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Old November 19, 2014, 01:32 AM   #1
Willkk
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COAL

I am new to reloading and have some questions. I have loaded some rounds (30-06) at standard length per the Lyman manual at 3.2 in. After reading about accuracy and overall length, I made a gauge by taking a case fired in my rife and cutting to slits on opposite sides of the neck with a Dremel tool so that a bullet slides easily. After clambering this cartridge I read with my calipers 3.311 3 consecutive times. So the questions:

1. Is this makeshift gauge suitable

2. The consensus for how far to back off the lands in a hunting rifle seems to deviate depending on who you ask. 0.010 or 0.025? Suggestions?

3. I have loaded with 48 grains IMR 4064 as a startling load on my standard length cartridges. I have read that If I extend the length should I expect lower pressures and velocity but if I extend to the lands I will get more pressure and velocity. This needs clarification for a new reloader. Is this relevant only if I extend to where the ogive touches the rifling? If I extend to -0.10 or -0.025 should I use less or more power to safely compensate?

Thanks
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Old November 19, 2014, 02:53 AM   #2
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I normally back off .025 . I use a COAL gauge, but have used the same type method you are using now before, and it works out the same for me. Generally you run into pressure spikes the deeper you seat the bullet in the case. As long as you are working within the range of charges listed for the bullet and powder you are using you shouldn't have to worry about backing off your load. Rule of thumb is start low and work up in .5 gr increments. I don't have my notes with me right now for .30-06 but I use IMR4064 and IMR4350 for .30-06. Hope this helps.
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Old November 19, 2014, 11:23 AM   #3
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Sensitivity to jump is dependent on the bullet as well as other factors. Secant ogive bullets often don't like a lot of jump, but you find all this out by experimenting. Often, makes little difference but .02 is about where most start.

Seating to touch the lands does increase pressures as the bullet can't/won't leave the case under low pressure as it would otherwise if allowed a "jump".
With bullets that don't like jump this is often done, but one really needs to look for pressure signs if doing this close to max load.
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Old November 19, 2014, 11:36 AM   #4
Bart B.
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Your makeshift gauge will work.

For hunting ammo (as well as combat stuff) cartridge length has to be what feeds most reliable from the magazine.

Bullet jump to the rifling will increase as the bore wears out. It may increase 1 or 2 tenths of an inch, which, for hunting purposes may not be a problem and it's still good enough for combat in service rifles. Match grade 30 caliber rifles have their throats erode away increasing bullet jump to the rifling 1/10th inch from where it started when they're no longer accurate enough to use. Yet they still shoot 1/3 MOA at 100 yards, 1/2 MOA at 300 and well under 3/4 MOA at 600. I've seen my bolt guns' throat erosion increase 1/10th inch and observed no visible change in accuracy through 200 yards and barely any at 300.

If you want to seat bullets a couple thousandths shallower every couple dozen rounds to keep the bullets jumping about the same distance to the rifling, go ahead.
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Old November 19, 2014, 02:50 PM   #5
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Quote:
Originally Posted by Willkk
…I made a gauge by taking a case fired in my rife and cutting to slits on opposite sides of the neck with a Dremel tool so that a bullet slides easily. After {chambering} this cartridge I read with my calipers 3.311 3 consecutive times. So the questions:

1. Is this makeshift gauge suitable
Yes. It's an old standby method. Three pointers for making it work best:
  1. Seat the gauge cartridge by removing your bolt and pushing the cartridge into the chamber with a dowel rod or your pinky until it stops against the headspace determinant (shoulder, belt, whatever). This will position the cartridge where the firing pin will push it and therefore at the actual position at which COL matters. If you don't do this and chamber and extract with the bolt, the friction between the bullet and neck will see to it that the case head is back against the breech face. This adds any extra headspace you may have to the COL final number.
  2. Eject the gauge cartridge by holding the gun horizontal (cleaning cradle works fine and is close enough) and using a cleaning rod to push it out by the bullet nose. This prevents the bullet sticking in the lands and being pulled out of its original position, which is a common problem with this type of gauge. Same with the RCBS Precision Mic's companion gauge.
  3. Many bullets have some amount of length variation, some over 0.010". So you want to take calipers and find several identical length bullets in your box and use these to gauge and then to set up your seating die to get a matching result.

Quote:
Originally Posted by Willkk
2. The consensus for how far to back off the lands in a hunting rifle seems to deviate depending on who you ask. 0.010 or 0.025? Suggestions?
This distance is a tuning factor individual to the chamber and bullet and powder combination. There is no correct amount except the one that works best in your gun. The more this is looked into, the more rules of thumb and pet distances off the throat seem to get thrown out the window.

