what would be the effects of seating a bullet very deep inside of the case? lets say, that you take a light 38 special load with normal over all length and seat the bullet flush with the mouth of the case. Would that cause a dangerous spike in pressure or would the pressure remain the same? And what about taking the same case with a very light load of powder, and seating the bullet all the way down on the powder charge, making a compressed load?

If the only thing you change is the size of the "boiler room" you are going to increase the pressure. The big question is ... how much is the increase in pressure? That is difficult to fore tell. It could become dangerous very quickly.

muck

VithaVouri (sp?) has a couple paragraphs on the subject in their manual. They found useing the 9mm Parabellum an example that seating the bullet deeper in the case from one of their listed loads COL caused a average rise in pressure of, as I recall, about 6K psi/mm. It can make a big difference in small cased cartridges.

This is not a criticism of your question at all. I'm genuinely curious to know what the advantage of doing such is. I own a .38 spcl and am intrigued by your question.

As long as you verify the Pressure is still Safe as you Seat farther in, there is nothing wrong with doing it.

And of course the only way to check the Pressure is with the always reliable, never fail, venerable old CHE & PRE. Use anything else and you are simply guessing.

In this specific application, PRE would provide the best data. If you got any CHE at all, then the Pressure is too high.

Best of luck to you.

Hot Core, very interesting information!

Red C., a friend and I have been loading down the 38 special and were thinking that with a small load of powder in a big case, that the powder would be inconsistant in ignition, ie. if the barrel was up or the barrel was down before firing. So.. Considered that if the bullet was seated down on the powder, this would always have the powder located near the primer and have consistant ignition thus improving accuracy. Now I'm talking minimum powder charges or less for the 38 special something like min. 38 S%W charges or less.

Use a denser powder.
Actually I would not worry too much about eratic ignition. You can crono the ammo and see if there is a difference. I don`t think it will show any variation in real world performance at handgun range though if any does show though.

BTW Trailboss is reported to work very well in filling large cases and giving consistant velocities. It might be what you`re looking for.

The SAAMI max for 38sp is 17,000 psi.

If we put 5 gr Unique, 158 gr XTP JHP, and 1.55" OAL.

Plug that into 17,000 psi and 53% case fill of powder in the big case.

If the bullet slides down to compress the powder at 100% case fill is 1.25" OAL.

Put that into Quickload and we get 38,000 psi.


I have never tested at 38 sp revolver that would not shoot 38,000 psi loads all day long, and I have tested allot of them.

I have no confirmed data on this subject but will toss out this idea:

The boiler room is the same regardless of the seating depth.....it takes extremely little pressure to push the bullet forward to the lands and there it stops until such pressure is built to force it into the lands and thereafter down the barrel.

So....while I'm not saying this is true, it's my guess that pressure is relatively unaffected by seating depth changes.

Essentially I'm saying that the boiler room is the size (PI R^2) of the case diameter times the distance from the inside rear of the case to the rear of the bullet as it's resting on the lands. Therefore seating depth will not change the boiler room.

comments?????

quote:

Originally posted by vapodog:
...The boiler room is the same regardless of the seating depth...

I think you missed that he is talking about a 38Spl and apparently a Wad Cutter.

With a Wad Cutter Seated "out", compared to flush with the Case Mouth, the area inside the Case behind that Wad Cutter might double(or close to it). Depends on how far out he considers "normal".
-----

Cheap liquor and doughnuts will do it to you every time.

quote:

Originally posted by Hot Core:

quote:

Originally posted by vapodog:
...The boiler room is the same regardless of the seating depth...

I think you missed that he is talking about a 38Spl and apparently a Wad Cutter.

With a Wad Cutter Seated "out", compared to flush with the Case Mouth, the area inside the Case behind that Wad Cutter might double(or close to it). Depends on how far out he considers "normal".
-----

Cheap liquor and doughnuts will do it to you every time.

Re read my post.....I did not mis-read the issue....

Furthermore I didn't make a statement.....I asked a question for discussion.....I'm still of the opinion that the boilerroom is not changed by seating depth!

quote:

Originally posted by vapodog:
...I'm still of the opinion that the boilerroom is not changed by seating depth!

Ahha, then you are simply - Totally Wrong-O!

well then....I'm listening-o!!!

Time out....I'm going to see Marley and Me and will be back later to explain how you're wrong!

