AR-15 loads for accuracy

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  • Last Post 10 March 2019
SteveC posted this 24 October 2017

So I decided to try the ar-15 with cast. Bought a Saeco #221 three cavity (which turned out to be a GREAT mold. All cavities round and within .2 grains of each other). Started out with Reloader 7 at 15 grains. Increased the charge by half grain increments. 15 and 15.5 grains were one and a quarter inch groups (at 100 yds.) but wouldn't lock the bolt on an empty mag. 16 and 16.5 loads went to 1.5 inch groups. 17 grains finally locked the bolt back but the groups went to 3 inches. After that, all the way to 18.5 gr. the groups went to 5" and above. With the AR are we limited to low velocity, non-functioning loads for accuracy or is there a better choice of powder to get both function and accuracy? I should say that my rifle is a Rock River 18 inch barrel with an 8" twist. Any suggestions appreciated.

                                                  Steve

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Ken Campbell Iowa posted this 25 October 2017

could you change the rifle to work with the lighter loads ? ...   use a lighter recoil spring etc. ?

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David Reiss CBA Membership Director posted this 25 October 2017

Try using Varget, 4895 or H335. Reloader 7 is a little too fast. You can use just about any powder in that burning rate and reduce jacketed loads 15 - 20 %. Try those before making any alterations, such as a different buffer. 

David Reiss - NRA Life Member & PSC Range Member Retired Police Firearms Instructor/Armorer
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RicinYakima posted this 25 October 2017

I'd second using H4895 next, slower burning but still easy to light off.

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SteveC posted this 25 October 2017

Thanks, guys. I'll try a different powder. It's just that I've never had a load go completely wild like that with so little change in the charge weight. I thought that I might be over-spinning the bullet with the 8" twist.Quickload says 2110fps at 16.5 gr. and 2180 at 17.0. At least that gives me some kind of baseline to shoot for.

                                              Steve

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bdrake71 posted this 24 February 2019

I learned that in order to get decent, functional accuracy with my 1-7" 20-inch 5.56mm and my 1-9" 223 20" inch .223 Rem AR15s, you have to almost think out of the box or acquire someone else's research...

When I used my Mihec Mold's 69gr Spirepoint gas checked mold (lubed with White Label Lube's BAC lube), I had to do two of the approaches that other folks have mentioned to get the MiHec bullet to operate in the 1-7" 5.56 barrel. I adjusted the loads to function with and lock the bolt back on an empty magazine with IMR4831 which allowed me to use a slower powder for less open space in the case than other powders which allowed me to have a consistent powder column and not have too high of a velocity to cause the bullet to peel off wildly. 

The medium-slow powder of IMR4831 did what you reported on the initial loading with Rel7., I saw a major shift in performance from 23.2gr, 23.5gr, 24gr, 24.5gr and 25gr in a 100 yard ladder test of 10 rounds each from a freshly scrubbed barrel over a sandbag rest on a sturdy bench. Here are my liner notes for that load when I did the test.

25gr - blown primers.  do not ever use cases or powder combo again.
24.5gr - 5" group and primers were flattened on the cases.
24gr - 4" groups
23.5gr - 2" groups
23.2gr - 2: groups but bolt doesn't lock back.

2" groups for me when I use it for Service Rifle matches will keep them all within the 10 and 9 scoring rings at 100 and 200 yards.  
23.5gr on a reduction formula put me at around 2100fps for muzzle velocity but I did the ladder test before I had a Chronograph and I've yet to replicate this test since I did it in 2014.  I might one day do another ladder test for the 23.2gr-23.5gr range to perhaps refine the group a little tighter and over a my Chrono for actual data over a reduction formula.

The 1-9" twist barreled AR-15 doesn't stabilize the heavy 68gr Mihec Molds bullet (or any jacketed bullet over 55gr) enough for me to consider it for any Match consideration although its decent enough for a 50-yard plinker.

I have tested the LEE Bator mold 55gr in both ARs (same lube and gas checks but with 20gr of IMR4895 it calculates at 2100fps and completely functions the two rifle uppers and my son's 16" 5.56mm carbine.) and they have worked but I've never developed a 100 yard for that cartridge as I have only developed it as a plinker load that functioned the rifle for the kids when they were younger to bang away with at 50 yards.  That said, I know that other casters have had good success with that bullet or Lyman's pointer 50gr model #225450 in their AR15s.

