First I heard of it!

[robertbank]

"It's fairly common knowledge that...for a given weight/mass...a lead bullet will cause a given powder charge to produce less pressure and higher velocity than a jacketed bullet, and this is true...to a point. You can, however reach a point that the lead bullet will cause a rapid, often dangerous pressure spike because of a phenomenon known as "Obturation." It comes from the violent force of the powder gases causing the bullet to elastically expand...or "bump up" as home casters refer to it. This obturation can be so sudden and violent that it fairly wedges the bullet in the bore...increasing its resistance and driving peak pressures off the scale in the attempt to make it move. So...don't get too cocky with powder charges simply because you're using a lead bullet. Beyond a certain point, it can land you in serious trouble in quick-time."

The above was recently posted on one of the gun forums I follow. Never heard of bullet obturation in the .45acp wedging in the bore from obutration thus causing pressure levels to go "off the scale".

Comments?

Take Care

Bob

[felix]

Very possible, Bob, but not likely using common sense. Heavy soft boolits, or heavy duty hollow base designs, are probably the most sensitive to what you are saying, and then only with way too fast powders for the job. ... felix

[freedom475]

Just had an experience similar to that while testing cast 475 loads....NOT posting data, just sharing my findings:Fire:

all loads were WDWW Plain Base

9gr. unique=928fps ave /10gr. unique=962fps ave /11gr.=1160 fps ave.....talk about a pressure spike! all loads were ave of 5 shots each.....mag primers gave 10fps increase in all loads chronoed.

[44man]

When I first got my .475 revolver and started to work loads with two boolits of the same weight, one with a GC one PB I found the gas checked one would stick cases with the same load the PB took. I could even go more powder with the PB.
Then the 45-70 BFR with a jacketed bullet and 4198 would take much more powder then my cast boolit of near the same weight. I got pressure spikes with the cast. One or two cases had to be beat out with less powder then the jacketed used.
I switched to 4759 and cured the problem.
These were all pretty hard boolits too with tin and antimony added to WW's.
It is not written in stone and cast has to be worked carefully too. Strange things can happen and a powder change can either fix it or ruin your day.
I only can say to be careful and work loads the same for any bullet/boolit.

[robertbank]

I would suggest that using a bullet sized .452 with any alloy in the 1911 pistol you are never going to see pressure spike caused by obturation of the bullet base. Using bevel base bullets I have obeserved virtually no obturation in the bases of recovered bullets.

Take Care

Bob

[MGySgt]

Just had an experience similar ...........

9gr. unique=928fps ave /10gr. unique=962fps ave /11gr.=1160 fps ave......

Question - what type of brass?

Just my findings/opinion

I was working with the 475 and Star Line Brass - 400 gr Keith, using Unique, and I found that at the lower velocities I was not getin ENOUGH pressure in the case to seal the chamber - hence black ring around case or Lead ring around case. When I gaot about 11 grains that problem went away and accuracy went up, along with recoil of course. The black/lead rings went away also.

FWIW - I am also looking for some old pressure data from a long time ago that stated HIGHER pressures with lead due to a better seal and less blow by.

Drew

[robertbank]

I have observed the blackened cases when using titegroup in the .45 Colt. While loads are consistant I think the cause is the pressure curve is so late the cases fail to seal the chamber (Starline Brass). Faster powders seem to create an earleir pressure spike sealing off the chamber and eliminating the scouring of the case.

Take Care

Bob

[jhrosier]

....I found that at the lower velocities I was not getin ENOUGH pressure in the case to seal the chamber - hence black ring around case or Lead ring around case. When I gaot about 11 grains that problem went away and accuracy went up, along with recoil of course. The black/lead rings went away also.
...

Thanks Drew!
In all my years of shooting, it simply never occured to me that leading and accuracy issues can start while the boolit is still in the case! It makes sense when you (finally) realize that the gas seal of the boolit can be ruined before it even gets out of the chamber.

Jack

[Glen]

That will only happen with very soft bullet loaded into very high pressure rounds. This is why the 454 Casull should not be loaded with soft bullets (when loaded at full throttle). For pretty much any other handgun load obturation takes place to much more subtle degree and is a benefit in helping to seal the gases behind the bullet.

[Three44s]

And .... it bears repeating.

When working up a load ...... don't try to close the deal to quickly ........ ie. big jumps in powder charge rates.

I too use .2,.3 or .5 gr. increments.

Three 44s

[freedom475]

Question - what type of brass?Drew
This was Hornady brass cut back to 1.375 to get the Keith to fit FA's 83.


