AR15 Platform : which caliber for a "do-it-all" (almost) purpose rifle ?

[LRRPF52]

You guys have me pondering now. Just out of curiosity, how far are 6.5G factory barrels throated too?

Say if I were to point up some 140 grain Berger hybrids/ .65-.66BC and seat them out close to the lands for single feeding, what velocity out of a 20" barrel could I expect?

The SAAMI Grendel chamber uses a compound throat, so there is taper from the neck to the leade, which helps center the projectile in the AR15 while having neck dimensions that are more forgiving for gas gun feeding.

For single feeding, I would look at the 130gr Berger & 130gr Norma before the 140gr Berger. All of these have significant case intrusion.

I just made a dummy cartridge with the 130gr Berger, starting at 2.360" COL, and it was jammed into the lands pretty hard. It extracted with medium force using the charge handle in the upper separated from the lower, but I wouldn't ever load that bullet to that COL in my SAAMI chamber.

I then seated it to 2.310", and I see no land engagement, extracted with ease. There are production mags that will already fit that COL, but you have to have uniform bullet length, and as you know, all the BTHP's have variance that is enough to cause hang-up inside the magazine when you push the COL, so your intent to point and uniform them all would take care of that.

A 20" will push a 130gr to 2460fps with powders like CFE and LVR. If you got a 9130 BR bolt and extension from Bustin, you could push to 2600fps.

The Grendel chamber really was designed to work well from the AR15 mag-fed, so there isn't a lot of jump. No matter what bullet I have tried, my gun consistently groups into just under .8" to 1.2" at 100yds, and 1.7" to 2.2" at 200yds, with just a cheap ER Shaw button pipe. It does that with 100gr NBT's, 107gr SMK's, 120gr SMK's, 123gr Scenar's, 123gr A-MAX, 123gr SST's, and 129gr SST's.

Some other bullets that will mag-feed that have high BC's are the 130gr Swift Scirocco, and the new 129gr ABLR, but for a target gun, I would lean on the 130gr Norma if you want higher BC and decent velocity. A 24" can push that to 2650fps using CFE loaded to 2.310", which will feed from many of the mags on the market.

I have 2 Lilja barrels on the way, so I will satisfy my accuracy nazi fix with those.

 

[steve123]

The SAAMI Grendel chamber uses a compound throat, so there is taper from the neck to the leade, which helps center the projectile in the AR15 while having neck dimensions that are more forgiving for gas gun feeding.

For single feeding, I would look at the 130gr Berger & 130gr Norma before the 140gr Berger. All of these have significant case intrusion.

I just made a dummy cartridge with the 130gr Berger, starting at 2.360" COL, and it was jammed into the lands pretty hard. It extracted with medium force using the charge handle in the upper separated from the lower, but I wouldn't ever load that bullet to that COL in my SAAMI chamber.

I then seated it to 2.310", and I see no land engagement, extracted with ease. There are production mags that will already fit that COL, but you have to have uniform bullet length, and as you know, all the BTHP's have variance that is enough to cause hang-up inside the magazine when you push the COL, so your intent to point and uniform them all would take care of that.

A 20" will push a 130gr to 2460fps with powders like CFE and LVR. If you got a 9130 BR bolt and extension from Bustin, you could push to 2600fps.

The Grendel chamber really was designed to work well from the AR15 mag-fed, so there isn't a lot of jump. No matter what bullet I have tried, my gun consistently groups into just under .8" to 1.2" at 100yds, and 1.7" to 2.2" at 200yds, with just a cheap ER Shaw button pipe. It does that with 100gr NBT's, 107gr SMK's, 120gr SMK's, 123gr Scenar's, 123gr A-MAX, 123gr SST's, and 129gr SST's.

Some other bullets that will mag-feed tha have high BC's are the 130gr Swift Scirocco, and the new 129gr ABLR, but for a target gun, I would lean on the 130gr Norma if you want higher BC and decent velocity. A 24" can push that to 2650fps using CFE loaded to 2.310", which will feed from many of the mags on the market.

I have 2 Lilja barrels on the way, so I will satisfy my accuracy nazi fix with those.

Okay, thanks for letting me know.

I have 600 6.5G brass waiting for another project. If Shilen would ever send me my 9 twist 17 cal barrel, "been 10 months now", I'd get my 17-6.5G AI project going. 30gr Golds/.281BC at 4300 fps would be pretty awesome too as long as were talking about cool cartridges.

