Yeah, another AR question...

[onerifle]

I've decided that the next addition to the family will be an AR.

I've narrowed it down to either a RRA Elite CAR4 or a Colt 6920/6721.

The RRA & 6721 have a 1:9 twist, the 6920, 1:7.

I'm leaning towards, but haven't committed to, the 6920.

Will the 1:7 shoot lighter weights such as XM193 ok for high volume practice? I don't assume that POI wiil be the same, but close 'enough' within 100 yards?

Primary role will be HD, with the ability to be an EBR a la 'civil disorder' scenario. I would like to look at adding an ACOG when the budget allows.

Bottom line- which rifle, and just as importantly- WHY?


Thanks to all.

 

[Aguila Blanca]

http://www.ammo-oracle.com/body.htm

I suggest that you read the whole thing.

I read it awhile ago. The 1:7 barrel is really optimized for much longer and heavier rounds than M193. I am not certain, but I think they said something in there about a 1:7 barrel spinning up M193 fast enough that the jacket sometimes flies apart before reaching the target. As I said, I am not certain I saw it there, but I vaguely recall reading something to that effect ... somewhere.

 

[Mulliga]

I am not certain, but I think they said something in there about a 1:7 barrel spinning up M193 fast enough that the jacket sometimes flies apart before reaching the target.

I think you're thinking of light 40 gr. varmint rounds with thin jackets (the Ammo Oracle comments on it in the bullet stabilization part of the document). M193 is fine in 1:7.

The 6920 is very popular and a good choice. Any of the "Tacticool" models from the big boys will suit your needs.

 

[onerifle]

http://www.ammo-oracle.com/body.htm

I suggest that you read the whole thing.

I read it awhile ago. The 1:7 barrel is really optimized for much longer and heavier rounds than M193. I am not certain, but I think they said something in there about a 1:7 barrel spinning up M193 fast enough that the jacket sometimes flies apart before reaching the target. As I said, I am not certain I saw it there, but I vaguely recall reading something to that effect ... somewhere.

Yep; I've read it, a few times. Thanks.

I guess I'm wondering if a 1:7 is too specialized and although optimum for heavier (69 gr, and above) bullet weights, too fast for the middleweights and XM193/M855, and a 1:9 is better at most, though not ideal, for heavier weights...?

Decisions, decisions...


(Pretty funny...I don't overthink my Marlin Guide Gun...it slings everything from 300 to 540 grains with considerable aplomb!)

 

[1911user]

1/7 is fine for 55-77 grain ammo, period.
1/9 will handle a little lighter weight bullet and anything over 70 grains MAY not stabilize.

 

[Jeff White]

I've probably got 10K rounds of M193 through my 6920. Not a problem at all. I'd go with the 1/7 twist barrel because it give you more options then the 1/9. Unless you intend on shooting varmints with very light loads (a 6920 is not really the optimum platform for that), you can do everything with a 1/7 that you can do with the 1/9 and as others have stated, you can shoot the excellent 75 and 77 grain defensive loads with the 1/7. Accuracy can be spotty with those loads in a 1/9. Some people have gotten acceptable results and some haven't, so I'd stick with the 1/7.

Jeff

 

[onerifle]

Thanks for the good info, folks.

 

[Don't Tread On Me]

Get the 6920. Here is why:


1] The premium over the RRA isn't that much (and is worth it)
2] Has real M4 feedramps (just an improvement)
3] Will have real handguards with dual heat shields, and they do not melt.
4] Will come with an H-buffer. (heavier)
5] Will come with a real M16 bolt carrier. (shrouded firing pin, more weight at rear)
6] Gas key will be staked on properly and will NOT come loose.
7] Will have the proper height front sight base to match the flattop.
8] Will have a chrome lined chamber and bore.
9] Barrel is pressure tested with proof loads up around 70k psi.
10] Bolt is also pressure tested and inspected.
11] Trigger group parts WILL be smoother, better machined, better finished.
12] 1/7 shoots anything over 50 grains fine. Heavier is better for accuracy and reliability.
13] Colt has superior resale value. This isn't a myth, look around and see.
14] Receiver extention plate and castle nut (what holds your stock on) is staked into place, and will NOT come loose.
15] M4 barrel profile will be LIGHT under the handguards as per the real military spec M4 barrel profile underneath the handguards. Most "M4geries" have HBAR thickness underneath making the caribine heavy.
16] Extractor will come with the new improved spring with an O-ring design (better extraction)
17] The buffer tube is mil-spec. Therefore, it will accept aftermarket stocks like VLTOR and others without having to buy a new tube.
18] Overall quality control and mil-specifications will be better on the Colt (finish might be better on the RRA though)
19] Colt will come with a sling, 2 twenty round Colt magazines, and a GI cleaning kit.
20] Grip will be attached with the flat head screw and not the hex head screw.


The only thing RRA has going for it is that they (I believe most if not all) come with the 2-stage trigger. That's about it.


The only negative on the Colt is that the trigger and hammer pins are .170 instead of .150. This isn't a big deal though. You won't want to replace (nor need to) your Colt hammer or trigger with sub-standard crap anyhow. Colt and even Bushmaster sell replacements, and they aren't expensive.

The take down pins that hold the upper and lower together are standard and will work with any other lowers or uppers. (Older Colt's had a fatter front pin)

This isn't to say the RRA isn't a fine rifle. The Colt is just slightly better.

 

[Vagabond]

I read all that also, BUT...

I have a Colt with a 20" Colt 1:7 heavy barrel, and fired 45 JHP REM, 55 FMJ REM and Winchester Q3131 and some 62 gr "SS109" Canadian Surplus to very contrary results. 10 rounds from each, and actually the firing order was 62/55/45/55 if fouling may have affected it. But the result was lighter was tighter. (I'll see if I have the backer with the center on it when I get back home. I can post some scans on a personal web site, but you'd have to trust me as to which round did what, cause Sen Kennedy hasn't got that new ammo rule in yet to make each bullet sign it's name as it makes impact... )

I know it isn't supposed to be that way, but I think I'll use that 45 grain JHP round for 100 yds or less target punching. I have had opinions from some of the others range rats that the lighter bullets actually handle the high RPM because it's "well made", that it's a higher speed (because it's lighter) and that the "engineers" at the ammo-oracle aren't engineers at all.
Glen Zediker, in his book, says there is no such thing as an "over-stabilized" bullet - like being too rich or having too much fun. Tubbs and Martin agree. THEY claim that all the 1:7 twist does is give you more ammo options, not less. I'll stay with the Pony and 1:7, but maybe a K barrel next time. Anyway, that's what makes horse races - pun intended.