Grendel gas pressures vs. 5.56 pressures....

[Variable]

Does anyone know what muzzle pressures the 6.5 Grendel produces at various barrel lengths? I'm personally interested in the Psi at 12.5" with a factory load like the Hornady 123 Amax, but for reference, education, and the use of others, I'll take whatever pressures you might have.

I'm also interested in comparisons between the Grendel and 5.56 at various lengths (12.5" personally ). Generic chamber pressures aren't too hard to find, and I know the 5.56 is loaded to higher pressures than Grendel, but what is going on farther down the bore? Percentage of powder burned at various lengths (especially @ 12.5" )?

Thanks for any help. I think it's pertinent not only to suppressors, but also to muzzle brakes too. The percentage of powder burned will also give some clues to how much muzzle flash should be exoected.

I'm thinking maybe some of you guys who use/understand Quickload might know. That's above and beyond my paygrade, so what do you guys know?


I asked in my suppressor thread, but it's in accsessories, so it might not get seen where the ammo and loading guys are. It's a semi-pertinent general purpose knowledge thing anyway, so I re-asked it here.

[cory]

Sounds like a JASmith question to me.

[Variable]

Sounds like a JASmith question to me.

Yeah, I specifically had him in mind when I asked.LOL I just didn't name him directly bescause I didn't want him to feel pressured.

[JASmith]

Yeah, I specifically had him in mind when I asked.LOL I just didn't name him directly bescause I didn't want him to feel pressured.

Pressured? When dealing with pressssssure?

Oh well...

To the specific question, it is a straightforward QuickLoad exercise. Best bet is to send a load recipe for the Grendel and one for the 5.56 and the rest should be easy provided the bullet and powder are in the QuickLoad Library. For various reasons, a load drawn from the Hodgdon or Western Powders site will be more comfortable for me to work with.

Cheers!

[Variable]

beast of a can) so I can't use it as a baseline for comparison

[SHORT-N-SASSY]

'Located a couple related Links for the 5.56:

http://www.sadefensejournal.com/wp/?p=1093

http://www.dtic.mil/ndia/2010armamen...hilipDater.pdf (Check Page 14, BARREL LENGTH and BORE PRESSURE)

[Variable]

Wow! Thanks SHORT-N-SASSY! That's pure gold for the M855 pressure!

That nails the muzzle uncorking pressure down pretty darn good.

5.56 M855 11.5" muzzle pressure would be pretty darn close to 10,140psi then.

A theoretical 12.5" 5.56 barrel firing M855 should be right around 9264psi.

[rasp65]

Variable I have a copy of a pressure curve of a 123 AMax in PDF form. PM me and I will email it to you.

[Variable]

PM sent! Thanks.

I had also just sent an email request to Hornady too. I'll post up anything I get back from them as well.

[rasp65]

Variable That's fine I made a weak attempt at posting it but was unable.

[Variable]

Thanks Rasp! I cheated, and turned the PDF into a JPG by taking a screenshot of it and then cropping it.LOL



Yikes! That's higher than I had hoped it would be. A good bit higher. It looks like about 12,500psi for a 12.5" barrel on that chart?

I had hoped the Grendel would have lower pressure than the 5.56, not more.

[SHORT-N-SASSY]

As I view the pressure curve and corresponding velocity curve of a conventional parallel bore, in the graph, above, I'm reminded to the principle of the tapered-bore guns of WWII: muzzle velocities over 4,800 fps (http://iaaforum.org/forum3/viewtopic.php?f=1&t=3595).

[Variable]

If that chart above is correct, it puts the pressure out of my 10.5 Grendel at roughly 15,000psi. That's about equivalent to an 8" 5.56 barrel.



Hold on a sec--- that chart shows a load of 27 grains of Win 748. My hand loads are 31.7 grains of Win 748 behind a 120gr. Nosler BT. I have no idea what the factory Hornady is, but it's a bit warmer than 27 grains of Win 748 I'd bet.

So the fricken' pressure is likely even higher if the data on that chart is accurate....

No wonder I got flashbanged when I lit my 10.5" Grendel off in my semi-enclosed deer stand....

We still don't know the percentage of unburnt powder, and I'm guessing the volume of gas escaping the muzzle would play into it as well.

[JASmith]

QuickLoad seems to be running higher peak pressures than shown in the Hodgdon and Ramshot pages. There is also a difference between the bullet base pressure and the chamber pressure (See QL 'change diagram' - 'Optional Diagrams' when the plot is selected.).

I got about the same pressure and burnt percents (94% ad 15ksi).

The server I use for images seems to be down -- I will post the charts when it comes back up.

[nincomp]

Several years ago Quickload overestimated the pressure on some (not all) Grendel loadings. Some reloaders were terrified by high Quickload results, even on loadings that had been physically pressure tested by Bill Alexander as safe. Bill Alexander explained that the geometry of the Grendel cartridge somehow did not meet certain assumptions in the Quickload software. I do not know if the glitch in Quickload has been fixed.

This issue comes up every few years.