I agree totally with Vapodog. Seating depth in itself will not cause dangerous pressure. In fact, in a rifle cartridge it may do just the opposite because, as he pointed out, it takes little pressure to start the bullet moving out of the mouth of the case. By giving it a longer "running start" at the lands and grooves, the bullet will engrave easier than if it were seated out to the lands themselves. Bill T.

controversial issue,
IIRC, my thought is that it does not increase pressure and considering that it is an accepted thought that seating a bullet out further increases initial pressure by not giving the bullet a head start at engraving the rifling, vapodog's argument makes sence also, especially given identical charges of the same powder for either seating depth.by moving the bullet right up to the rifling, you are defining the boiler room's maximum volume and i would think pressure would be the highest with this condition because of the immediate resistance that engraving would introduce to a bullet starting out from a dead stop.....

The longer the bullet is seated the lower the pressure, at small change rate compared to what happens when it sticks into the lands and suddenly acts like it has two more grains.

If the neck is too long or too tight, then you really get some pressure.

What does it all mean?
OAL effect on pressure is subtle, compared to that "running start" effect.

FWIW the Weatherby freebore is just another way of "increasing the boiler room" and thereby lowering pressures and thereby allowing a bit more powder!

quote:

Originally posted by vapodog:
be back later to explain how you're wrong!

FWIW the Weatherby freebore is just another way of "increasing the boiler room" and thereby lowering pressures and thereby allowing a bit more powder!

Trying to think back and I do remember being WRONG one time - I thought I was Wrong, but I was actually Correct.
-----

Ready for your thoughts on how a 38Spl with a Wadcutter Seated flush with the mouth, using normal Powders associated with the 38Spl, has the same Internal Pressure as another 38Spl loaded the same, but with the Wadcutter out 3/8" or so.

Is this some (incorrect)Logic you picked up while sharing doughnuts with your close and personal buddy?
-----

While you are explaining, I'd appreciate it if you would tell me why folks are talking about Rifle Cartridges, Freebore and hitting the Lands when the discussion is about a 38Spl.

quote:

Originally posted by Hot Core:
Ready for your thoughts on how a 38Spl with a Wadcutter Seated flush with the mouth, using normal Powders associated with the 38Spl, has the same Internal Pressure as another 38Spl loaded the same, but with the Wadcutter out 3/8" or so.

Is this some (incorrect)Logic you picked up while sharing doughnuts with your close and personal buddy?
-----

While you are explaining, I'd appreciate it if you would tell me why folks are talking about Rifle Cartridges, Freebore and hitting the Lands when the discussion is about a 38Spl.

The principal remains the same regardless. Something you must take into account is that most all .38 Wadcutter bullets are about as soft of a projectile as you can get. Most are swaged out of pure lead. Therefore the resistance of the rifling is much less than a jacketed rifle bullet. I have taken .38 Special loading data for light target loads and loaded them into .357 Magnum cases with zero ill effects, and no noticable increase in pressure. Yes, I know it's a "no no" to interchange data between calibers, but the load was so mild to begin with, I couldn't see any trouble brewing. There wasn't any. The spent cases literally fell out of the cylinder. About the only time excessive case volume will cause bad things to happen is with greatly reduced charges of slow burning rifle powder in large, overbore Magnum rifles. Even that isn't guaranteed, and is a "sometimes problem" that has never really been fully explained. In the Lyman Cast Bullet Handbook they list a load of 20.0 Grains of Unique under a 552 Grain cast bullet in the .460 Weatherby Magnum. You can't make a much bigger "Boiler room" than that. The load is a pussycat to shoot.

The size of the space left in the case simply doesn't equate automatically to higher pressures. As was pointed out, it will most always lower them. The mention of the freebore in Weatherby factory rifles is actually an excellent example of how to increase velocity without increasing pressure. Rifling resistance will always increase pressure more than too much case compacity, except for the condition I outlined with slow burning powders. Bill T.

quote:

Originally posted by Hot Core:
Ready for your thoughts on how a 38Spl with a Wadcutter Seated flush with the mouth, using normal Powders associated with the 38Spl, has the same Internal Pressure as another 38Spl loaded the same, but with the Wadcutter out 3/8" or so.

Try this:....or maybe you already know the result....

Load a .38 Special with no powder ....only a primer and seat the bullet flush with the front of the case and put it in the revolver and fire it.....where did the bullet wind up?

Warning.....you might want a 5/16 hardwood dowel on hand to dislodge the bullet!

