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  #1  
Old 07-20-2010, 03:09 PM
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Headspace on the Bullet,


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I borrowed this picture from UncleNick and posted it on another forum. The question was asked, "what OAL for a 45 ACP LSWC", so I put up this picture.
I got spanked by the local reloading guru and I wasn't sure how to reply.
Here is some of what he said about this method of determining OAL.
Using the barrel as a gage is OK but do not allow the cartridge to headspace on the bullet. That is NOT OK! The pictures posted by steve4102 indicate it is OK (headspace on the bullet, third choice from the left) and that does not agree with major reloading companies reloading manuals.
In no case should you ever allow the cartridge to headspace on the bullet. That is not OK. The bullet needs some run on engaging the rifling. With out that run the bullet stalls in its exit from the case and the fast rising pressures can become too high. While it may not blow up the gun it may do a number on the case, or blow the primer out of the case and into your face (hot primers on the skin are not conducive to smooth skin!).
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Old 07-20-2010, 04:00 PM
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Is an advanced loading tecnique is all. Good tools and measurements required. Past that, is pure phisics.

Gotta be carefull when you get to the edge of a cliff. The last step is a "doosey".

Just be carefull with what you do.

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  #3  
Old 07-20-2010, 04:29 PM
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the odd thing is that, with loads reduced enough to reliably cycle the action, using the bullet to headspace is exactly how may of us tried to get the .38 super to shoot worth a hoot. Do have to realize wree using 135-140gr. SWC and loads reduced until reliable cycling was achieved (so were way-way under max), but the results were good enough to keep us doing it for years (or until chambers were made to headspace from the case mouth).
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  #4  
Old 07-20-2010, 04:48 PM
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I have never understood how a cartridge can be made to headspace on the bullet. I've never inquired either. So....how does it work? Does the bullet touch the rifling and the rifling provides the stop? It seems that would have to be the case as there is nothing else there to engage the bullet.
What about pressure then?
Does this apply to all bullets or only to lead? What is the advantage to this as opposed to headspacing on the mouth of the case? In fact, in a .45, the case is going to headspace on the mouth no matter what, if it is within spec, isn't it?
Pete
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Last edited by Pete D.; 07-20-2010 at 04:50 PM.
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  #5  
Old 07-20-2010, 05:47 PM
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Works perfectly with lead bullets, and frankly I don't see the harm with jacketed bullets in the .45 ACP. Low pressure pistol rounds are a world apart from, say, the .300 Weatherby.

I'd say the person complaining about it is exposing their ignorance.....
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  #6  
Old 07-20-2010, 05:51 PM
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Lead SWC (with the traditional sharp corners) bullets only. Seated out until the sharp edge of the SWC is jammed into the start of the rifling (helps to use .001" over groove diameter), which if seated uniformly, will give more uniform headspace than the dinky semi-rim. YES, it does raise pressure significantly, but in the .38super's example, were loaiding to the MINIMUM that would give (1) reliable functioning and (2) good accuracy. Just basically chunking those 140's out there at about 830fps.


Modern .38supers are often chamber-cut to use the end of the case for headspace rather than rely on that rinky-dink semi-rim.

-------
Back in the ancient days, some would buy .351WSL barass and trim it back until it headspaced on the end of the chamber. Kind of a .38 1/2 super as the cases would all end up a bit longer than .38supers. Same rules, MINIMUM loads, just enough to cycle and give good accuracy.
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  #7  
Old 07-21-2010, 01:46 AM
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Ok

Quote:
Lead SWC (with the traditional sharp corners) bullets only. Seated out until the sharp edge of the SWC is jammed into the start of the rifling (helps to use .001" over groove diameter),
Thanks. I'll have to give this a try with a box of .45s. I'm wondering, though, about the net effect......what advantage is there? I understand the rationale for the .38 Super but getting the .45 to shoot well isn't the issue. Gaining an advantage one way or the other is.
I'll hafta try.
Pete
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Old 07-21-2010, 05:47 AM
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If you measure, you'll probably find that not a single piece of .45 ACP brass in your inventory is at even minimum length. Yup, they'll ALL be short. So how then do we headspace on the case mouth as intended?

