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Posted: 8/7/2012 2:44:04 PM EDT


Pretty awesome from an info perspective. Anyone have something for 6.5 that's like this?
Link Posted: 8/7/2012 5:48:47 PM EDT
How did you come up with this?
Where did your numbers come from? Im guessing not real world testing?
For some reason those numbers and the graph dont look right.... Not sure how the larger case of the 6.8 is going to increase rate at such a similar line as the 300blk. Something is just off, I am having a hard time putting 2 and 2 together, will have to revisit after a beer and some sleep.

Otherwise, thanks for putting this up here!
Link Posted: 8/7/2012 9:13:37 PM EDT
Numbers are old/low on the 6.8SPC 110gr V-Max.
Link Posted: 8/8/2012 1:40:34 AM EDT
Found it at the 6.8 forum, just reposted here. I didn't come up with it, just thought it was neat, might be useful!

I haven't seen any SPC2 numbers, do you have a chart that's like this for it?

I know the 8.5" SPC2 is getting crazy numbers, I'll post them up here:

SSA 115 grain OTM Tactical: 2150 - 2170
SSA 110 grain Accubond Tactical: 2200 (the old combat load was 2350 but SSA doesn't load them that hot now)
SSA 110 grain Pro Hunter: 2100
SSA 100 grain Accubond: 2200 (SSA is supposed to start loading these hotter but have been waiting for new powder)
SSA 90 grain TNT (not plinking round): 2519
SSA 85 grain TSX (old combat loading) 2678. I haven't fired the newer Tactical load yet but I hear it is around 2580 - 2600.
Hornady 110 grain OTM: 2200
Hornady 110 grain Vmax: 2190

(LWRC PSD in 6.8)

Pretty sure 85 gr from 8.5" at 2678 is absolutely insane. That's faster than light loads on an 11.5" 5.56.

I really want to keep liking 6.5, but this 6.8 is making it hard. Being able to hunt out to twice the effective range of a 5.56 with an SBR sounds nice. Only if someone made an M4-S for it (contacted Ops Inc about it myself, if anyone else wants to).
Link Posted: 8/8/2012 2:42:04 AM EDT
Velocity is one thing, retained energy is another.

http://shootersnotes.com/pictures/GrendelBarrelVel.jpg

I get 2700fps with the 100gr Nosler Ballistic Tip from my 16" Grendel, and 18-20fps of velocity per inch seems to be the norm across a lot of people's blasters.  Not sure if that would stay linear going down in barrel length, but assuming 25fps loss per inch, a 10" could push the same at 2550fps.
Link Posted: 8/8/2012 4:11:54 AM EDT
I knew I recognized that data from somewhere!

http://300aacblackout.com/resources/300-BLK.pdf

That's the AAC .300 sales material to the military, it seems. I'd been using it to plan out my own 6" .300 PDW.

Problem is with assuming a constant velocity loss... they're curves. I'm interested in the 'knee' of the curve, which means the part where it's the best trade of length for velocity, the most efficient spot.

Looks like .300 should be 6-9", 6.8 should be about 9-13", and 5.56 should be 11.5-17". That's comparing slope to slope. (And a little bias on what I think each one is for. I'd personally go .300 up to 8", 6.8 from 8.5-13" and 5.56 from 14.5-17".)

Yes, this is imperfect data, old SPC dataset, and it all depends on powders, ect, but I think it's good info on the basic nature of what barrel length the cartriages want...

...so I'm interested to see one of 6.5.
Link Posted: 8/8/2012 4:16:05 AM EDT
Quoted:
Velocity is one thing, retained energy is another.

http://shootersnotes.com/pictures/GrendelBarrelVel.jpg

I get 2700fps with the 100gr Nosler Ballistic Tip from my 16" Grendel, and 18-20fps of velocity per inch seems to be the norm across a lot of people's blasters.  Not sure if that would stay linear going down in barrel length, but assuming 25fps loss per inch, a 10" could push the same at 2550fps.


