Pressure, obturation and the 45 Colt

[Larry Gibson]

It takes 5000 to 7000 +/- psi to fully obturate a case to seal against the chamber wall. How much depends on the thickness of the case and how "hard" the brass is. Annealing thicker cases such as Starlines can help. With the 45 Colt i ran into the problem some years back when doing a thorough test of VV N32C powder with 200 gr cast bullets for cowboy action loads in a M92 Rossi. Withe many of the loads [also including several factory loads] I had gas escaping back and hitting my forehead. The gas blowback wasn't evident with revolvers or with the closed breach Contender I was using to measure the psi. However, incomplete obturation of the fired cases [Starline, Federal, Winchester and Remington] was very evident.

What I found from the data recorded with the Oehler m43 PBL was the faster the rise to peak pressure, the greater the obturation. What is needed to get complete obturation with 45 Colt cases that were FL sized with carbide dies while keeping the psi in the 14 - 15,000 range or less was to move the peak pressure point as close to the mouth of the cartridge case as possible. This was done by using the fastest and most easily ignitable burning powders generally available. The powders that performed best were Bullseye, 700X, WSP and Red Dot with charges in the 7 to 7.2 gr range under the 200 gr cast bullets. I also found those powders to give the best obturation at 14,000 psi or less with 250 gr +/- cast bullets. With lighter weight bullets the powder charges needed to increase but at full case obturation the psi exceeded 14,000. Bottom line is if you use a slower burning powder or one that doesn't ignite as quickly then you'll probably just have to put up with minimal case obturation.

I found not using a carbide sizer, which FL sized the case body, but instead to use an older steel FL sizer [mine is a RCBS] that just sizes the cases to the chamber spec taper. Yes, the cases need to be lubed. I clean the cases, use a spray lube on them, deprime/FL size with the RCBS die then a short cleaning to remove the lube and they are ready to load on my Dillon 550B with a Lee deprime die in station #1 to ensure the flash hole is clear. All my 45 Colt loads loaded as such give full obturation in my revolvers and M73 carbine.

[Rickf1985]

I believe bullets obturate where brass expands. Different types of expansion altogether. Irrelevant maybe, but correct terms matter. I have found in several instance where published data is way above max. I certainly would not want to shoot max let alone way above it in an antique gun!!!

[Larry Gibson]

Actually, in Firearms Encyclopedia obturation is defined as "The sealing of the propellent gases inside the chamber and bore of a gun, preventing any escape rearward into the action. In all firearms (except those using caseless ammunition) this is accomplished by the cartridge case itself. Under pressure of expanding powder gases, the ductile case is forced tightly against the chamber wall, preventing rearward escape of gas."

Cast bullets themselves, in revolvers, may expand/obturate to fill the cylinder throats but of the bullet is, to begin with, or expands/obturates larger than bore/groove diameter of the barrel the bullet will actually be swaged down and, therefore, does not "obturate" to fit the bore/groove diameter of the barrel. If the bullet is traditionally lubed, then the bullet will be further swaged down as it rides bore/grooves on a layer of that lube. Such a bullet does not "obturate" in the barrel as most believe.

[JFoster48386]

Has anyone suggested annealing the brass every time you load it? I've started annealing most of my brass before I reload/load it. Starline has something in their FAQ section about annealing the .45-70 brass before each reloading to get the best case/chamber seal. Shooters have also reported better consistency when annealing their brass. I started doing it with .45 Colt to be used in my rifle but decided to just anneal it all regardless if it will be shot in a rifle or pistol.

Jon.

[Larry Gibson]

If I had to anneal the cases for every time I reloaded them, I'd find something else to shoot. I have annealed cases occasionally over the years but it was mostly with cartridge cases formed from other cartridge cases. In over 60+ years of reloading pistol cartridges for use in pistols and rifles I've never found the need to anneal. However, that's just me. Anyone else is certainly free to anneal cases if they want to.

[HWooldridge]

I once annealed a pile of old Remington 45 Colt cases that had been reloaded countless times and were beginning to split with some regularity. I also annealed some 44-40 cases that had gone through a bunch of load cycles and were splitting. The process did extend case life for a few more firings but I eventually started getting loose primer pockets and began scrapping them.

However, both of those were exceptions to the rule and I don’t habitually anneal anything.

[Ford SD]

You could be oversizing your cases

Take several of your higest presure cases and partaly resize the case were the the bullet sits ( top 1/2 inch or so)

think bottle neck of a straight wall case

try to fit the empty partaly sized case in your revolver cylinder. if it will not fit size it a little deaper
then try it in your other guns

I do that for my 44 mag paper puncher plinker loads

the brass last longer

[John Guedry]

Cases with soot? Thats what you bought a tumbler for.

