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Chasing 223 / Slowing down UPDATE: # 29 w/ pic

garandman

garandman

Bolt Gun Bodacious
So... my reloading history... half moa and under with bolt guns, moa + with gas guns / AR15. I know what I'm doing a little bit, but the AR15 has eluded me.

Current project..... ` 1:7 twist AR 14.5" bbl.... been able to get 1.5 moa with 77 SMKs. Talking with JP Rifles (and others, thinking about replacing this bbl with a JP 1:8 matched bbl / bolt ) ..... they say 77SMKs may not stabilize well out of a 1:7 14.5" bbl @ 100 yards. This will be a 300 yards and under gun (with a 1-6x LPVO and 45deg offset red dot)

So I'm gonna try some 69 SMKs in the 1:7 bbl.

Usually I've always had good luck up near max powder charges, but with this AR, I can't get much below 1.5" @ 100 y,

I'm wondering if I might get better groups with the 77 SMKs at lower velocity / powder charge, or if better stability is likely with the 69 SMKs.... and what is the relationship btwn internal ballistics / velocity and bbl twist rate. If I can't get good stability / grp size in the upper end of recommended powder charge ranges, might the lower end give me better results?
 
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garandman said:
May have more to do with the 14.5" length (edited post above for clarity) What's your bbl ?
Click to expand...
Disagree.
While I have not played with 14.5" that I can recall, I have played with many longer and even shorter bbls that were tested with 77 grain Black Hills OTM ammo in 1:7 and they gave groups in the 1/2 MOA class with strings of 20 rounds at a time.

Yes, there are effects if the bbl is very short, but when the context is to get state of the art performance from a 77 gr 223, the 1:7 is the correct twist and 14.5" isn't going to cause an instability in that 77 grain bullet.

Think about it this way. When you study that same 77 bullet after leaving the muzzle of a longer bbl, the velocity immediately drops off. However, if your 14.5" bbl has a typical muzzle velocity that matches up to the 20" velocity downrange, it is still going faster out of your 14.5" than the one from the 20" at 600 yards, and since that bullet is still stable way past 600 yards, the length only affected the muzzle velocity but not the stability.

I would suggest trying a 20" Service Rifle bbl at some point in your trials. For example if you get one from WOA and just follow the generic pet loads, you are going to find that good loads stay about 1/2 MOA. It may not be your loading, but your chamber and bbl characteristics that limits your performance with an AR. Get a good Service RIfle bbl and you will get state of the art performance when you do your part.
 
RegionRat said:
You are headed the wrong way. Think about trying an 80 grain in your 1:7, but there is no reason 1:7 will not be good for 77 or 69 grain SMK.

https://bergerbullets.com/twist-rate-calculator/
Click to expand...

Got some Bergers coming.

Can't get 80 gr to fit an AR mag (2.260)

Reason I'm going lighter is cuz I've been told by some ppl who should know that the 77's prolly won't stabilize in a 14.5" bbl . Not at 100 yd, any way. They more excel at distance.

I'm not interested in a 20" bbl. I want a 14.5" barrel for this particular gun. (I already owned a nice WOA 20" DCM CMP competition rifle with free float bbl, etc)

THIS gun is not intended for that use.
 
We load the 80 class for accuracy work out past 300 yards. The cost of this is single loading since they are too long for the magazine. The 77 is roughly the spot where the case capacity and mag length issues max out.

Many folks have spent time on perfecting the balance in their chamber and reamer designs to squeeze the best performance out of the AR platform for Service Rifle. The benefits to folks with no interest in Service Rifle is still there. You can get lots of lift from that community in terms of a single rig that can make accurate shots at 600, yet deliver rapids at 200/300 from the magazine. Lots of things to like about that if you like heavier bullets.

The use of the AR platform extends into those 12 twists with 40 grain varmint bullets too. The varmint rigs can run an even heavier and longer profile bbl. The ones I get from White Oak (lost count of how many I have burned up) are all capable of rapid strings of 10 rounds into under 1/2 MOA with typical varmint loads.