For example, Berger used to suggest, as Tobnpr did, that secant ogive bullets should be loaded very close to the lands if not actually jammed into them. They eventually got so much feedback from people whose rifles did not shoot their secant ogive bullets well that way, but that did shoot them well seated deeper—sometimes a lot deeper—that they now recommend differently. They suggest working up a best accuracy load with the bullet jammed 0.010" into the lands. Once you have that, you seat the bullet deeper by 0.030" and 0.060" and 0.090" and 0.120" and see if any of those shoot better. If so, go through working up the best powder charge again to tune the group tightness in.

In another version of that, in the 1995 Precision Shooting Reloading Guide, Dan Hackett described a 220 Swift that he could not get to group tighter than 3/8" (a big group for a benchrest shooter). He was seating the bullets 0.020" off the lands, as he always had believed was best. Then one day, in changing bullets to a Nosler Ballistic Tip, he accidentally turned the micrometer on the seating die the wrong way and wound up seating 20 rounds 0.050" off the lands instead of 0.020". Rather than pull them down, he decided just to shoot them in practice. To his amazement, these rounds that were "too far off the lands" gave him two 5-shot 1/4" groups and two bughole groups in the low 1's. So much for the universally "best" seating depth.

Quote:
Originally Posted by Willkk
3. I have loaded with 48 grains IMR 4064 as a startling load on my standard length cartridges. I have read that If I extend the length should I expect lower pressures and velocity but if I extend to the lands I will get more pressure and velocity. This needs clarification for a new reloader. Is this relevant only if I extend to where the ogive touches the rifling? If I extend to -0.10 or -0.025 should I use less or more power to safely compensate?
Below is a graph of actual pressure measurements done in the early 1960's by Dr. Lloyd Brownell for a round nose bullet started out touching the lands and seated progressively deeper.



What Dr. Brownell believed explained this was that as the bullet goes deeper into the case the jump to the throat gets longer, giving gases more time to bypass the bullet and start up the bore in front of it. Only at the pressure minimum does the pressure decrease resulting from that bypass cease to dominate the pressure term, and the fact the deeper seated bullet is tightening the powder space starts to take over as the dominant term, and pressure begins to rise again.

I note that with pointed bullets, seating deeper opens the bypass space around the bullet more quickly than the gradually tapered sides of a round nose rifle bullet normally do, so the drop can be sharper. Below, with kind permission from Recreational Shooting Software owner, Jim Ristow, you see a 20% pressure drop occur when the bullet first tested touching the lands, then again seated 0.030" deeper and further off the lands.

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Old November 19, 2014, 05:34 PM   #6
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Here is another way to check COAL using a dowel rod. With the bolt closed and cocked to keep the firing pin from protruding, insert a dowel rod down the barrel until it contacts the bolt face. Now make a fine pencil mark at the junction of where the dowel rod exits the bsrrel. Rrmove the dowel rod, open or remove the bolt, and using a finger or empty case hold a bullet in the chamber back against the rifling. Now with the bullet held against the rifling, reinsert the dowel rod until it contacts the tip of the bullet. Make another similar pencil mark at the junction of dowel rod and end of barrel. The distance between the two pencil marks is the COAL with the bullets seated lightly against the rifling. Then proceed accordingly to make any COAL changes as desired or required for loading in the magazine.

Last edited by condor bravo; November 19, 2014 at 06:54 PM.
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Old November 21, 2014, 12:22 AM   #7
Willkk
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Wow. Thanks guys. That's alot of good info. I loaded 4 up at 3.291 in (.020 from lands) and went to the range today. I put a starting load of 48 grains IMR 4064 as per the Lyman manual. I also loaded 4 at 48.5 grains, and 4 at 49 grains. I sighted in with 10 rounds of the starting charge but standard COAL of 3.2 in. These grouped at about 1" at 100. Not bad, it looks like the new bed job did the trick. As these were my first hand loads I checked for signs of over pressure and saw none. I then fired the 4 rounds I made with the same charge but at a COAL of 3.291 in. These grouped very well, my guess is 3/4 inch but when I checked the case I noticed the primer was definitely flatter and some signs of cratering around the firing pin. It was nothing major but I am new to reloading and not quite sure where the line is drawn at high pressure and too much pressure so I am to gun-shy (pun intended) to fire the 48.5 and 49 grain loads. How much is too much? I'll put pics up tomorrow, but is that abnormal to have this happen at starting charges?
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Old November 21, 2014, 09:47 AM   #8
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WillKK

You were wise to monitor for signs of overpressure in your loads.

