Broken 6mmAR Bolt

[SHORT-N-SASSY]

And, today's postscript:




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ETA:

Re Recoil Energy: The 6.5mm SAUM 4S has 28% less than the .300 WSM, in this comparison.

[SHORT-N-SASSY]

And, today's response from CMMG:

[SHORT-N-SASSY]

CMMG Pistol, Banshee 100, MKW-15 6.5mm Grendel, 12.5" barrel ---


TO:


And the answer I received from CMMG Tech Support, yesterday, "Yes, the MKW does."

[SHORT-N-SASSY]

And, in that this model is classified as a "pistol", the question re the legality of mounting a pistol grip on the fore-grip came to mind. I researched the matter: < http://www.guntrustguru.com/can-i-add-a-...istol.html >. "The ATF's current position is that a firearm with an overall length of 26 inches or more does not meet the definition of "capable of being concealed on the person" . . . As a result, a person may add a vertical fore grip to a firearm with an overall length of 26 or more inches . . ."

The key question, then: What is the overall length of the CMMG Pistol, Banshee 100, MKW-15 6.5mm Grendel, 12.5" barrel, with the flash hider removed. That was the question I posed to CMMG Tech. The answer: "27.3 inches".

[biodsl]

I want one of these in 6mm ARC. Could be the ultimate door-kicker gun.

[SHORT-N-SASSY]

Using the gundata.org Ballistic Calculator, dialing-in the respective muzzle velocities from 12.5" barrels, I compared the 6.5mm Grendel (A) loaded with the 123-grain SST projectile (BC - 0.510) against the 6mm ARC (B) loaded with the 108-grain ELD Match projectile (BC - 0.536) up to 500 yards ---

[Fess]

My memory is not the greatest, but isn't the true BC of the SST significantly lower than advertised? I recall one post where someone stated that it is more like .485. Sorry if I got this one confused with another.

[SHORT-N-SASSY]

http://www.hornady.com/bullets/rifle/6-5...c-lapua#!/

[biodsl]

My memory is not the greatest, but isn't the true BC of the SST significantly lower than advertised? I recall one post where someone stated that it is more like .485. Sorry if I got this one confused with another.

Your memory is correct, Fess. LRRPF52 made that observation a while back. I'm assuming it's based on drop-at-distance compared to the Amax.

[Fess]

Thanks, biodsl. Part of the reason that I remember it is that the 120 grain SST for the 6.8 has a listed BC of .400, and the designs are not too dissimilar. The 6.5 SST is sleeker for sure, but side by side shooting was not as radically different as you would expect from a .400 vs .510 BC. I vaguely remembered that either LR1955 or LRRPF52 had commented that the real-world BC was significantly lower than Hornady's advertised .510. I had to take muscle relaxers for my back the last couple of days, so ALL of my memories are a bit vague lately!

[SHORT-N-SASSY]

http://www.ar15.com/forums/ar-15/New_Hun.../#i5708853

[Fess]

I did some more searching and found a couple of more recent posts. I can't figure out how to create images of the original posts, so I'll give the quotes and then links to the threads.

One problem when quoting a G1 BC is that it is not an accurate representation for a boat tail bullet design. The effective G1 BC for a typical boat-tailed bullet varies with its velocity.
Sierra Bullets for example, will provide multiple G1 BC's to be used in differing velocity regimes. Bryan Litz performed shooting tests with the 123 grain SST and found the effective G1 BC to vary dramatically with velocity.

"Here are Litz' numbers for the 123 SST, which I believe is the same (or at least very close) to the AMAX:

G1
overall .462
below 1500 .406
2000-1500 .432
2500-2000 .467
3000-2500 .491
Above 300 .526"


This quote are from post #6 of a 2015 thread discussing the then-new A-MAX. https://www.65grendel.com/forum/showthre...23-amax-BC
I should note that Hornady is not actually lying, it just posted a G1 BC in a velocity range above that reached by a 6.5 Grendel. It was later determined that the SST and AMAX were not the same shape.

This second quote is the one that I was thinking of when I made my earlier post. It just took a while to find. It was made by LRRPF52 on 07-16-2019:

"123gr SST is more like .463 G1, nowhere near .510 G1."

It can be found at post #8 in this thread: https://www.65grendel.com/forum/showthre...-Perplexed

I don't think that Hornady has recently changed the shape of the 123 SST, but anything is possible.

[SHORT-N-SASSY]

I today sent the following email-request to Hornady Manufacturing Co. ---

[Mad Charlie]

Good job! SnS. I will be very interested in what they have to say.

[SHORT-N-SASSY]

As we await a response from Hornady, I researched the issue:

Comparing Advertised Ballistic Coefficients with Independent Measurements
http://www.65grendel.com/forum/showthrea...post114343
(See the attached PDF file) The Report covers January, 2009 thru June, 2011.

Introducing the ELD-X: Hornady's newest and most sophisticated bullet is a BC breakthrough
http://www.thefreelibrary.com/Introducin...0436981663

And, as stated by BluntForceTrauma in his July 16, 2015 Report, Litz found the Ballistic Coefficient of the Sierra 6.5mm 123-grain MatchKing projectile to be 0.522, not 0.510, as advertised.

The following compares the 6.5mm Grendel (A)123-grain Sierra MatchKing, Ballistic Coefficient (G1) - 0.522, muzzle velocity (12.5" Barrel), 2420 fps, with the 6mm ARC (B) 108-grain Hornady ELD Match, Ballistic Coefficient (G1) - 0.536, muzzle velocity (12.5" Barrel), 2380 fps, to 500 yards, w/ 10 mph crosswind ---

[SHORT-N-SASSY]

I today received the following response from Hornady Manufacturing Co. ---





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Thank you, Hornady.

And, then, there's the Hornady 6.5mm Grendel 123-grain ELD Match Hornady Black factory load: BC - 0.506 (G1).

All in all, I think it's fair to state that the Bryan Litz Report was an eye-opener, a whole new ball game for extended-range shooters.

[SHORT-N-SASSY]

And, the Nosler 6.5mm ABLR gets high marks on this Forum

http://www.65grendel.com/forum/showthrea...post193445

Comparing the 6.5mm Grendel (A) loaded with the 6.5mm Nosler ABLR 129-grain projectile, BC - 0.530 (G1) against the 6mm ARC (B) loaded with the Hornady ELD Match 108-grain projectile, BC - 0.536 (G1), from 12.5" Barrels, up to 500 yards, with a 10 mph crosswind ---

[SHORT-N-SASSY]

To update:

The Ballistic Coefficient used for the Nosler ABLR 129-grain in my last Post was based on this information ---


< http://www.nosler.com/accubond-long-range-bullet >

i've since come upon the following:


< http://www.longrangehunting.com/threads/...ost-966832 >

I now compare the 6.5mm Grendel (A) with the 6mm ARC (B) substituting the updated Ballistic Coefficient (0.553) for the 6.5mm 129-grain Nosler ---

[SHORT-N-SASSY]

ETA:

Bryan Litz on the importance of proper twist rates for low-drag bullets ---


(See his Post on longrangehunting.com, above)

[biodsl]

BFT adopting the 1:7.5 for the twist rate for the SixFive barrels was a smart move. But we already knew that...