I am struggling to find a bullet/load that will shoot consistently in my .223. I'm using a Hornady OAL Guage to help determine what my seating depth should be and I have a couple questions about using this guage.
1. When trying to determine the distance to the lands, I get different measurements with different bullets. I thought this measurement should be the same with all bullets. Am I wrong and should the measurement be different with different bullets?
2. If the measurement should be the same with all bullets, then I must be varying the pressure that I am pushing (light) the bullet into the lands. How much pressure should I use? And, how does one be consistent?
3. How far off the lands should I seat the bullets as magazine length is not an issue? I ask that because the 60 grain bullets are flat base and are seating in way past the shoulder neck junction and I'm sure compressing the load. That's based on the current measurement of my OAL Guage.
4. What's the lightest bullet that should work in a 9" twist .223 barrel?
I know there might be a lot more issues causing poor groups, but I want to concentrate on this first.
Thank you in advance.
Steve
1) Cartridge base-to-ogive measurements (CBTO) can differ with different bullets. One reason for this is because the seating die stem contacts the bullet well out on the ogive toward the meplat (tip) when it pushes the bullets down in the neck during the seating process. However, the caliper insert tool we use to measure CBTO seats much farther down the ogive (nose) very close to the top of the bearing surface. Different types of bullets, and even bullets from within the same Lot number can differ in the distance between these two critical contact points, thereby introducing variance into the measurements. A second reason is that the ogive radius of different bullets will not be the same, and thereby the diameter of the noses will not be the same at various points along the ogive. When the bullet is seated out in the throat at "just touching" the lands, the contact point on the ogive is just slightly above the full diameter of the bullet (i.e. caliber, or bearing surface diameter). Thus, different bullets will seat closer or farther out in the case depending on the ogive radius of the bullet.
2) I generally start any new bullet at .015" off the lands for charge weight testing. Most of the different bullets I use generally shoot "ok" there, if not necessarily "optimally". More importantly, their seating depth optima almost always lie somewhere between .003" off the lands, and .030" off the lands, which is the seating depth test range I typically start with. Obviously, .015" off the lands in close to the middle of this range, so that I'm not moving the bullet in/out more than half the total seating depth range during the seating depth teasting. In my hands, moving a jumped bullet only .015" in either direction is not usually enough to cause a great change in effective case volume, pressure, or velocity. By seating bullets to the middle of the test range, you can minimize having to go back and tweak the charge weight again because you changed the seating depth
after the initial charge weight testing enough to markedly alter pressure/velocity.
3) I start all the bullets I use jumped (off the lands) for a number of reasons. If I am not satisfied with their performance when jumped, I can always go back later and test them seated into the lands. So unless I know for certain that a specific bullet wants to be jammed, I won't start there. If loading to mag length isn't necessary in your case, I'd measure the distance to "touching" and use that as my baseline or zero measurement. Anything
longer than "touching" would be "jammed" by such and such a distance, anything
shorter would be jumped by such and such a distance. If the bullet is too short to reach the lands and still have sufficient shank left in the neck to hold it effectively, then obviously you'd be forced to start it seated farther away from the lands to get enough bullet shank into the case neck.
4). Some have had success with bullets as heavy as the Hornady 75 gr BTHP or the 77 gr Sierra Matchking in 9-twist barrels. However, they would be the very upper limit you might get away with, and they aren't a sure thing in every 9-twist barrel. Something more in the 40-69 gr range would be optimal, bullets in the 70-73 gr testable as "maybes".
Use of the Hornady OAL gauge seems give a lot of people fits. I have always found it very straightforward to use, but not everyone feels the same. I use the Hornady OAL gauge as follows: I place a bullet in the neck, loosen the set screw, and allow the push rod to slide back until only about half of the bullet nose is visible (i.e. the bullet is seated deeper in the case than it will be at "touching"). First, I insert a cleaning rod that will reach the chamber from the barrel muzzle end, and pull it back enough so that a bullet just touching the lands won't hit it (i.e. interfere with the correct measurement). Then, I insert the case into the chamber with my left hand (I'm right-handed), holding the tool by the collar at the end of the shaft that has the set screw. I maintain slight pressure to keep the case solidly in the chamber, then slide loosen the set screw with my right hand and slide the pushrod/bullet out until I feel the very slightest "touch". I maintain very slight pressure on the pushrod so as not to jam the bullet into the lands, then tighten the set screw sufficiently to hold the pushrod at the proper position.
NOTE: don't over-tighten the set screw, as the pushrod is plastic and it can create a permanent dent in the groove in the pushrod that may make future measurements in that area difficult. Then I reach around the rifle and use the cleaning rod to gently push the entire assembly back out; then I use calipers to take the CBTO measurement.
IMPORTANT: The freebore of the chamber is the part in front of where the end of the case neck seats where the lands have been removed. The longer it is, the longer a bullet you can seat in the neck without having to jam it into the rifling. On a rifle with a generous freebore diameter, let's say about .0005" over bullet diameter, the bullet will slide in easily until the ogive just barely touches the angled front edge of the lands as they ramp up to their full height (i.e. the "throat"). However, some rifles may have a freebore diameter that is only a few ten thousands over bullet diameter (at least on the reamer print). I mention this because my .223 bolt rifles all fall into this category. When I use the Hornady OAL gauge with these rifles, the bullet is actually tight in the freebore, or "lead" section of the chamber and they don't always slide easily until "touch" is felt. Sometimes you have to apply a little more pressure to get the pushrod/bullet moving again in the tight freebore and it can make accurate measurement at "touching" more difficult. If too much pressure is used, it is hard to stop the bullet/pushrod exactly at touching without jamming the bullet into the lands a few thousandths, or even more. The longer the freebore is, the more difficult the measurement.
Nonetheless, the best way is to simply practice with a single bullet, over and over and over, until you develop a feel for taking the measurement properly, and can generate the exact same measurement repeatedly. I can't imagine such practice should require more than 5 or 10 minutes before you start to get a good feel for the approach and how the tool works.
Finally, you will likely receive a variety of responses on how to use the Hornady OAL gauge, or possibly even other methods. I won't comment on those as I do it exactly the way I described above for a number of reasons. Nonetheless, you can try different approaches and decide what you think works best in your hands. Any/all can work, but it is important to eventually pick one and stick with it in order to obtain consistent measurements over time.
