Can you determine COL to lands if you know the free bore and base to ogive measurement of a bullet? For example, my recently received 284 barrel is supposed to have a free bore of .220". Berger 180 Hybrids have a base to ogive of .803" and the OAL of the bullet is 1.534". My COL to lands ended up being 3.271" (COL to the ogive is 2.540"). I would expect a reamer to extend the case neck area maybe .020" past the trim to length. Then .220" free bore would make COL ogive to lands about 2.400" (2.160 +.020 +.220). I'm at 2.540". How do you do the math?
Calculate COL if free bore is known?
- Thread starter Nomad47
- Start date
Ya don't, The actual variable of your gauge checking bullet too base,,and the actual size of the bore may be different where each contact the specific diameter of the bullet ogive.
Remember, "ogive" isn't an actual place on a bullet that's the same for every make of bullet, it's simply the place that your gauge touches and is specific only to you and the bullet you measure at the time. That measurement only pertains to you.
Trying to rely on your bore and your gauge being exactly the same is "iffy" at best. your much better served to check the bullet in the bore for a measurement and transfer that data to your OAL, and OAL variables.
That's my take on it anyways, I'm a realist and prefer actual physical measurements in a situation like this where the measurement is so easily and readily obtained.
bozo699
Gold $$ Contributor
necchi said:
Ya don't, The actual variable of your gauge checking bullet too base,,and the actual size of the bore may be different where each contact the specific diameter of the bullet ogive.
Remember, "ogive" isn't an actual place on a bullet that's the same for every make of bullet, it's simply the place that your gauge touches and is specific only to you and the bullet you measure at the time. That measurement only pertains to you.
Trying to rely on your bore and your gauge being exactly the same is "iffy" at best. your much better served to check the bullet in the bore for a measurement and transfer that data to your OAL, and OAL variables.
That's my take on it anyways, I'm a realist and prefer actual physical measurements in a situation like this where the measurement is so easily and readily obtained.
I Agree
I have the OAL gauge and the bullet comparators and I always use them to determine seating depth or at least a starting point. I also use those initial measurements to watch for throat erosion. But I was trying to determine OAL ahead of when I actually received the barrel.
So let me re-phrase the question. If I want the shank (bearing surface) of a 180 Berger Hybrid (7mm) to be around .270" in the neck, how much free bore would I order for the reamer?
And as far as ogive is concerned, I've always thought that was the point on a bullet that contacted the lands. In other words, on a 243 caliber barrel, for example, which has a groove diameter of .243" and a land diameter of .237", the ogive would be the location on the bullet where the diameter was .237". I could measure the I.D. of my bullet comparators to see if that is actually the case.
So let me re-phrase the question. If I want the shank (bearing surface) of a 180 Berger Hybrid (7mm) to be around .270" in the neck, how much free bore would I order for the reamer?
And as far as ogive is concerned, I've always thought that was the point on a bullet that contacted the lands. In other words, on a 243 caliber barrel, for example, which has a groove diameter of .243" and a land diameter of .237", the ogive would be the location on the bullet where the diameter was .237". I could measure the I.D. of my bullet comparators to see if that is actually the case.
What is known? The first known, for me, is the length of the chamber from the bolt face to the shoulder of the chamber, when determining the distance from the bolt face to the shoulder I find ‘the go, no and beyond gage’ nice but not helpful. What else is known, (should be known)? The two diameters of the barrel, the two diameters of the 30/06 is .308 and .300, somewhere between the two diameters of the barrel is the point the bullet will contact the rifling, considering the difference between the two diameters is a tapper/bevel cut the contact means the contact point is short. For reloaders that do not use datums and are limited to just talking about datums as being a line and as a results are required to purchase their equipment, as in “I use the Hornady...etc.. or the Sinclair etc.. Me? I make gages.
Going the other way as is measuring the length of the case from the head of the case to the contact point (difference between the two diameters)...use datums or make a transfer, use the transfer to set-up the seater die, no Hornady tool, no Sinclair tool.
And I am a fan of getting all the bullet hold I can get.
F. Guffey
Going the other way as is measuring the length of the case from the head of the case to the contact point (difference between the two diameters)...use datums or make a transfer, use the transfer to set-up the seater die, no Hornady tool, no Sinclair tool.
And I am a fan of getting all the bullet hold I can get.
F. Guffey
Bullet jump
« Reply #13 on: 10:19 PM, 11/12/11 »
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“Just wondering how you guys determine your bullet jump. I have read about sizing the case lightly for low bullet tension and smoking the bullet to see where it touches. This method just seems inaccurate like i am jamming the bullet in the rifling, or my extractor is pulling the bullet to the side and rubbing off the smoke-soot. should I be making the bullet too long and letting the bolt push the bullet in the case to get my measurement?â€
Sizing the case neck lightly, smoking, jamming the bullet and the extractor pulling the bullet? I remove the bolt, I do not shred the neck, it is not necessary to smoke the bullet and or case and I am the fan of of all the bullet hold I can get.
I drill the flash hole/primer pocket out to a diameter that will accommodate a cleaning rod, I then size the case, after sizing the case I seat the bullet I am loading for, the COL must be short enough to prevent the bullet hitting the rifling.
