.22 LR poor accuracy with conversion kit

[Chemistry Guy]

At about 45 yards with a rest my 16" AR pretty much puts 10 rounds of .223 through a single big hole exactly at my point of aim. If I take out the bolt carrier and put in my CMMG .22LR conversion kit, my groups explode to about 4-5 inches and are centered about 6 inches below the point of aim. I am using Federal value pack ammunition.

Is this decrease in accuracy because of the barrel diameter mismatch (a few thousandths), the barrel twist (1 in 9), the cheap ammo, or some other effect related to the conversion kit?

Also, I know that .223 shoots flatter than .22LR, but 6 inches at less than 50 yards seems excessive. Is this typical?

 

[wally]

Probably all of the above has and effect including the time of flight, hence bullet drop, will be about 3X for .22LR compared to what it is for .223.

These are the reasons I went with a dedicated .22LR upper (Spike's Tactical). I get about 1.5" groups with the Federal bulk pack in mine.

 

[TonyAngel]

What twist rate is your barrel? Most ARs these days have something between a 1:7 and 1:9 twist rate. .22lr does best with something like a 1:16 twist rate, if I remember right. Depending on the actual diameter of your bore, that may be an issue too. My memory is bad with numbers, but again, if I remember right, the bore of the .223 may be 1/1000th over size for the .22lr round as it is. If your bore is on the outside of spec for a .223, that may exacerbate the problem.

Since you already have the setup, I'd suggest maybe a couple of things. A few guys have had decent luck shooting the 60gr .22lr loads, but most that I've seen have good luck did so with sticking to the longer bullets. When I was messing with a conversion with a friend of mine's rig, we had good luck with the CCI mini mag solids. They're a bit longer than the hollow points. The ones we had were anyway.

In any case, you may want to try out a bunch of different kinds of ammo. Even the most expensive .22 is going to be cheaper than the cheapest .223. Oddly enough, I saw a guy at the range shooting his CMMG conversion with cheap bulk Federals and was able to consistently hit clay pigeons at 100 yards. I suppose it's the luck of the draw.

 

[benEzra]

Also, I know that .223 shoots flatter than .22LR, but 6 inches at less than 50 yards seems excessive. Is this typical?

That's reasonable. It's partly just the longer exposure to gravity due to the much, much slower velocity (.22LR takes 2 or 3 times as long to get to 50 yards as .223 does, and d=1/2at^2, so 2x the time gives you 4x the drop and 3x the time gives you 9x the drop, if I figure correctly).

There's also the fact that even an AR's light recoil tends to raise the muzzle a little while the bullet is in the barrel, so that reducing recoil (such as by going from .223 to .22LR) reduces barrel lift and hence lowers the point of impact. The second effect is less pronounced with .223 than with harder-kicking calibers, and is less pronounced with ARs than in guns with the barrel axis well above the center of the buttplate (like a mini-14).

 

[Cosmik de Bris]

.223 takes .224 projectiles, .22LR are .221 I think. The slight sloppiness doesn't help.

 

[Wahoo95]

Try some 60gr Aguila SSS and watch that group tighten up to around 1"!

 

[kcmarine]

Hm.. was it just a conversion bolt & carrier or a whole upper? A .223 barrel will fire .22 ammo somewhat accurately, but it does allow the bullet some area to "bounce around" inside the barrel.

 

[iamkris]

That's why I finally built a dedicated upper. Besides being very messy, the Ceiner kit in the AR gives pretty lousy accuracy. I have it relegated to a kids fun gun now. The dedicated upper is mine.

 

[Nikdfish]

You didn't say what weight bullet you were shooting. If it was 36 grain (or lighter), that could well contribute to loose groups. In my personal experience with a 1 in 9 twist you need to stick with 40 grain or heavier for best accuracy. With mine, I got nearly the same results with 40 grain as with the 60 grain Aquila SSS sub-sonics...

This was fairly rapid fire (1-3 seconds per shot) at about 25-30 yards. The top targets were shot using 60 grain Aquila sub-sonics, the lower targets were shot using 36 grain Federal bulk.




Nick

 

[jpwilly]

My AR 22lr CMMG conversion kit shoots 40gr Wolf Match Target into 1/2" groups at 50yrds in my DPMS with 20" SS Bull Barrel and Federal Bulk into 1-2" groups. My bbls are 1-9" twist also. All 22lrs are ammo sensitive. Turning your AR-15 into a 22lr doesn't help things but they can be accurate enough with the right ammo. 60gr SSS sucked in my rifles and is dirty dirty dirty. I still have 3/4 a brick of the junk for the same money get Wolf MT and be happy all day long!