Vs seated at the case mouth, if you push a lead ball down into the case to touch the primer, the expansion ratio, efficiency, velocity, and peak pressure will be higher.

Interestingly, the noise is the same.

Another thought to ponder is Cowboy Action Shooting, which for the most part is done with low velocity lead projectiles. Jacketed bullets are not allowed. This sport was the reason for the development of Trail Boss Powder. This powder has a great deal of volume compared to the powders many shooters were using to establish these loads. Trail Boss basically prevents double charges by taking up enough space in the case to prevent a double charge by warning the loader by having it spill over the top of the case. Still, a lot of CAS shooters still use reduced charges of the more common powders like Bullseye and Unique. All allow for a "bigger boiler room", without any sign of high pressure. Bill T.

quote:

Originally posted by billt:
...About the only time excessive case volume will cause bad things to happen is with greatly reduced charges of slow burning rifle powder in large, overbore Magnum rifles. Even that isn't guaranteed, and is a "sometimes problem" that has never really been fully explained. ...

Hey Bill, I agree with nearly all you said right there. Years(and YEARS) ago one of my Term Papers was on the Secondary Explosion Effect(aka Detonation, aka Pressure Excursion).

Here is an example of where a KaBoom nearly happend in a 223Rem size Case when an Inappropriate Powder was used. I used to support Seafire's Blue Dot Loads, but I no longer do. They have the potential to be way too dangerous, even when it appears everything is OK for hundreds of shots. Then a Pressure Excursion happens due to the Erratic Burning and it either locks a firearm up or creates a memorable KaBoom.
-----

Hey Vapo, I kinda thought you were just messing with me.

I could not imagine you misunderstanding about the Pressure changing with the Case Volume behind the Bullet. Made as much sense as you getting a HSGS and explaining how they are accurate to XX,YYYpsi.

Now "no Powder". You will have some folks going for the doughnuts.
-----

By the way, anyone out there who still doesn't understand how Seating Depth effects Internal Pressure, I'd recommend you run the parameters through one of the Software Internal Ballistics Programs. By doing that you can get an idea of what is happening but... do not take the numbers as gospel. Those Pressure Numbers are provided by a Mathmatical Model of a nonexistant Firing System and can not account for all the Variables we have in our individual firearms.

However, you can see the "Pressure Trend" as you alter the Seating Depth. Nothing tricky about it.
-----

No Powder!

quote:

Years(and YEARS) ago one of my Term Papers was on the Secondary Explosion Effect(aka Detonation, aka Pressure Excursion).

VERY INTERESTING!

Hot Core, would you by any chance have a digital copy of that?



I was developing a very low load for my hornet, using H4227/AR2205. One bullet did not exit the barrel. The noise level was about the same but there was the absence of the bullet strike noise and a slow hiss as the pressure escaped from the chamber. Stuck bullet? Actually, no. It just slid out with a gentle nudge from the cleaning rod. Go figure! (The idea is to have a 'silent' subsonic load with a heavy bullet for better possum killing).

quote:

However, you can see the "Pressure Trend" as you alter the Seating Depth. Nothing tricky about it.

Except for one little detail....the detonation of the primer immediately moves the projectile to the forward most position regardless of the seating depth....thus the boiler room is the same regardless of seating depth.....

quote:

Except for one little detail....the detonation of the primer immediately moves the projectile to the forward most position regardless of the seating depth....

You did say that in your initial post but does the bullet actually stop or even slow down? Pistol powder ignites and burns very quickly and a primer only can lodge a bullet halfway down the barrel. With a rifle, the primer might not dislodge the bullet from the case (correct me here - I seem to think larger cases absorb the pressure. I would go and test it right now but I don't feel like removing a stuck bullet!)

It is likely that there will be some amount of increase in pressure....but not the same as if the lands were also moved with the bullet.

Too bad there's no way to test this as I'm not at all convinced that software can forecast this particular issue....

OK, so I went and tested it!

I used a cast bullet which remained in the throat but left the gas-check in the case mouth. So, with a large enough case like the 303 Brit, the primer does not dislodge the bullet from the case. But I know that it does in a pistol cartridge. (Now to get the gas-check out the case mouth).

quote:

It is likely that there will be some amount of increase in pressure....but not the same as if the lands were also moved with the bullet.

My thinking too. I think there is a point between very deep and very long at which the pressure will be lowest. But this will likely not apply to pistol cases and even less likely with revolver cartridges due to the very long 'free-bore' and forcing cone effect.