Your link is broken. And yeah, 6.5 has a very good BC, SD, etc. I /want/ to like 6.5 for a hunting round (I don't want to have to deal with as much recoil to reach out, I don't want to deal as much with wind and drop...), but I'm trying to objectively compare it to 6.8 in ranges in which they'd both be humane (ft-lb) choices.
Link Posted: 8/8/2012 5:48:57 AM EDT
Quoted:
Quoted:
Velocity is one thing, retained energy is another.

http://shootersnotes.com/pictures/GrendelBarrelVel.jpg

I get 2700fps with the 100gr Nosler Ballistic Tip from my 16" Grendel, and 18-20fps of velocity per inch seems to be the norm across a lot of people's blasters.  Not sure if that would stay linear going down in barrel length, but assuming 25fps loss per inch, a 10" could push the same at 2550fps.


Your link is broken. And yeah, 6.5 has a very good BC, SD, etc. I /want/ to like 6.5 for a hunting round (I don't want to have to deal with as much recoil to reach out, I don't want to deal as much with wind and drop...), but I'm trying to objectively compare it to 6.8 in ranges in which they'd both be humane (ft-lb) choices.


Within normal hunting rages the 6.5 and the 6.8 are so close as to not matter. The 6.8 has more ammo choises (and more hunting specific bullets) than the 6.5, and better industry support. Otherwise they are a wash. Inside 300yds, the BC advantage of the 6.5 is not enough to beat the 6.8, but the 6.8s velocity is not high enough to beat the 6.5s BC eather. Realisticly, unless your pushing the 140vlds, 350yds is going to be the cap for most of your hunting rounds, and the 140s cap at ~400-425 depending on barrel and velocity you can get them too.

FWIW: 6.8 100gr Accubonds are pushing 2750-2775 in most spc 2 16" barrels.

Link Posted: 8/8/2012 1:39:24 PM EDT
Looks like the 6.5 kills the 6.8 from a 12.5" barrel.

http://www.ar15.com/forums/t_3_121/566213__ARCHIVED_THREAD____Intermediate_Cartridges_and_Their_Differences.html&page=4#i5440487
Link Posted: 8/8/2012 5:14:30 PM EDT
SSA 2nd generation 115 gr SMK OTM w/cannelure, 5 shot averages:

20” barrel: ave vel = 2561 fps; 10 fps extreme spread

16” barrel: ave vel = 2525 fps; 18 fps extreme spread –– lost 36 fps from 20"

12.5” barrel: ave vel = 2384 fps; 12 fps extreme spread –– lost 141 fps from 16"

10” barrel: ave vel = 2265 fps; 27 fps extreme spread –– lost 119 fps from 12.5"

7.5” barrel: ave vel = 2035 fps; 27 fps extreme spread –– lost 230 fps from 10"

EDIT: You can see that at 16" this 115 gr is a little faster than the initial data for the 110 gr. Here's more data, including a faster yet load:

10.5" Noveske barrel, 6.8

- 85 grain SSA TSX (Tac Load): 2787, 2823, 2777 , 2804, 2809
Low: 2777
High: 2823
Average: 2800
Spread: 46


- 110 grain S&B PTS (V-Max): 2249, 2238, 2270, 2268, 2256
Low: 2238
High: 2270
Average: 2256
Spread: 32


- 110 grain Hornady BTHP: 2312, 2376, 2342, 2358, 2333
Low: 2312
High: 2376
Average: 2344
Spread: 64

So is 110 gr at 2344 fps from 10.5" the SPC2 endpoint? It is about 75fps faster than the initial (old) data. Looks like the SPC2 from SSA is about 26 fps faster too 16″ 6.8 SPC II 1:11″ SSA 110 TSX: 2575 fps, so SPC1 to 2 is about a 75 fps gain at best?

