6mm ar15 or 6.8 based help

[Delicatessen]

I am considering building a 6mm based ar. I am primarily interested in a handy size say 18” barrel or less with the higher bc 6mm out to say 600-800 yards with more energy than 77gr. So I have been looking quite a bit at Grendel and 6.8 based 6mm’s (6mm ar/lbc/6x6.8/240 tomahawk/6mm tac). My priorities are:

1: feeding reliability
- my main concern with Grendel based on experience a few years ago. Intrigued by the new frontier 6.8 lower/upper that is way more affordable than lwrc.

2: component availability
-especially barrels and bolts, seems to lean more towards Grendel. Like the idea of Lapua brass. The 6.8 based ones seem very limited in barrel makers.

Any experience with these as far as shorter 18” or less performance and feeding reliability?

 

[Strykervet]

Go Grendel, FTW.

6.8 ain't a long range round but it delivers more energy than the 5.56 at the same engagement distances that the M4 was designed for, ie, 300m or less but sometimes, maybe, on certain days, just maybe 400m+. Bullet selection is 110gr. or 110gr., your choice.

6.5 can do all that and more. You have more of a range of bullets to choose from though you'll probably find the 120gr. Nosler BT (Bill A turned me onto these and they've been amazing) or 123gr. work best.

There are some 6mm wildcats but I'm not sure how useful they are. IMO 6.5G is the ideal optimized round for the AR platform, if you need more you need a bigger rifle.

 

[Delicatessen]

Sorry just to clarify I am talking about 6mm wildcats based off the parent cartridges: so when I mentioned 6.8 it was for things like 240 tomahawk, 6x6.8, 6mm tac. It seems these may be too long to seat the high bc stuff but just curious about. I have plenty of standard cartridge ars just curious to try a 6mm as it seems Like it could be a good balance.

 

[Baron85]

I’m very curious about this my self. Would like to hear that the 6mm 6.8 variants are equal or better than the 6mm Grendel variants since I already have a 6.8 and brass so would minimize that expense. Plus I have had great luck with the 6.8 brass so far.

 

[steve123]

For my 6mmFatRat I found the 95gr bullets to be ideal. 2870 fps in a 22". It has the same wind drift as the 105's that go approx 100 fps slower, and these give noticeably less recoil.

I think the 95's would work better for the 6.8 based cases too due to shorter length.

Lapua brass is such great brass! That's most of the reason I stayed with 6mmFatRat. Reliability has been good. Also there's a cartridge almost identical to 6mmFatRat, but it's turn neck version, that has won Benchrest events against 6mmPPC!!!

All the hype over 22 cal versions got me excited to try one of them but, nah, I'll stick to 6mm for now at least.

 

[Delicatessen]

What magazines do you use for the 6mm fat rat? This is where I was running into issues years ago when I tried a 6.5 Grendel. I was using asc type ok in the 10 round range but not much more...this may have been corrected but just trying to figure out if higher capacity magazines are working reliably. That is the only real reason I am considering a 6.8 based one.

 

[steve123]

I use C-product 6.5 grendel 10 round mags. I tried their 26 round mag and it didn't work well.

High cap the 6.8 case mags are probably a better choice, the slimmer case is also likely a better choice for the most reliability??

 

[Constructor]

I’m very curious about this my self. Would like to hear that the 6mm 6.8 variants are equal or better than the 6mm Grendel variants since I already have a 6.8 and brass so would minimize that expense. Plus I have had great luck with the 6.8 brass so far.

They run apx the same velocity depending on powder used and accurate load found. The 6.8 case will handle more pressure and last longer. The 6.8 bolts last longer.

 

[Baron85]

They run apx the same velocity depending on powder used and accurate load found. The 6.8 case will handle more pressure and last longer. The 6.8 bolts last longer.

So are you saying the 6.8 based 6mm is the better choice for the 600-800 yard max range?

 

[Constructor]

So are you saying the 6.8 based 6mm is the better choice for the 600-800 yard max range?

No, that is just 3 good points.
Lapua may make the most consistent Grendel brass and that can mean very good accuracy. Norma may be #2 and their brass will last longer than Lapua. Just my opinion and everyone has one- If hunting and target shooting either cartridge 6.8 or G based would be fine. If it was a duty/combat/shtf kind of build I would stick with the 6.8 based cartridges. It has stronger bolts and better mags including the SIX8 pmag.

 

[Yondering]

If you're looking to use high-b.c. 6mm bullets, it'd be silly to go with the 6.8 case. I mean, it shouldn't even be a question. The guys wanting some sort of 6x6.8 wildcat are going for mid-weight 6mm bullets at typical hunting distances, not high b.c. bullets at extended target distances.

The Grendel case is the way to go in this situation. It leaves plenty of room in the mag for long bullets, and some of the high b.c. 6mm bullets are plenty long. I'm partial to the 243 LBC because I've had such good results with it and the accuracy and high velocity I can get with BHW/Columbia barrels, but there are other options too. Also just FYI, Columbia has a 30% off sale right now on new barrel orders.