But hey... I also own AR15 uppers in 6.5 Grendel (20") ,7.62x38 (16"), a 300 BLK (16") and a .30 Herrett Rimless (16") and at one time I built a wildcat 20" .30 Apache (7.62x45mm)....so my AR15 cast bullet load data runs the gamut...not to mention my AR10 cast loads in 7.62x51 and 6.5 Creedmoor...but those are mostly poly-coated and gas checked cast bullets in 20" uppers...

Bruce

And this is my first post on the forum outside of my introduction.  I hope I gave you some  good data to work with.

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Larry Gibson posted this 24 February 2019

"I should say that my rifle is a Rock River 18 inch barrel with an 8" twist.......With the AR are we limited to low velocity, non-functioning loads for accuracy or is there a better choice of powder to get both function and accuracy?"

The OP's loads under 16.5 gr RL7 were under the RPM Threshold.  The heavier loads were obviously over the RPM Threshold as evidenced by the loss of accuracy.  There are those who doubt the RPM Threshold yet here we see another sterling example/proof of it. With the 8" twist the OP's loads are pushing too much RPM above the 16.5 gr load. 

To answer the OP's question a slower powder, heavier bullet, harder bullet and even PCing can help.  The velocity is going to have to be kept lower in the same velocity range the 16.5 gr loads was if you want that accuracy level and reliable functioning. Some alter the springs and buffer but I don't.  It is the 8" twist that is the limiting factor unless just plinking or close range shooting is desired. 

LMG

Concealment is not cover.........

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joeb33050 posted this 24 February 2019

The OP's loads under 16.5 gr RL7 were under the RPM Threshold.  The heavier loads were obviously over the RPM Threshold as evidenced by the loss of accuracy.  There are those who doubt the RPM Threshold yet here we see another sterling example/proof of it. With the 8" twist the OP's loads are pushing too much RPM above the 16.5 gr load. 

LMG

Would you tell us what = RPM, is /are the lower and upper RPM thresholds?

Thanks;

joe b.

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Larry Gibson posted this 25 February 2019

The RPM Threshold where accuracy begins to be lost for GC'd ternary cast bullets, especially those with bore riding noses, that are conventionally lubed the RPM Threshold for best accuracy generally is going to fall between 120,000 to 140,000 RPM.  The Threshold may be pushed up by manipulating some of the variables (alloy/BHN, powder burn rate, bullet design, quality of casting) and it also can be lowered, mostly with too soft an alloy, ill fitting bullets, poorly cast bullets, and too fast a burning powder. 

"Usable" accuracy at shorter range can be had above the RPM Threshold.  However, for best accuracy with linear group expansion out to longer ranges of 300 - 600 yards the load will be found within the RPM Threshold parameters. 

LMG

Concealment is not cover.........

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x101airborne posted this 25 February 2019

There is lots you can do to an AR-15 or variant to make it run at lower pressures. Be aware that modifying the weapon then using any full pressure loadings without returning the weapon to original condition will cause undue wear / damage to the firearm and probably whomever is shooting it. 

1. You can change out buffers. Look on google or whatever and check buffer weights. They are all different weights for one reason or another, some even use them to change the cyclic rate of fully automatic weapons. Most buffers are very reasonably priced and you can either use different self contained (standard) buffers or you can use something like the JP captured spring and buffer assembly. If you do use the JP, it can be a bit of a bear to take it out of the buffer tube till you develop a technique. 

2. You can change out recoil springs. Again, these are readily available, fairly reasonably priced and easy to change. You can buy them in different lengths, weights, etc. 

3. You can trim 3 coils off your buffer spring, then as you shoot a load, trim off 1/2 a coil at a time till it functions. If you feel a dull thud on your shoulder during recoil, stop. You cut too much and will have to buy a new spring. 

