I’ve been messing with a spreadsheet that ‘predicts’ (or at least shows) how a particular bullet occupies space/sits in your brass/barrel, based upon a few easy measurements. I’m sure this has been done before. It gives COAL (handy for those mag length rounds), bearing surface and whether or not the bullet base is above or below the shoulder. It also gives the required amount of bearing surface in the neck, based upon your parameter (.100, .200, etc.). You will need to know your touch #. (1.722 in this barrel)
This is intended to let you see if a bullet might work in your barrel, or if it’s too short, or too much below the NSJ, or in the donut, or whatever. Just a tool. As shown, the Hornady 87 VMax is below the NSJ, but only by a bit, and it’s mostly boattail that would probably be OK in the donut, depending on how low it sets. I think in this barrel it would work OK.
This does not take the place of cutaway photos showing bullet in the brass, etc., but it does show what it might look like in your barrel. Again, this is just to get you close. Maybe you buy that new bullet you saw on Accurate Shooter or maybe you think that .857” of jump is just a bit too much for your application.
This is just a screenshot of a few bullets for my Wilson 6BR barrel. My freebore on this barrel is .104, but that # is not used in any calculations. You would be able to change the BTO number for say, an .055 freebore simply by subtracting the difference in the freebores and reducing the BTO. For instance, all of the figures that you see are for a .104 FB. .104-.055=.049, so subtract .049 from the 1.722 BTO and you’d get close, about 1.673 BTO. All of the ogive measurements are made using a Hornady comparator that has been modified to accept a standard sizing bushing. In this case, a .237, which is lands size in a 6mm. I have other bushings for .17, .20, .22 and .30.
Let me know what you think. Responsible, adult-like comment/questions are welcome. At the very least, a database of bullet measurements can’t be a bad thing…
This is intended to let you see if a bullet might work in your barrel, or if it’s too short, or too much below the NSJ, or in the donut, or whatever. Just a tool. As shown, the Hornady 87 VMax is below the NSJ, but only by a bit, and it’s mostly boattail that would probably be OK in the donut, depending on how low it sets. I think in this barrel it would work OK.
This does not take the place of cutaway photos showing bullet in the brass, etc., but it does show what it might look like in your barrel. Again, this is just to get you close. Maybe you buy that new bullet you saw on Accurate Shooter or maybe you think that .857” of jump is just a bit too much for your application.
This is just a screenshot of a few bullets for my Wilson 6BR barrel. My freebore on this barrel is .104, but that # is not used in any calculations. You would be able to change the BTO number for say, an .055 freebore simply by subtracting the difference in the freebores and reducing the BTO. For instance, all of the figures that you see are for a .104 FB. .104-.055=.049, so subtract .049 from the 1.722 BTO and you’d get close, about 1.673 BTO. All of the ogive measurements are made using a Hornady comparator that has been modified to accept a standard sizing bushing. In this case, a .237, which is lands size in a 6mm. I have other bushings for .17, .20, .22 and .30.
Let me know what you think. Responsible, adult-like comment/questions are welcome. At the very least, a database of bullet measurements can’t be a bad thing…
