How Important is Case Fill

Two or maybe three issues.

The first is "squib load detonation". This is the idea that the primer can "flash over" the top of a light charge and cause it to act essentially as a high explosive. I believe the idea started as a result of blown-up .38 Specials used with tiny charges of Bullseye. I personally regard the whole thing as a myth, but can't prove it.

Second is that fast powders in big cases provide the potential for double, triple, ??? charges. That is what is responsible, IMO, for those blown-up .38s. When I use such combinations, I take great care to ensure that I am not getting double charges.

The third, maybe, is position sensitivity and erratic velocities. There have been instances where the shooter will get one result if the gun is pointed upwards, another result if pointed downwards, and a third result if held horizontally. I believe this is a problem that has largely disappeared with modern powders.

There are two really good powders for your application. One is AA 5744, and the other is Trail Boss. Neither needs or wants a magnum primer. I prefer Trail Boss and keep a large keg of it around. Its only downside is that it is somewhat more expensive. It's just so hard to get yourself into trouble with it that I am glad to pay the premium.

I have zero experience with 450 BM. But in my experience loading for other cartridges I get better accuracy with loads that come close to completely filling the case. If there is too much empty space the position of the powder inside the case can vary and that can lead to inconsistent powder burn.

I think this is part of the reason some powders prove to be accurate in some cartridges and not others. With some a max powder charge may leave a lot of empty space in some cartridges and fill up others.

My best advice is to stay safe by using Trail Boss. It won't be the cheapest option. For that, you'd want to look at Titegroup and you would have to work up your own loads. If I were to do it, I would start with .45 Long Colt data and use Quickload to determine the adjustment for the longer case. Titegroup should be consistent with low fills -- that's what it was designed for. I recommend Trail Boss as a better option. https://www.hodgdon.com/wp-content/...39.271432957.1593031833-1593136859.1590674505

My biggest concern is double charge.. I always try to fill the case as much as possible so I get a spill over with double charge.

When I was a youngster all the guns rags were talking about the 45colt with really lite loads of bullseye blowing up their revolvers. Detonation was the accepted excuse at the time and I even heard shape charging was causing it from the blast going up instead of forward.

This went on for a few years ( late 70s-early 80s) and then it slowly disappeared.

Is it a real concern, I have no idea, but the gun magazines showed 45 Colt after 45 Colt blown up with Bullseye and said that detonation was the problem.
Then later they said shape charging was the problem, then they said double charging was the problem.

Then for some reason everyone quit talking about it.

Then I read nothing about it for years and years.

I don't know what to tell you except that I still think about those articles when I'm loading large cases with fast burning powders, so I stay away from doing that.

If someone could prove that a detonation can't happen that would be one thing. But they can't prove that it doesn't happen either so what can you believe.

Then you hear that person with a blown up revolver say "there is no way I double charged that round" Again, we don't know. We can suspect he double charged, but we don't really know.

I keep a certain amount of case fill and don't load light loads with fast powders in large cases because I err on the side of caution with this issue.

TB and IMR 4227 are good options for this application.

I have always loaded my cases to be at least 1/2 filled for my 45 loads.
It has served me well for the last 15 or so years.
If you fill all your reloads are at least half way with something with closer to a medium speed pistol burn rate (the scale being bullseye and red dot being "fastest" and something like H110 being "slow" for pistol) you will never get one of these "magic detonations", which I bet are all accidental double or triple charges.

Hell I have accidentally double charged my 45s, but when the case is totally full or overflows with powder you kinda can't help but notice it. Then even if I still didn't catch it and tried to seat a bullet on a full shell there's no way it will seat.

Never assume you will never double charge a round. If you load with filling less than 1/3 of the case it's not safe and that's all there is to it.

I see a lot about "case fill" being an issue with light loads in large cartridges. My question is how big of a deal is it?

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When there is a lot of empty space in the case, there can definitely be case-position sensitivity. I do the "powder forward" test on all my revolver loads that don't have good case fill, and I have personally seen over 300 fps difference between powder-forward and powder-rear tests with one particular powder, while another powder with the same case-fill had less than 40fps difference. I have even tested a new powder in 45acp recently that had large extreme spreads due to case position sensitivity. I don't use powders like that.

Trailboss would be the place I would start. I have not seen published loads for it in 450b, but you could fill all the empty space behind the bullet (do not compress it) and you will not be over pressure.

http://www.hodgdonreloading.com/reloading-education/tips-and-tricks/low-recoil-loads

Slappy White said:

Is powder really that hard to ignite?

