21st Century - Calibrated Bullet Seating Die vs. Others

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Barry Davies
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#16 Postby Barry Davies » Fri Sep 01, 2017 8:51 am

Further on the subject of seating.
The first point of contact of a projectile is within 1/2 mm of the transition from full diameter ( .308 ) into the ogive --so is this not where you should be measuring seating length from?
I have seen seating length measuring devices that pick up the projectile further down the ogive at some diameter which bears no relation to the actual first point of contact.
It makes sense to manufacture a seating length measuring device using the same reamer that chambered your barrel. Better still use the cut off portion of your barrel which has rifling in it.
Ideally the seating stem should pick up the projectile as close to the transition point as possible but this creates problems in design due to the larger external diameter of the stem.

ajvanwyk
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#17 Postby ajvanwyk » Fri Sep 01, 2017 11:21 am

Barry, this sounds rather interesting, and for my young nontechnical mind slightly complicated.

What I think I understand from your suggestion is that if I manage to use the camber and a portion of the bore, is that It should be able to ensure that the "rifling" contact the transition point or ogive more consistently....as this is where the projectile would be engaged when shooting. is this correct? If so, am I then right to assume that instead of current seating die designs that have a micrometer top to adjust the stem, you in actual fact need the adjustment at the bottom of the seating die and therefore adjust the entire chamber insert or rather the base of the case up or down?

Albert
Albert
Rosedale Rifle Club

KHGS
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#18 Postby KHGS » Fri Sep 01, 2017 11:27 am

Barry Davies wrote:You can lap the seating stem for ever and a day but it will still contact all projectiles at the same diameter. Inconsistency in seating length is solely brought about by variations in ogive shape.
Barry has the right idea --seat long, measure, and reseat


Quite correct Barry, my post did indicate this & ideally if you are going to be using various bullet styles a lapped stem for each style is required for best results.
Keith H.

Barry Davies
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#19 Postby Barry Davies » Fri Sep 01, 2017 12:04 pm

Albert--
PM sent

ajvanwyk
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#20 Postby ajvanwyk » Fri Sep 01, 2017 1:28 pm

Thank you gents, I understand this much better now.
Albert
Rosedale Rifle Club

Gyro
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#21 Postby Gyro » Fri Sep 01, 2017 2:17 pm

Did anyone here ever hear of the BGC ( Bob Green Comparitor ) tool as this measuring tool is being alluded to here ? I know some shooters thought it good. Maybe some still do ....... mmmmmmm

Gyro
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#22 Postby Gyro » Sat Sep 02, 2017 4:01 am

Mr Greens measuring tool was primarily ( if I remember rightly ) for identifying the variations that may exist in ogive shape before seating the bullet. In the above comments I believe some are identifying a variation in ogive shape during the seating process, then dealing with that re the implications that has for ogive/leade interference ? Mr Green reckons it beneficial to batch those 'different' bullets before loading because of the supposed effect on the BC of the different shapes. What to do ?

FWIW, these days I have two batches : fired and unfired but am always interested in some PROPER research to suggest I need more batches. Regards Rob.

Audax
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Re: 21st Century - Calibrated Bullet Seating Die vs. Others

#23 Postby Audax » Mon Oct 23, 2017 7:34 am

Lapping is the answer to a ridge free bearing surface against your bullet down from the tip, but as Barry says the stem will contact all bullets at the same OD, and that length will vary within a batch....!

Try using the seating stem once lapped to measure the overall dimension of the bullet ie base to top of stem and batch once, then using an ogive gauge with an opening ID of ~0.286"for a 284 bore {tapering at your rifle leade angle, say 1.5 degrees} which will effectively measure base to lands contact point on the bullet, and batch again.

This method will separate bullets by the slight variations in BC , and depending on how particular you want to be what tolerance is acceptable.......!!!


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