compressed loads

flyrobb · Jan 28, 2016

Based on this comment from Road_Clam in a different thread about Unique it got me thinking, so I went to the bench to see what he was talking about. Up to now I guess I haven't used powders that filled the case like Unique and yes, 5.8 grains fills the case close to the top and 6.3 dang near fills er to the top.

+1 , when I was getting up to my 5.8gr charge i'm seeing the powder level nearing the top of the casing and I was thinking out loud to myself "dam, that looks like i'm getting near a compressed load". So i'm guessing the 6.3 gr charge must be compressed.

So when is a load considered compressed, how much can you safely compress a load or should you avoid them altogether?

oldylocks · Jan 28, 2016

Wow, this is a great thread... I was loading some .223 today and ran into loads that were "compressed"... I would really like to know more about this subject... thanks for a timely thread.

moxie · Jan 28, 2016

Some manuals indicate some compressed loads with a "C" or other annotation. But sometimes they are not annotated when the load is clearly compressed. As long as you are using a recognized manual, don't worry. The loads are safe. It can be useful to tap full cases to get the powder to compact a bit. And it's a good idea to use slow, firm, pressure when seating the bullet.

This is discussed in the front part of some manuals, e.g., Speer. It pays to read ALL of the info in the front of the book. Don't just jump to the data tables.

Rule3 · Jan 28, 2016

As mentioned the manual or online data will say compressed.

Just do not compress TrailBoss, it does not like it!!

In most situations the more case capacity is filled, the better the load is. This occurs more tith slow powders. That;s we we freak out over tiny amounts of a fast powder like TiteGroup in a LARGE case. Or even worse a full cases with FAST powder.

fredj338 · Jan 28, 2016

It all depends. Compressed loads per say are not dangerous, but powder burn rate & case capacity play a huge part in whether a powder can be compressed. A couple of examples:
The 9mm is a high pressure, small capacity case. Many powders will be compressed with a max load. A high loft/fast powder, like Clays, will not take much if any compression before producing an over pressure event. Yet i doubt you could get enough 2400 into a case & even compressing it 110%, be over pressure.
Rifles can be much more forgiving. The fastest rifle powder is still slower than the slowest pistol powder. Still, case capacity & powder burn rate are important. I tend to use slower powders in my rifle calibers & the loads are almost always 100% compressed. Using a drop tube can prevent somme compression or crushing of the powder. Stay out of the rifling, never had an over pressure event.

BLUEDOT37 · Jan 29, 2016

flyrobb said:
So when is a load considered compressed...

Use your digital caliper to measure the bullet's overall length, then zero the caliper before moving the jaws & removing the bullet. Seat your bullet in the case to the desired COAL". Now use the tail/extension of the caliper to measure from the case mouth's lip to the top of the seated bullet. The reading on your caliper's display is the depth the bullet was seated to inside the case. (Disregard the minus sign.)

Use this reading to determine if the powder charge you want to use will contact the base of the bullet when seated, once dispensed in an empty case. You can use the tail of the caliper, extended to the reading you got above (after closing the jaws & zeroing it) for this determination.

This is most useful, when you're loading a different style bullet, to determine if/how much deeper it's being seated vs. a previous bullet with the same charge.

The more the bullet's base contacts the powder, the more compressed it is, from light to heavy. On heavily compressed loads there's a procedure to verify it stays crimped to the seated length.

.

scooter123 · Jan 29, 2016

According to the Lee manual Richard Lee tested compressed loads when he was starting out and found that compression actually slowed the burn rate to some extent. In addition back when the 45-70 was the standard US Military load the black powder in the case was compressed heavily enough that it require a separate powder compression stage to load 70 grains into the case. When you think about it it makes sense that compressing the powder charge will slow the burn rate, because powder that is loose in excess volume it's exposed to the flame front on all surfaces, if it's packed into a mass it can only start burning once the flame front reaches that particle.

I would not and do not fear a compressed load that uses a slower powder. However I have found that trying to compress a charge of Unique in a 380 ACP case with a Hornady XTP resulted in the hollow point cavity being closed up due to the pressure needed to compress the charge. Note, I run my 380 loads at maximum because I've determined it is the only way to insure reliable function with my Sig P290.

Nevada Ed · Jan 29, 2016

Most manuals do not show a compressed load but just have the grains of powder.
However my newer Lyman does show compressed loads with the little $6.50 manuals with 4 calibers........ 38 special, 380 Auto etc.

You can also look up Nosler data........
It does not have that many loads but it does give you the VOLUME of the powder in each loading.

I have found in the short 9mm case....
a LOT of FULL loads with the bullet style is no where near, being a fit, mostly with Blue Dot powders and other bulky types.
How they said they got that bullet and powder at the OAL, is a mystery to me.

