I wrote a section on this in Volume I of the 6.5 Grendel Handbooks back in 2012-2013, pages 19-21.
The section is titled: Barrel length and gas system length configurations.
Some shooters who have run certain hand loads through a 20 rifle with rifle-length gas, have then taken those same loads to see how they do in a 24 or even 28 rifle with rifle-length gas, and experienced apparent extreme pressure signs, where brass begins to separate at the head/web junction with the case walls just above the extractor groove location (See Figure 10).
This is what cases look like when you have too early extraction:
You can run that load through the 20 RLGS and brass comes out without these bulges.
Put the exact same load into 28 RLGS and you will see this problem.
Its a cyclic rate problem.
You can load a hotter load in the 20 RLGS and not even see this happen, use a reduced load in the 28 RLGS with the same components and it will still be there.
Its not the brasss fault, but the cyclic rate due to port location, plug dwell time, and carrier/buffer mass not able to resist the imparted inertia.
Cyclic rate timing is essential to master on any gas-operated firearm. The AR-15 does quite a good job of it when everything is balanced with port location, port size, plug dwell time, carrier mass, action spring weight, and buffer mass relative to the propellant mass, bore volume, projectile mass, working pressure, and propellant burn rate.
Think of it as a teeter-totter. On one end is the pressure-containment vessel and gas system, while on the other end are the reciprocating masses and spring.
The fulcrum is the bolt lock-up.
If you out-run the ability of the reciprocating mass and locking system to keep the case locked in the chamber until pressure subsides, you will have expanded case heads, partial or full case head separations, failure to extracts, torn case rims, etc.
Timing of the unlocking cycle is essential to avoid this.
OP used a 1.8oz buffer with CLGS, and dropped one end of the teeter-totter on the ground.
Thats a perfect recipe for partial case head separation.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
LRRPF52 Wrote:Do you see how you have contradicted yourself now, while refusing to look at the buffer mass and cyclic rate?
A lack of understanding of how this system works has led to a series of conjectures and contradictions that simply do not match up with what the OP has posted, and Ive had to waste a lot of time addressing these falsehoods in this thread.
If you arent familiar with basic behavior of partial case head separations, it isnt helpful positing all kinds of theories in a thread where the OP came looking for help.
There's nothing I've said that's a contradiction.
And I have fully evaluated and understand the buffer mass and cyclic rate physics.
And I fully understand the system of an AR firing a bullet from beginning to end. The overall complexity of it is minor in my professional opinion because of many more complex engineering "problems" that I've faced in school and my career. It literally and figuratively isn't rocket science to me.
A lack of fully understanding the materials science properties of metals and alloys and the entire math behind their deformation at temporary, permanent, and absolute failure phases has led to a series of conjectures and contradictions that simply do not match up with what the OP has posted, and Ive had to waste a lot of time addressing these falsehoods in this thread.
If you arent completely proficient at the math behind materials science as described above it isnt helpful positing all kinds of theories in a thread where the OP came looking for help.
OP I just want to say it's been a good thread. I appreciate you sharing all that info and your experience and pictures. I'm out of this thread for good now. Take care and be safe!
So it's not really likely that the tear is going to outrun the pressure drop.
I agree fully with all of this except the above point. In my limited view, the tear must outrun the pressure drop to continually grow. if pressure has dropped below the tear (or continual tear) threshold, then it should stop. I think maybe its the way I have explained it that caused confusion and in reality we are in alignment in this regard.
DeNinny Wrote:There's nothing I've said that's a contradiction.
And I have fully evaluated and understand the buffer mass and cyclic rate physics.
And I fully understand the system of an AR firing a bullet from beginning to end. The overall complexity of it is minor in my professional opinion because of many more complex engineering "problems" that I've faced in school and my career. It literally and figuratively isn't rocket science to me.
A lack of fully understanding the materials science properties of metals and alloys and the entire math behind their deformation at temporary, permanent, and absolute failure phases has led to a series of conjectures and contradictions that simply do not match up with what the OP has posted, and Ive had to waste a lot of time addressing these falsehoods in this thread.
If you arent completely proficient at the math behind materials science as described above it isnt helpful positing all kinds of theories in a thread where the OP came looking for help.
