Aces High Bulletin Board
General Forums => The O' Club => Topic started by: Maverick on June 21, 2016, 11:21:01 AM
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I am thinking of doing a couple builds here shortly. If you have an issue with that, ar's or shooting in general please refrain from bothering to post your opinions here.
One will be a standard caliber, the NATO round with a 1:8 twist to use a larger variety of bullet weights / designs. No issue there really.
The other I am contemplating one of 2 calibers, the 300 blackout and the 6.5 Grendel. I really don't know enough about either to decide. I tend to like mid to longer ranges out to 300+ yards for some shooting. I'm not convinced the 300 is really that good given the slow velocities and I am not interested in a suppressor at all. Does the Grendel outperform it.
Ammo is not an issue as I load so as long s I can get components I have ammo.
I'm not doing an AR10, I have enough stuff in that round already and nothing will ever compare to shooting my Garand (converted when rebarreled a few years ago).
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I don't have firsthand experience comparing the two, but I'm fairly active in the AR community locally. My understanding is, the only real reason for 300 blackout is subsonic with a suppressor. If you're not going that route, I would go 6.5 all day.
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Some results for you to look through:
https://www.google.com/search?q=site%3Aar15.com+300+blackout+vs+6.5+grendel (https://www.google.com/search?q=site%3Aar15.com+300+blackout+vs+6.5+grendel)
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Are you doing the traditional direct gas impingement or are you going to make a reliable gas piston operated AR-15? Also, you really need a 20" barrel for shooting anything past 100 yards, else the bullet velocity will be too low to properly fragment.
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Are you doing the traditional direct gas impingement or are you going to make a reliable gas piston operated AR-15? Also, you really need a 20" barrel for shooting anything past 100 yards, else the bullet velocity will be too low to properly fragment.
Uh... Not sure where the implication that gas impingement is unreliable is coming from, nor the idea that a bullet won't fragment properly out of a 16" barrel... There's a roughly 100fps difference between 20" and 16".
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I just finished a 6.5 Grendel AR a few weeks ago. Based on an Alexander Arms lightweight 16" barrel.
The ONLY reason I can see to go with the .300 over the 6.5 is if you want to shoot subsonic suppressed. With a suppressor and subsonic loads the .300 can be almost 'movie' quiet.
In every other aspect the 6.5 Grendel is far superior. For shooting out past 300yds like you're talking about, the Grendel is far, far better then .300. Even though it's not as flat shooting as .223, the 6.5 is better at long distance, it has a higher BC and bucks the wind much better.
So far mine with factory loaded Hornady 123gn AMAX (after about 30 rounds to break in the barrel) is easily a 1 MOA rifle. As of now I have only had a chance to shoot mine at 100yds, but I plan to take it out to 300-400 yds this weekend to verify my scope dopes/holdover.
Come fall I plane to take a caribou with it, and maybe a sheep next year.
P.S. this is the barrel I used, looks like it's still in stock and for $195 for a double fluted barrel I don't think you can beat the value. http://www.shopalexanderarms.com/Barrels-6_5_Grendel_16_Lite_Barrel.html
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Are you doing the traditional direct gas impingement or are you going to make a reliable gas piston operated AR-15? Also, you really need a 20" barrel for shooting anything past 100 yards, else the bullet velocity will be too low to properly fragment.
Fragment?? for hunting you want penetration and expansion, not fragmentation. If he's only target shooting then who cares.
I did the research on this before buying my 16" barrel. With Hornady 123gn SST doing 2450fps at the muzzle. I'm right at their minimum recommended expansion velocity at 300yds. (which is not to say that it wouldn't still kill an animal farther out with proper shot placement) Which is fine for me, I'm not good enough to take a 300yd+ shot on big game. I've read that Nosler partition and Barnes TSX have lower minimums, so if you reload they may be better.
In my research I remember reading on AR15.com a thread where Mark LaRue (of LaRue tactical) took a bull elk at 480+yds with a 6.5 Grendel AR. Don't remember barrel length or cartridge used though.