4. You can lighten your bolt carrier. I said bolt carrier, not the bolt. If your rifle has a "full auto" style bolt carrier in it, ditch it for a light weight semi auto only carrier. If you already have a semi auto only carrier you can trim a little at a time to help the rifle run. With light loads, you probably cant trim too much off. I don't know that for a fact, I have never gone that far to know. All the carrier does is add mass to the bolt, cycle the gas to unlock and give it an axis to turn on. Trimming the carrier is best done on a mill for precision. 

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RicinYakima posted this 25 February 2019

Larry, do you have a formula for that? As in 1 in 10 inch twist at X f/s equals y rpm. It is late at night and don't want to do the math.

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Larry Gibson posted this 25 February 2019

FPS x 720 divided by twist (in inches),

Example: a 311299 out of a M1903 30-06 at 1850 fps would be;1850 x 720 = 1,332,000 divided by 10 = 133,200 RPM

LMG

Concealment is not cover.........

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delmarskid posted this 25 February 2019

https://brdc.us/product/aluminum-ar-15-low-mass-bolt-carrier-red/

Aluminum bolt carrier group

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bdrake71 posted this 01 March 2019

Midway has the "new" LEE .225" 55gr spirepoint flat nose 2-cavity bullet mold on Clearance for under $16 if anyone would like to purchase one to experiment with in an AR15 or any other 223 caliber rifle.

Bruce

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JeffinNZ posted this 01 March 2019

How on earth do Lee still manage to produce domestically made products for such a reasonable price?  Remarkable.

Cheers from New Zealand

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delmarskid posted this 02 March 2019

Should I ask them? The shop is an hour and a half away from us. We got lost going to a wedding and turned around in the parking lot. It felt like a visit to Mecca.

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shastaboat posted this 09 March 2019

Last summer I built a designated cast AR15.  Ordered a custom 20" barrel from McGowan with 1 in 12" twist and pistol porting.  I also installed a 2' cut down recoil spring and a weightless buffer and adjustable gas block.  I wanted to shoot my standard BA load which is 10 gr of 2400 and LEE's 55 gr cast bullet at 2000 fps which has proved to be very accurate in both my BA guns with 1 in 12" twist barrels.  I can shoot jacketed with this rig too by shutting down the gas block and installing a standard length spring and weighted buffer.  I just finished loading over 1000 rounds at about 6 cents each total for my spring ground squirrel shoots.  Fast twist barrels will require velocity to drop to a1600-1700 fps.  I get 1" or better groups with this combo and it cycles 100%.

Because I said so!

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John Alexander posted this 09 March 2019

shastaboat,

We have tried to attract AR15 users into CBA competitions without luck. It would be a great thing for our Association given their popularity. I don't know what is holding AR15 shooters back but with the 1" or better accuracy you cite you should be able to clean up in either production or hunting rifle class. I urge you to give it a try.  If you are not near a CBA match location please shoot in some of our postal matches.  Seeing an AR do well in an organized match would encourage others to give it a try.

John

 

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max503 posted this 10 March 2019

My Lee 2 cavity 55 grain mold has been giving me fits.  My bottom pour pot drips.  That semi-solid drop of lead on the end of the spout would get in the cavity and mess things up.

The latest Fouling Shot has an article about a guy who is casting HBWC's.  He was having the same problem, with that semi-solid drip-drop interfering with his thin bullet skirts.  He said he brushed the drop away with the edge of the sprue cutter plate just before filling the mold.  Why didn't I think of that?

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shastaboat posted this 10 March 2019

I appreciate the invite but I have never been a competitor in anything.  Just not my nature I guess.  I do compete and challenge myself with every weapon I own. (50+).

As for partial drip or drip from bottom pour pots.  Drain your pot, clean it out and use some valve grinding compound and lap in the plunger and spout.  I'm casting with my Lyman Digital now which I had to return to Lyman on warrantee because it was leaking around the spout, not through it.  I'm casting at 760 deg and keep it moving and warm.  I do not water drop.

Because I said so!

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shastaboat posted this 10 March 2019

AR's are inherently accurate if installed with a decent trigger.  I use a JARD 2lb and a 3x9x40 Cabellas Pineridge scope with a dual redicle scope that was designed for .223/5.56.  It also has mill fine lines for extended ranges.  Also we all know that cast bullets prefer a slower twist rifling.  

Because I said so!

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