Chuckles in Aerospace Engineering. I put myself through the NATO/West German AeroE course from 1986-1989, repeatedly referencing and studying that coursework from pure intellectual curiosity and a passion for aviation that I, my family members, and neighbors were all involved with in military developmental aerospace communities.
The materials science, gas dynamics behavior, and mechanical engineering involved in the AR-15 or any other firearm are childs play compared to the AeroE sciences, but I take them very seriously and perceive them coming from that space. There are other things I have done specific to this I will keep close to the vest, but funded technical analysis of US and foreign weapons has been something my family and I have been involved with for decades. Just in the private sector alone, I have been involved with final QC and design input on production rifles, in addition to Total Quality Management training from the business end.
More importantly though, Ive been a student of this particular firearms design prior to that, first gaining hands-on with it in 1987 and have never let go of it since that time.
The first 20 years of intense study, deployments, builds, troubleshooting, and researching the better historical accounts of it was the "climbing the mountain" phase.
Not until I really dove back into the 1959-1967 designs looking at it from a reloading perspective, did things start to finally make much more sense.
Getting into 6.5 Grendel in the 2000s expanded that understanding much further, because you learn to see what things you took for granted before.
A Chemical Engineering or structural engineering degree isnt much help in that regard, especially if it leads you to false conclusions that ignore some of the basic tenets of metallic cartridge behavior and pressure-containment systems and their specific failure nodes. Basic engineering principles are absolutely essential, but you really need more extensive training and experience in the field to correctly diagnose catastrophic malfunctions. Why were so many false conclusions jumped to early-on in this thread by supposed school-trained engineers?
A false sense of intellectual acumen with limited applied knowledge in the field can then lead to really bad initial assumptions, which are then doubled-down on-as has happened in this thread, with patently-absurb conclusions about Lapua brass being suspect, unsupported phenomena of case head failures, and refusal to see the obvious.
Ive seen other engineers who have made multiple errors and assumptions about pressure containment, because they came from a structural engineering background without formal or long-term experience in firearms engineering, but still decided to get into firearms. The basics apply, but there still is a mountain to learn.
In this case, ego allowed posters in this thread to derail it instead of waiting for us to get all the relevant data before the culprit became obvious.
Instead of accepting that, there is now an expectation of appeal to authority fallacy where there is no authority.
Any salty ME with decades of firearms experience will look at this and agree that the extremely lightweight 1.8oz buffer, combined with CLGS allowed for early unlocking to occur.
Literally all of the evidence we have seen points directly to that.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
Been quietly observing and have enjoyed some very intelligent, although different theories of cause and effect.. I would like to see a picture of the inside of the upper receiver behind the cam pin cut out to see if there is any significant gouging...
lazyengineer Wrote:Well, we made it 16 pages before the personal snipes started flowing. Not bad really - most other forums hit that much sooner I suppose.
Engineers can be one of the most catty bunch Ive ever seen, and hold grudges too.
The culture in engineering communities is a weird construct of geeks, nerds, with managers who have to wrangle it all somehow.
Ive seen some of the greatest minds kicked to the curb from classified programs that would have really brought value to the enterprise had they stayed, but egos couldnt be kept in check.
Short story for me is I dont like seeing bad ideas being thrown around when someone comes here for help.
I have a very strong sense of ownership of keeping the information here valid and useful, as was how I found it when I came here looking for help in 2009 on powder selection and recommendations from guys who had been loading for it for 5 years.
Imagine if I had gotten bad advice from some well-meaning types with pedigrees, who overlooked the obvious. I wouldnt have had much respect for the memberships ability to relay correct information.
This was literally the main incentive for collecting and formatting a set of Reloading Handbooks for this cartridge.
Excess cyclic rate and how to avoid it is discussed in those handbooks, as they deal with specifics to how the AR-15 works, knowing that many people would be building their own.
The work we put into those was peer-reviewed by prominent firearms and ammunition engineers in the field, not just some amateur attempt to throw out a set of reloading books.
Between the authors, were looking at:
Decades of aerospace and weapons test and evaluation experience for at least 2 of us, cumulatively amounting to over 100 years.
A PhD in biology and research in biotech who did the terminal ballistics testing.
Alaskan big game guide, NRA Hi-Power Master, and accomplished trophy hunter.
We had Bill Alexander and heads of ballistic research at several of the big name cartridge manufacturers review the drafts, so this isnt about me.