I haven't actually chrono-ed mine yet, so I don't know if my muzzle velocity matches the published.
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http://www.65grendel.com/forum/
These guys will answer all your Grendel questions.
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Saggs and all, thanks for the input. I have pretty much figured on the 6.5. I have never had a rifle in the 6mm caliber so I'm kind of curious to see how it would perform. Now coming up with an upper for my budget will be a bit of a task.
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Would be curious to keep track of your build progress Mav....I have a Stripped Stag lower here that im going to try and start in the next few days if the darn Giessele trigger I ordered would just get here :furious.......Im putting a DD upper on it, should be a nice 3gun shooter.
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With a suppressor and subsonic loads the .300 can be almost 'movie' quiet.
Movie quiet? Movie quiet is noisy, that stupid zip zip sound they make doesn't sound anything like a suppressed rifle.
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Exhibit A: Fragmentation of the 5.56mm based on velocity. The way this tiny bullet works is by explosively fragmenting inside a target. When the velocity is too low, it just makes tiny little wounds. (http://farm5.static.flickr.com/4026/4212874291_6774d9c7cc.jpg)
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Uh... Not sure where the implication that gas impingement is unreliable is coming from, nor the idea that a bullet won't fragment properly out of a 16" barrel... There's a roughly 100fps difference between 20" and 16".
Exhibit B:
This is a barrel length vs muzzle velocity chart. Actually quite a bit of difference.
(http://sadefensejournal.com/wp/wp-content/uploads/2012/02/barrel6.jpg)
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Exhibit C:
Higher stresses and lubrication burn off from direct gas impingement versus what this paper calls an "external piston".
http://www.ewp.rpi.edu/hartford/~ernesto/SPR/LeBlanc-FinalReport.pdf
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Exhibit A: Fragmentation of the 5.56mm based on velocity. The way this tiny bullet works is by explosively fragmenting inside a target. When the velocity is too low, it just makes tiny little wounds. (http://farm5.static.flickr.com/4026/4212874291_6774d9c7cc.jpg)
Designed fragmentation is pretty specific to small light calibers like .223 because they are just to light to reliably expand. And because the military is not allowed to use expanding bullets, they make fragmenting FMJ rounds like M855 and M193. I was thinking in terms of larger heavier bullets since we where discussing .300 AAC and 6.5 Grendel.
It's apples and oranges. Nobody hunts anything bigger then varmints with lightweight .223 FMJs. Since we where talking about the 6.5 Grendel, and since I built mine for medium to large game hunting I was talking about hunting bullets.
We're both right, just talking about different things.
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Exhibit C:
Higher stresses and lubrication burn off from direct gas impingement versus what this paper calls an "external piston".
http://www.ewp.rpi.edu/hartford/~ernesto/SPR/LeBlanc-FinalReport.pdf
Sure, if you never, ever, ever, ever, clean your rifle then a piston 'might' be more reliable. But I think that 50+ years of military service and millions of DI rifles in the hands of civilian sportsmen have proved that DI rifles are plenty reliable if given proper care.
The only disadvantage I've ever seen to DI rifles is the gas in the face if you're shooting suppressed. Some people don't like the spring noise I guess, but that's never bothered me.
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What Saggs said in the first post - the 300 BO round is not much different than a 762x39 round IMO, and the only reason I have one is to have a round that is versatile for using both suppressed and unsuppresed fire. It's really the best round out there for the AR platform now which allows you to do both well. If you don't care to suppress a rifle, you're not taking advantage of 1/2 of the benefit of 300BO, so 300BO is out on that score for the OP IMO. One thing to take into consideration is the magazine issue - 300BO you can use PMag and standard metal mags. 6.5G, not so much, so you'll need to get a separate stock of magazines for just one rifle, but considering the $ of mags, not a huge deal, but one to be brought up at least.
