Pressure on low 4895 load vs. hi 4064 load, wtf?

[Snakum]

My brain is cramping trying to get my gourd head around this stuff.

I was trying to duplicate my HSM Match 168gr SMK using IMR4895 and I noticed as I got the load to run neck and neck with HSM at 100, 200, and 300 yards I started seeing signs of pressure: powder taste, bolt getting sticky, slightly raise "rim" around the firing pin strike on the primer. And this started at 43.2gr of 4895 in my 10FCP-K. So I backed off and lived with a load that required a different zero/dope than my HSM.

This week I am duplicating HSM trajectories again, this time with IMR4064 and at about 43.6 it seemed to be getting a little hot in my weapon. I backed off two grains to 43.4 ... perfect. Shoots a clover leaf at 100 yards. And 42.9gr IMR4064 in my LC brass does the same. Dead on POI for both cases ... got a load for mil spec cases and commercial brass that can use the same dope table. But the POI is 2" higher than the low charge 4895 at roughly the same point back from pressure signs. It's as if the 4064 shoots "hotter" than 4895 before pressure signs start to show up.

Is this just a function of the powder and to be expected across all different brands? Ie one brand will show pressure signs at velocity X while the next will show pressure signs at velocity Y?

 

[Victor N TN]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

While they are in the same ball park IMR 4064 and IMR 4895 have different burn rates. Any time you change powders and some times even different lots of the same powder, you will get a slightly different burn rate. Duplicating someone elses load is very hard to do unless you know the muzzle velocity and what powder they are using. Most commercial loads have "cannister" or bulk powders that are not available to the private handloader.

 

[Snakum]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

Thanks for the reply Victor.

I understand burn rate diffs. I'll try to ask it differently:

If I take two different powders up to the point that equal pressure signs appear in my rifle with both powders (cases from both powders begin exhibiting the same symptoms in roughly equal proportions), why is it that they aren't shooting relatively close to the same velocities at that point?

 

[Snakum]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

Guess I'm still not asking the question clearly.

 

[benjaminzero]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

As explained by victor above: The Burn Rates are different.
Speaking in vast generalities:
A slower burn can be beneficial in longer barrels or rounds with large case volumes. Fast burn can be beneficial in shorter barrels or small case volume.
Example: Short Barrel + Slow Burn Powder
- The powder is not getting a full burn and energy is being wasted after the bullet leaves the barrel. You don't meet your intended velocity so you increase charge. Now you have pressure signs. A faster burning powder gets a fuller burn in the barrel with less waste, and you reach your velocity at a lower charge. Less pressure signs.

But Simply: Different Powder ---> Different Result

Also: Any particular reason you are trying to match the trajectory? I assume you have a bdc on your scope? Otherwise you can have perfectly safe loads that outperform factory loads.

 

[9H_Cracka]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Snakum</div><div class="ubbcode-body">

If I take two different powders up to the point that equal pressure signs appear in my rifle with both powders (cases from both powders begin exhibiting the same symptoms in roughly equal proportions), why is it that they aren't shooting relatively close to the same velocities at that point?

</div></div>

Because they are two different powders.

 

[Snakum]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The powder is not getting a full burn and energy is being wasted after the bullet leaves the barrel. You don't meet your intended velocity so you increase charge. Now you have pressure signs. A faster burning powder gets a fuller burn in the barrel with less waste, and you reach your velocity at a lower charge. Less pressure signs.</div></div>

That's it. That's what I was trying to understand. Makes sense now. Being so new to it all I don't explain what I'm trying to understand very well.

Thanks for the info.

 

[Snakum]

Re: Pressure on low 4895 load vs. hi 4064 load, wtf?

About duplicating load, I spent all the time and money for powder and primers because I have a lot of HSM Match ammo that shoots very well for me. I also have a lot of milspec brass, as well as commercial brass. I also wind up with IMR4064 and IMR4895 sometimes due to stocking at my local shops.

As of about 30 minutes ago I can now grab my milspec cased 4064 handloads or my commercial brassed 4895 or my HSM Match and use the exact same dope table for any of it. Whatever powder I wind up with for the month, whatever case I might have, I can now confidently take it to the range and know it'll shoot moa to 600 yards with one dope table.

It took a lot of money and time, but not a single shot was wasted. I am working on my breathing, trigger control, and sight picture with every single round sent. I'm also learning a ton about reloading.