My biggest failure here was overlooking that post the OP made where he asked about the Strike Industries short pistol RET (shorter than a carbine RET), with its tiny little 1.8oz buffer.
Thats the nail in the coffin for diagnosing what happened here, when you look at the failure node on the brass clocked with the extractor.
Another thing Ive learned is I now have to monitor more closely people dropping into diagnostic threads where its very likely that bad information will be immediately posted, false conclusions posited without substance, then those ideas defended rigorously before we have all the important data.
I can tell you now not do engage in that kind of behavior. Its not helpful to people coming here looking for help.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
Oh, another thing. Anyone with even a never-been community college degree needs to check their basic spelling and grammar.
Ive lost count of how many times the word too has been misused on this forum.
Ive tried to be polite by just not saying anything, but it needs to be fixed.
For anyone with higher degrees, Im not going to take you seriously if you cant demonstrate English usage fundamentals that were conquered in the 3rd grade when I was growing up.
It speaks to credibility. Feel free to correct my mistakes as well. Im still one of those guys who capitalizes, punctuates, and keeps text messages grammatically correct as much as possible, despite auto-corrects campaign to put the wrong words in at every chance it gets.
Too: also, not to be used in-place of to. Guys, it takes longer to type it even, so why are you using incorrectly?
Maybe we need an adult remedial education program.
On a forum that focuses on technical subjects with potential risks, maybe step up your spelling and grammar game.
I shouldnt have to ask engineers to do this. Thats a given for all the general ed coursework you had to do prior to getting into higher ed.
It just irks me, and Im not "that guy, and dont like being placed in the position of being that guy.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
09-29-2022, 08:18 PM (This post was last modified: 09-29-2022, 08:21 PM by LRRPF52.)
Zeneffect Wrote:I never claimed to be anything more than stupid, so I'll take a pass.
Hey. Im willing to eat my own words if Im wrong.
The experience with why I think Im right is based on literally over 35 years of hands-on with this rifle design, to include a lot of under-the-hood research and work that is meant to mitigate or prevent these types of failures.
NRA Basic, Pistol, Rifle, Shotgun, RSO
CCW, CQM, DM, Long Range Rifle Instructor
6.5 Grendel Reloading Handbooks & chamber brushes can be found here:
Although slightly off topic, from a first glance it has appeared that the belts in many of the examples that I have seen are remarkably flat on their outside surface. They indeed often do look like the belts on belted magnum cases. This puzzles me since in my experience, bulges caused by pressure ted to be more rounded. Can anyone propose an explanation of why they are so flat.
Thanks.
Fess Wrote:Although slightly off topic, from a first glance it has appeared that the belts in many of the examples that I have seen are remarkably flat on their outside surface. They indeed often do look like the belts on belted magnum cases. This puzzles me since in my experience, bulges caused by pressure ted to be more rounded. Can anyone propose an explanation of why they are so flat.
Thanks.
I could be off on this, but seems like an equal pressure outward and axially on the cylinder that is unsupported, so a more or less uniform expansion of that cylinder...? Not sure if anyone has measured that portion to see if the wall is indeed a straight cylinder or has some bowing or conical-like stretching in it.
(My brain thinks completely grammatically, but the connection to my fingers sometimes hiccups... and my eyes don't always catch the little redline squiggly thingy that the text box gives when something is mis-spelled.... old age I guess!)
"Down the floor, out the door, Go Brandon Go!!!!!"
09-30-2022, 03:22 AM (This post was last modified: 09-30-2022, 03:32 AM by Old Bob.)
I know why the OP had a case blow-out. He wasn't holding his jaw right when he pulled the trigger. Or, he wasn't wearing his favorite socks & left his rabbits foot at home. Seriously, I'll go by the fellow who has been deep into the depths of the 6.5 Grendel for 20 years or more.
For anyone who wants to brush-up on there writing skills I suggest, The Elements of Style by William Strunk Jr. & E.B White. It helped me a lot.
LRRPF52 Wrote:The fallacy of this argument was already pointed out, but I dont recall a refute to it.
Sample sizes, assumption of the forum being a comprehensive collection of all failures, and another posters search showing up multiple other brass types to his query.
Did you perhaps overlook those like I did the 1.8 ounce buffer?