I didn't see any indication of what bullet weight you were using
Your powder loads could be OK or you might be too aggressive depending upon what bullet you're loading for.

Bullet weight is important and some bullets have longer stems (base to ogive lengths that could be set into the neck) so case capacity and max loads are generally limited by the bullet compressing the powder. Lighter bullets tend to have shorter stems and leave more case capacity for powder without resorting to compressing the powder. Compressing powder generally leads to slightly elevated pressures while seating the bullet out towards the rifling tends to slightly reduce the pressure. It all depends upon how much space is available for gas to expand before the bullet leaves the neck.
Setting the OAL out to where the bullet touches the rifling causes the pressure to sharply peak because the bullet resists moving it the rifling when there is still resistance from the stem still being stuck in the neck. I would recommend that you avoid seating the bullet out so it touches the rifling.
Being at least 0.020 off the rifling is a pretty good recommendation, especially if you are not measuring every round as you load it.

For a 150 grain bullet, the Sierra manual say max load is 52.1 for IMR 4064.
For 165 grain and 175 grain bullets, it says 48.7 is the max load for IMR 4064.
Interestingly, for the 168 SMK bullet, it says 51.3 is the max load for IMR 4064 (case powder capacity before compressing the load is impacted by the bullet length and recommended seating depth).
For a 190 grain bullet, it says that 46.6 is the max load using IMR 4064.
For a 200 grain bullet, it says the max load is 45.4.

The Sierra manual is a bit conservative but all of their data is based upon actual tests. Berger's new manual on the other hand is based upon calculated max capacities. Hornady's manual if very conservative, and Nosler's is closer to Sierra in values but their bullets have different dimensions.
The Lyman manual is a compilation of data from other sources - they don't do any testing - and some of their sources are pretty old.
Older data tends to be a bit more aggressive. I tend to shy away from Lyman's max data.
I generally use Sierra data and powder manufacture's data (who also do their own testing) and only use Lyman references with a lot of caution.
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Old November 21, 2014, 10:35 AM   #9
AllenJ
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Quote:
1. Is this makeshift gauge suitable

2. The consensus for how far to back off the lands in a hunting rifle seems to deviate depending on who you ask. 0.010 or 0.025? Suggestions?

3. I have loaded with 48 grains IMR 4064 as a startling load on my standard length cartridges. I have read that If I extend the length should I expect lower pressures and velocity but if I extend to the lands I will get more pressure and velocity. This needs clarification for a new reloader. Is this relevant only if I extend to where the ogive touches the rifling? If I extend to -0.10 or -0.025 should I use less or more power to safely compensate?
1. Yes, you've made a good gauge. I've done the same thing minus the dremel cuts and got accurate results.

2. I don't think you're going to see a huge accuracy improvement by adjusting your seating depth in a hunting rifle from what the reloading manual recommends. That is a bold statement, especially since I don't even know what rifle you have or what bullet you're using, but it has been my experience with my hunting rifles using Nosler, Sierra, Speer, Hornady, and Barnes bullets. Your results may differ though, testing is the only way to find out. I would find the most accurate load using the book recommended COAL, then do test loads with that powder charge while moving the bullet out .010-.020 at a time.

3. See Unclenick's post (#5).
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Old November 21, 2014, 08:17 PM   #10
tobnpr
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Quote:
They suggest working up a best accuracy load with the bullet jammed 0.010"
Thanks for that post...I looked up their article on this, and I'm going to try it on the two we use with VLD's.

When they refer to "jamming" it ten thousandths into the lands, not sure I understand the mechanics of that.

When using a modified case and comparator, we're seating the shoulder of the case in the chamber, then pushing the bullet out until it engages the rifling.

Say ten thousandths is added to the base-to-ogive measurement as suggested, and we seat the bullet accordingly and chamber the round.

As I'm seeing it, doesn't this just prevent the shoulder from seating against the chamber wall as it normally would- holding the entire case back ten thousandths?

Closing the bolt, we'd then be forcing the case neck into the leade since ten thousandths of clearance just isn't there between the case base and the boltface. I'm of the apparently incorrect assumption this would be noteworthy of careful consideration because we're crimping the case neck around the bullet, and contributing more to a pressure spike. If there's light neck tension, how do we know we didn't just end up seating the bullet deeper into the case?