 

[Constructor]

I don't know about all of the 6.8 based 6mms but the TAC6 is not a full length 6.8 case and will shoot 105s and 108s at mag length. Seems like most are reporting around 2700fps out of an 18" barrel using CFE and SWM.
If you are target shooting 10 rounds at a time Cavity Back Bullets in Montana sells Windowed PRI mags that will allow loading out to around 2.36". BTW those mags will work with the 6.8 or Grendel based cats.

 

[Yondering]

Or just use the Grendel case to start with, and you don't need special cut magazines or reduced capacity from shortening a 6.8 or 223 case.

 

[Delicatessen]

I am curious about the Grendel based cartridges but had bad experiences with prior magazines in more than 10 rounds. Have you used any higher capacity magazines? If so which ones have worked for you?

 

[ZY100]

For SA, another option to consider--6 x 45 aka 6mm-223. Not super fast, and 18" might be a little short, but other than a barrel swap, BCG, Mags, feeding all easy-peasy. Depends on your needs....

http://bulletin.accurateshooter.com/2015/08/6mm-223-across-the-course-rifle-project/

From the link (bolt gun with >18 barrel) The load for 600 yards was with a 95gr Berger VLD bullet, with 23.0 grains of Reloder 15, Lapua cases, and the same Federal 205M primers. This load is 2,604 fps, with an extreme spread of 4 fps over a 10-shot string.

Its good to have options...

ZY

 

[towerofpower93]

I am curious about the Grendel based cartridges but had bad experiences with prior magazines in more than 10 rounds. Have you used any higher capacity magazines? If so which ones have worked for you?

I use the E-lander 24rd mags with a Larue 6.5G and have had no issues so far over a few hundred rounds.

 

[Reticlelife]

If you didn’t see the 6mm Advanced Rifle Cartridge thread, it looks like Hornady is prepping to drop a new SAAMI standardized 6mm Grendel variant called the 6 ARC. Necked down, and shoulder pushed back a little. Looking forward to seeing it when it drops.

Until then, I have a 243LBC I thoroughly enjoy.

 

[Yondering]

I am curious about the Grendel based cartridges but had bad experiences with prior magazines in more than 10 rounds. Have you used any higher capacity magazines? If so which ones have worked for you?

My preference is E-Lander or ASC. I actually like the E-Lander mags a bit better, but ASC gives longer OAL so I use those when needed. I use both sizes of E-Lander (I forget, 17 and 25 rd maybe?) and the 15rd ASC mags. I like Magpul Ranger Plates on them, but that's just a preference. I'm using these for 6.5 Grendel and 243 LBC.

I actually use ASC for my 6.8 mags as well, and have had no more or less issues with the Grendel than I have with 6.8. That's been very few issues, not zero but mostly related to load development and action tuning. Also - my Grendel-based rounds seem to feed fine from the 6.8 mags too.

 

[Yondering]

For SA, another option to consider--6 x 45 aka 6mm-223. Not super fast, and 18" might be a little short, but other than a barrel swap, BCG, Mags, feeding all easy-peasy. Depends on your needs....

http://bulletin.accurateshooter.com/2015/08/6mm-223-across-the-course-rifle-project/

From the link (bolt gun with >18 barrel) The load for 600 yards was with a 95gr Berger VLD bullet, with 23.0 grains of Reloder 15, Lapua cases, and the same Federal 205M primers. This load is 2,604 fps, with an extreme spread of 4 fps over a 10-shot string.

Its good to have options...

ZY

That's not much of an option, at least definitely not "easy-peasy" for high b.c. 6mm bullets in an AR15.

Key words about your link are "bolt gun". That 95 VLD in a 6x45 needs at least ~2.400" OAL, which is still .100" longer than even an ASC mag. Yeah, you can do it with cut mags and cut magwells, but it's not easy, it's slow, and you gotta wonder - why?

 

[ZY100]

Yond, I disagree.

His two priorities where easy feeding and component availability. Per my post that part is easy. I also told him it was not not fast, 18" was a little short, and for clarity the data was from a bolt gun. (And brass forming is one pass through the sizer die)

Like I said, it is good to have options.

As for energy and BC better than a 77gn .223, that depends on bullet/powder/vel, but you know that. It might not be for him, and definitely not the best option. But the neat thing about our sport is there are many cartridges people might not know about. This is a benefit of the interwebz, information sharing.

So I take it you are not a fan of the cartridge. Cool, I get that. I personally like my 6.5G, 6 Fat Rat is cool, 6 ARC looks interesting, etc. But that was not the question.

ZY

 

[Yondering]

Yond, I disagree.