[rickt300]

Well about the pressure aspect. If the brass isn't expanding enough to seal the chamber how much pressure is the cylinder getting? If the case doesn't grab the chamber is it being thrust back into the frame? It would seem obturation is pretty important. If the brass itself takes say 5-7000 psi to expand then a 14,000 psi load is only putting 7-9000 psi against the cylinder right?

[Larry Gibson]

"If the brass isn't expanding enough to seal the chamber how much pressure is the cylinder getting?"

Very little if any.

"If the case doesn't grab the chamber is it being thrust back into the frame?"

Yes.

"It would seem obturation is pretty important. If the brass itself takes say 5-7000 psi to expand then a 14,000 psi load is only putting 7-9000 psi against the cylinder right?"

If the pressure is high enough to hold the case in the chamber but low enough the case head doesn't stretch to the rear then there will be little thrust pressure put on the from the cartridge case. However, the cylinder itself will be moved back in the frame by the pressure of the expanding gas behind the bullet.

[rickt300]

"If the brass isn't expanding enough to seal the chamber how much pressure is the cylinder getting?"

Very little if any.

"If the case doesn't grab the chamber is it being thrust back into the frame?"

Yes.

"It would seem obturation is pretty important. If the brass itself takes say 5-7000 psi to expand then a 14,000 psi load is only putting 7-9000 psi against the cylinder right?"

If the pressure is high enough to hold the case in the chamber but low enough the case head doesn't stretch to the rear then there will be little thrust pressure put on the from the cartridge case. However, the cylinder itself will be moved back in the frame by the pressure of the expanding gas behind the bullet.

So a modern steel cylinder should easily be able to take18-19,000 PSI. I know some of the very early black powder colts weren't heat treated. I can see why they were loaded very lightly. Just how many of those super old antiques made before 1895 are still out there slinging lead and should the rest of us be hindered by those few pistols?

[Larry Gibson]

So a modern steel cylinder should easily be able to take18-19,000 PSI. I know some of the very early black powder colts weren't heat treated. I can see why they were loaded very lightly. Just how many of those super old antiques made before 1895 are still out there slinging lead and should the rest of us be hindered by those few pistols?

Yes.

That is the pressure level of the "classic" 8.5 gr load of Unique under a 250 - 260 gr cast bullet. My regular 45 Colt load is the 452-200-RF ove 7.2 gr of Bullseye or 700X. Measured psi runs 14,000 +/-. I have no problems with case obturation in my Uberti M73. A 5 gr Bullseye load under the Lee 452-230-TC runs 16,000 +/- PSI.

Consider also the pressure level of the 45 ACP cartridge for which there are factory cylinders available for many SAA clones. I have on for my Uberti "Evil Roy" SA and shoot loads with measured psi's of 20 - 24,000 without giving it a second thought. My normal load 45 ACP load is a 452-200-SWC over 5 gr Bullseye which runs a measured 18,000 psi and I mostly shoot those in the Evil Roy SA.

[gwpercle]

Every time you reload brass ... it work hardens .
Try annealing the cases ... this will soften the work hardened brass and they will seal at the desired pressure .

I was loading light 41 Special loads into some 41 Magnum brass , that had been reloaded 5 - 6 times ...
and I was getting sooty cases with those light loads ...
I Annealed them and ... Wah Lah ...
No more sooty cases ...
Give annealing a try ... it worked wonderfully for me !
Gary

[Jhon]

Arriving at the party late... but kinda amused at the OPs question/problem at the start. Not to be disrespectful but it very much seems like a non-issue. For myself, I've shot factory Cowboy loads in a brand new Ruger Vaquero and these days shoot handloads at decent hunting velocites, cast and jacketed, out of a Rossi Puma 92. I've bought new Starline brass and plenty of pre-owned used brass as it came available. I can tumble clean to bright and shiny but I have to tell ya, in all my 45 Colt shooting, rifle and revolver, dirty brass, sooted brass, is a feature of the calibre not a reloading problem. True of other calibres also, 45ACP being another notorious one. If you want to play around with minimizing it good for you. The time might be better invested in chasing accuracy perhaps, or knock-down ability, or consistency etc etc. But each to their own. Good luck.

[rickt300]

Well finally shot all I had loaded so I have a pile of empty brass. As soon as I get done with the Whelen I am fooling with right now I will do several things mentioned here. One will be to seat the bullet out as far as is reasonable. The other is to reach a point where my cases, no matter how tough from many firings obturate which I consider an important part of a revolvers function. Last will be to regulate my sights to the desired load. I am going to use some Unique, Blue dot,and maybe some 4227.