I'm not sure what is causing your struggles with the 223 AR, but there are far too many that deliver well under 1 MOA with regularity using less than stellar ammo and when given good ammo are nearly as good as bolt guns. If you are shooting for accuracy under 350 yards, and don't mind the weight of a heavy bbl, the AR platform is pure hell on prairie dog colonies.

There are few recommendations I will make, but go try a Service Rifle or Varmint upper from WOA and see what the state of the art AR platform is all about.
 
Doom said:
The 77SMK has a stability index around 2 at 2000fps. Not even close to being an issue. It would be good if we knew what powder and charge weight you were using.
Click to expand...

CFE223 from 23.0 to 24.4 gr in 0.2 grain increments and Varget in a buncha different charge weights. AR Comp is next.

All in mag length... 2.256 to 2.262"
 
garandman said:
I'm not interested in a 20" bbl. I want a 14.5" barrel for this particular gun. (I already owned a nice WOA 20" DCM CMP competition rifle with free float bbl, etc)

THIS gun is not intended for that use.
Click to expand...
I'm only pointing to those rigs as an example of a known quality and record of performance with 1:7 in an AR platform.

Many AR bbls have performance level that isn't going to make you happy unless you are a "door kicker" where reliability trumps MOA.

I have not tested any recent JP bbls but anyone who says that a 77 SMK or TMK in a 1:7 14" AR is unstable or not accurate at any distance above sonic is not giving you fair advice.
 
RegionRat said:
I'm not sure what is causing your struggles with the 223 AR, but there are far too many that deliver well under 1 MOA with regularity using less than stellar ammo and when given good ammo are nearly as good as bolt guns. If you are shooting for accuracy under 350 yards, and don't mind the weight of a heavy bbl, the AR platform is pure hell on prairie dog colonies.

There are few recommendations I will make, but go try a Service Rifle or Varmint upper from WOA and see what the state of the art AR platform is all about.
Click to expand...

Yeah... I believe ya ... the ARis a very capable platform.... And I do believe I should be able to get at least 1" groups out of a 14.5 barrel.

Just understand this is not a service rifle setup. This is a fun/plinking/self defense gun.
 
RegionRat said:
I have not tested any recent JP bbls but anyone who says that a 77 SMK or TMK in a 1:7 14" AR is unstable or not accurate at any distance above sonic is not giving you fair advice.
Click to expand...


It was JP that gave me that advice. They should know....
 
jelenko said:
++
FWIW, I'll add that JP charges a lot for what you get. The barrels from WOA or CLE are every bit the equal of anything JP ships.
Click to expand...

WOA doesn't sell 14.5 bbls. (MY DCM CMP 20" WOA bbl was excellent) Neither does Wilson Combat. I'll check Compass Lake.
 
jelenko said:
They either don't know or are trying to sell you something.

Here's one of the authorities on stability JBM Calculations Stability calculator
As someone mentioned a few posts above, a 77 SMK going only 2000 fps has a stability factor of 2.078. Anything over 1.5 is rock solid.
Click to expand...

I think their point was the 14.5" bbl was the problem. ...it doesn't produce good stability / group size at 100 yds, but at 3 / 5 / 600 yd, g-t-g. They recommended a longer bbl for 100 yd groups.

No offense, but... I'll take their word over the interwebz word. :)
 
If it won't shoot at 100 yards it won't magically get better downrange. The 77 smk stabilizes in a 20" 1:8 twist just fine. I would be looking at either a bum barrel( will it shoot any bullet well?), barrel nut torque, is this a free float handguard? What barrel profile? Lots of variables to accuracy in the AR platform, but when you get them right, they will really shoot.
 
there is no reason that a 14.5 with a 1:7 won’t stabilize a 77. Length of the barrel has nothing to do with stability other than added velocity and a 1:7 will stabilize a 77 down to subsonic speeds.

that said, finding where the gun wants to shoot is another matter, but if the barrel is a good barrel it will shoot 77s.
 
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