1.8oz buffer is significantly less weight than your typical 2.9oz carbine buffers.
I would never put that light weight of a buffer in a CLGS .223 Rem, let alone 6.5 Grendel.
OP basically duplicated somewhat one of the main problems they experienced with the Edgewater spring guide in Vietnam, shooting the new M193 with ball propellant, only his chamber is really clean and more likely in-spec.
I apologize for overlooking this critical piece of information that now pretty much nails the coffin shut on early locking with CLGS and 1.8oz buffer.
More pics of the throats and the buffer/flat spring. I think you are absolutely right LRRPF52. This is not a carbine buffer/spring/tube - it is a pistol/pdw. I did tune the gas down for this system - it's an adjustable block, but not enough evidently. Is it even possible to tune it down enough to use a 1.8 oz buffer or is it time to get a regular carbine buffer/tube setup now? Don't answer that - I'm an AR newbie but learning fast...
My take on the throats are that the PSA and Odin are similar with large chamfers, and the Faxon has a smaller radiused throat. In any case, I shot 50 rds in the Faxon with Starline brass today doing ladder testing for 123gr ELD-M and 130gr TGKs with Shooters World Match Rifle and was getting higher vels than the A2520 load with no signs of pressure at all in the brass. FWIW...
These probably don't matter anymore, but for posterity...
Odin throat:
[ATTACH=CONFIG]19153[/ATTACH]
Faxon throat:
[ATTACH=CONFIG]19154[/ATTACH]
PSA throat:
[ATTACH=CONFIG]19155[/ATTACH]
Buffer and flat spring in Odin pistol:
[ATTACH=CONFIG]19156[/ATTACH]
LRRPF52 Wrote:I wrote a section on this in Volume I of the 6.5 Grendel Handbooks back in 2012-2013, pages 19-21.
The section is titled: Barrel length and gas system length configurations.
Some shooters who have run certain hand loads through a 20 rifle with rifle-length gas, have then taken those same loads to see how they do in a 24 or even 28 rifle with rifle-length gas, and experienced apparent extreme pressure signs, where brass begins to separate at the head/web junction with the case walls just above the extractor groove location (See Figure 10).
This is what cases look like when you have too early extraction:
You can run that load through the 20 RLGS and brass comes out without these bulges.
Put the exact same load into 28 RLGS and you will see this problem.
Its a cyclic rate problem.
You can load a hotter load in the 20 RLGS and not even see this happen, use a reduced load in the 28 RLGS with the same components and it will still be there.
Its not the brasss fault, but the cyclic rate due to port location, plug dwell time, and carrier/buffer mass not able to resist the imparted inertia.
Cyclic rate timing is essential to master on any gas-operated firearm. The AR-15 does quite a good job of it when everything is balanced with port location, port size, plug dwell time, carrier mass, action spring weight, and buffer mass relative to the propellant mass, bore volume, projectile mass, working pressure, and propellant burn rate.
Think of it as a teeter-totter. On one end is the pressure-containment vessel and gas system, while on the other end are the reciprocating masses and spring.
The fulcrum is the bolt lock-up.
If you out-run the ability of the reciprocating mass and locking system to keep the case locked in the chamber until pressure subsides, you will have expanded case heads, partial or full case head separations, failure to extracts, torn case rims, etc.
Timing of the unlocking cycle is essential to avoid this.
OP used a 1.8oz buffer with CLGS, and dropped one end of the teeter-totter on the ground.
Thats a perfect recipe for partial case head separation.
LRRPF52 - I really appreciate all the work you (and the others as well!) have put into this thread. I've learned more about the Grendel and ARs in general from this thread than anything I have seen on YouTube or read. This forum is a real gem! Thanks for all the time you put into this - I know it was a lot! I just ordered one of those awesome boonie hats to show some appreciation!
stonehog Wrote:with no signs of pressure at all in the brass. FWIW...
Stone,
Be aware that typical pressure signs on brass mean you are already overloaded in Grendel. As you know, overpressure in an AR is unforgiving. My point is, don't wait until you see indications on brass before backing off. Velocities and tables are more helpful in this calibre.
Be aware that typical pressure signs on brass mean you are already overloaded in Grendel. As you know, overpressure in an AR is unforgiving. My point is, don't wait until you see indications on brass before backing off. Velocities and tables are more helpful in this calibre.
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