Travis Haley ran a 300BO rifle for an entire year on every course he taught and attended, if you check out his writings and videos on it, he probably has the most thorough explanations and valid opinions regarding all aspects of the practical uses of the 300BO round.
Considering the ranges brought up in the OP, the 6.5 is a better choice, as at mid to longer ranges it is typically superior to the 300BO, and the 6.8 as well. Plus with a 556 rifle with a 1/8 or 1/7 twist barrel set up for heavier bullets like the Mk262 or other 77gr/etc rounds, Maverick should have a pretty hard hitting rifle in that one for mid range already, so a 6.5 will give performance that'll push out a little further compared to that, where as a 300BO won't.
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Designed fragmentation is pretty specific to small light calibers like .223 because they are just to light to reliably expand. And because the military is not allowed to use expanding bullets, they make fragmenting FMJ rounds like M855 and M193. I was thinking in terms of larger heavier bullets since we where discussing .300 AAC and 6.5 Grendel.
It's apples and oranges. Nobody hunts anything bigger then varmints with lightweight .223 FMJs. Since we where talking about the 6.5 Grendel, and since I built mine for medium to large game hunting I was talking about hunting bullets.
We're both right, just talking about different things.
A post-Vietnam War study found that it only took two 5.56mm rounds to kill a person with a 90%+ probability. This is how the 3 round burst came about. If 2 rounds had 90% probability of killing someone, 3 rounds would almost guarantee it.
Also, this pretty specific to the U.S. 5.56mm round. It enters the body, yaws 90 degrees, flattens out, undergoes around 70 g's, and then catastrophically fragments. It takes about 7 inches to do this, so it definitely penetrates first. Interestingly, the Soviets were not able to replicate this type of wounding with their AK-74.
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Suppressed 300BLK is on my wishlist, maybe one of the light scout setups.
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A suppressed 45 is the wtg if your going that route. I sold my 300blk because ammo was three times the cost of my ak's and my carbine 45 suppressed is more deadly with modern hollow points like federals Hydro shock and HST. The 6.8 is a better platform that inst a 223/762.39. The 300 is going to stay around and i do see it becoming more popular once people get out into the woods and find out that the 223 is very light for north american game.
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A post-Vietnam War study found that it only took two 5.56mm rounds to kill a person with a 90%+ probability. This is how the 3 round burst came about. If 2 rounds had 90% probability of killing someone, 3 rounds would almost guarantee it.
Also, this pretty specific to the U.S. 5.56mm round. It enters the body, yaws 90 degrees, flattens out, undergoes around 70 g's, and then catastrophically fragments. It takes about 7 inches to do this, so it definitely penetrates first. Interestingly, the Soviets were not able to replicate this type of wounding with their AK-74.
This was true in pre-1968 AR's that had the 1/14 twist. The complaint was...not very accurate.
Post 1968 they went to a 1/12 twist, stablized the bullet, more accurate. The soldiers complained that the enemy didn't go down immediately like they did with the unstable 1/14 flight travel of a 5.56mm.
At least this is what I've read in books.
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This was true in pre-1968 AR's that had the 1/14 twist. The complaint was...not very accurate.
Post 1968 they went to a 1/12 twist, stablized the bullet, more accurate. The soldiers complained that the enemy didn't go down immediately like they did with the unstable 1/14 flight travel of a 5.56mm.
At least this is what I've read in books.
While you are correct in a change of the rifle twist, that did not have any effect on bullet fragmentation. The fragmentation is due to the bullets center of mass being so far rearward. It yaws violently once entering the human body and breaks up. Still does to this day with enough velocity.
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I would argue it does not yaw 90 degrees when entering the body. At least with a 1/7 -- 1/12 twist rate. Maybe if it hits a rib, yes.
Just youtube ballistic gel tests. You'll see in a nice straight line, with normal expansion of the gel due to cavitation (normal for every high speed bullet) but the tests I've seen, with none-HP 62 gr or 55 gr bullets, most retain their weight with very little fragmentation UNLESS it hits a bone.