After seating the bullet in the test case I remove the bolt, chamber the test case then with a cleaning rod I push the bullet out until it hits.contacts the rifling, once the bullet contacts the rifling there is no advantage in jamming the bullet further into the rifling. Once the bullet stops I remove the test case, with bullet hold it is not likely the test case will give a false reading.
Once the test case is removed it becomes a transfer, to transfer the chamber measurements to the press/seater die back the seater stem off to prevent contact with the bullet, back the die off to prevent contact with the test case then install the test case/transfer in the shell holder and raise the ram, once the ram is raised lower the seater die until it contacts the case, once contact is made back the seater die off/2 turn then secure the die to the press with the lock nut, after securing the die to the press lower the seater stem until it contacts the bullet, once the seater plug/stem contacts the bullet secure the seater stem to the die.
After the stem is secured to the die measure the height of the stem above the die, the height of the stem when measuring off the lands is .000, after measuring the height of the stem calibrate the dial caliper .000. To seat a bullet off the land .020 lower the stem .020 (then secure the stem with the lock nut). To prevent starting over when making adjustments record the stem height above the die (again then calibrate the dial caliper to .000.
Again I an not a fan of jamming the bullet against the rifling, I am a fan of the running start, I want my bullet to have a jump/running start, because? Time is a factor.
F. Guffey
« Reply #13 on: 10:19 PM, 11/12/11 »
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“Just wondering how you guys determine your bullet jump. I have read about sizing the case lightly for low bullet tension and smoking the bullet to see where it touches. This method just seems inaccurate like i am jamming the bullet in the rifling, or my extractor is pulling the bullet to the side and rubbing off the smoke-soot. should I be making the bullet too long and letting the bolt push the bullet in the case to get my measurement?â€
Sizing the case neck lightly, smoking, jamming the bullet and the extractor pulling the bullet? I remove the bolt, I do not shred the neck, it is not necessary to smoke the bullet and or case and I am the fan of of all the bullet hold I can get.
I drill the flash hole/primer pocket out to a diameter that will accommodate a cleaning rod, I then size the case, after sizing the case I seat the bullet I am loading for, the COL must be short enough to prevent the bullet hitting the rifling.
After seating the bullet in the test case I remove the bolt, chamber the test case then with a cleaning rod I push the bullet out until it hits.contacts the rifling, once the bullet contacts the rifling there is no advantage in jamming the bullet further into the rifling. Once the bullet stops I remove the test case, with bullet hold it is not likely the test case will give a false reading.
Once the test case is removed it becomes a transfer, to transfer the chamber measurements to the press/seater die back the seater stem off to prevent contact with the bullet, back the die off to prevent contact with the test case then install the test case/transfer in the shell holder and raise the ram, once the ram is raised lower the seater die until it contacts the case, once contact is made back the seater die off/2 turn then secure the die to the press with the lock nut, after securing the die to the press lower the seater stem until it contacts the bullet, once the seater plug/stem contacts the bullet secure the seater stem to the die.
After the stem is secured to the die measure the height of the stem above the die, the height of the stem when measuring off the lands is .000, after measuring the height of the stem calibrate the dial caliper .000. To seat a bullet off the land .020 lower the stem .020 (then secure the stem with the lock nut). To prevent starting over when making adjustments record the stem height above the die (again then calibrate the dial caliper to .000.
Again I an not a fan of jamming the bullet against the rifling, I am a fan of the running start, I want my bullet to have a jump/running start, because? Time is a factor.
F. Guffey
I am also a fan of getting all the bullet hold I can get. And that is why I am a little disappointed with the barrel I just received. I had two choices and chose the .220 free bore. And what I've got is .203" of the shank contacting the neck when the 180 Hybrid is touching the lands.
I am starting out at .020 off the lands as I prefer to "jump" and that gives me .223" of shank contact. I would prefer more.
I am starting out at .020 off the lands as I prefer to "jump" and that gives me .223" of shank contact. I would prefer more.
Nomad....the neck length on a .284 is aprox. .285 ,,,,soooo I usually try to stay .035" above that to avoid the "donut" area.....so that gives a "useable" neck length of .250"....if you are jumpin .020 with .223 of shank your ok ...and ,,,can even jump .040 if the gun likes it,and be shanked in .240".........with all the various bullets in 7mm it is difficult to find a do all FB....with your set up the 180 class (VLD-SMK-Hybrids) are optimum...things sound "just rite" to me....Roger
PS...your not robbing case capacity by shovin em wayy in either.....
PS...your not robbing case capacity by shovin em wayy in either.....
All this math would also have to include the leade angle that the particular chambering reamer cuts. The most common leade angle is 1 degree 30 minutes, but there are others being used. Another advantage of buying your own reamer spec'ed. to the dimensions/ bullet seating depth, chamber neck dia. etc. that you want, not some one-size-fits-all. Ditto for what bozo699/ Wayne said. 
Thanks, Guys, for all the info. Good points, expiper. I'm definitely above any potential donuts. And I'm pleasantly surprised with more case capacity than I was expecting. I am going to have to buy new ammo boxes 
these 180s are too long for 'short action' boxes.
BTW, anybody know if I can get .020 or .030 off the lands with 162 AMax's - and still keep the bullet in the case?
these 180s are too long for 'short action' boxes.BTW, anybody know if I can get .020 or .030 off the lands with 162 AMax's - and still keep the bullet in the case?
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