6mm Gas Gun

[Reaper 31]

Not in a current position to build a new bolt gun but I have enough parts to get a new upper put together. I can go either large or small frame AR so wondering what 6mm cartridges yall may suggest? I'm interested in a 6mm CM or the 6mm ARC. Anyone out there shooting a 6mm on a gasser?
Thanks

 

[Disfunctional_Engineer]

6Creedmoor is an AR10/LR308 platform caliber. 6 ARC or another 6 Grendel style caliber would be where I'd want to go. If you are looking for light weight bullets in a 6MM 6X45 is out there too but the case length really would get in the way of having heavier bullets as an option. It's a neat idea if you're short on components but otherwise kind of meh IMO because the load data I've seen allows only 75gr and down at mag length for an AR.

 

[Reaper 31]

Can you still get decent loads/ velocity with the heavier bullets seating them to magazine length?

 

[Ledzep]

6mm Creedmoor in a large frame platform is going to have way more gas issues than a 6mm ARC in an ar-15. Velocities are very barrel length dependent.

6mm ARC at 24" you're looking at ~2700-2750fps with 105-110gr bullets. At 18" more like 2600. The case on the ARC are short enough to allow for the heavies to be seated to magazine length and function. Don't exceed book load data in an AR-15. To keep the load on the lugs the same as a 5.56 at 60ksi, the ARC/Grendel/PPC bolt face cartridges need to be kept around 52ksi.

 

[craigos]

i shoot Hornady 108 ELD factory load in my JP LRP-07 (AR10) --- shoots light out like 1/3 moa all day long.

ARC is interesting in a AR15 but as above at 2600 fps ... eek

 

[Reaper 31]

i shoot Hornady 108 ELD factory load in my JP LRP-07 (AR10) --- shoots light out like 1/3 moa all day long.

ARC is interesting in a AR15 but as above at 2600 fps ... eek
[/QUOTE]
ok you just caught my attention, are you saying the ARC tops out at around 2600fps? Shoot i thought the Hornady video had it up around 3k?

 

[FCS]

Not 6 ARC but 6mm AR, 22” barrel with +2 gas and 108s shoot best at 2660-2675 fps window.
Can I push harder/faster, yes but accuracy suffers and case abuse goes up rapidly.

 

[Disfunctional_Engineer]

I didn't realize they had hotter bolt gun only loads. Although you'll miss out on some velocity there I would think running 8K under max loads would really be nice from a brass and barre life perspective.

 

[Ledzep]

i shoot Hornady 108 ELD factory load in my JP LRP-07 (AR10) --- shoots light out like 1/3 moa all day long.

ARC is interesting in a AR15 but as above at 2600 fps ... eek

Again, in a 16-18" barrel. If you run a 20-24" barreled ARC it's more like 2700-2800.

Run a 6 Creed at 16-18" and you'll be in the 2800fps ballpark.

You either get 6-8" worth of barrel OR 200fps going from the 6 ARC to the 6 Creed (factory 108 vs. factory 108). But you also increase the frame weight (ar15 vs. LR-308 platform), and the amount of powder being burned, ammo weight, and lose a ton of barrel life.

ETA: Then, there is the aspect of dropping down to 90-95gr bullets in the 6mm ARC, and within the "effective range" (I'll say 0-600yd) achieve flatter trajectories while maintaining most of the terminal side of things.

To each their own, but I'm done with large frame AR's. Too big, too bulky, too much gas. I can't really quantify it, but the AR-15 is entirely more comfortable for me to carry and shoot. Worth the velocity hit, IMO.

 

[Reaper 31]

Oh ok. Man I originally built my bolt gun back in '15 on a 700 long action when I shot in FClass but I don't do that anymore. Had I a short action I would have just re-barreled to a 6mm. Honestly I prefer gas-guns though.... just preference

 

[FCS]

6 Creedmoor, GAP-10, 105s at 2950 is fairly easy to do from 22” bbl w/o stressing brass / system.

 

[Reaper 31]

"To each their own, but I'm done with large frame AR's. Too big, too bulky, too much gas. I can't really quantify it, but the AR-15 is entirely more comfortable for me to carry and shoot. Worth the velocity hit, IMO.
[/QUOTE]

I hear what you're saying in the large frames. Idk but maybe this is where heavier buffers over adjustable gas block arguments come in on taming recoil.

 

[FCS]

Longer gas system, heavier buffer, heavier buffer spring K and proper port size help a lot.

 

[Bullspotter]

Longer gas system, heavier buffer, heavier buffer spring K and proper port size help a lot.

Spot on!!

 

[Disfunctional_Engineer]

Longer gas system, heavier buffer, heavier buffer spring K and proper port size help a lot.

My kid would rather shoot my rifle length 243 win AR10 than my carbine length 5.56 gun. Naturally dad's wallet cringes more than he does at the recoil difference but I digress.

If it's too harsh an adjustable gas block is not horribly expensive.

 

[FCS]

223 Wylde, 16”, intermediate gas, shoots pretty soft and ammo cost is appreciably less.
If ya need an “excuse” for a new upper.

