Alright, stupid question: Various books and posts and such give OAL measurements. However, it is concluded by most (or many) that measuring to the ogive is more accurate than OAL. So, how does one know what the ogive measurement should be for any particular projectile, since only OAL is listed? I have previously posted about variance in OAL and learned that while my OAL varied, measurement to ogive was within +/- .002. When I measured various projectiles, I found varying lengths of up to .015. So, I use the ogive. But,....I have no data to determine what that measurement should be.
- Thread starter flhtci2006
- Start date
Use the Hornady tool to measure the jam depth on your chamber, then take that measurement, and adjust your seating die to duplicate the measurement. You will find, that very small (.003") changes do affect the accuracy, as well as the pressure.
if you are currently loading an accurate round. load one that is correct c.o.a.l. and then save it and buy a hornady ogive comparator tool to measure the bullets as they are produced. it will help get you very consistent loading measurements.
Something else to note here.
Comparators are not all the same. So someone saying their BTO measurement here and then finding that yours doesn't match their measurement when in theory it should can be due to using different comparators. So just keep your method consistent with the one you end up using and take everyone else's measurements with some caution if you are trying to reference anything from posted seating depths etc.
Comparators are not all the same. So someone saying their BTO measurement here and then finding that yours doesn't match their measurement when in theory it should can be due to using different comparators. So just keep your method consistent with the one you end up using and take everyone else's measurements with some caution if you are trying to reference anything from posted seating depths etc.
Books give a maximum OAL because it is a minimum standard by which you can know that that length will fit any common manufacturer's magazine. There has to be a standard maximum OAL length for that reason. That's all it's good for. If you happen to have a longer magazine or single load, then your only limits are the freebore and/or the minimum seating depth of the bullet in the case. Sometimes there's a compromise. I can get better accuracy out of a load that won't fit in my magazine, but I want to use the magazine, so I have to load shorter to accomodate. But, once that is established, I always use length-to-ogive measurements for die setup.
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The comparator tool is invaluable.
However, in some rifles like my 5R with a huge throat you can't load to the OG or the bullet will just fall out of the brass.
In that case you load as long as your mag will accommodate.
However, in some rifles like my 5R with a huge throat you can't load to the OG or the bullet will just fall out of the brass.
In that case you load as long as your mag will accommodate.
Okay, I gave too little info. I have the Hornady comparator. And like SMSchulz, if I load to the lands on my AR15, the projectile will fall out. As I recall, the jump distance is .140. For those with cannelure, (H2267) I set the length so I crimp with maybe 50 to 75% of the cannelure exposed. This is, an OAL of about 2.235 and I think base to ogive was 1.865 (can't remember). But, for the Sierras (1390), there is no cannelure. Since the ogive is located different than the H2267, I can't use the same base to ogive measurement from the H2267. COAL for the 1390 is I believe .050 more than the H2267. I guess my main issue, is for projectiles without cannelure, how do I make sure of proper seating, since the chamber won't give me any true info. (note: for my hunting bolt rifle, I use the chamber measurement and set for a jump of about .004. For the AR, can't do.
If you're shooting 1 at a time off a tray, then maximum the length to the ogive or seating to or in the lands is a good way to keep it the same; However, if you're shooting from a magazine, develop your best load based on the magazine length round. I like the longest length possible. It will most likely be different powder weight than your one at a time feeder loads, but consistency is what you're after.
A field ready rifle doesn't need to be finicky.
After you have that load working, Take measurements for that bullet , and record it for future reference. Sometimes the ogive and COAL don't stay the same as bullet manufacturers replenish their stock.
A field ready rifle doesn't need to be finicky.
After you have that load working, Take measurements for that bullet , and record it for future reference. Sometimes the ogive and COAL don't stay the same as bullet manufacturers replenish their stock.
I modified a FL sized case by dremeling a slit through the neck. The bullet then slides more easily and just enough to still have some retention on the bullet so when you extract the case, the bullet stays at the depth where the lands are contacted. The black marks were from using a sharpie to verify previous depths.
OP, I just ran across this 2 part article and I thought you might find it interesting.
http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/
It does a good job of explaining ogive and the various methods used to determine it.
http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/
It does a good job of explaining ogive and the various methods used to determine it.
This indeed is an excellent article. Thank you. Now, if reloaders would give the CBTO as part of their load data, it would really help, as COAL is general at best.
OP, You may need to re-read the article. Specifically section "measuring, recording, communicating CBTO."
CBTO is specific to a rifle. Also, gauges are not standardized and if someone were to give a CBTO for their .308 it may be maxed at 2.21. But another rifle may and probably does have a different max length.
CBTO is specific to a rifle. Also, gauges are not standardized and if someone were to give a CBTO for their .308 it may be maxed at 2.21. But another rifle may and probably does have a different max length.
In addition, communicating CBTO to another person with a different distance to the lands causes pressure increases in the chamber as the bullet is seated near the lands that the reloader needs to be aware of.