His two priorities where easy feeding and component availability. Per my post that part is easy. I also told him it was not not fast, 18" was a little short, and for clarity the data was from a bolt gun. (And brass forming is one pass through the sizer die)

Like I said, it is good to have options.

As for energy and BC better than a 77gn .223, that depends on bullet/powder/vel, but you know that. It might not be for him, and definitely not the best option. But the neat thing about our sport is there are many cartridges people might not know about. This is a benefit of the interwebz, information sharing.

So I take it you are not a fan of the cartridge. Cool, I get that. I personally like my 6.5G, 6 Fat Rat is cool, 6 ARC looks interesting, etc. But that was not the question.

ZY

No, it has nothing to do with being "a fan of the cartridge" or not. It has to do with your suggestion not matching the question.

First line of the first post, he wants to shoot high bc 6mm bullets, in an 18" AR15. The 6x45 with high bc 6mm bullets does not fit in an AR15, without single feeding or extensive modifications to the magazine, receivers, and barrel extension. Bolt action data is not much use here.

You keep mentioning how it's good to have options, but this one is not a very good option for what the OP asked. It is fine for the light to mid-weight 6mm bullets, but that's not what was asked.

If you want to use long high b.c. 6mm bullets in an AR15 and have them feed from the magazine, you need a shorter case than the 5.56 or 6.8.

 

[Constructor]

OP,
Do you want to use 95gr, 103, 105 or 108gr bullets? I doubt anything in a AR15 will shoot the 110s. Hornady is coming out with the 6mm ARC and loading 108s.

 

[Delicatessen]

I was going to try the 95 and 103. I figured the 110/115 is too much for mag length in most cartridges.

 

[Delicatessen]

The 6 arc intrigued me so I may wait a little to see what support they roll out with it in terms of barrels from more sources/dies. My main concern is reliability with feeding in higher capacity magazines. I may try to find someone with a Grendel here and try the e lander magazines before building an upper for something in the 6 mm based off Grendel.

 

[Constructor]

I think after the 6mm ARC is out on the market with dies it will kill all of the other 6mms that were based on the Grendel case, 243LBC, 6mmAR, Predator. I don't think 40fps is worth doing a wildcat like the turbo 40 where you have to fireform.

 

[RMB]

I went with the 6mm AR/Gendel. So far very impressed. 20" barrel (should have gone with 22") with 1:8 twist. Loves the 87 Grain Vmax and 95 Grain SMK with 8208 or 4895. I have to agree with the above.....with much cheaper dies....and the 'off the shelf" options for the rifles, brass and loaded ammo the 6mm AR (and the others) will remain a specialty item.
At this point.....I am committed to the 6mm AR...It will be interesting once the 6MM ARC is in production....the actual specifies of the firearms and ammo and real world performance. The 224 was advertised as the 'second coming" and kinda fell flat on it's face. Glad I didn't drink that Kool Aid 2 years ago....
As for the mags...I got mine (10 rounds) from Atherius Arms and have not had any issues. I don't know who they use as the vendor.

 

[Yondering]

I went with the 6mm AR/Gendel. So far very impressed. 20" barrel (should have gone with 22") with 1:8 twist.

I wouldn't sweat the 2" length difference. Some data on barrel lengths in that range: I have two 243 LBC barrels (both from BHW/CRA), one 24" and one 19". With the same loads in both, I see a pretty consistent 90 fps difference between the two with the 105 BTHP. I've observed that with Varget, H4895, and LeverRevolution. With the loads I'm using, that amounts to about 0.3 mil difference in drop at 600 yds, and less than a tenth per 10mph full value wind.

I did more load development today with Lever and the 105 BTHP, in Lapua brass with CCI 450 primers. At the top load, the 24" barrel averaged 2853 fps, and the 19" barrel averaged 2764 fps. Both could have been pushed higher, primer pockets were tight and the brass looked good after 3 reloads of this load, but this is a very reasonable load for Lever in this cartridge. Note - that same load in Fiocchi brass formed from 7.62x39 required 1.5gr less powder to reach the same velocity.

The velocity difference between these two barrels is a little higher with lighter bullets (heavier bullets are usually more efficient in short barrels) but still not too bad. For example it's ~110 fps difference with the 70gr TNT and Lever.

I'm mostly using the 100gr SGK in my 19"; because I have a bunch and that rifle is a lighter barreled hunting setup. That bullet can be pushed 50-60 fps faster than the 105gr HPBT in this cartridge, but it's obviously more of a short range bullet. With the loads I'm using, it drops about 0.7 mil more at 600 yds, and 0.3 mil more wind per 10mph. Based on velocity and expansion threshold, I'd probably not use it on game beyond 400-450 yards (obviously conditions and ability to hit the target may dictate a much closer limit), but that's still a pretty reasonable distance for a small cartridge like this.

 

[TxWelder35]

I was going to build an AR soon but I think I’m going to hold out for the 6mm ARC. I have a feeling it’s going to be a game changer like 6.5cm