Measuring distance to lands .308

[fpchief]

I recently had a thread and was determined that i was loading way too hot. Well, messing around with measuring the OAL, i checked again with the hornady gauge and got 2.74. Got that a few times. Doing some research, seems like most folks get around a 2.85-2.95 on their distance to lands. i am using the gauge correctly. I do not have a comparator. At 2.74, the distance is shorter than what i can find as the SAAMI standard for length of a .308 which is about 2.80....any ideas, help?

[fpchief]

BTW, it is a REM 700 5R .308

[mehavey]

It is total dependent on bullet shape.

Case in point:

The 77gr SMK loaded to 2.26" OAL in my AR is 0.020 off the lands
The 52gr SMK loaded to 2.26" OAL in same gun is 0.015" into the lands

What bullet were you using to measure with?

[PA-Joe]

Most people talk about the COL and distance to the lands. The Hornady comparator is measuring the length to the Bullets Ogive. They are somewhat different measurements.

[mehavey]

Measuring Overall Length (OAL) gives you only nose-to-tail distance. It does not indicate where you might be in relation to the radius of the bullet starting into it's actual interference fit into the rifling. If the Hornady/Stoney Point gauge is used to average the overall length of several different bullets (out of the same box /lot of the same bullets), then you can get an average OAL associated with that bullet design engaging the rifling. Because bullets vary, that average may span ~0.003"-0.005" differences, though. That's why it's a good idea to stay an average of ~5-6 thousandths short of that interefence OAL to be sure you're actually off the lands.

...Unless you use a Comparator...

Then you individually seat each bullet by adjusting its individual ogive distance instead of its tip-to-tail distance. This usually is only practical with a micrometer-controlled competition seating die, and then you are probably good to a thousandth or so.

[Unclenick]

Cartridge overall length just guarantees the round will fit in a SAAMI compliant magazine. Since the bullet touches the rifling lands way back a the start of the ogive coming off the bullet bearing surface, it should be obvious a wadcutter would have to be seated to much shorter than a pointed bullet to be the same distance off the lands. Among common rifle bullet styles, the long ogives on VLD (very low drag) designs will be seated longest and round noses will be seated shortest when they are the same distance off the lands.

[mapsjanhere]

Does anyone have a link for that ogive gauge? Would be nice not having to do the COAL measurement for every new bullet.

[PA-Joe]

http://www.hornady.com/store/Bullet-Comparator-Kits/

[mehavey]

-delete-

[mehavey]

Would be nice not having to do the COAL measurement for every new bullet.

If you are seating for a set distance off the lands, you must do a separate COAL measurement for every different bullet you intend to use.

[mapsjanhere]

yes, but it would be nice to be able to do that by determining the ogive contact point, not by having to go through the whole "measure the bullet in the rifle" spiel again.

[dwhite]

I believe the old cleaning rod off the chambered round is the best way to determine distance off the lands. It's a bit of a pain but it works well and is pretty accurate. As throat depth varies rifle to rifle I can't see how you could gauge this accurately unless your gauge is calibrated to the lead in the rifle.

This Hornady Comparator looks like a complicated way of doing the same thing unless you're looking for the ultimate in accuracy and are going to test rounds varying lengths by a few thousandths of an inch.


All the Best,
D. White

[mehavey]

...would be nice to be able to do that by determining the ogive contact point, not by having to go through the whole "measure the bullet....

Even then, each different bullet will contact the rifling at a different location on the jacket.... leading to a different comparator-length reading for the cartridge using that particular bullet.

No free lunch using the comparator -- just more precision.

[TXGunNut]

When I develop a load for a rifle I always include COAL in my load data, except in my book it means comparator overall length. Once I determine the optimum COAL for a given rifle it's a simple matter to try another bullet, will only need a minor tweak if anything.

[F. Guffey]

"seems like most folks get around a 2.85-2.95 on their distance to lands. i am using the gage correctly. I do not have a comparator. At 2.74, the distance is...."

You do not have a comparator but you used a Hornady gage so I will assume you have a Hornady dial caliper.