In my Savages I set headspace directly from the SAAMI "go"gauge at first, then to fireformed brass. There's NO room behind that case head... (I'm using the practical definition of headspace, not the technical one of base to datum for this discussion). In other rifles, there could be a couple of thousandths to as much as eight thousandths for the .308 as an example- but it varies- so wouldn't the distance we're forcing the bullet into the rifling be the net of whatever's left after we've reduced boltface to case head clearance to zero?

What am I missing here? My head hurts...
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Old November 21, 2014, 10:24 PM   #11
Bart B.
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Case mouths are not crimped into bullets seated to set back a bit. Unless the case length is the same as chamber length; bolt face to chamber mouth. The bullet seats deeper in the case while the firing pin drives the case shoulder hard against the chamber shoulder.

Not a problem over many decades of thousands doing it.

The distance between case head is called 'head clearance' and it can be zero.
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Last edited by Bart B.; November 21, 2014 at 10:29 PM.
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Old November 22, 2014, 09:15 AM   #12
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OK, so let's assume there's room for the case neck to move forward in the chamber.

Then, it comes down to the force required to push the bullet further into the case mouth (neck tension)- versus, the force required to push it into the rifling.

Apparently, it doesn't take much force for the latter- even with only .001 neck tension, the bullet won't move in the case when doing this?
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Old November 22, 2014, 10:11 AM   #13
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I've closed bolts very hard on military 30 caliber ammo requiring 40 to 50 pounds of force to move their bullet in their case necks using short throat chambers. Bullets seat back several thousandth as well as rifling grooves a few thousandths deep on their ogives.

My soft seated 30 caliber bullets need only 5 or so pounds of force to move them in case mouths. They seat about .010" deeper when chambered and the rifling only lightly marks them.

I use the pounds of force needed to move bullets in case necks. A given difference between case mouth and bullet diameter yields different amounts depending on case-bullet friction, case hardness and seating depth.

My 30 caliber resized case mouths are a thousandth or so smaller than bullet diameter when used for single round loading. Case necks sized down in the die that's .002" smaller than loaded round neck diameter enlarge a bit coming out of the die. I think it's best to express the popular "neck tension" term to the difference between the sized neck diameter to what it is after the bullet is seated. That's reality. And soft brass has less grip on the bullet than hard brass for the same difference and bullet seating depth.
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Old November 22, 2014, 01:15 PM   #14
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So if I understand you, you are saying that if the bullets have light neck tension (which is pretty common), it's possible that one might not be jamming the bullet, and instead seating it deeper in the case?

Easy enough to find out, I'll try to find time to experiment with this and see what happens. I don't have bushing dies (yet), so I have no idea what my average neck tension might be with a FL sizing die. I'm curious to see what the result is.
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Old November 23, 2014, 04:02 PM   #15
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That's correct. It is what soft-seating is. I first learned about it in a long range class given by Mid Thompkins years ago. He described the neck tension as enough to hold a bullet in place, but said that he could still force it deeper with his fingers. He loaded this way for himself and his whole family of long range National and International champions.

If you don't soft-seat and just go for jamming the lands, as Bart said, typical normally loaded .308 bullet has around 50-60 lbs pull, and that matches the seating force pretty well. It's hard to grasp a bullet and exert that much force with finger tips alone, if you've ever tried. This is why we have bullet pullers. But that force is nothing compared to the force it takes to fully engrave a bullet in rifling. Harold Vaughn measured this on a hydraulic press with a load cell and got around 1200 lbs slowly pushing a jacketed bullet into the rifling with a ram. So, the amount of jam you get into the lands does depend on bullet push/pull force, but it will always be overcome long before you have complete engraving. A 1.5° degree throat taper is common, and that angle has a tangent of .026. So if you seat 0.010" forward of where the bullet first kisses the lands, the resulting engraving will only be 0.00026" deep, or about 1/15 the height of 0.004" lands.

1/15 of 1200 lbs is about 78 lbs. But that ignores the complication of the mismatch between ogive radius and throat angle that engages at one part of the bullet first. Typically you'll find the front edge of the contact marks have that 0.26 mil engraving, but the back end is just a scuff. So the actual force is probably about half that, or about 39 lbs. That's close to how far you can drive a bullet in before you start seating it deeper. Also, keep in mind that the necessary force is not all from push on the bolt, either. The camming action of the bolt lugs are what seat it to the deepest point of the engraving as you lock the bolt closed. So the shooter's perception of the effort will mainly be that he feels some added resistance just before he starts turning the bolt handle down. But that's about it.
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