FWIW - I am also looking for some old pressure data from a long time ago that stated HIGHER pressures with lead due to a better seal and less blow by.
Drew

Search 454 casull data...there's an old page from FA that is now a German site that list the old original 475linebaugh and 454data. This data is a little more like it:mrgreen: and it's not for reformed 45-70 cases.:Fire:

www.shooting-center.de/casull_lade_e.htm

[Char-Gar]

Glen and the others have nailed it. Under certain conditions of soft alloy and high pressure, bullets can stretch out quite a bit. You will never see this in the 45 ACP or similiar rounds that run at less that red line pressure. I don't load and shoot any such mega guns, so this is all just theory as far as I can concerned.

[freedom475]

so this is all just theory as far as I can concerned.

Yeah, this pressure spike might happen with Unique powder as it reaches max.....regardless of boolit make-up

[Larry Gibson]

"It's fairly common knowledge that...for a given weight/mass...a lead bullet will cause a given powder charge to produce less pressure and higher velocity than a jacketed bullet, and this is true...to a point. You can, however reach a point that the lead bullet will cause a rapid, often dangerous pressure spike because of a phenomenon known as "Obturation." It comes from the violent force of the powder gases causing the bullet to elastically expand...or "bump up" as home casters refer to it. This obturation can be so sudden and violent that it fairly wedges the bullet in the bore...increasing its resistance and driving peak pressures off the scale in the attempt to make it move. So...don't get too cocky with powder charges simply because you're using a lead bullet. Beyond a certain point, it can land you in serious trouble in quick-time."

The above was recently posted on one of the gun forums I follow. Never heard of bullet obturation in the .45acp wedging in the bore from obutration thus causing pressure levels to go "off the scale".

Comments?

Take Care

Bob


The guy probably writes for Wikpedia.

Larry Gibson

[Char-Gar]

Yeah, this pressure spike might happen with Unique powder as it reaches max.....regardless of boolit make-up

Freedom.. In my 48 years of loading and shooting for sixguns I have send down range something around a three quarters of a million rounds. Many of these rounds have been loaded with Unique. I have never pushed Unique (nor any othere powder) to the max. I have never shot a max load of any kind. My mentor told me about such things.. "If you want to drive a bigger nail, get a bigger hammer".

I have never ka-boomed a firearm, have never shot one out of time, stretched a frame or had any kind of damage due to hot loads.

As I read these boards, I read about all sort of things that have taken place with handguns and shooter, that have no relevance to my experience. I don't doubt they happen, but they don't happen to me.

As I said... "As far as I am concern, this is just theory"

[Bass Ackward]

"It's fairly common knowledge that...for a given weight/mass...a lead bullet will cause a given powder charge to produce less pressure and higher velocity than a jacketed bullet, and this is true...to a point. You can, however reach a point that the lead bullet will cause a rapid, often dangerous pressure spike because of a phenomenon known as "Obturation." It comes from the violent force of the powder gases causing the bullet to elastically expand...or "bump up" as home casters refer to it. This obturation can be so sudden and violent that it fairly wedges the bullet in the bore...increasing its resistance and driving peak pressures off the scale in the attempt to make it move. So...don't get too cocky with powder charges simply because you're using a lead bullet. Beyond a certain point, it can land you in serious trouble in quick-time."

Bob



Bob,

I have seen this, absolutely. But I attribute it lube break down during excessive obturation which leads to galling. Galling is a bonding of lead and steal otherwise known as a plug. Once the plug begins the pressure increases and the galling increases even more until the center of the bullet is blown clear reducing pressure. This is more likely to happen with smaller capacity cases and fast powders using soft lead and hard waxy lubes.

You can look at this two ways meaning more pressure than the metal hardness can handle or poor quality lube for the bore condition or a combo of both.

I disagree with his hypothesis that a cast bullet reaches higher velocity on lower pressure. under some conditions this can be true, but in others it can be the reverse using the same powder and charge. This is mostly because of a seating depth issue. Often a cast bullet will be shorter with more weight outside the case compared to a jacketed bullet of the same weight. But not necessarily. Seating depth is the biggest factor here over bore friction.

[freedom475]

Freedom.. In my 48 years of loading and shooting for sixguns I have send down range something around a three quarters of a million rounds. Many of these rounds have been loaded with Unique. I have never pushed Unique (nor any othere powder) to the max. I have never shot a max load of any kind. My mentor told me about such things.. "If you want to drive a bigger nail, get a bigger hammer".

I agree.....I was not trying for a max load here, just accuracy at 100yrds. If I want the 475 to really boom I use H110/296, but the novelty of a 400gr. at 1400fps wears off REALLY QUICKLY:mrgreen:.

The 9gr Unique load is real pleasant to shoot , and if I want to take a few shots while out hiking without ear-plugs I'm not completely deafend by the blast.:Fire: