I tried to set up a 6.5 Grendel used in a manual mode and had stuck case problems.
I have been doing the same with a couple 6.8 SPC wildcats and am able to manually eject full power loads easily.
I think case taper is the problem.
This may have implications for military selection as well.
The Grendel is close to the 308 but not as large as the 6.8SPC.
I know maximizing case capacity was a goal but ejection should be easy or problems may occur.
What are the opinions of the horde?
The hype over the 6.8 SPC being the Next Great Service Cartridge is long gone, and neither is any other existing cartridge being considered. These days they're working on case telescoped technology.
When you say "manual mode" do you mean you've turned off the gas system and are operating your AR as a single shot?
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03-01-2018, 03:17 AM (This post was last modified: 03-01-2018, 04:04 AM by bj139.)
Like this. No gas block is necessary. Magazine fed, charging handle operated.
No evil "barrel shroud", forward assist or dust cover. Should be PA deer hunting legal.
One American 30 and one 6x6.8. Both based on the SPC.
Something besides case taper is your problem. Cases extract from my TC Encore just fine even though a lot of full power and inadvertent extra high pressure loads have been fed it. Same for other Grendel rifles I use.
BTW, the inadvertent high pressures resulted from cases stretching (14-15 reloads with no trimming) to the point where the case mouths were jamming into the start of the throat.
Hence, a process of elimination needs to be applied to discover the cause of the extraction problem. The SAAMI-defined case taper is the last item to consider.
A place to start is verifying that your extractor claw has the correct dimensions. I discovered this when I used the .308 bolt face instead of a PPC bolt head in my Savage Model 16. The problem went away when I did what should have been done in the first place and installed the PPC bolt head.
This does not rule out the possibility that the reamer used to cut your chamber was out of spec.
This can be easily checked by comparing an unfired case with a fired case that was difficult to extract. That includes measurements at key points in addition to visual comparisons.
Good luck and keep us posted on what you discover.
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The process of a case gripping the walls of the chamber during powder combustion is called obturation. It's one of the devils that plagued the M-16 in its early days. There is a lengthy article about this phenomenon, written by the military man whom discovered it. Can't remember his name, but he wrote a letter to the top brass about the failures of the spent cases to extract from the chambers during firefights in Vietnam. He referred to his letter as the "letter read 'round the world." Might be able to find it using that in your search string. Add "M16" to it, and your luck should improve. Very interesting reading. The failures to extract got a lot of good men killed. Sad, as well as being something that stokes the fires of rage that the rifle and round were not more thoroughly tested before being fielded. Add to that, the troops were told the rifle was "self-cleaning." Nothing could have been further from the truth, given the powder recipe they used in those days.
I think an Ackley case obturates more than a standard case because it has that small amount of extra cylindrical value. I do not know if Ackley cases are less tapered than a standard case. Maybe, to wipe out the original chamber. Might be why they stick better than standard cases. Opinions and comments welcomed...
The man's name is Richard Culver. Marine. Lots of stuff about his M16 experiences on the 'net..."
Case taper is the same on the SPC as the 5.56 but the case is shorter. Shorter cases should result in less chamber "sticktion" if that's a word.
Grendel case is shorter, so maybe less also. I would think Bill Alexander has this all worked out but I haven't read anything about it.
When I shot my Howa bolt last week, the bolt handle was difficult to lift with factory Wolf ammo which is what got me thinking.
Could be the two BHW barrels shown above have much smoother chamber walls as well.
I am expecting a 20" Ballistic Advantage barrel from UPS today.
I will assemble it with no gas block and see how difficult ejection is. The chamber should be smoother than my BCA Grendel.
Maybe time to take a few gas blocks off others and shoot to see.
03-01-2018, 04:44 PM (This post was last modified: 03-01-2018, 04:46 PM by bj139.)
JAS,
I had problems with a 357 Herrett Contender nearly 40 years ago.
I had to hammer the action open after forming cases and shooting starting loads.
