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Old January 30, 2011, 08:09 PM   #1
k4swb
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Bullet Seating Depth vs. Pressure

Since I started reading the forums I have given a lot of thought to bullet seating depth. I never worried too much about it before, I just used what worked in my guns. The round must fit the chamber, magazine and not fall out when handling.
I decided to do a test on one of my .45s. I used some Ranier’s 200 gr. PSWC, Hornady 185 gr. XTP, Oregon Trail 200 gr. SWC and some Berry’s 200 gr. PHP bullets.
I took ten of each and seated them to the absolute maximum that would function in my handgun meaning they would chamber without touching the rifleing, feed through the magazine without hanging up and the bullet wouldn’t fall out while handling.
I also took ten each and loaded them as deep as I could. I decided the depth must leave enough of the bullet body out of the case to get a taper crimp on it. On the hollow points there isn’t a lot of wiggle room. Too deep and you run out of bullet body. On the other end of the HP you get to where you don’t have enough grip to hold the bullet in the case. With the SWC style you can have a fairly large difference between absolute maximum and a minimum of where the case is almost off the bullet body. I found it to be well over .200” in my gun.
Powders used were WST, W231 and Unique. All loads were at maximum and in some instances a little more because I know what works in my guns.
Off to the range I went.
I don’t have a pressure instrument and have to rely on a few years of judging pressure signs by looking at cases and primers. Firearm was a Ruger P90.
After firing all the rounds and carefully inspecting the brass afterwards my conclusion is, in MY gun there really isn’t any reason to even consider seating depth as regards to pressure. As long as the round functions it appears to be safe in MY gun. All the cases/primers looked pretty much alike without ANY primer flattening or case bulging and felt recoil was not noticeable.
I did notice that the longer rounds appeared to be somewhat more accurate but I had expected this from other tests.
While I was at it I ran a much smaller sample through my fairly new Taurus 24/7 OSS DS .45. Same results.
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Old January 30, 2011, 10:15 PM   #2
bullspotter
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Would be nice to get some crono results with this test, the 45 is a somewhat of a low pressure round, it may allow for some changes like you did, however i wouldnt do it myself, I like to work up loads if i change anything like seating depth or bullets with different bearing surfaces. Pry a good thing you didnt use a 40 to run your test.......... May not have been so lucky with your max and over max loads with that large of a change in seating depths. Personaly I think .20+ seating change with a max load or over could get very nasty in a hurry, 2nd I think what you did was unsafe, and stupid, and i truly hope you are never next to me at the range...... I also truley hope you dont think you can all ways get away with this kind of thing now because your few years of looking at cases and primers for pressure sighns and found NONE made it seem like everything was ok, bullet seating depth can creat a large pressure swing........ If you think that it dosent because of your test you are wrong, sooner or later you will find out how wrong you are in a bad way......
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Old January 30, 2011, 10:54 PM   #3
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I had a small lot of IMI 45ACP brass that would not hold a 230gr Golden Sabre securely, occasionally the bullet would be set back further in the case during the feeding process. I did noted that felt recoil was a bit stiffer too at times, I eventually traced it back to IMI cases having thinner brass at the mouth. This particular lot was pulled down IMI and sold by Midsouth, I went back to R-P brass and solved the problem. A lot of what we do is learn by doing, never assume anything, always follow your manual and do not substitute components. + 1 for bullspotter!! William
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Old January 30, 2011, 11:10 PM   #4
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k4swb, it's an interesting project and test idea you've had here, but I worry that you are making some pretty wild conclusions with horribly small data and evidence. As was mentioned by bullspotter, you did this with a relatively tame cartridge in .45 Auto. Try it with 9mm (high pressure) or .40 S&W (high pressure combined with less meat around the chamber) and you could be picking brass shrapnel from your face & hands and magazine guts off the ground. Further, you also used a pretty stout .45 Auto pistol for the tests.

Again, it's an interesting and compelling tests... but you didn't even have a chrono. I appreciate the thread and the post, but I hope that you don't use your results as firm conclusions that you can translate to other chamberings.

Seating depth differences is something I always keep in mind but I don't have any accurate way to come to any firm conclusions. Sadly, after reading your findings, I'm not even one inch closer.

W.T.W., I have found myself with so darn many different headstamps in .45 Auto, I keep mental notes of what I like and what I don't care for. Heck, in all my different calibers, actually. And though I only have a few pieces of the IMI .45 Auto brass you mention, I found exactly, exactly the same thing. No reliable grip on my bullets. Checking for case mouth tension in my semi-auto handloads is something I do religiously and the few pieces of IMI .45 brass showed me that it's brass that I herd and recycle. I won't reload the stuff.

