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Posted: 3/28/2010 6:07:40 PM EDT
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I just built some loads for my brothers .308 with my comparator from Hornady, which I will be testing, not him, so no worries for him. But I am using a much longer cartridge than listed in Nosler's manual. Now here is my question:
When I seat the bullet out further, does it make a huge change in pressure? I am working below the max load, I am using 44 grains of RL-15 and the MAX charge is 46 grains of RL-15. My average of 10-sizings with the comparator was 2.304 from the ogive to the base. To build my loads I back 10 rounds down to 2.285 and then moved 10 more to 2.295. All measurements are from the base of the cartridge to the ogive of the bullet. Again, I don't know how many of us here use comparators, but this is my first go around with it and I want to make sure I am not setting myself up for something bad. Thanks in advance for any help. |
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When I seat the bullet out further, does it make a huge change in pressure? . Maybe, seating into the lands can cause higher pressure. Scroll down to "From the Lab". http://www.barnesbullets.com/resources/newsletters/september-2007-barnes-bullet-n/ |
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Quoted:
I just built some loads for my brothers .308 with my comparator from Hornady, which I will be testing, not him, so no worries for him. But I am using a much longer cartridge than listed in Nosler's manual. Now here is my question: When I seat the bullet out further, does it make a huge change in pressure? I am working below the max load, I am using 44 grains of RL-15 and the MAX charge is 46 grains of RL-15. My average of 10-sizings with the comparator was 2.304 from the ogive to the base. To build my loads I back 10 rounds down to 2.285 and then moved 10 more to 2.295. All measurements are from the base of the cartridge to the ogive of the bullet. Again, I don't know how many of us here use comparators, but this is my first go around with it and I want to make sure I am not setting myself up for something bad. Thanks in advance for any help. Sir, comparators are called comparators because they allow the user to compare one dimension with another. What your actually trying to accomplish when using a comparator is the distance from the ogive of the bullet to the throat of the rifle chamber. You cannot make this comparison without also knowing the rifle chamber dimensions. Cartridge overall length (OAL) is important because you want to make sure it will fit into the chamber of your rifle. The amount the bullet protrudes into the lands and grooves of the rifling will definately cause the ignition pressure to elevate by some amount but the first step in determining what the best cartridge OAL is to determine the depth of the throat of your rifle chamber. There are a number of devices for measuring this dimension including Hornady which now markets the Stoney Point gage, but a cheap and simple method is to blacken the ogive of your bullet with soot or a magic marker and feed the cartridge into the chamber of your rifle and close the bolt (all safety precautions apply). Once you can see that the throat of the rifle chamber is engaged onto the bullet you can measure the OAL and adjust your seating depth accordingly. Generally speaking most bullets will shoot best when seated between .005" and .010" away from the throat of the rifle. This isn't always true, some secant ogive bullets like to be engaged into the rifling but that's a whole 'nuther subject. The other consideration you should determine is the magazine length of your rifle. For most of us that like to load more than one round into the rifle at a time the maximum length of cartridge that will fit into the rifle magazine becomes important. Even a bolt action rifle will have a limit on the length of cartridge that will fit into the magazine so you'll want to check that dimension to determine what your max cartridge OAL should be. HTH, 7zero1. |
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Yes, I am using a Hornady L-N-L gauge. Sorry for the mix-up. I am just wondering about how the pressure is affected inside the casing. Sir, generally speaking pressure will increase as the bullet becomes seated into the lands and grooves (throat) of the rifle. Since I don't have any actual means of gaging the pressure increase I can only say that pressure increases somewhat based on my comparison of fired cases between those fired with the bullets seated into the lands and those with the bullets seated away from the lands. In my experience seating the bullet into the lands allows me more volume inside the case to add powder. You can do this but be very careful. Some powders don't like to be compressed at all, and some shoot better with no compression at all. HTh, 7zero1. |
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Lawle, I have the same setup and measuring tools as you. It is my impression that Hornady gauge will allow you to know how far to set the bullet so it will contact the lands and grooves of the barrel. What you want to do is minimize the "jump" of the bullet - because it results in an increase in inaccuracy, but at the same time back off a bit to reduce the increase in chamber pressure that results from a bullet being in the lands and grooves.
.01 to .005" is the distance of the ogive to the lands and grooves I use to determine my COL. |
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Lawle, I have the same setup and measuring tools as you. It is my impression that Hornady gauge will allow you to know how far to set the bullet so it will contact the lands and grooves of the barrel. What you want to do is minimize the "jump" of the bullet - because it results in an increase in inaccuracy, but at the same time back off a bit to reduce the increase in chamber pressure that results from a bullet being in the lands and grooves. .01 to .005" is the distance of the ogive to the lands and grooves I use to determine my COL. Sir, while I don't entirely disagree with your comments, it has been my experience that different bullets have different "sweet spots". That is to say for example: A Sierra 77gr SMK will shoot well at magazine length given over .100" from the throat where a Sierra 80gr. SMK will shoot well loaded much closer to the throat at .010" away. The JLK 80gr VLD shoots best in my experience when loaded .030" into the throat. In my humble opinion the purpose of having the gage and varying the seating depth is to allow the reloader to experiment with different dimensions of seating depth to determine what combination works best in his rifle. 7zero1 out. |
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Quoted:
Quoted:
Lawle, I have the same setup and measuring tools as you. It is my impression that Hornady gauge will allow you to know how far to set the bullet so it will contact the lands and grooves of the barrel. What you want to do is minimize the "jump" of the bullet - because it results in an increase in inaccuracy, but at the same time back off a bit to reduce the increase in chamber pressure that results from a bullet being in the lands and grooves. .01 to .005" is the distance of the ogive to the lands and grooves I use to determine my COL. Sir, while I don't entirely disagree with your comments, it has been my experience that different bullets have different "sweet spots". That is to say for example: A Sierra 77gr SMK will shoot well at magazine length given over .100" from the throat where a Sierra 80gr. SMK will shoot well loaded much closer to the throat at .010" away. The JLK 80gr VLD shoots best in my experience when loaded .030" into the throat. In my humble opinion the purpose of having the gage and varying the seating depth is to allow the reloader to experiment with different dimensions of seating depth to determine what combination works best in his rifle. 7zero1 out. Exactly. The gage saves a lot of time, trial and error. It gives you a measurement to start your experiment. A lot of the conventional wisdom does not apply. D. Tubb and others have been jumping SMK's and even VLD's .025" to .030" in some rifles to get their best groups. My jump experiments usually go .025", .015", and .0.5" to rifling. The most promising of these gets fine tuned. Jamming is a different animal and pressure can get goofy. I've had problems jamming that required such a reduction in powder to get the pressure lower that the end result was unusable loads.Too slow. VLD's are too finicky for most people's patience to endure. Know that going into it. |
| Lawle - If I'm not mistaken I think you are asking if just the fact of the bullet being seated out further in the case itself causes pressure problems ? I'm no expert on interior ballistics but I don't think seating the bullet out further than SAMMI specs will cause much of a difference in pressures if the bullet is not engaging the rifling yet - that's where your gauge set comes into play - to be sure of your bullet position in the chamber. As long as you can confirm that the bullet is not into the rifling yet I think it is reasonably safe - I've never had pressure signs in many different cartridges from seating the bullet out longer than specs. including smaller ones like the .22 hornet etc. just need to be absolutely sure you have at least a little freebore. |
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