The culprit was thick necks which did not allow the neck to expand and release the bullet.
After reaming it was fine. That taught me a healty respect for starting at starting loads.
The TC single shots have some primary extraction built in which the AR in manual mode does not.
With 10% reduced loads in my BCA Grendel barrel they were mostly ejectable without mortaring but with factory loads mortaring was necessary.
Something isn't right. A properly cut chamber should not stick cases. The 338 edge, and nosler cartridges have half the taper of the G, in twice the case length. As well as higher pressures.
I read a bit more about the M16 case sticking in Vietnam and that was due to rusty chambers.
The rims were being ripped from the cases while still in the chamber.
03-02-2018, 02:11 PM (This post was last modified: 03-02-2018, 02:21 PM by bj139.)
Djgrendel Wrote:Something isn't right. A properly cut chamber should not stick cases. The 338 edge, and nosler cartridges have half the taper of the G, in twice the case length. As well as higher pressures.
I just checked with SAAMI and the 22 Nosler has the same taper as the 6.8 SPC. SAAMI says 175 ten thousandths/inch.
224 Valkyrie has the same as well as all the other Noslers.
6mm and 6.5 Creedmoor have 64 ten thousandths/inch or less than half as much.
You have not yet shown a comparison between the Grendel taper and that of the other cartridges. Last time I did that the Grendel taper was surprisingly close to the .308 Win and rhe .223 Rem. On addition, the body length is shorter than that of the .223 Rem.
To put things more bluntly, chamber taper is not your problem unless the reamer maker or guy who resharpened it screwed up royally.
To repeat, you can check the actual condition by measuring and comparing diameters at keypoints on fired and unfired brass.
Start a checklist and follow it through. The folks on this forum are only too happy to list suggested things to check. Start with the things that seem most probable and move to the least likely.
On more time, your problem is not the result of a design defect in the SAAMI Grendel chamber.
JAS,
Check out my original post for a jpeg at the bottom with a selection of cartridges showing case tapers.
I had to do this to maintain table alignment.
The board somehow made the thumbnail very small.
I am only reporting on what I find, nothing more.
SAAMI has complete specs on these cartridges on their website if you care to look. No measuring necessary.
If a gas gun has the power to rip rims from cases, case taper should not be a problem except in manual operation as I noted.
Bj139,
Just to be clear here, when you say stuck cases, do you mean you fire a single round, then attempt to pull the t-handle to expend the cartridge and its very difficult to extract?
If that is the case, i am not surprised. I have built several single shot AR's in the last year and a half, and manual extraction after firing a single shot AR can be difficult depending on a few variables.
In the AR, there is no extraction can or lateral lever to assist in unlocking the bolt. Par for the course isn’t it? Try and extract any bolt fired cast without the bolt handle. Similar results would be in order.
Just the conclusion I’ve come to after thinking about this.
Nothing kills the incentive of men faster than a healthy sense of entitlement. Nothing kills entitlement faster than a healthy sense of achievement.
Using the datum dimensions for the .308 Win and Grendel, I see that the .308 taper is 0.0120 in/in while the Grendel is 0.0123
in/in which means the Grendel has a bit more taper than the .308 Winchester.
I see. Well heres my best advice for building a single shot(gas-less) grendel AR that extracts well(or .223 for that matter)
1) Works smooothest when bolt and barrel are a factory matched set. This lets the bolt rotate easier during extraction. I have hypothized that if using a non-matched set, you could lap in the bolt/chamber interface, but have never tried myself.
2) You really need a side-charging upper. I have used a Gibbs and a BCA. The side charger really allows you to perform a clean, continuous, firm pull to to extract.
3) Loads. light to moderate loads will extract much easier. If using hot loads extraction will be difficult, even with the tips above performed. I have two good nodes with a few loads, but typically use the lower one for this reason.
![[Image: 38576826620_a8a7a1fb20_c.jpg]](https://farm5.staticflickr.com/4670/38576826620_a8a7a1fb20_c.jpg)
