Too little powder

[BondoBob]

I think this question got lost in another post and should have been in it's own post.

Can someone explain to me how loading below the starting load of powder could result in an over pressure situation. I have no intention of testing this theory, just want to understand it.

It's obvious to me how too much powder can cause over pressure, but how does too little do that? I would think moving the bullet would always offer less resistance than exploding the chamber. Am I wrong?

[Unclenick]

Ignition of powder is based on the assumption the primer is igniting a column of powder that burns from the primer end forward. The small spaces between the grains then limit how fast the flame spreads forward and, therefore how fast it ignites the powder. When a rifle case's fill density gets below about 60%, the powder can lay sloped along the bottom side of the case, exposing a much larger surface area to the flash hole than just the end of a column of powder. That can allow a lot more of it to light up at once, producing the equivalent behavior of a faster burning powder than it would be when lit mainly from one end of the case only. In .30-06, Dr. Lloyd Brownell observed the effect could, on occasion, produce pressures double that of a normal full load.

If instead of slow-burning rifle powder, you are working with small quantities of a fast powder, fast burn rate has already been taken into account, so the ignition position isn't nearly as much of a pressure variation factor.

The above is all an issue with rifle powder and cases. I don't think I've heard of it happening with handgun cases. However, some slow handgun powders, like 296/H110, burn too slowly to remain lit when a bullet jumps forward through the barrel-to-cylinder gap in a revolver. This means that when you underload them, they are not making much pressure when the bullet jumps that gap, and the pressure can occasionally bleed off faster than the powder can make it. This results in the powder burn being interrupted and the load extinguishing and "squibbing out," leaving the bullet stuck in the barrel. The next round fires and runs into that obstruction before the gap is exposed, so all the pressure builds up without the bullet moving forward and making more space. That bursts the gun.

Finally, with all cartridges, if you get powder quantity low enough and slow enough, rather than make enough pressure to keep the case expanded against the chamber, the bullet can get out, and then the pressure escapes backward through the gap in the chamber between its walls and the unexpanded case. This also leaves a bullet stuck in the barrel, which is very dangerous if the next load is normal.

[Aguila Blanca]

Originally Posted by Unclenick

The above is all an issue with rifle powder and cases. I don't think I've heard of it happening with handgun cases. However, some slow handgun powders, like 296/H110, burn too slowly to remain lit when a bullet jumps forward through the barrel-to-cylinder gap in a revolver. This means that when you underload them, they are not making much pressure when the bullet jumps that gap, and the pressure can occasionally bleed off faster than the powder can make it. This results in the powder burn being interrupted and the load extinguishing and "squibbing out," leaving the bullet stuck in the barrel. The next round fires and runs into that obstruction before the gap is exposed, so all the pressure builds up without the bullet moving forward and making more space. That bursts the gun.

I have heard of it happening with handgun cartridges, but I can't point to a specific article or web post. It was awhile ago.

I load .45 ACP with Winchester 231, and I can see how this could easily be a factor. A standard load of 5.3 grains of Win 231 doesn't occupy much of the volume in a .45 ACP case. I have to really look to verify that each charge dropped, and I can easily fit a double charge with no overflow or spillage. With a starting load I could probably fit three drops into the case. So I can see how a light charge could all gravitate to the bottom of the (horizontal) case in use, allowing the primer flame to shoot over the top.

This is why I decided to use Trailboss for .44 Colt and .45 Colt rather than Win231, even though I can find load data for Win 231 in .45 Colt. In that big case, a light load is just the proverbial "drop in the bucket."

[reynolds357]

Originally Posted by BondoBob

I think this question got lost in another post and should have been in it's own post.

Can someone explain to me how loading below the starting load of powder could result in an over pressure situation. I have no intention of testing this theory, just want to understand it.

It's obvious to me how too much powder can cause over pressure, but how does too little do that? I would think moving the bullet would always offer less resistance than exploding the chamber. Am I wrong?

To greatly simply it, you can get an explosion instead of a burn.

[caligula]

Hodgdon developed Titegroup to eliminate this problem. Was having erratic performance from light loads with Unique behind a 200gr RNFP I was developing for target work. Changed to Titegroup for both .45 Colt and .45 ACP and happiness reigns.

[the45er]

Originally Posted by caligula

Hodgdon developed Titegroup to eliminate this problem. Was having erratic performance from light loads with Unique behind a 200gr RNFP I was developing for target work. Changed to Titegroup for both .45 Colt and .45 ACP and happiness reigns.

Interesting. My current 45 ACP load is 5 grains of Unique with a 200 grain coated bullet. I notice every now and then I get a seemingly light load and sometimes it seems a bit heavy. I’ve never measured a big difference in weights of powder drops when I’ve checked them. This might explain that. I only shoot for combat accuracy so it’s not a big deal for me. As long as the bullet goes out the end of the barrel in all of my 45s, I’m a happy camper!

[Unclenick]

It's strange. Unique and Bullseye are both century-old target load powders now, and both have been popular in 45 Auto. But if you are running at the very low end of pressure, Bullseye will light up more consistently and so will Tightgroup.

[Don P]

It's strange. Unique and Bullseye are both century-old target load powders now, and both have been popular in 45 Auto. But if you are running at the very low end of pressure, Bullseye will light up more consistently and so will Tightgroup.

Yep I load 45acp with 3.6 grains of Titegroup under a 230 grain coated bullet and get a chrono of 600 fps. This load will also function in ALL my 45acp semi-autos

[joeanybody]

So if I may interject with a question that may be a bit on the stupid side: how do u know if your charge is less than 60% fill? I have light loads for 45/70 that I designed a cotton wad to prevent that from happening. Only because I wasn't sure and just wanted to err on the side of caution

[Aguila Blanca]

Fill a case with the powder of your choice, dump the powder into the tray, and weigh it. That's a full case. Multiply by .6.

Or, if you want to be more precise, figure out where the base of your bullet extends to in the case. Mark the case, fill to that level, weigh the powder, and figure 60 percent of that.