ELD X vs BTHP Match (jackets)

[308220]

Discovered a head scratching "problem" while reloading for my 6.5-284 Norma. I originally settled on the 143gr ELD-X when I got my 26" barrel from Pacnor as my main bullet. Great bullet btw. Very accurate. My "problem" came when trying to get the velocity I was initially after. Tried multiple powders. I cannot for the life of me get this bullet over 2950fps without getting extreme pressure and blown out primers. Some literally fell out of the pocket when I ejected the case on brand new Lapua brass. Accuracy was 1/2 MOA consistently. Out of curiosity, to see if I just had a "slow" barrel, I bought a box of 140gr bthp from Hornady. I seated the bullets to the same length to touching the lands and used the exact same powder charge (same powder). The 140gr nets me 3040fps and is just as accurate. With little to no pressure.





So my question is this, are the jackets really the same? Because its not adding up? A difference of 3 grains in bullet weight isnt going to amount to 100fps in velocity increase.

 

[MtnCreek]

I believe the 143eldx has a longer bearing surface and I believe the jacket is thicker. If primers are falling out, you should stop and figure out what's going on. That's well beyond just a tad too hot load.

 

[One1Bravo]

I believe the 143eldx has a longer bearing surface and I believe the jacket is thicker. If primers are falling out, you should stop and figure out what's going on. That's well beyond just a tad too hot load.

@MtnCreek, can you give a quick explanation how bearing surface and jacket thickness relate to velocity? I'm a new reloader, trying to soak up all the information I can.

 

[MtnCreek]

I don't know that jacket thickness relates to velocity, just commenting on op's question re jackets. Additional bearing surface can contribute to increased pressure.

 

[One1Bravo]

I don't know that jacket thickness relates to velocity, just commenting on op's question re jackets. Additional bearing surface can contribute to increased pressure.

Gotcha, that's what I was thinking.

 

[spife7980]

Just general inquiry: what were your measurements for the 143 vs the 140?
You said you put them at the same point off the lands, does that leave the 143 stuffed further in the case than the 140 which reduces the volume and thus drives up pressure?

And yes, longer bearing surface=more bullet in contact with the barrel=more friction/resistence to movement. Thicker jackets could also be more difficult to obturate (the bullet sealing the bore) but that would be a minimal factor all other things considered.

I wouldnt assume that it is the same jacket or even the same source material. Not a direct relationship but I know the speer varmints have batches where the jacket is just much tougher than the next lot.


What powders are you using?
And 2950 seems high enough that you are likely just plain over max, you are according to the books but we know that those can be conservative. Blowing primers arent conservative though.

 

[308220]

Yeah, I glanced over the bearing surface difference when I compared the 2 bullets when I got them. The 143 def has more bearing surface.

143 OAL 2.965/140 OAL 2.948

I used RL 17, RL 26 and H1000. RL 26 gave me the best results. RL 26 with 54.5 grains gets me to 3040fps with the 140 bthp. And I could go up probably half a grain more. The 143 just cant get any velocity compared to the 140. 2930-2950 seems to be the "comfort zone" for the 143gr in my barrel. Anything more, and its blown primers.

 

[308Gunner]

If the 143 load is accurate at 2950 and you are not seeing pressure I would stick with it. If you want more velocity get a bigger case.