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I wouldn’t have thought so, until I found I burned kernels in my magnum pistol.
Since I started so low it wasn’t burning all of the powder at its preferred pressure before the bullet “left scene”.

Slappy White said:

And would magnum primers solve the issue?

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Using a magnum primer increased the initial starting pressure of the burn, causing a more complete burn of the same amount of powder, increasing performance. Because I know there was not enough room for the powder to shift, it was not from position sensitivity.

I agree with @.38 Special, though I can not prove so either.

Slappy White said:

Is it dangerous?

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I thought I’d use slower powders, to avoid the dreaded double charge, as it would pour out the top.
But as got my own “Tao”, my handloading way, the process, I found it was not necessary. I batch load, hundreds at a cycle. After a single case is charged a bullet is seated. No doubling of anything. I can stop at any interruption, lock the door, and return to the process.
(I look like an octopus loading, but it’s good exercise. Ever hand weigh eight hundred 45Auto charges? I trust my measure now...)

I have found it to be of little consequence when using powders appropriate for the intended cartridges.

But where’s the fun in that?

I don’t know if you’re loading on a progressive, but I use the RCBS lockout die to try to help avoid double or zero charges. We’re just getting into 450, but for the 460 it’s been loaded on a single stage and that process uses a loading block so after powder charging, the entire batch of cases are visually inspected before bullet placement.
We were going to start with 296, and the online data for a 225 FTX shows 40.4-44.4gr. That seems like it’d be quite a bit of case fill. I’m curious as to what you were thinking for a “light” plinking load? BTW, we’re loading for an AR platform.

One early example of rifle destroying events was known at the time as SEE, or secondary explosion effect. It was related to light charges of slow burning powder in rifle cartridges.

Dr. Brownell at U Mich did extensive research on pressure factors several decades ago. One of his resulting graphs showed peak pressure becoming very erratic below 30 KPSI. In a related incident one of his grad students had a bullet lodged in the barrel, and prepared a blank cartridge to clear it. When he touched it off, the firearm exploded. Again, this was slow burning powder.

Some pistol powders are position sensitive and some are not. In my test, TiteGroup gave the same MV with the powder forward in the case vs. rearward in a pistol case.

I'm in the Trail Boss camp. It's designed for light plinker loads.

The information I have read about rifles (Firearms Pressure Factors by Lloyd Brownell PhD, 1990, Wolfe Press) the unfilled case problem or Secondary Explosion Event (SEE) has never been explained to everyone's satisfaction. In rifles, it seems to be more common when very slow powders are loaded with the case half (or more) empty. But no one can make it happen on command. Hence the unsatisfactory solution.

However, small doses of fast powder do show the problems explained above. Erratic velocities, extra charges and so on. .38 Special's recommendation of Trail Boss for a full case is a good solution to both potential problems.

Archie said:

The information I have read about rifles (Firearms Pressure Factors by Lloyd Brownell PhD, 1990, Wolfe Press) the unfilled case problem or Secondary Explosion Event (SEE) has never been explained to everyone's satisfaction. In rifles, it seems to be more common when very slow powders are loaded with the case half (or more) empty. But no one can make it happen on command. Hence the unsatisfactory solution.

However, small doses of fast powder do show the problems explained above. Erratic velocities, extra charges and so on. .38 Special's recommendation of Trail Boss for a full case is a good solution to both potential problems.

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I agree that it has never been explained to everyone's satisfaction. If you want something to chew on, here's my hypothesis:

Powder burns faster under pressure. I wonder if there could be pressure waves propagating in the case. If so, powder in the high pressure area would burn faster, and as the wave transited that area, it would be amplified. A few passes through the case and it might pick up enough amplitude to break the firearm. If the case is nearly full, the powder acts as a dispersive medium, to break up the wave.

Like I said, a hypothesis.

We know there's pressure waves in the gun.
If you look at a muzzel velocity by barrel length chart you will notice there are certain lengths to avoid, where the bullet velocity doesn't increase like every where else along the chart.
One example is a 21 inch barrel on a 223. The velocity is the same on a 21 as it is on a 20. Then there's another lull, at 13 inches I think.

Case fill:
In my opinion it is important.

In my roundball 30-40/30-06 loads (the most extreme example I have)
If I tip em up before firing i usually get around 950fps avg
Tipping em down got just around 830fps a good

Everything else just gives me a wee bit of vertical stringing if I leave excessive space
But for practice ammunition in a firearm that isn't going past 300 yards i don't worry much.
I just get more picky and careful about it when I need hunting or accuracy loads.