Compressed loads question

J

jonnefudge

New member
Educate me on compressed load. I see a lot about this on the forums but don't really understand the risks involved. From what I understand it is very dependent on the specific powder? And how do you measure the compressing level/percent?

I will try some new loads with Norma 203-b for my 308 and might get into some compressed loads depending on the pressure signs.
 
Its mostly a "degree" thing.
I'm sure there are many specific variations,but in general,if your load manual shows tests of compressed loads,a little compression is OK.But not much.
Most powder is pretty solid. It doesn't really compress.Your bullets can deform or even get pushed back out to a longer overall length.
Don't forget,with many loads,the bullet intrudes beyond the neck.
I don't use much ball powder.I understand it may clump up if compressed.
A drop tube can help settle more powder in the case.
I'm not the authority,but generally once the powder reaches near the base of the neck,you are USUALLY still OK,but any more? Its diminishing returns.
You won't gain much more,
Powder is all about controlled burn rate via deterrent coatings and granule shape.
Consistent ,repeatable flame space through the charge matters,too.Crushing down the granules does not help much.

IMO,instead of compressing ,use a drop tube.Try a foot long one,on a stand

Then as the powder reaches the base of the neck,call it good.Of course,still follow manual recommendations.

IF, optimistically,you fill the neck with another grain of powder...you might get 50 fps....or 30...

Under what circumstances does that make a noticeable difference?

What is the goal? What are your priorities? Why do you load?

If it is to reach an arbitrary number...that's OK,if its your goal

An undistorted bullet base is critical to accuracy.
 
There are no risks to compressed loads--provided you work up the load and the load is noted as compressed in your manual.
If "compressing" worries you, use another powder or get a long drop tube for the powder funnel and it will "pack" on the way down.
Powders that would concern me are high bulk density spherical powders that don't compress--but, then I have NEVER seen such a load recommended in a manual.
The POWDER is not being compressed--the air space is being compressed.
There is a large difference between the density of gun powder—about 1.5 g/cc—and the bulk density of gun powder (from about 0.55-1.00 g/cc).
You could compress TrailBoss A LOT, but DON'T--apparently that powder and its shape does not take well to compressed loads.
You can compress the flake and stick powders quite a bit, and folks have done so quite successfully for over 100 years.
 
Really no risks per say with compressed loads, assuming your manual calls for them and you work up the load and look for signs of high pressure while test firing.

My favorite and most accurate loads have been slightly compressed loads. Normally get extremely consistent SD and ES.

One time I was looking for a 1000yd load in my .308 for F-Class FTR shooting. I was looking for velocity along with accuracy. So I was having to work up to the max load I could find between manuals and powder manufacture. Well, one case gave me way too much compression and there was no way in the world I could get a max load even loading the bullet long. So I ended up changing case brand that had more capacity, and that case was able to take a max charge and still give me room to make a slightly compressed load.

Sometimes you just have to play around with the components to get what you're looking for.

A long drop tube helps as well.


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Getting back to Trail Boss briefly, noylj might have followed through with why TB does not take well to compressed loads. Otherwise not doing so could lead to an incorrect assumption, namely that doing so could lead to excessive pressure. That was thought to be the case until Hodgdon finally revealed that compressing could result in erratic accuracy, not excessive pressure. TB actually seems to "settle" some without actually being compressed. Partially fill a case with TB and then tap the case lightly a few times on the bench and there then seems to be less powder in the case. I use TB considerably for reduced loads for over a dozen rifle calibers up to and including .416s and .458s. Those rifles then get attention that they wouldn't ordinarily get. I judge the powder charges visually and they are maximum charges by the formula.
 
Norma 203B is a double base powder. I have always been told to never compress charges of double base powders. If your load information doesn't call out a compressed load do not use it in a compressed load.
After a quick glance at the Norma reload data for 308 I found no compressed loads for 203B. If you find data that lists a compressed charge of 203B you should contact Norma to find out if it is safe to use.
The only time it is safe to use a compressed charge is when it is recommended in a published data manual.
 
Ya don't really need a drop tube to load compressed loads. After putting powder in the case put the head on your thumb and cover the mouth with a finger on the same hand and tap on the side of the case with a pencil. I never have done compressed load's It your running much of a compress load, I don't know where the point is, the powder is to slow for that case, just choose a bit faster powder.

I have heard that if loads are compressed to much, they will push the bullet back out to some degree. For me, there are to many powder's for me to fool with a compressed load. I'll go up to say 95% load but that keep's the powder level just below the neck of the case and I load to seat the bullet right at the bottom of the neck or further out, close as I get to compressed.
 
It really depends on the powder, case, bullet combo. With some combo's it is impossible to put enough powder in a case to get a dangerous load. A compressed load in that circumstance won't hurt anything. With other combo's you can create a dangerous situation with a load no where near compressed.

As a rule I find best accuracy when using a powder that fills the case to near capacity or even slightly compressed. But you can't do that with every powder.
 
As some have said, a compressed load is fine to use provided it is a published load. One of my best loads for my 280 Rem is 63 grs of H4831SC under a 120gr Barnes TTSX. I believe it to be about 101% case fill. I think you will find most compressed loads do not go much past 101-103% case fill.
 
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