Would a fast burning, double base, pistol powder ignite quicker if held tight or if allowed to 'float'?

quote:

Originally posted by 303Guy:
But this will likely not apply to pistol cases and even less likely with revolver cartridges due to the very long 'free-bore' and forcing cone effect.

Good point. Not to mention if a .38 Special is fired in a .357 Magnum, or a .44 Special in a .44 Magnum, etc. You have just increased the "running start" with everything else equal. Bill T.

quote:

Originally posted by 303Guy:
Would a fast burning, double base, pistol powder ignite quicker if held tight or if allowed to 'float'?

I know with slow burning, hard to ignite powders like 2400 it is recomended the cartridge have a very firm crimp to provide uniform ignition. I don't think this is such an issue with the faster burning powders like Bullseye. Bill T.

quote:

I know with slow burning, hard to ignite powders like 2400 it is recomended the cartridge have a very firm crimp to provide uniform ignition

This seems to be true of Lil'Gun in the 22 Hornet. I went the complete other way and reduced neck tension but compresed the powder under a heavy bullet. At reasonably high pressure, the powder ignition became consistant and velocity became respectable as did accuracy. But that powder is very sensitive to case volume and a whole lot of things in the Hornet case including seating depth. I had a load which was producing rapid (and surprizing) barrel heating but with an accidental seating too deep, barrel heating ceased and there was a change in muzzle report and apparent velocity. From that, I increased the powder charge and achieved the same result with less pressure increase than seating too deep. But this did change the degree of compression.

Wow!
In my opinion there are some dangerous comments being made here. In straight walled cases and other cases with high bullet diameter to case volume ratios, small increases in seating depth can dramatically increase pressures. This is easy to empirically demonstrate by keeping powder charge the same and slowly increasing seating depth. Velocities will rise despite a constant seating depth. Hmmmmm, thats funny, where does the extra velocity come from?
In straight walled cases seating depth most definitely determines size of "the boiler". This is especially true with very fast powders. With fast powders often used in rounds like .38 SPC, you can achieve near peak chamber pressures before the bullet even hits the lands. In many revolvers, I suspect that often absolute peak pressure can occur before the bullet hits the lands (long cylinder and throat). To say that the primer instantly blows the bullet into the lands is preposterous. In many cases, a good deal of powder will already be burning before the bullet hits the lands.
MikeN, please be careful with wadcutter seating depth. It plays a huge role in pressure!

Take care,
Wes

quote:

Originally posted by 303Guy:

quote:

Years(and YEARS) ago one of my Term Papers was on the Secondary Explosion Effect(aka Detonation, aka Pressure Excursion).

VERY INTERESTING!

Hot Core, would you by any chance have a digital copy of that?....

The old folks jokes are noted.

That was done way, w-a-y back prior to Personal Computers of any kind. Computers were room size, had MASSIVE air conditioning systems to pull the heat off the "Tubes".

That was when you had to hand write the paper, give it to a young lady financing her way through school by Typing out the papers. Then mark her errors and hand to her for correction. Repeat until it was almost Typo Free and hand it in.

So, no I don't have a copy.

However the information the Paper was derived from can be gleaned from NRA publications from the 1940s through about 1965, plus PO Ackley's Books.
-----

Since addition of Powder to Vapo's premise totally alters the dynamics of the discussion, I don't see where considering the use of a 38Spl without Powder makes any sense.

Do a lot of you folks shoot 38Spls with Primer Power only?

I do have(or had) some of the All Plastic Speer 38Spl Primer Powered Target Plinker "Thingys". You insert a Primer into the Plastic Case as normal, Insert the Plastic Slug and shoot at a Target hung in front of a box of Rags. You have to fabricate "Paper Sights" to compensate for the new trajectory, but they kinda work. Push out the Spent Primer with a nail, recover the Plastic Slug from the box and you are ready to reload them again - no Powder is used.

That is the only use I can think of for a Primer Powered 38Spl, unless you are trying to intentionally lock a firearm up. I'm apparently not "in tune" with doughnut powered thinking.

Can anyone here post a link to an article that shows and explains that seating depth of a bullet alone can and will increase pressure? If not all we are dealing with is opinion, nothing more. Bill T.

quote:

Originally posted by billt:
...all we are dealing with is opinion, nothing more. ...

Hey Bill, Gotta disagree with that. As has been pointed out by WESR, the effect can be seen very easily by watching Velocity.