The latest data on 140 6.8 vs 139/140 6.5 is about 51 fps difference, 16" to 16", so the 6.5 is going to catch up to that almost right away.  /EDIT

Interestingly, the 6.5 is getting more veloicty than the 10" at 115 gr 6.8 than the 10.5" 123 gr 6.5. Just a tiny bit more (10 fps more, IIRC), but eight more grains, but .5 more barrel... kind of a wash. The 7.5 is terrible, loses almost double in 2.5" what the 10" lost in 3.5". Can really see why LWRC is taking their 8" off market and staying at 8.5" for the 6.8. So far it looks like the lower you go, the better the 6.5 gets in comparison, at least until 10/10.5. Weird. It's a winner at 12.5 past 175y, it's a winner at 10/10.5 right about at the barrel, it's a winner in longer barrels further out...

Seems like the 6.5 is a better SBR round than the 6.8 (at least until 10.5), which seems backwards to both what seems to make sense as well as the general thought process. I'm keeping looking for data points, though.
Link Posted: 8/8/2012 7:21:16 PM EDT
Quoted:
I knew I recognized that data from somewhere!

http://300aacblackout.com/resources/300-BLK.pdf

That's the AAC .300 sales material to the military, it seems. I'd been using it to plan out my own 6" .300 PDW.

Problem is with assuming a constant velocity loss... they're curves. I'm interested in the 'knee' of the curve, which means the part where it's the best trade of length for velocity, the most efficient spot.

Looks like .300 should be 6-9", 6.8 should be about 9-13", and 5.56 should be 11.5-17". That's comparing slope to slope. (And a little bias on what I think each one is for. I'd personally go .300 up to 8", 6.8 from 8.5-13" and 5.56 from 14.5-17".)




Take what numbers those clowns post with a grain of salt. Skewed numbers is their specialty, even more so when they are trying to make the 300blk look good compared to the competition.

I know you have found this out already but the 6.8 numbers in that other chart are on the weak side. 2700fps+ is common with a correct spec 16" barrel.
Link Posted: 8/8/2012 7:34:24 PM EDT
Quoted:Take what numbers those clowns post with a grain of salt. Skewed numbers is their specialty, even more so when they are trying to make the 300blk look good compared to the competition.

I know you have found this out already but the 6.8 numbers in that other chart are on the weak side. 2700fps+ is common with a correct spec 16" barrel.


It's pretty amazing it's doing just under 2700 from an 8.5" at 85gr.

AAC is known for bad numbers?
Link Posted: 8/9/2012 5:22:08 AM EDT
We also have to look at terminal ballistics.  I personally prefer a long, high SD pill that plows through tissue medium, which is why the Grendel has an edge in this arena.

The 120gr SST in 6.8 comes academically close to some of the common Grendel loads for hunting, with a great bullet that has good SD.

The MV's are nice to have high, but "What does the bullet do on and through target?" are the real questions that should drive the build.  The 6.8 has proven a highly capable SBR blaster for hunting, but a lot of people haven't really tried it with many other calibers, to include the Grendel.

There are guys who have shot some exotic game with TC's in both Grendel and 6.8 from 14" barrels, and the guy I'm thinking of in particular said he prefers the Grendel since he has a selection of pills that are so long, they drive deeper through the game he has taken with them, giving a higher probability of pass-through and deep tissue intersection.

Guys have been doing a lot of experimentation with 160gr pills in the Grendel subsonic, and getting very deep penetration through multiple water jugs, so even if you pushed a 140gr or 130gr around 2000fps from an SBR, you will still get deep penetration.  It then becomes an issue of expansion threshold if you want optimum expansion from the bullet you're shooting, or are willing to shoot below the manufacturer's recommended expansion threshold impact velocity to determine your effective range for ethical killing.
Link Posted: 8/9/2012 4:44:46 PM EDT
Kind of found it:



Just need to get something towards the lower end.

...I think I saw something like this posted but the link didn't work. Hm.

Edit: It's not too terribly useful without data. Numbers, and I think it's just using a calculator. Need to keep searching.
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