But I think it's worth mentioning... even though I use my fair share of R-P brass in .45 Auto and other calibers, I also find R-P brass to be some of the thinnest in the case mouth also. I won't bother to list the dozen-plus different head stamps I regularly use across many different handgun calibers, but I have no doubt, none whatsoever, that R-P brass is amongst the thinnest in most calibers.

It's not junk brass, it doesn't give me cracks or failures or short life... but I don't get as much case mouth tension with it that I get with other head stamps. And when I flare the case mouth and when I seat bullets, I can easily feel less resistance in the operation compared to most other brass.
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Old January 30, 2011, 11:13 PM   #5
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9mm is a much higher pressure round, and published OAL's can vary from 1.010" to 1.169". With certain powders, a 0.020" reduction in OAL can result in a substantial increase in pressure.

I second using published data including seating depth (which normally will have to be calculated since manuals list OAL instead).

Running a few different scenarios in QuickLoad will show you just how fast you can get into trouble.
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Old January 31, 2011, 11:12 AM   #6
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I appreciate the comments and everyone's concerns, even the guy that said I was stupid.
As I stated, this was done in 2 of MY .45s. I did not recommend anyone else to try this. Normally I load to a seating depth that is the longest that will function through my mags, fit the chamber and have a decent grip on the bullet. I was just curious what would happen with the bullet seated to deeper than standard depth and I found out, in two of MY .45 ACPs. Nothing.
One day this spring I may try it again with the chronograph setup and see what that shows.
There was a reason I chose the .45 ACP. Easy to work with and fairly low pressure.
If anyone wants stick to the absolute published data then that is the way for them to go. I sometimes choose to experiment with components and can't always find exactly the combination I wish to use. I always start with something that seems really low and work from there. When starting with my WSL load I started with something that didn't function the gun but did exit the bbl and when I was through I had a fantastic shooting load. When the book data finally caught up they were right with me.
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Old February 1, 2011, 07:01 PM   #7
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From your above post it sounds like you are on the right path. Makes sense to me.

As a precaution when seating and crimping bullets test an occasional cartrige by firmly pressing the bullet on the bench to see if the bullet will set back.

Best of luck and skill with your endavor. Eagle
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Old February 1, 2011, 07:56 PM   #8
k4swb
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By now I can pretty much look at a crimp and see if it will be OK. Haven't had a bullet set back in a very very long time.
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Old February 1, 2011, 08:48 PM   #9
Brian Pfleuger
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QuickLoad suggests that a load of 8.0gr Unique under a 185gr Hornady XTP seated to 1.275 will produce a 45acp max load at 20,728 psi.

That same load, extended to 1.375 predicts just 16,064 psi.

Same again, seated to 1.175 predicts 29,921 psi.


Proof pressure for the 45acp must be something like 27,000psi (30% over pressure).


That tells me that a known safe max load of unique under a 185gr bullet in 45acp can be pushed to proof pressures with just a .010 difference in seating depth. Experimenting in that realm with pressure test instruments and/or remote firing mechanisms seems foolhardy to me.
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Old February 2, 2011, 02:23 PM   #10
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There is some evidence that certain powders are more pressure sensitive than others.

Likewise, as has been said, 45acp is a lower pressure round to start and the guns typically are built sturdier than those for certain other calibers.

Ken
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Old February 2, 2011, 05:02 PM   #11
k4swb
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What I'm trying to convey is that if you start load development you usually start with somewhat low powder charges. At starting levels I have never even considered seating depth other that for functionality in my guns. If a starting load were to show ANY signs of pressure with any reasonable seating depth and I wanted to continue to use this seating depth all I really need to do is back off the powder charge slightly, but I've never had this happen. There is a larger leeway in seating depth than most people on the forums realize. As long as the round functions all the way from the press to the chamber you can adjust pressure with powder charges. Go watch a benchrest match. Loaders are throwing all kinds of charges without a scale in sight and changing seating depth to suit themselves and not consulting specs anywhere. The proper seating depth for MY handguns is anywhere that will keep the crimp on the bullet body with enough force that the bullet does not fall out of the case and fit the magazine and chamber. This is the first thing I determine whan working up loads and I do not consult a manual for this. Only then do i even get into powder charges.
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Old February 2, 2011, 05:57 PM   #12
Brian Pfleuger
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Quote:
Originally Posted by k4swb
What I'm trying to convey is....

Interesting, because what you actually said was the opposite of that....

You stated that you can seat bullets at ANY depth with MAX loads.


Now, you are trying to convey that you can start at any length with MINIMUM loads and it will be perfectly safe.



What you said in your first post is dangerous and foolhardy. What you said in your last post is almost "Reloading 101". Pretty opposite statements, IMHO.


