5.56 AR10

[Krawlven]

Random early morning thoughts.

Has anyone built an AR10 around a short action cartridge?
5.56, 6.5 grendel, etc ?

There are plenty of heavy loads that wont really fit most AR15 type mags.
It sounds like an interesting idea to me. Of course if you go through the trouble of building a long action rifle, why not use a long action cartridge ? Then you're back to checking max mag length.

Since this group is custom everything, and unlimited budgets ( some sarcasm ) it seemed likely someone has already tried this, or at least had the same idea.

 

[lte82]

Colt did, it’s called the 901. AR10 that takes both 308 and 5.56 uppers and mags.

 

[Near miss]

My thoughts:
What is the practical difference in accuracy at, let's say at 800 yards, between 80gr-90gr that is single loaded against a 77gr loaded to max length using HK mags or whatever other option that allows for max OAL?

 

[Krawlven]

Like a light house for the wayward, 1J calling them home...

R

My thoughts:
What is the practical difference in accuracy at, let's say at 800 yards, between 80gr-90gr that is single loaded against a 77gr loaded to max length using HK mags or whatever other option that allows for max OAL?

No idea, probably not much.
Didn't think it was a good or practical idea, just possibly interesting.

 

[TonyTheTiger]

My thoughts:
What is the practical difference in accuracy at, let's say at 800 yards, between 80gr-90gr that is single loaded against a 77gr loaded to max length using HK mags or whatever other option that allows for max OAL?

I can say from experience that the 77gr at 2650-2750fps that you commonly see from mag length 223 loads can't hold a candle to a long bullet like a 75 or 80gr ELD at 2900fps that you can get if there are no mag length restrictions.

 

[Near miss]

I can say from experience that the 77gr at 2650-2750fps that you commonly see from mag length 223 loads can't hold a candle to a long bullet like a 75 or 80gr ELD at 2900fps that you can get if there are no mag length restrictions.

Can you give a description of this real world example?

As in another thread one noted 1moa at 1000yds is doable with single loading, but it was national competition. I do not expect to those ARs to be battle-rifles / able to shoot lots of rounds without problems occurring.
But what kind of results did you see from the mag loaded 77 grainers?

 

[charnicus]

There are mags that allow loading to 2.31. That’s pretty significant over say 2.245~.

 

[TonyTheTiger]

Can you give a description of this real world example?

Pretty much all the things you would expect from a significantly higher BC bullet going a good bit faster.
Visual and audible feedback from hits and misses improved quite a bit, a lot more wind forgiveness and of course they shot flatter, which isn't a big deal on known distance targets.
Those are the things I noticed while shooting mag length vs long loaded stuff back to back, but I'll post my dope and maybe the numbers will tell the story better than my observations. First is mag length 77gr SMK's, second is 75gr ELD's at about 2.41" OAL.

 

[Rocketvapor]

77 SMK is a pretty crappy bullet for 'Long Range' nowadays.
If you already have an AR-10, a girly cartridge upper might be useful.
Pew, Pew, Pew @ 1000

A 22 Nosler using 6mm Hagar brass loaded to 2.55" or so with heavy bullets in an AR-10 Might be something to think about. Just need bolt, barrel and mags.

 

[TonyTheTiger]

77 SMK is a pretty crappy bullet for 'Long Range' nowadays.

Yeah, it is, but Hornady's 75gr bthp or Nosler 77gr CC is about the same. The only mag friendly bullet I've tried that offered significant ballistics improvement was the 77gr RDF, and I abandoned that because it shot great half the time and horrible the other half.

 

[lte82]

Can you give a description of this real world example?

As in another thread one noted 1moa at 1000yds is doable with single loading, but it was national competition. I do not expect to those ARs to be battle-rifles / able to shoot lots of rounds without problems occurring.
But what kind of results did you see from the mag loaded 77 grainers?

Someone is exaggerating. Nobody is shooting 77's at 1000 yards at the long range nationals, much less making them shoot 1 moa. The AR / service rifle guys are all shooting 308's with either 168 hybrids, 185 juggernauts, etc.

77's don't do terrible at 600 yards, especially the lapua 77's when loaded out a bit. The higher BC bullets do better though when the wind is moving.

 

[Near miss]

Someone is exaggerating. Nobody is shooting 77's at 1000 yards at the long range nationals, much less making them shoot 1 moa. The AR / service rifle guys are all shooting 308's with either 168 hybrids, 185 juggernauts, etc.

77's don't do terrible at 600 yards, especially the lapua 77's when loaded out a bit. The higher BC bullets do better though when the wind is moving.

By 77gr I was not referring to nationals I mentioned, where the guy used 90gr if I remember correctly.

But I mentioned 77gr as it seems to be the sweet spot between long enough OAL and BC.

Sorry for slight offtopic, but I took a photo of PMAG versus HK HR mag.

The PMAG is actually nearly touching the bullet, it scrapes the carbon layer upon inserting, where the HK mag has lots of room.