 

[1slow01z71]

Man this thread makes me get the itch to build yet another AR. Ditch the 20" WOA 223 wylde barrel for a 20" 6.5, and order a short 6.8 barrel for the stamped lower Ive got to handle my deer hunting within 500yds. I need more calibers to load for like a hole in the head though. Does CFE223 work well in these cartridges? Im pretty well switching to that for my 308 and 223 stuff, would be nice to only need one powder for almost all my shooting.

 

[phreakmode]

I shoot several of the cartridges mentioned.

6mmAR
6.5mm LBC
6.8 SPC

At some point splitting hairs becomes the work, but truly the shot or hunt should be the work, that's what it's all about. This thread contains what you need to make an informed decision, either by direct statements or references..

Make a choice, get out, pull triggers, shoot more, don't get caught up in an analysis loop.

 

[Greg Langelius *]

...And Unknown, please call me Greg. It's a small thing, but nobody has called me 'Langelius' since I got out of The Corps in early 1968...

Appreciated...

Greg

 

[VTSEAL]

I certainly agree that there is no "single do it all rifle", but given a reasonable list of use cases, there are certainly a number of utilitarian rifles that would fit the bill and meet most needs without too many compromises. For my pick, I'd suggest an 18" or 20" 6.8mm SPC rifle would fit the bill well enough for plinking, hunting, and most days at the range under 600 yds... An 18" or 20" AR in .308 would probably be my second choice; but that carries a higher cost in both rifle, loaded ammo, and reloading components...

I jumped in on the 6.8 bandwagon several years ago, about the same time a good friend dove into 6.5 Grendel and we've had fun comparing notes over the years. He's more of a bench shooter than I am, and likes to think how great his 24" Grendel would be if he could find a range past 200yds... But he hand loads lots of nice precision 6.5 ammo and I know all of his Grendels are shooters. I have been very happy with nearly all of the 6.8's that have come through my stable and love that fact that I have yet to find an upper that doesn't absolutely love the SSA 110gr Sierra Pro Hunter. Similarly I have yet to find an upper that would choke down the Remington 115gr SMK's; something about that load has never worked for me. With hand loads, I am very pleased with the 6.8 and regularly shoot it out to 500 @ our local range. Without question the Grendel is shooting flatter at that distance, but my buddy and I won't hesitate to swap rifles and have a great time banging steel from both calibers.

Will be taking out one of my 6.8's with 110gr SSA TSX for a deer trip at the end of the year, and have no reservations that I should have brought more rifle. It has the added bonus that it is a legal caliber in any state that allows semi automatic rifles, and no concerns about caliber that you may have in certain states for deer hunting with a .223. Of course you do have to explain to nearly everyone you talk with when hunting that just because it is an AR, it isn't a standard .223...

 

[LRRPF52]

Man this thread makes me get the itch to build yet another AR. Ditch the 20" WOA 223 wylde barrel for a 20" 6.5, and order a short 6.8 barrel for the stamped lower Ive got to handle my deer hunting within 500yds. I need more calibers to load for like a hole in the head though. Does CFE223 work well in these cartridges? Im pretty well switching to that for my 308 and 223 stuff, would be nice to only need one powder for almost all my shooting.

CFE223 is a medium-slow burning, double-based, high energy powder that is easy to get a case-fill with in the Grendel, but it needs start pressure to burn consistently. In the Grendel, that means cup and core pills need to be longer and have at least 120gr of weight, at least in my and others' experiences.

When I tried it with the 107gr SMK, velocities were all over the place-couldn't make heads or tails what was going on, but with the 123gr A-MAX, it is superb, with textbook burn characteristics that are extremely forgiving, with what appears to be a very mild initial peak, and all kinds of velocity.

Others who have used it for lighter solids like the 100gr Barnes TTSX, and a light solid from another company we're experimenting with show that it does well with the solids, which is why I say I think it needs good start pressure, where the projectile resists being swaged into the lands more than lightweight cup and core bullets do.

In the .308, you might want to stick with bullets like the 175gr SMK, 178gr Hornady BTHP, 178gr A-MAX, etc.

 

[1slow01z71]

CFE223 is a medium-slow burning, double-based, high energy powder that is easy to get a case-fill with in the Grendel, but it needs start pressure to burn consistently. In the Grendel, that means cup and core pills need to be longer and have at least 120gr of weight, at least in my and others' experiences.

