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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Help..Throat length / Freebore / bullet jump
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<blockquote data-quote="Raffy" data-source="post: 2617551" data-attributes="member: 118545"><p>Are you having a reamer made or are you having the gunsmith cut the throat to length based on your freebore wishes?</p><p></p><p>You should just make some dummy rounds with all of the bullets you plan to potentially shoot and give them to the gunsmith to work off of or send them to the reamer manufacturer. They should know what to do with all of that.</p><p></p><p>For what its worth I just finished load development on virgin brass with the 180 hybrid and I settled on 2.355 as my cbto using my hornady ogive comparator. Your ogive comparator and my ogive comparator will not reliably give the same measurement unless you and I have compared our comparators against the same standard, ie. the same loaded case.</p><p></p><p>My cbto on those rounds was ranging between 3.088-3.095 from the same box of bullets. Im hoping to work on increasing velocity with further load development, however I had my reamer freebore set to what my loaded round was plus allowing for a specified 0.02 jump. It ended up being 0.221. That reamer is set to shoot 180 eldm's at the neck shoulder junction and has an extra .02 added for the 2 thou jump everyone always talks about. The 180 berger hybrids shoot bugholes and are jumping a really long ways. The eldm measures 2.402 cbto + .02 = 2.422. That means on paper the hybrid is jumping circa 0.067. [ATTACH=full]393670[/ATTACH]</p><p></p><p>However a caveat is that measuring bullet cbto to either jam or touch on your lands will not be the same actual measured distance to the lands on paper. The shape of the ogive will determine how the bullet fits and a stumpy shaped bullet will not touch at the same point as measured compared to a sleeker bullet. Case in point the 180 eldm is fatter up higher on the nose at the ogive vs the slender sleeker nose of the 180 hybrid, yet they are very near the same in bullet oal length compared to their bto measurements. Think of it this way, if you have a 2 inch hole and you measure how far down into that hole a tennis ball will sit compared to a beach ball, the tennis ball will sit deeper than the beach ball due to the size of the balls. I hope that made sense.</p><p></p><p>I guess my point is .02 bullet jump is not gospel. It works a lot, but its not the only way. You can always tune seating depth regardless of the amount of jump a bullet has to make, even if it is a lot. The 180 eldm and the 180 hybrid I mocked up will both fit within your 3.2 mag box. Dont be afraid to cut a longer throat than your magazine can accommodate, but your seating depth may need to be reduced slightly in order for you to tune your load to your barrel either way you do it.</p><p></p><p>Here is a picture of the 3 shot group I shot with the 180 hybrid yesterday from my 7 saum at 100 yards. I think that flyer on the top was my fault. [ATTACH=full]393671[/ATTACH]</p></blockquote><p></p>
[QUOTE="Raffy, post: 2617551, member: 118545"] Are you having a reamer made or are you having the gunsmith cut the throat to length based on your freebore wishes? You should just make some dummy rounds with all of the bullets you plan to potentially shoot and give them to the gunsmith to work off of or send them to the reamer manufacturer. They should know what to do with all of that. For what its worth I just finished load development on virgin brass with the 180 hybrid and I settled on 2.355 as my cbto using my hornady ogive comparator. Your ogive comparator and my ogive comparator will not reliably give the same measurement unless you and I have compared our comparators against the same standard, ie. the same loaded case. My cbto on those rounds was ranging between 3.088-3.095 from the same box of bullets. Im hoping to work on increasing velocity with further load development, however I had my reamer freebore set to what my loaded round was plus allowing for a specified 0.02 jump. It ended up being 0.221. That reamer is set to shoot 180 eldm's at the neck shoulder junction and has an extra .02 added for the 2 thou jump everyone always talks about. The 180 berger hybrids shoot bugholes and are jumping a really long ways. The eldm measures 2.402 cbto + .02 = 2.422. That means on paper the hybrid is jumping circa 0.067. [ATTACH type="full" alt="20220912_011211.jpg"]393670[/ATTACH] However a caveat is that measuring bullet cbto to either jam or touch on your lands will not be the same actual measured distance to the lands on paper. The shape of the ogive will determine how the bullet fits and a stumpy shaped bullet will not touch at the same point as measured compared to a sleeker bullet. Case in point the 180 eldm is fatter up higher on the nose at the ogive vs the slender sleeker nose of the 180 hybrid, yet they are very near the same in bullet oal length compared to their bto measurements. Think of it this way, if you have a 2 inch hole and you measure how far down into that hole a tennis ball will sit compared to a beach ball, the tennis ball will sit deeper than the beach ball due to the size of the balls. I hope that made sense. I guess my point is .02 bullet jump is not gospel. It works a lot, but its not the only way. You can always tune seating depth regardless of the amount of jump a bullet has to make, even if it is a lot. The 180 eldm and the 180 hybrid I mocked up will both fit within your 3.2 mag box. Dont be afraid to cut a longer throat than your magazine can accommodate, but your seating depth may need to be reduced slightly in order for you to tune your load to your barrel either way you do it. Here is a picture of the 3 shot group I shot with the 180 hybrid yesterday from my 7 saum at 100 yards. I think that flyer on the top was my fault. [ATTACH type="full" alt="20220910_201724.jpg"]393671[/ATTACH] [/QUOTE]
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Help..Throat length / Freebore / bullet jump
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