 

[Ledzep]

It's got very little to do with recoil for me. It's bulk, weight, size, balance... I had a 6.5 Creedmoor large frame AR. It started off as a PSA kit and I just swapped parts as I could afford them-- to the point it was hardly PSA anymore. It would shoot okay prone or on a bench but was too heavy to really want to walk around with to do coyote hunts, for sure heavier than I'd like for antelope. The accuracy was mostly okay but as with any AR, if you're not 100% on top of things it'd throw fliers that basically meant your target needed to be 2 MOA or bigger to have a warm fuzzy about hit probability... Which basically meant that for hunting it needed to be inside of 400-500yd (not unreasonable anyway)...

But it begged the question, Why lug all of this weight for a 500yd rifle?

IME I've had better luck getting AR-15's to shoot better, have had less issues with over-gassing, they're lighter, and they just feel 'right'. Like I said, hard to quantify. Could just be that I'm a little guy. lol.

 

[FCS]

It's got very little to do with recoil for me. It's bulk, weight, size, balance... I had a 6.5 Creedmoor large frame AR. It started off as a PSA kit and I just swapped parts as I could afford them-- to the point it was hardly PSA anymore. It would shoot okay prone or on a bench but was too heavy to really want to walk around with to do coyote hunts, for sure heavier than I'd like for antelope. The accuracy was mostly okay but as with any AR, if you're not 100% on top of things it'd throw fliers that basically meant your target needed to be 2 MOA or bigger to have a warm fuzzy about hit probability... Which basically meant that for hunting it needed to be inside of 400-500yd (not unreasonable anyway)...

But it begged the question, Why lug all of this weight for a 500yd rifle?

IME I've had better luck getting AR-15's to shoot better, have had less issues with over-gassing, they're lighter, and they just feel 'right'. Like I said, hard to quantify. Could just be that I'm a little guy. lol.

All valid points.
Most common barrel contours are fairly heavy, to help mitigate recoil of larger cartridge.
Doing a 6mm Creed or similar, probably don’t really need that heavy a contour.
Lighter contour barrel will be a custom deal, cost goes up.

Hmmmm....now I might have to build a lighter weight larger frame just to see how it does for accuracy, how much recoil does go up.

 

[Reaper 31]

Any of y'all shooting PRS gas gun series?

 

[Dino11]

6mm Creedmoor in a large frame platform is going to have way more gas issues than a 6mm ARC in an ar-15. Velocities are very barrel length dependent.

6mm ARC at 24" you're looking at ~2700-2750fps with 105-110gr bullets. At 18" more like 2600. The case on the ARC are short enough to allow for the heavies to be seated to magazine length and function. Don't exceed book load data in an AR-15. To keep the load on the lugs the same as a 5.56 at 60ksi, the ARC/Grendel/PPC bolt face cartridges need to be kept around 52ksi.

This was shot yesterday on a new Faxon 18" 6mm ARC barrel, I know the SD is high but it is a new barrel. These were 105gn Nosler RDF's.

This was not even a max load for the round, Hornady's test barrel was an 18" not 24" so the number reflect the 18" barrel on their site.

 

[Reaper 31]

What are your initial thoughts on this cartridge? Great as promised, low recoil?

 

[Dino11]

I have been playing with it since the beginning of July.

Between my son and I we have three of them. My son has a Faxon 20", shoots pretty good not may rounds shot from it.

I myself have two 18" rifles, a Faxon which is to early to tell how it shoots only 150 rounds through it.

And I have an Odin Works match grade which shoots 1/2 MOA or better. What I will say is if you hand load your not going to find a better cartridge in this category, it is amazing.

What I have found is the accuracy is in the 2650 to 2700FPS range, at least for the Odin barrel. I love the Nosler 105 RDF and have done a lot of testing with them, they simply blow the Hornady bullet away.

I reload for about .35 a round, so it is very affordable to shoot, recoil is very low, scope never leaves the target you can actually see your hits.

I have only shot out to 600 yards to date, but can hit an 8" plate repeatedly at that range. This is one accurate round if you load, and is pretty good with factory loads.

 

[Ledzep]

Are you looking at bolt gun data or gas gun data? Your numbers seem fast for 52ksi loads.

My 18" AR-15 with book max (gas gun) loads is doing 2600-2675. Same for factory ammo (2596 with 108's, 2660 w/105 black).

My 18" Cz527 with max book (bolt gun) loads is doing 2750fps.

My 28" bolt gun shoots the factory stuff at 2820 and my hand loads up north of 2900. Pretty consistent 20-25fps per inch, and about 125fps going from 52,000 psi to 62,000 psi.

 

[Dino11]

I'm not looking at any book data, actual numbers I am getting from my guns.

Yesterdays data:

18" Faxon Barrel
29.4gn Leverevolution
Nosler 105gn RDF
CCI 450 magnum primer

Your comparing apples to oranges... Their is a reason it is called Advanced Rifle Cartridge.