When I tried it with the 107gr SMK, velocities were all over the place-couldn't make heads or tails what was going on, but with the 123gr A-MAX, it is superb, with textbook burn characteristics that are extremely forgiving, with what appears to be a very mild initial peak, and all kinds of velocity.

Others who have used it for lighter solids like the 100gr Barnes TTSX, and a light solid from another company we're experimenting with show that it does well with the solids, which is why I say I think it needs good start pressure, where the projectile resists being swaged into the lands more than lightweight cup and core bullets do.

In the .308, you might want to stick with bullets like the 175gr SMK, 178gr Hornady BTHP, 178gr A-MAX, etc.

Sorry, Im not familiar with the "cup and core" terminology. Ill have to look that one up. Ive had good luck with it under 77s in 223 and 178s in 308. I primarily shoot the heavier bullets as I like to shoot further away and the heavies aren't really that much more expensive than the lighter bullets at least in 223/308. I use WC844 for my lighter 223 plinking loads so Im really trying to get down to one main powder I use and that meters well so I can load it on my Dillon instead of toiling away in the office for hours on my rock chucker.

The main use for the Grendel will be to shoot while the big guns are cooling down on the firing line. I primarily shoot 308 and 300WM but will be adding a 6.5CM as well next year. I built my 20" 223 gun with the intentions of using it for that but thus far I have not be too impressed with the velocities Ive gotten with varget and 77gr pills. Im headed out here shortly to try my CFE loads in this gun, if I don't get 2700+ I will be pulling the barrel most likely for something like the 6.5 Grendel or 6mm fat rat. Im a big fan of the amax line as it seems to be the best bang for the buck and hornady makes them in either caliber.

Are there any "varmint" type loads for the Grendel? We occasionally go to NM and while there we usually set up on a prairie dog town from a few hundred yards away and have fun. I can easily go through 3-400 rounds on those days so it would be nice to have a light, fast, and inexpensive load for that.

It would be going on this gun

Is there really that big of a velocity loss going from a 24 to a 20? Reason I ask is my all weather case would not fit a 24" barrel and then add the can on top of that Im looking at a LONG AR barrel. Im using a MUR upper receiver so I should be good there strength wise.

Ive never really looked into 6.5 or 6.8 as Ive been happy with what Ive got but am in the beginning stages of researching my next AR move. I don't like the fact that I need to buy expensive mags for either gun, that sucks. I love pmags since I cant break them and theyre cheap. I do have a 5.56 PRI mag but haven't even tried it yet. Bought it with the intentions of stretching out my COL with 77s for more powder capacity to see what I could get away with as well as trying out some 75gr amaxs that are 223 mag length voodoo it seems.

 

[Unknown]

I'll throw another wrench into how to figure out which rifle is "best". The army marksmanship unit compared 30 caliber 123 grain bullets at the same velocity as 6.5mm bullets of the same weight and velocity. Their finding was that the 30 caliber round had sufficiently less recoil to make it worth use in many of the 3-gun matches where long distances (over 300 yards) wasn't a factor. Obviously, the 6.5 bullet at distances beyond 300 yards will have MUCH less drop and wind drift than the 30 caliber round at those distances. The 30 caliber round sheds velocity much faster than the 6.5mm.

The reason why the 30 caliber round has less recoil was interesting, but I'm not going to try and explain why here. The bottom line is that the 30 caliber had less recoil. I would presume that the same physics would apply to the 6.8mm, but to a lesser extent.

 

[LRRPF52]

There aren't any expensive magazines for the Grendel. I've never paid more than $20 for a Grendel mag, and most have been in the $15-$17 region.

When we say "cup & core", that describes most of the bullets in the market where the copper jacket starts out as a long tube with a base, and has lead poured into it, then the jacket is swaged into its overall shape, including ogive and boat tail.

We are usually delineating from the solids when we say "cup & core".

The .223 Remington actually does very well on medium game with premium bullets, more so than a lot of people would ever give it credit for, but it doesn't have good BC's for bucking wind until you get into the 75gr A-MAX, and some of the single-fed pills that are built for target use. That keeps you generally in the 200yd or less effective range on medium game, and the Nosler, Hornady, & Swift bonded pills do well, along with the Barnes TSX and TTSX's.