175 SMK v 178 ELD-M: Length Question - Ogive and Mag Length.

[03psd]

So I finally got my headspace and brass issue solved and was loading some of my standard 175gr SMK 42.7gr Varget loads. They measure 2.3075" base to ogive and 2.875" COAL. My maximum mag length is 2.90"
I decided to try some of the Hornady 178gr ELD-M bullets and ran into a problem. At maximum magazine length of 2.90" COAL, the base to ogive length is just 2.28". Bear in mind I am a novice reloader but I know COAL isnt an important measure as long as they fit in the magazine but ogive measurment and jump to lands is where consistency and accuracy are effected. Giving up over .02+" in ogive length just to fit them in the magazine seems like a bad deal to me. Is my thinking on this correct? In a general sense, will some bullets just not work for certain guns? Mine is a AIAT .308

Thanks

 

[918v]

You are looking at this the wrong way. A certain CBTO for the SMK does not guarantee good results for the ELDM. In my rifle the 175SMK likes to be .050" off the lands while the 178 likes to be .005" off.

Second, your comparator does not measure the actual point at which the bullet contacts the rifling. Using a CBTO length from a 175SMK and transferring it to the ELD does not result in the same jump length. You should establish the actual jump length using an actual 178ELDM projectile.

 

[03psd]

You are looking at this the wrong way. A certain CBTO for the SMK does not guarantee good results for the ELDM. In my rifle the 175SMK likes to be .050" off the lands while the 178 likes to be .005" off.

Second, your comparator does not measure the actual point at which the bullet contacts the rifling. Using a CBTO length from a 175SMK and transferring it to the ELD does not result in the same jump length. You should establish the actual jump length using an actual 178ELDM projectile.

Ok, I need to procure a tool to measure the chamber/leade and see how long I can actually load either bullet and I will do so, however, that doesnt change the fact that I am still limited by magazine length. I agree with you and have found SMK to like,or at least tolerate, some jump (.05"). I believe the ELD-M like to be much closer, as you mention above (.005"). So what if I cant get them that close without them being too long to fit the magazine? The difference you noted in what the SMK likes and what the ELD-M likes is .045",which correct me if I am wrong, is a considerable amount in a reloading sense.
I may very well still be confused. I appreciate the education on this.

 

[918v]

If the 178 is too long for your magazine at the optimum oal, then try the 168 which might like more jump. In my rifle the 168 likes to jump .035" at an oal of 2.830". The accuracy node occurs at a 100 FPS faster velocity which pretty much negates the bc advantage at 308 ranges.

 

[Dave62677]

if you want to get the good accurate Cartridge base to barrel land number, Here is what i do

1st Get a hornady oal gauge to measure it ( For example you get 2.307)

2nd Measure the headspace of that Hornady mod case (For example you get 1.619)

3rd Determine what headspace of your reload cartridge (For example you go for 1.621)

Then if you reload the cartridge with Headspace of 1.621, Your Cartridge Base to Ogive kiss the land number should be 2.309" +/- .002


You have to shove a bullet in the barrel to see the contact point to get your number.

 

[ShebasDad]

I'm just starting with my reloading adventure so here' my stupid question for the week... Will the 178gr ELDMs work with a 0.065 jump?

The rifle I'm going to load for is a R-700 AAC SD 20" 1:10 w/ a stock barrel and chamber and Wyatt DBM w/ a max coal of 2.88. 2.875 to make sure they will feed leaves me with a 0.062 jump.

I measured to the lands and theirs no chance getting any closer. I can get a little closer with 168s but they haven't worked very well in this rifle in the past.

After several searches I found alot of conflicting opinions. The plan right now is to use Varget starting @ 42 gr and work up towards 45 and try them out next weekend. Any and all help is much appreciated

 

[padom]

I found the 178's liked to be much closer to the lands than say a 175smk... load to max mag length and test them out. Only you will know by testing..

 

[308pirate]

if you want to get the good accurate Cartridge base to barrel land number, Here is what i do

1st Get a hornady oal gauge to measure it ( For example you get 2.307)

2nd Measure the headspace of that Hornady mod case (For example you get 1.619)

3rd Determine what headspace of your reload cartridge (For example you go for 1.621)

Then if you reload the cartridge with Headspace of 1.621, Your Cartridge Base to Ogive kiss the land number should be 2.309" +/- .002


You have to shove a bullet in the barrel to see the contact point to get your number.

I don't think you understand what headspace means. Headspace is a chamber dimension that is pretty much fixed when a rifle is barreled, not a cartridge dimension that can be adjusted during the reloading process

I suggest to anyone looking for information on how to check jump to ignore the above.

 

[ShebasDad]

Thanks that's kinda what I figured ... and planed on. Just so many people saying different things on the ELD-M's I've seen jumps from .005 to .06.

Let the games begin! .... God help me

 

[918v]

Think about this for a minute:

In my rifle, the optimum jump length for the 178 is at .010” off the lands. The coal is roughly 2.925”. The optimum jump length for the 175SMK is .065” off the lands and the coal is 2.830”. The optimum jump length for a 175 Berger OTM is .125” at a coal of 2.810”.

But, if you can imagine this, the seating depth (the position of their bases within the case) is the same. It’s not about the amount of jump to the lands. It’s about bullet base exiting the muzzle at the optimum time.

 

[Dave62677]

I don't think you understand what headspace means. Headspace is a chamber dimension that is pretty much fixed when a rifle is barreled, not a cartridge dimension that can be adjusted during the reloading process

I suggest to anyone looking for information on how to check jump to ignore the above.

The HS of your chamber action won't change, i'm talking about the reading off the hornady modified case. Think about it when you have one brand new modified case from hornday measured HS at 1.619 , and one homemade modified case measured HS at 1.625. Your ogive reading from the Bullet comparator will be different from both case even if you seat your bullet at the same spot on the rifling.

 

[308pirate]

I see now.

One of the reasons why I use a Sinclair tool to measure the distance from the ogive to the case head when the bullet is just touching the rifling. The Sinclair tool relies on a case fired in your chamber which, despite minute variations in brass expansion, makes the cartridge length measurement pretty repeatable.