 

[FCS]

I'm not looking at any book data, actual numbers I am getting from my guns.

Yesterdays data:

18" Faxon Barrel
29.4gn Leverevolution
Nosler 105gn RDF
CCI 450 magnum primer

Your comparing apples to oranges... Their is a reason it is called Advanced Rifle Cartridge.

Question is what pressure are you running? Name doesn't add velocity, hence Ledzep's question. No doubt you are getting those velocities from your rifle, but that doesn't answer the question of what pressure are you running to get said velocity.

 

[Dino11]

I have no way to measure pressure. But if you are basing your number from Hornady's book number they are well known to be very conservative. Just look at the test barrel they used, industry standard is 24" they used an 18". You gotta ask why. I think what it come down to is finding that sweet spot where everything just works and becomes more efficient. Hence the name, it is more advanced to other rounds in it's class. I'm not trying to advocate anything, those are the numbers I am seeing and I have the proof to back it up.

Plus those Nosslers just kick ass, they have a BC of 571, I'm sure that helps out some. They are long and very sleek.

 

[Ledzep]

I have no way to measure pressure. But if you are basing your number from Hornady's book number they are well known to be very conservative. Just look at the test barrel they used, industry standard is 24" they used an 18". You gotta ask why. I think what it come down to is finding that sweet spot where everything just works and becomes more efficient. Hence the name, it is more advanced to other rounds in it's class. I'm not trying to advocate anything, those are the numbers I am seeing and I have the proof to back it up.

Plus those Nosslers just kick ass, they have a BC of 571, I'm sure that helps out some. They are long and very sleek.

They used an 18" barrel because most people are going to use a 16-18" AR-15. People complain when companies publish 24" data for gas-gun calibers that are produced primarily with 16-20" barrel lengths. Gives "hyped" velocity numbers.

While I will say the velocity numbers published in the Hornady load data are about 25-75fps slower than my personal guns, they're not 200fps slower. That's all I'm saying. If you believe in it and you're not breaking things, rock on.

 

[FCS]

6 ARC isn't any more advanced than the 6mmAR.
You have proof that you can get more velocity running more pressure. Ledzep said exactly the same thing mentioning gas gun load vs bolt gun load being differentiated by 52K psi for gas gun, 62K psi for bolt gun.
105 Nosler is long and sleek, meaning deeper in case which drives pressure up for same powder charge.
Isn't that the data is more conservative, more so that Hornady is limiting the pressure to 52K for gas gun.
You are getting nearly 24" bolt gun velocity from an 18" gas gun, one way that happens.....

 

[Dino11]

I need to slow them down some... I found that the accuracy comes in at around 2650 to 2700FPS. I'm not trying to get velocity numbers, I want to hit my POA. Those rounds yesterday were short of being steller for accuracy, not bad but not real good either. I am basing those numbers off what my Odin barrel riffle likes.

This bullet stays supersonic out past 1400 yards, even at the slower velocity. They are just very efficient for what they are. But this barrel is not yet broken in so I need more time behind the trigger before I even think about working a load for it.

 

[Dino11]

Hornady 105 on the left Nosler 105 on the right

 

[Ledzep]

As far as chamber pressure between 2 different bullets goes, bearing surface length is going to play the biggest part. The RDF has less, so should produce less pressure for a given charge weight (all else being "equal"), but by the looks of that picture it won't be drastic.

As far as seating depth, my experience is that pressure is on a curve. Higher when either in or near the lands, and also again when you stuff the bullet WAY into the case. The lowest pressure points happen with a decent jump that isn't intruding on case capacity. With an AR-15 you basically seat to mag length and roll with it unless there's interference issues.

ETA: Things may have changed, but my experience with the RDF's is that they have great BC, but are finicky and/or inconsistent. Especially lot to lot. YMMV

 

[Dino11]

The Hornady bullet spec is 2.200 OAL, if you load it longer than that it will jam into the lands.

I load the Nosler at 2.215, so I am .015 longer on OAL so pressure is not a thing on my loads because they are deeper into the case. I can do this because the bullet is more slender and the ogive is a little further down the bullet. I don't load to OAL, I use a comperator and measure at the olgive. This gives me a more consistent bullet jump. Sometimes the OAL will be 2.213 sometimes it will be 2.215 it does vary a little. But the same amount of bullet will always be in the case, so pressure from one bullet to the next is consistent. My seating die also contacts the bullet at the same location that the comperator does to seat the bullet. Consistency is the key to accuracy. I just do things a little differently than most folks, but I have been doing it this way for almost 40 years.

 

[steve123]

I didn't like the large frame AR's compared to the small frame AR.
The funnest long range AR's I've owned were/are a 6mmART40 and currently a "6mmFatRat, 95smk at 2870 fps in a 22" 8 twist", the recoil with a brake is slight indeed!
I had 105 Amax going 2875 fps with H4895 in the 26" 6mmART40 and it shot better than some bolt rifles. I also got 2nd place with it in a 2 day tactical match about 8 years ago, that's how capable an AR can be.