.308 ogive question for novice reloader

[woodspider]

Ok I am using a .308 RCBS precision mic for determining my sps tactical's ogive, I took 5 measurements closing the bolt in a manner I would at the range, removing the device measure repeat 5 times. Here are the reads
1) .206 2).210 3).208 4) .211 5).208
for an average of = .2086

I then took some loaded ammo factory stuff that shoots well in my gun and measured the bullet seating depth getting the averages:

8 rounds of FGMM 168 BTHP for an average of = .2592
8 rounds of Corbon/Dakota Arms .175 bthp average of= .2461

Im planning to work up some loads comparable to the stuff that seems to work in my gun already, or at least Ill try to ,
Now should I just try to match the seating depths of the fgmm and the corbon stuff? or work up my own fresh loads with a seating depths goal of .010 off the lands,?
(meaning .010 off of the ogive average of .2086 ? , meaning using .2186 as a end goal) then load a few test fire then try a few different depth moves working toward that .2186 goal(baby steps)?
I dont understand why the huge disparity and why the factory loads are so deep compared to the RCBS mic read? Am I on the right track? Have I got the basic understanding here? any advice appreciated.
Thanks
WOODY

 

[Xdguy]

Re: .308 ogive question for novice reloader

If you can get good accuracy loading them deep, then why load them long. Less cance of runout and missing mag length. Just my opinion though.

 

[Fuzzball]

Re: .308 ogive question for novice reloader

"for an average of = .2086
....factory stuff that shoots well...
8 rounds of FGMM 168 BTHP for an average of = .2592
8 rounds of Corbon/Dakota Arms .175 bthp average of= .2461"

Your good shooting factory ammo is jammed some 50 and 40 thou into the lands?

 

[Teggy1]

Re: .308 ogive question for novice reloader

The ogive differs from bullet to bullet (makes). Like the above poster said, according to your measurements you would be jamming factory rounds into the lands, highly unlikely.

 

[XTR]

Re: .308 ogive question for novice reloader

Guys, there is a sticky on the top of this forum

Hand Loading for Long Range 3: finding start OAL



try it

 

[woodspider]

Re: .308 ogive question for novice reloader

So the tool to measure ogive in my rifle with the rcbs mic is fkin useless looks like I'll surf a bit for an actual tool that measures each individual brand/grain of bullet.
This is useful thanks kinda learning as I go sorry for the ignorance

 

[Tomcat]

Re: .308 ogive question for novice reloader


I think the two tools you are looking for are:


http://www.sinclairintl.com/.aspx/pid=34262/Product/Sinclair_Hex_Style_Bullet_Comparators

http://www.sinclairintl.com/.aspx/pid=35491/Product/Sinclair_Bullet_Seating_Depth_Tool

The the bullet seating depth tool to find your chamber depth, use that handy hex nut to find the bullet base to ogive measurement.

1 - first drop a bullet (not a complete ready to fire shell, but simply a bullet) in the chamber and let gravity drop it onto the throat. It will seat on the lands. Use the guage to determine length to base of bullet - that is the first collar on the guage.

2 - drop a fired empty shell case in the chamber and use that guage to set the second collar.

3 - use caliper to find that length - as shown in the instructions.

3 - use that handy hex nut to find the length of that bullet from base to ogive.

4 - add the two together - what you have is the length of an assembled bullet from base to ogive, when the bullet is touching the lands.

You can use this as a basis for experimenting with various bullet lengths.
Be careful when seating bullets to the lands - that causes pressure spikes which can be harmful.

OAL measurement is important when constructing bullets that must fit in magazines, base-to-ogive measurements are important because thats the critical dimension where the bullet first comes into contact with lands.

 

[Tomcat]

Re: .308 ogive question for novice reloader

I just re-read TresMon's post up top in the sticky - he is really smart, - yes that is a good way to do it.

His measurements give the dimension to the bolt face, the Sinclair measurements are to the base of a fired shell - presumably that has been fire formed to your chamber.

Not sure which would be better, if either are.

 

[MitchAlsup]

Re: .308 ogive question for novice reloader

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: woodspider</div><div class="ubbcode-body">Ok I am using a .308 RCBS precision mic for determining my sps tactical's ogive, I took 5 measurements closing the bolt in a manner I would at the range, removing the device measure repeat 5 times. </div></div>

In order to use the RCBS precision mic you first have to throw away the plastic bullet. Neck size a prepaired unprimed unpowdered case, seat a bullet long (like 3.000) and then close the bolt. Measure the real bullet in a real case with the precision mic.