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+--- Thread: 65G Bolt-face Depth Infographic (/showthread.php?tid=12953)
65G Bolt-face Depth Infographic - BluntForceTrauma - 03-12-2017
Guys, I've created an infographic to try and show the issues involved in using either a 0.136- or 0.125-inch bolt-face depth in 6.5 Grendel ARs.
If you assume the extractor is the same overall length and has the same extractor pin location as a standard 5.56 extractor, then a 0.125 bolt-face depth requires a weakened extractor lip, whereas a 0.136 depth allows either a standard 5.56 extractor lip or, for an enterprising company, an enhanced 6.5 Grendel extractor.
Feel free to repost these graphics all over the web whenever you're trying to explain 6.5 Grendel bolts.
65G Bolt-face Depth Infographic - brian y - 03-12-2017
Nice job BFT
65G Bolt-face Depth Infographic - JASmith - 03-12-2017
Nicely done!
65G Bolt-face Depth Infographic - Sticks - 03-12-2017
Now go slap LRRPF52 for not doing this sticky.
Thanks BFT!
65G Bolt-face Depth Infographic - Red Dawn - 03-12-2017
Thanks BFT knowledge is the key.
65G Bolt-face Depth Infographic - Bill Alexander - 03-12-2017
That is very nicely done.
I see with interest that the justification for a 0.125" bolt face depth continues to be that the bolt is perceived to be stronger and that the lugs are better supported. I am going to go out of my comfort zone a little here and make a few notes about some of the small details that we sneak into the design to alleviate the effects of the larger rim recess. It goes without saying that the bolts have a good metallurgy and that the heat treatment is improved. The perception is that the alloy is AISI 9310 steel. It is in fact very closely aligned to this but we select an alloy known for its enhanced fatigue life over regular 9310. It is not specifically a stronger alloy just resists crack formation better.
Steel aside, the bolt lugs are very slightly tapered to increase the root area but more importantly stiffen the ring of material that they sit upon. Radii are increased as expected and the minor diameter at the base of the lugs is slightly bigger than one would casually observe. This all stiffens the ring of material that sits under the front of the lug, so too do we reduce the chamfer at the front of the bolt recess leaving more material in this area. Given the bigger rim, the chamfer on the case base is greater allowing the internal radius at the bottom of the bolt face to grow. This material in this area very quickly offsets the extra 0.011" of face depth even without other adjustments. (Remember that 0.011" of material is about 2-1/2 sheets of copy paper in thickness and in this instance it is in an area that is already machined away so the bulk stress raiser is already present.)
There are additional changes in the area of the extractor groove which is always a feature that effectively undercuts the two adjacent lugs.
A correctly machined Grendel bolt is substantially stronger than a 5.56 bolt simply opened out during production to suit a Grendel rim. My only reservation has come from the military requirement that the unit should survive being fired with a breach obstruction of a projectile in the start of the rifling. While this test will always destroy an AR functionally, a good 5.56 bolt will stay intact, though deformed, but a Grendel bolt will break lugs. The constraint of a near standard geometry barrel extension is the driver for this as some changes in shape, not size or diameter in the barrel extension could yield a bolt/barrel extension combination that is magnitudes stronger.
65G Bolt-face Depth Infographic - Djgrendel - 03-13-2017
Once again, I'm blown away by Mr Alexander's foresight...Thanks to him, and thank you BFT for having such a great forum.
65G Bolt-face Depth Infographic - kmon - 03-13-2017
Thank you Gentlemen for once again providing the Horde with useful information and insight
65G Bolt-face Depth Infographic - sierracharlie338 - 01-24-2018
Quality info here. Thank you