Oh, and the loaders at benchrest shoots are not haphazardly loading rounds with any charge and length they decide on at the moment. I guarantee you that they have used those charges and lengths enough to know what is safe and what isn't. At least the smart ones.
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Old February 2, 2011, 08:04 PM   #13
k4swb
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Quote:
Interesting, because what you actually said was the opposite of that....

You stated that you can seat bullets at ANY depth with MAX loads.

Interesting, because what you actually said was the opposite of that....

You stated that you can seat bullets at ANY depth with MAX loads.
Actually what I said was I could seat the bullets to any depth I wanted to IN MY TWO GUNS. In my guns I saw no pressurure signs. I never said anyone could do this in just any gun. Bullet seating depth seems to be something that alot of new loaders get hung up on. If you look in a manual they will list just one OAL for each bullet with numerous powder charges. This seems to confuse alot of loaders when in reality it is just another variable and should not be consider etched in stone.

When one BR shooter looks over at another and asks how many clicks he's set at on his powder measure and then dials that in on his, he has absolutely no idea what charge weight that is and they do this quite often. He MAY have a ballpark idea but that is it.

One other thing to consider, If anyone thinks that someone actually loaded every bullet/powder/seating combination listed in a manual and then fired it they would be badly mistaken.
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Old February 2, 2011, 09:22 PM   #14
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Your statement of there is a larger leeway in seating depth then most people on the forums realize is a bad one. This must only be true in YOUR GUNS i guess. I have seen more then one gun come apart, mostly due to squibs that the shooters were unawair of, and 2nd is bullet setback. And of couse the overcharge.

I love how you state you can pretty much look at a crimp and see if it will be ok, after somone talked about the bench test, you must have robo eyes, you do know that crimp often (not always)has little to do with holding the bullet in a streight wall pistol case (like .45-9mm .40 ext)VRS case tension on the bullet right. Im sure that you also know brass can get springy over time and not size down properly, thus causing poor case tension on the bullet, causing a bullet set back no matter what the crimp looks like. I guess only your eyes will see that, mine sure dont.

Look at the data Peetza posted and tell me nothing was differnt in your testing with the loads you fired, just because your few years of judging pressure signs by looking at cases and primers found nothing, dosent mean that something was not changing. I asure you something was changing, you may have not felt it, or saw it, but it was their. Maybe they were all safe in YOUR magic guns, maybe not... But to get on here and Tell people their is a larger leeway in seating depth then most people realize is just not true. we dont all have your guns!! LMAO

Lastly reread my 1st post (#2) and point out to me were i said YOU were stupid. Thanks.....
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Old February 2, 2011, 09:32 PM   #15
k4swb
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Quote:
Lastly reread my 1st post (#2) and point out to me were i said YOU were stupid.
I'm pretty sure I never mentioned anyone's name or anything specific at all in reference to the stupid remark.

I'm really enjoying the replies to my original post. I'm finding out that alot of reloaders, both old and new evidently never think and examine what they are really doing when they reload. They just look in a book or jump on the forums, get a recipe and if it goes boom they call it a day. Reloading to me got boring years ago by dong just this and I started experimenting with different and sometimes not listed powders and other component combinations. Others may never get to the point that they know enough and are comfortable doing this and that is all good for them. To the uninitiated it may sound like what I did was dangerous but I assure you it was not.

Last edited by k4swb; February 2, 2011 at 09:40 PM.
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Old February 2, 2011, 10:16 PM   #16
wildphilhickup
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Interesting - data?

"bullet seating depth can creat a large pressure swing.."

I have NEVER heard of this. Is there data out there that supports this?

I have been reloading for a little over 35 years. Probably around 2 million + rounds.

I would be interested in seeing the data / physics for this.
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Old February 3, 2011, 06:41 PM   #17
bullspotter
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Wildphil, look at post #9 by peetza, shows a load with changes in pressure by adjusting only the seating depth. pressure spike may also happen if the round is to long and the bullet is jammed in the lands, causes a high start pressure because the bullet dosent get a jump start before it gets resistance from the lands.

4761+ rounds a month for 35 years is alot of reloading!!!!!
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Old February 3, 2011, 11:59 PM   #18
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I've read the same thing about pressure spikes with seating depth. Its pretty easy to understand, the smaller area the gas has to expand in, the higher the pressure, but in reverse, the closer the bullet is to the lands the less room it has to "jump" and build up speed so pressure spikes there as well. At least thats what I got out of it.

While looking up data on my weatherby .308 I read that its got a deeper throat so theoretically the bullet needs to be set in shallower so theres less jump and the bullet has a better chance to go in center, instread of slighly off. This would supposedly give you better accuracy. Since I'd already found a load I liked (I think it was 42.2 gr of viht 150 under a 168 gr v-max with hornady match brass and CCI primers) I decided to test this out. I made up batches of 5 (I always test in batches of 5) slowly going out from max AOL until just before the bullets touched the lands (i used a dummy round that was seated WAY out found out the max length I could). I then hooked up my CED at the range and tried it out. Checking my numbers for deviation and checking the brass and primers.

