely.
__________________
Gun control is hitting what you aim at..
flashhole is offline  
Old October 19, 2012, 10:10 AM   #11
swmike
Senior Member
 
Join Date: June 25, 2005
Location: Marysville, WA
Posts: 658
If you want to settle powder quickly, just put a finger over the case mouth when filled with powder then touch the base of the case to a running vibrator case cleaner. A couple of seconds and it's "no more crunch".

For portable use like loading at the range, there are many battery powered vibrating devices that can be used
__________________
My definition of Gun Control--- A steady grip and hitting your target.


"In God we trust, all others are suspects."

"If I shoot all the ammo I am carrying, either I won't need any more, or more won't be of any help".

____________________________________________
swmike is offline  
Old October 20, 2012, 01:55 PM   #12
RC20
Senior Member
 
Join Date: April 10, 2008
Location: Alaska
Posts: 2,049
It should be noted that case capacity does vary a fair amount and what is an ok load in one is not in another.

Some nasty things can happen so be very careful in those areas of compressed
RC20 is offline  
Old October 20, 2012, 11:33 PM   #13
mohr308
Senior Member
 
Join Date: January 15, 2012
Location: Western New York
Posts: 423
That's a neat trick, another use for the tumbler.
__________________
Lock and load, the zombies (democrats) are coming (to take your guns)!
mohr308 is offline  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 03:33 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.08886 seconds with 8 queries