Usually, we don't.

Unless you headspace on the bullet itself, the round will headspace on the extractor. That will be the only thing holding the round in place against the firing pin strike. The good news is that it usually works just fine - but it does depend upon a properly cut extractor hook, a good strong extractor spring and a properly cut and undamaged case rim.
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Old 07-21-2010, 07:02 AM
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With lead bullets you should have a lower start pressure than jacketed. That can cause problems with powder ignition.

Not only will raising the start pressure a bit potentially help the powder burn more uniformly, it also helps seal the bore and prevent powder gasses from getting past. Should reduce leading in the barrel as well.

Like Rocky says ya gotta headspace on something.....
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  #10  
Old 07-21-2010, 12:14 PM
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Steve4102,

What your Guru posted is stated by loading companies so the load tables in their manuals remain valid. But seating bullets touching or even jammed into the throat is how most all benchrest shooters used to load before they figured out at least a little space gave better accuracy. Middleton Tompkins (more gold medals than anybody else) still loads with land contact for himself and his family of international champions. The only caveat is that because this practice does raise pressure 20% or so, you need to develop your maximum loads with the bullet in that position and not rely on the load manuals to apply. Touching the lands only becomes dangerous if you've worked up a high maximum load in your gun, then you change the seating to that touching position without dropping the load and working it back up. Even then, it will still likely be within the proof pressure range unless the maximum you worked up was already above normal SAAMI maximum.

Lead bullet loads are typically well below maximum. What you will find, headspacing on the bullet as I showed in position three, and as I have done with all my many tens of thousands of cast bullet target loads since the mid 1980's, is that accuracy will be increased and leading will be reduced. This is because the touching bullet is aligned with the bore when it fires. Because, as Rocky said, .45 ACP cases shorten rather than stretch with each load cycle, most .45 ACP loads headspace on the extractor. This tilts the cartridge slightly to the side when the firing pin strikes, and since lead bullets are soft, they just swage into the bore at that new angle. This makes them scrape lead against the throat entry, contributing to leading, and it throws their center of gravity off so they wobble in flight, opening up groups. For swaged lead 185 grain SWC's, for example, I got about 40% reduction in group size off bags by switching from standard COL to headspacing on the bullet. This was with 3.8 grians of Bullseye, fired in an accurized Goldcup.

Here are a couple of examples to quantify the effect. Below is a measured pressure from RSI's site of a bullet both on and 0.030" off the lands. 3 traces touching the throat and four set back.




Here's a plot adjusted for reading error from a 1965 study of pressure where only 10% difference occurred relative to the lowest pressure seating depth.



Note that in the above, a round nose bullet was used. It allows more gas bypass than most pointy shapes, so closing in on the lands made a more gradual seal. Note also that pressure grows when you seat too deeply, which is also a pressure hazard to keep an eye on.
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Last edited by unclenick; 07-22-2010 at 06:23 AM. Reason: typo fix
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  #11  
Old 07-21-2010, 04:54 PM
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Thanks everyone, I appreciate the help.
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  #12  
Old 07-27-2010, 03:29 AM
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Steve4102,
A very long time ago, a Master Pistol Shooter took me aside and told me I was having dinner at his house that week end and to be there at 0800hrs. With dinner that night came a day long session at his loading table. It was he who introduced me to seating bullets, for the M1911 A1. since that day I've loaded enough.45 ACP to make a pile I couldn't see over. At 6'7" that would be a BIG pile. The key is to seat bullets so the face of the case is even to the end of the barrel shroud as shown in the illustration. POINT #2, DON'T FORCE THE ROUND INTO THE CHAMBER!!!!!!!!!!!!!!! You're not interested in showing how strong you are, you're interested in seating depth. Or you should be. I have never had a single problem from it. My serious load is 5.1--W231-200 GR Hornady HP/XTP-CCI Primers used in a Colt Combat Commander. Accurate and works fine. Hope this helps.
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