Tech??? How far to back down off max load?

[SemperFiDawg]

Once you guys start finding signs of overpressure, how far do you back down. Here's the scenario. I'm reloading for my 6.5-284 and my most accurate load is 47.3 grains of H4350, but my bolt starts getting sticky at 47.6 grains. From what I can gather an increase in chamber pressure relative to ambient temp is equivalent to that of 0.1 grain of powder for every 3 degree Fambient temp. If this is correct, then a 12*F increase from the day I tested the ammo will put me right back to max pressure just due to and increase in ambient temperature alone. Does this sound reasonable and if so, how far do I need to back down?

 

[bohem]

Re: Tech??? How far to back down off max load?

1) H4350 is very temp stable.
2) Sticky bolt lift is starting above your accuracy node so it's still OK on the accuracy node
3) Case life can be tracked by measuring the extractor groove diameter, when it grows 0.001" the case is junk and you're over pressure.

I'd measure the extractor grooves on 10 pieces of new brass, load and fire at your accuracy node on a hot day and remeasure them. If they didn't grow then you're fine.

I don't know where you got the pressure/temp correlation from but I haven't seen that in anything I've shot, especially from H4350.

 

[SemperFiDawg]

Re: Tech??? How far to back down off max load?

Thanks bohem. As far as temp-pressure correlations go, check this out
http://www.shootingsoftware.com/ftp/Pressure%20Factors.pdf

 

[Fuzzball]

Re: Tech??? How far to back down off max load?

"Once you guys start finding signs of overpressure, how far do you back down."

I don't think "start finding signs of overpressure" is well enough calibrated to say. Maybe five grains would do it. ??

 

[bohem]

Re: Tech??? How far to back down off max load?

I'll take a look through the PDF, thanks for the reading material.

 

[MitchAlsup]

Re: Tech??? How far to back down off max load?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: SemperFiDawg</div><div class="ubbcode-body">Once you guys start finding signs of overpressure, how far do you back down. </div></div>

At least 1%. so in the case of 47-ish gr of <something or other> you should back down 0.47 gr or just round this to 0.5 gr.

You have an accuracy node within 0.5% of pressure signs. This is only safe if you are meticulous in every aspect of reloading and case inspection. That is, you are living on the edge, not over the edge, but on it.

What I would do: Survey the accuracy node range to as fine as you can measure on the scale. Then see if you can't back down to 47.2 or even 47.15gr and live there. After this, then survey the jump distance and see if there is a way to assemble the load so that 47.15 gr will shoot accurately.

If the accuracy node refuses to move or keeps wanting to be closer than 0.5% to pressure signs, try another powder.