JASmith Wrote: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.

Grendel:

Near Base 0.4426
Near Shoulder 0.4328

Difference 0.0098

Datum Length 0.8000

Taper 0.0123

.308 Winchester

.308 Win

Near Base 0.4703
Near Shoulder 0.4553

Difference 0.0150

Datum Length 1.2500

Taper 0.0120

SightedIn Wrote: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.

bj139 Wrote:Are you actually measuring this? You are quite a bit off from SAAMI.

bj139 Wrote:2) I have found the side charger is more difficult to extract due to the force on the bolt not being in line with the bolt but to the side by more than an inch.
A charging handle has a more direct line of pull on the bolt being above the bolt by about 1/4 inch.

3) I agree with you on the light loads being easier to eject.

bj139 Wrote:Who is the father of making the case less tapered to increase capacity? Why PO Ackley, of course.
On searching I found this from https://www.shootersforum.com/wildcat-cartridges/80843-i-think-po-ackley-something.html

"nvshooter's Avatar
nvshooter nvshooter is offline
Beartooth Regular

Join Date: Oct 2010
Location: Nevada
Posts: 4,884
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.

bj139 Wrote: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.

SightedIn Wrote:To each his own I guess. I have used t-handle extraction method and the side-charge handle extraction, and i personnaly prefer side pull.
I extract with palm side up, giving a good firm pull, but not a jerk, all the way back, and release. Never a struggle for me to extract in that manner.
Hope that helps