It can also be easily seen with "PRE" as stated in my first post.

And it is extremely easy to verify either of our "opinions" by simply trying what either of us suggested. No document written by anyone is needed, nor is any Engineering Level Class.

Best of luck to you.

quote:

Originally posted by Hot Core:
No document written by anyone is needed.

Only if you trust opinion. I don't simply because they are like you know what, and everyone has one. I'll repeat. In all of the material written and published on the subject of reloading, can anyone show me any written reference that seating depth alone will increase pressure? It's either written, or it isn't. If it has been it shouldn't be too difficult to find. I have been a reloader for 40 years, and I've never read or seen it in the dozens of loading manuals I have accumulated over the last 4 decades. It would seem if this is such a crutial part of establishing pressure in handloaded ammunition, there would be written reference to it. I would like to see it, if in fact it exists. Bill T.

quote:

Originally posted by Hot Core:

quote:

Originally posted by billt:
Can anyone here post a link to an article that shows and explains that seating depth of a bullet alone can and will increase pressure? If not all we are dealing with is opinion, nothing more.

Hey Bill, Gotta disagree with that. As has been pointed out by WESR, the effect can be seen very easily by watching Velocity .

It can also be easily seen with "PRE" as stated in my first post.

And it is extremely easy to verify either of our "opinions" by simply trying what either of us suggested. No document written by anyone is needed, nor is any Engineering Level Class.

Best of luck to you.

So....let me see here.....does this mean that one can gauge pressure by using a chronoghaph????????????

quote:

Originally posted by vapodog:
So....let me see here.....does this mean that one can gauge pressure by using a chronoghaph????????????

Or the thermometer on your back porch. The hotter it gets, the bigger the numbers! Bill T.

quote:

Originally posted by billt:

quote:

Originally posted by Hot Core:
No document written by anyone is needed.

Only if you trust opinion. I don't simply because they are like you know what, and everyone has one. I'll repeat. In all of the material written and published on the subject of reloading, can anyone show me any written reference that seating depth alone will increase pressure? It's either written, or it isn't. If it has been it shouldn't be too difficult to find. I have been a reloader for 40 years, and I've never read or seen it in the dozens of loading manuals I have accumulated over the last 4 decades. It would seem if this is such a crutial part of establishing pressure in handloaded ammunition, there would be written reference to it. I would like to see it, if in fact it exists. Bill T.

Bill,
If you would simply read the 3rd post in this thread "Ol' Joe" cites a source. I have never seen this written anywhere either. I haven't read anywhere either that dropping an anvil on my foot will hurt. You are right, everyone has an opinion. My 3 yr old has opinions.

Opinions aside, I have already done this sort of experiment on several occasions and know for a fact that in both 9mm, 10mm, and 45acp that with the same powder charge, seating bullets deeper results in higher velocity. From what I remember, the relationship was more than just linear.
Again, the question then becomes "Why the higher velocity?" The answer is the same reason that your loads will shoot faster on a 105 degree day than at 20 degrees. The same reason that coating a bullet with Moly will reportedly decrease the velocity with the same charge of powder. Pressure.
More specifically, velocity is related to (not equal to) the area under the curve for the function of time vs pressure. This is calculus, and I'm not really intellectually equipped to give a thorough explanation of the math. All else being equal (barrel friction, barrel length,etc), velocity is closely related to pressure. This area under the curve concept is useful for understanding the phenomena.
Again, please do not advise to some posters that it in necessarily safe to seat your bullets deeper! Are there any physicist in the room who could explain this better?

Wes

quote:

Originally posted by WESR:
Again, please do not advise to some posters that it in necessarily safe to seat your bullets deeper!

Why?, because you suggest it is unsafe? That's nonsense. There are bullets manufactured that have multiple crimping grooves at different positions along the bearing surface to accomodate the same bullet seated to different levels, so said cartridge can be functionable in different actions. Remington's .45 cal. 405 Gr. Soft Point is one. It can be seated to several different levels with the same exact powder charge. Deeper, to operate in lever actions, which requires a shorter O.A.L., or longer for single shots. The same with many of the 500 Gr. .458 bullets for the .458 Win. Mag. and .460 Weatherby cartridge. Nowhere in any loading manual does it say, or even suggest, higher pressures will be encountered with deeper seating. With personal liability being a greater concern today than ever before, if such a danger existed I'm sure it would be noted. It is not. Stop pressing alarm bells. There is no fire. Bill T.