Off the lands? The 2.800 + or - a few is not off the lands, the 2.800 is the minimum length, finding maximum overall length is up to you some use the 'bullet and dowel' some use the case that looks like a squid, it has a shredded neck, some spend $40.00 or so dollars with RCBS, I drill the flash hole/primer pocket out to a diameter that will accommodate a cleaning rod. I size a case, seat a bullet below the minimum length, chamber the round with out the bolt installed then use a cleaning rod to push the bullet out until it contact the the lands, then remove the bullet/case and call it a transfer for maximum overall length.

After removing the test case/transfer I install it in a shell holder, before raising the ram I raise the seater stem in the die and back off the die lock nut. After partially installing the die, I raise the ram, once the ram is at the top I lower the seater die until it lightly contacts the mouth of the case, after contact I back the die out, reloaders choice) then secure the die to the press by tightening the lock nut on the die. After securing the die to the press I lower the seater stem until it contacts the bullet, once the seater stem/plug contacts the bullet secure the stem to the die with the stem lock nut, that's it! the die is adjusted to seat the bullet to the lands "SORTA" head space is not included because the the case was seated against the shoulder and head space is measured from the bolt face.

Starting over like tomorrow is a new day is up to the reloader, If I am loading for one chamber and I am seating the bullet off the land and I have a off the lands rather than start over every day I save the transfer test case so when I load that particular bullet I use it to set up the seater die to zero off the lands, if I choose to back the bullet off .020 thousands, I use the dial caliper to measure the height of the stem above the seater gage, the height of the stem is zero, to seat the bullet off the lands .020 thousands, I lower the stem .020 thousands, no Horandy ogive tool, no RCBS tool, no comparator.

Yes there is a difference between the distance from the bullet nose back to the round contact area where the bullet touches the lands, for most of my life that is the difference between paying .25 cents a bullet and paying 1.00 dollar a bullet, in the old days everything was relative, bullets did not cost as much then as to day but I had less money to spend.


This method could be time consuming if you purchase bullets in bulk/small lots like 5 at a time but if you purchase bullets 500 to 1,000 at a time, place the transfer/test case in the box with the bullets and use it to zero the seater die. If you think factory, commercial loads, new ammo is a good thing you can match the overall length by using one to to set-up the seater die. Again if you want to play with moving the bullet out, use the height gage/dial caliper to zero the stem then make adjustments.

F. Guffey

[Unclenick]

Fpchief,

Rereading your original post, I think we've taken you off on a tangent. It appears to me you were measuring Cartridge Overall Length (COL, see the right-most dimension on my drawing in my last post, above) and not distance off the lands. COL affects distance off the lands, but it's not the same thing. For COL, many bullets are too short to seat out to 2.800".

Often, lighter bullets have crimp cannelures (see the bullet in my drawing) that are meant to go most of the way into the case mouth for crimping and that will make the round shorter than 2.800" when they do. The Hornady 150 grain FMJ, for example, is supposed to seat in a .308 Winchester cartridge to just 2.780" COL. The Hornady 150 grain BTSP, SP, and SST bullets are supposed to seat to 2.735", about like you got, for the cannelure to line up correctly.

2.800" is just the maximum SAAMI dimension for commercial cartridges. There is no minimum. That maximum is used by manufacturers to ensure cartridges won't be too long to fit in a .308 Win. magazine. It's not required that you meet that number for the ammo to shoot. Shorter is fine.

[Calif-Mini]

I think that the posts here show great attention to detail and exacting distances that are used for seating depths to achieve optimum accuracy.

WOW... I am not this sophisticated but have an idea I want to try and think it can help everyone with this specific task.

I ask all here:

If you were to use an RCBS "Precision Mic" for 308.... try not to scoff yet...... and removed the black simulated bullet, then substituted the exact bullet you shoot by drilling out the base to the 8/32 thread the Mic uses, screw it on with an 8/32 stud, and then use the mic as intended.....wouldn't this show a comparative depth to use or at least a consistent starting point.

