Can someone check my math

[Pigdog]

hi Iam trying to calculate how long a bullet will seat in my case and my OAL for loaded rounds for bullets without having to buy 100 of each type to actually check. This is my calculation can someone more math inclined tell me if I'm completely wrong please!!!

Ok so my reference projectile is a 123 scenar which I measure base to ogive of .682 and 1.300 oal, in my rifle at the lands this gives me a COAL of 2.803. (I realise COAL is not the most accurate but this is what I want to work with for now)

A 147ELD M measures .795 to ogive and 1.432 oal. If my calculations are correct this bullet will seat .113 deeper in my case (.795-.682) and the COAL would be 2.822 with this bullet at the lands based on the scenar being 2.803 at lands (1.300-.682=.618) 147eld (1.432-.795=.637) so (.637-.618=.019) then .019+2.803=2.822 Does this look correct im just looking for a rough coal figure without having to buy each bullet so I can see where they will seat based on various bullets base to ogive and oal.

 

[Richard Coody]

i will be interested to see if this works.

variations in the ogive and how accurately you can measure the actual begining of the bearing point (where the ogive starts) would bother me.

i will stick with my old timey way.

 

[ballisticdaddy]

Just as an example I have tried to do the same forward thinking while the smith was wrapping up my last two builds. Even with the copious amounts of information available the weak link is the measuring device(s). One set of mass produced (Even Mitutoyo) calipers to the next will not be exact now introduce a bullet comparator and the actual projectile also mass produced. I also length sort my projectiles for match loads and they will range .004 to .006 from the shortest to longest over 500 pieces. I would imagine if you requested one of the members would send you one projectile to prove or disprove your numbers without having to purchase an entire box of 100.

 

[JLT]

The logic and arithmetic are correct.

 

[Pigdog]

Hey guys yer I realise there will be +- in the various parts of this I'm kinda just looking for a ball park figure to say go or no go for a bullet to see how much deeper or shallower it will seat and change in oal just wondering if there are any MAJOR flaws in my calc

 

[Pigdog]

thanks JLT I just posted as you posted.

 

[dbduff]

Variation in measuring instruments causes a lot of problems. Variations abound. The smaller you get in your measurements, the more opportunity for misinformation, not intentional, non the less frustrating. It is literally like two translators giving slightly different interpretations of a statement. Not intentional, frustrating non the less.
D

 

[hogpatrol]

Not sure about your bullets but some online vendors and Cabela's sell sample packs.

 

[LCazador]

Hey guys yer I realise there will be +- in the various parts of this I'm kinda just looking for a ball park figure to say go or no go for a bullet to see how much deeper or shallower it will seat and change in oal just wondering if there are any MAJOR flaws in my calc

I would measure base of bullet to bullet tip. You can get bullet length from manufacturer and that will be an actual vs. measuring to ogive.

 

[CharlieNC]

The diameter of the bullet where you measure the ogive vs the diameter of the bullet where it engages in the lands may not be the same. So differences in the taper of the bullets may lead to errors. It will be interesting to see how this turns out for you.

 

[Ned Ludd]

Your approach should be fine to get a ballpark idea. I've done it before, just to make an estimate, and it works ok within some margin of error.

Are you trying to figure out 1) whether the COAL of a loaded round with the different bullets will work in your action/mag length, or are you more interested in 2) whether the freebore of your rifle will accommodate the other bullets at a similar seating depth, or 3) both?

If you have plenty of length for COAL (or are single-feeding) and are primarily interested in optimal freebore for the different bullets (#2 above), you can also make a fairly decent estimate by comparing base to ogive with your "reference" bullet, or even by directly comparing bearing surface lengths, if you have those values. If you primarily interested in #1 above, you can probably get just as good an estimate by comparing nose length only. In each case, you're making some assumptions, but for the purpose of rough estimates, there are several different ways you can calculate comparative dimensions.