I felt safe doing this in the weatherby because of the "3 rings of steel" and the blow off vents built in. Also its a bolt action.
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Old February 4, 2011, 09:53 PM   #19
wildphilhickup
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Predictions & Facts

Quickload suggests / predicts - but that is not reality.

Referring to pistol loads, not rifle, regardless of the seating depth, with a given "acceptable" powder charge, you will NEVER exceed Max Pressure.

Yes, between 1984 - 1994 I was reloading ~20,000 rounds per month.

THANKS!
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Old February 4, 2011, 09:57 PM   #20
semi_problomatic
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thats alotta bullets
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Old February 5, 2011, 09:54 AM   #21
Sevens
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Commercial ammo supplier?

You weren't also shooting all that ammo yourself, were you?
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Old February 5, 2011, 10:37 AM   #22
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That'd be like having to replace your barrel at least twice a year!
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Old February 5, 2011, 03:14 PM   #23
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"Prediction vs data"

For those of you who doubt that small reductions in COL can produce large increases in pressure when loading small, high-pressure pistol cartridges, I offer the following quote from Speer Manual #10 (page 349):

Quote:
"But, more important, loads that produced 28,000 cup went to 62,000 cup when bullets were purposely seated 0.030" deeper!"
That sentence was based on pressure MEASUREMENTS, not calculations.

Interestingly, I have not been able to reproduce that result with CALCULATIONS made using QuickLOAD. So, those of you who think that the "predictions" may be OVER-stating the effect should really be worrying that the predictions may be UNDER-stating the effect.

Anyway, the effect is surely real, and completely consistent with known physics and chemisty of combustion.

The idea that you can tell when a low-pressure cartridge like the .45 ACP is going well over the SAAMI pressure limit by looking a the fired case or primer is just plain wrong. Those same primers are intended for rounds that are loaded to 45,000 cup. And, cases don't necessarily fail before the guns with some of those low-pressure cartridges, either.

If you really want to experiment with this type of thing (which I do), then I suggest that at a minimum, you should be using QuickLOAD, a chronograph, and learn how to measure pressure rings of fired cases using a micrometer. And, you need to be skeptical about what differences you can really see in your measurements of different loads, considering the normal variations that occur in all of your measurements when you try to load identical rounds. That takes some knowledge of statistical methods.

In reloading, just experimenting with something without understanding what is really happening and then saying "I did it and it didn't hurt me" is about like saying "I am standing in the highway during rush hour and I haven't been hit." People can just keep saying it until it's no longer true, and then it's too late. So, I don't think those statements are helpful, except for telling me which reloaders to NOT shoot beside.

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Old February 5, 2011, 03:33 PM   #24
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QuickLoad uses a powder burning model.

Stray to far from the data used to build and verify the model and other affects can show up.


All models are wrong.

Some models are useful.
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Old February 5, 2011, 04:06 PM   #25
SL1
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Quote:
QuickLoad uses a powder burning model.

Stray to far from the data used to build and verify the model and other affects can show up.

Agreed!

The trouble is that you can very easily stray from the data and not know it when you adjust QuickLOAD parameters. The well-known limits on reductions of H-110/W-296 and the use of small charges of slow powders with light bullets in bottleneck rifle cartridges are no where to be seen in QuickLOAD.

Quote:
All models are wrong.

Some models are useful.
Agreed!

QuickLOAD is best used by first matching the data for your cartridge in the manuals that you have, THEN seeing what changes in seating depth, etc. have on your pressures BEFORE you try them out in your gun. And, of course, when you do try them out, it is instructive to note when the results start to differ from your QuickLOAD predictions, because that is a pretty clear sign that you are getting into an area where the model is significantly wrong. There are some pressure-tested load data that I cannot match with QuickLOAD - - for example Lil'Gun in the .357 Magnum cartridge. So far, I have resisted the urge to use that powder for that reason. There is also Brian Pearce's experience with chronographed velocities going DOWN with increased charges of H-110 in the .357 Magnum, which QuickLOAD cannot predict.

Wouldn't it be nice if we could all afford piezo-electric pressure measuring equipment and the test barrels to use it? Oh, wait, there is also that quote from a Speer manual that says they modified a revolver to allow piezo pressure measurements, and the pressure curve in the revolver looked a LOT different than the pressure curve for the same loads in the test barrel. So, I guess we are ALL somewhat in the dark when it comes to what pressure is really doing in OUR particular guns.

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