I think this can work and be as accurate as any method for each bullet used.

Thanks, Ed

[HiBC]

What I do:Take a fired case from the rifle we are working with.It would be a good idea to decap,but do not resize it.Slightly squash the neck with a vise or pliers.Just a little.The intent is to come up with just a touch of neck tension.
You should be able to just start a bullet with your fingers.Leave it long.
Carefully chamber then extract the round.The rifling will push the bullet in the case to length.Measure the overall length and write it down.You now have a ballpark overall length that will put you at the lands with the ogive.
Pick a clearance you want that will compensate for variables and you have a maximum.Then look at mag box length.You work with the shorter of the two

[Calif-Mini]

Actually that sounds like a simple way to achieve the measurement.

I guess you then just seat to COAL?

By using the RCBS method you can get the comparative distance down on the curve a little rather than on the extreme end which may vary a little.

Either way it will give you something to start with.

Good thinking.

[Unclenick]

Just to be sure the elements of the discussion still aren't speaking at cross-purposes, I cooked up an illustration. The Precision Mic, or else the Hornady LNL OAL gauge + LNL bullet comparator in combination, or else one of the home use methods described above, are used to establish a bullet seating depth at contact with the lands of the rifling in the throat. You can measure the COL that results, then make your loaded rounds whatever amount shorter you think you want to use. Indeed, it is best to fire test rounds with light loads over a range of such depths to find the best seating depth for your bullet and cartridge. Every bullet and cartridge seems to have one or sometimes two particular positions it likes best for accuracy.

All the above assumes you are not using any crimp cannelures on the bullet. If you do, they will fix the COL at a length the bullet manufacturer decided was best for his bullet design in general purpose applications. This is not tuned to any particular rifle.

[F. Guffey]

I recommend a reloading manual, I do not advise disregarding the information/data, when a reloader chooses to disregard the information/data I believe they should be able to explain why (rational).

Minimum Overall length, if you have a copy of Richard Lee's book about modern reloading check the data, he list minimum length after pressure units which comes after velocity FPS.

Backing the bullet up into the case changes the data, moving the bullet out changes the data, and ,as always, time is omitted, for someone to say it does not matter is a good reason to follow the data in the manual. IT is said the reduction of space caused by seating the bullet is the reason a deep seated bullet causes high pressure, if time and travel are related it is possible the time the bullet takes to get to the throat could take longer that it takes the powder to reach peak pressure, so minimum length matters to me.

The difference between minimum length ogive and maximum overall case length ogive can be measured in thousands if one can grasp the term 'relative'.

Drill the flash hole/primer pocket to a diameter of a cleaning rod, size a case, seat a bullet to minimum length, in your case that would be 2.800, remove the bolt, chamber the test round and push the bullet out until it contacts the lands, remove the test case and measure the length again, the difference in the two reading will give you in thousands the difference between minimum ogive length and maximum overall ogive length, but with disregard to the length of the magazine, manufacturers have done just about all they can do to protect a reloader from him/her self. A mindless discussion starts out with a shooter loading for a Weatherby chamber and complaining the box/magazine is too short for his long throated chamber. And the test case can still be used be used as a transfer, transfer? A means of moving one meaasurment from a the chamber (that is dark) to the seater die (also dark inside), and there is the option of purchasing more equipment.

F. Guffey

[Unclenick]

I think Lee's minimum COL is an attempt to make up for being unspecific about the bullet beyond its weight and construction type. For example, in the .308 you could observe his minimum length while loading the Hornady 150 grain SST to its crimp cannelure (2.735" COL), but could not do so with the Hornady 150 grain round nose, whose cannelure is located to get 2.520" COL.

In other words, Lee is indirectly saying his load data would not be valid for that round nose bullet seated as designed. You would need to reduce his charges for it.

By contrast, the bullet maker manuals normally list separate COL's for each bullet of a given weight that they make. The drawback is they also only list one range of powder charges for all that must be safe at the starting end for the deepest seating bullet in the group, shortchanging the performance of the ones that seat further out.

Some days there is just no free lunch.