OKFC05 · Jan 29, 2016

IMHO, if you're having to use a vibrator on the case to get all the powder into a pistol cartridge, you're using the wrong powder. I've seen people go nuts trying to stuff a powder into a case when a more dense alternative is available, and I just don't see the point in all that hassle. A run over the chrono often showed the theoretical "super load" just wasn't making the creator's goal.
(added) often fell short when using data from 10" test barrels and loading for 4 to 6" real revolver barrels.
I specified "pistol" because rifles are a different story if the barrel is long enough to benefit from the added super slow powder. However, I have one shooter associate who was unhappy with his old 30-06, so he bought a 300 short magnum with long barrel, and had me load it to the max. Then he took it hunting and got the long barrel hung on everything, and cut the barrel way back. What he wound up with after all that was + 100 fps more MV and one gigantic fireball.

fredj338 · Jan 29, 2016

scooter123 said:
According to the Lee manual Richard Lee tested compressed loads when he was starting out and found that compression actually slowed the burn rate to some extent. In addition back when the 45-70 was the standard US Military load the black powder in the case was compressed heavily enough that it require a separate powder compression stage to load 70 grains into the case. When you think about it it makes sense that compressing the powder charge will slow the burn rate, because powder that is loose in excess volume it's exposed to the flame front on all surfaces, if it's packed into a mass it can only start burning once the flame front reaches that particle.

I would not and do not fear a compressed load that uses a slower powder. However I have found that trying to compress a charge of Unique in a 380 ACP case with a Hornady XTP resulted in the hollow point cavity being closed up due to the pressure needed to compress the charge. Note, I run my 380 loads at maximum because I've determined it is the only way to insure reliable function with my Sig P290.

I think your or Lee's context is off. Yes, black powder ALWAYS wants to be compressed, that is to prevent detonation. Smokeless, no, I doubt most calibers, most powders, the burn rate slows under compression. With slow powders, burn rate might slow a bit, but to make a blanket statement would have one believe a compressed load of Clays would actually slow down, maybe, but not before it took the gun apart.

fredj338 · Jan 29, 2016

OKFC05 said:
IMHO, if you're having to use a vibrator on the case to get all the powder into a pistol cartridge, you're using the wrong powder. I've seen people go nuts trying to stuff a powder into a case when a more dense alternative is available, and I just don't see the point in all that hassle. A run over the chrono often showed the theoretical "super load" just wasn't making the creator's goal.

Well yes & no. Sure, trying to get enough 2400 into a 9mm case would be an extreme, but generally, slower powders provide higher vel @ lower pressures. It is a balancing act though as case cap becomes really important. Certainly a safer bet trying to reach a vel goal vibrating powders vs pushing faster powders at the ragged edge of pressures. Most of my 9mm loads are compressed with bullets 124gr & heavier, not an issue.
In rifles, same story, why we have powders like 4831sc & 7828ssc, to allow more slow powder to be stuffed into the case for higher vel & still have lower pressures.

John R · Jan 29, 2016

If loading data indicates it's a compressed load your not going to have any problems.

Nevada Ed · Jan 29, 2016

While I have used COMPRESSED loads of powder in the short 9mm case with a 115 and 124gr plated RN design bullet over the last two year with slower powders like..........

Unique and SR 4756.

Yes they do achieve high fps but they hit the wall with the "C" load and that is as far as they can go but they will usually be near or at a +P loading.

I like to have a load that is close to 98% volume or less if possible and this is one reason that I also use HS-6 powder in my FULL loads, since it is usually around 78% volume and less hassles, seating the bullets and spillage of powders during the loading process.

scooter123 · Jan 29, 2016

fredj338 said:
I think your or Lee's context is off. Yes, black powder ALWAYS wants to be compressed, that is to prevent detonation. Smokeless, no, I doubt most calibers, most powders, the burn rate slows under compression. With slow powders, burn rate might slow a bit, but to make a blanket statement would have one believe a compressed load of Clays would actually slow down, maybe, but not before it took the gun apart.

Fred, Richard Lee started out as a Precision Rifle shooter and the context of his statement was in Rifle calibers using Rifle Powders. If you take the time to check you will find that it's actually quite common for rifle loads that approach the maximum charge level to be compressed with the typical Smokeless powders used and the point of Richard Lee's statement and my passing it along was that in many contexts compressed charges can be perfectly safe. The caveat is that any load you build should be within the confines established by published load data for the powder you are using. I rather doubt that you'll find a compressed charge of Clays is within safe parameters for any caliber out there. Does that clear it up for you?

flyrobb · Jan 29, 2016

Nevada Ed said:
Most manuals do not show a compressed load but just have the grains of powder.
However my newer Lyman does show compressed loads with the little $6.50 manuals with 4 calibers........ 38 special, 380 Auto etc.

You can also look up Nosler data........
It does not have that many loads but it does give you the VOLUME of the powder in each loading.

I have found in the short 9mm case....
a LOT of FULL loads with the bullet style is no where near, being a fit, mostly with Blue Dot powders and other bulky types.
How they said they got that bullet and powder at the OAL, is a mystery to me.

Yes I noticed that in the Nosler data. Wonder why more manuals don't include this info? Seems like that is handy info to know.

The Lyman 49th shows compressed loads with a + after the load.

compressed loads

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