5.56 / AR Load Development

[treillw]

I have an AR with a red dot on it. I'm trying to do some sort of load development for it, but it's much different than bolt guns. I can hardly tell where I'm aiming at 50 yards, trying to shoot groups with it. I guess if a red dot is my sighting system, I can't be too worried about precision. But at the same time, I don't want it shooting 8" groups because of the load at 100 yards either. Any tips on how to do load development better? I don't really want to add a magnifier to it, or buy one. I thought about using my cell phone or some other device to get a better sight picture for load development. Mounting my cellphone up on a tripod and using the camera might work. Hopefully I'm not the only one that is this crazy!

What do you look for in AR load development? Just creep up to the max book load, shoot it over a chronograph, and watch for pressure signs? Pressure signs are different than in a bolt gun - what are they?

I know many people go over the book max with bolt guns. Is this a bad idea with an AR?

I have a 14.5" barrel and a 10.5" barrel, shooting 77 grain TMKs. What should be my goal?

Thanks!

 

[mkk]

What's the twist rate in your barrel?
Put an optical scope on it for load development, once you have settled on an acceptable load put the red dot back on.

 

[treillw]

What's the twist rate in your barrel?
Put an optical scope on it for load development, once you have settled on an acceptable load put the red dot back on.

I thought about doing that, but I've seen that change the guns harmonics significantly in the past. I had a 300 win barrel that was defective. I shot all kinds of loads through it and couldn't get good results, so I was checking everything I could to try to fix it. My scope weighs about 24 oz. Groups were stringing 4" in a vertical line with my scope. I put my buddy's 2.5 pound Nightforce on it and it started stringing 4" from left to right. Crazy, but makes sense.

Both barrels are 1:7 twist.

 

[ID_Matt]

I thought about doing that, but I've seen that change the guns harmonics significantly in the past. I had a 300 win barrel that was defective. I shot all kinds of loads through it and couldn't get good results, so I was checking everything I could to try to fix it. My scope weighs about 24 oz. Groups were stringing 4" in a vertical line with my scope. I put my buddy's 2.5 pound Nightforce on it and it started stringing 4" from left to right. Crazy, but makes sense.

Both barrels are 1:7 twist.

How does the weight of a scope change a guns harmonics? This is the first I have heard of this.

 

[mkk]

Barrel twist is good to stabilize that bullet

Your comment about the scope affecting barrel harmonics........................

 

[treillw]

How does the weight of a scope change a guns harmonics? This is the first I have heard of this.

How could it not change the gun's harmonics? You're significantly changing the mass of the object vibrating. If you have two metal bars of the same size, one made from steel and one made from aluminum, they will vibrate at different resonant frequencies.

Tuning a rifle is simply playing with how much time it takes for a bullet to travel down the barrel and the impulse imparted into the rifle by the explosion - you're trying to get the bullet to release when the barrel is at a vibration node in its three dimensional movement and not when the barrel is traveling between stable, relatively motionless, nodes. Changing the seating depth by a mere .010", or less, changes how a gun shoots (with some exceptions in very easy to tune rifles). Precision is about obsessive compulsive consistency.

Going from a lightweight scope to a Nightforce cinderblock increased the rifle weight by roughly a pound and a half. The rifle I'm speaking of was around 7 pounds - a lightweight 300 win mag Cooper M92. Increase its weight to 8.5 pounds (by 21%) and it's going to behave much differently. It is going to effect how the gun recoils and vibrates (harmonics) - how many people notice the difference in their shoulder and don't want a lightweight magnum.

No, it wasn't that I don't know how to shoot a lightweight gun, etc, etc. The barrel was defective. Cooper rebarreled it and I can shoot half minute groups with it all day long now. I reached out on this forum, and others, for help on trying to get it to shoot - if you dig through it, I may have posted photos of the different results from the different scopes, or at least mentioned it. I probably still have the targets in my basement as well, but I'm not that interested in proving my point.

Move your gun from a lead sled to sandbags - it can change how the rifle groups. Put more preload on a bipod, the gun will recoil differently and have a different point of impact. You should shoot a gun in practice the same way you are going to shoot it during its intended use.

The scope I have that can easily be transferred onto an AR is a Nightforce. Going from a red dot that weighs practically nothing to a, again brick Nightforce, is going to change the gun weight significantly. It might not effect harmonics as significantly with a caliber as small as 5.56, since the recoil isn't nearly as bad as with a 300, but theoretically it has to change it. Besides, I'd rather not play musical scopes and do something simple to get a potentially better result.

Back to reality, we're talking about an AR with a red dot on it. It's not a precision rifle. But I don't want to spend all that time and money reloading and perfecting a load for a gun that isn't going to exist and potentially end up right back where I started, based on my past experiences.

 

[treillw]

Barrel twist is good to stabilize that bullet

Your comment about the scope affecting barrel harmonics........................

See above.

 

[mkk]

good luck working your load up

 

[justinspicher]

I am not sure why you would reload for precision with a 14.5 and a 10.5 AR barrel, then decide to just use a red dot, that seems kinda pointless. Why not just use factory loads?

 

[The shotty]

Do you have or have access to a chronograph? If you’re not willing to put a scope on for load development I’d do a 10 shot ladder test looking for velocity nodes and pick a powder charge in the middle of a node. You can’t run gas guns as hot as bolt guns so I absolutely would not push past book max especially as you’re limited to mag OAL unlike some bolt gun applications where you seat the bullet further out so you don’t have the same case pressure. I have a few guns I only do this method of velocity tuning and never mess with the load again as it has acceptable results on target for my application

 

[BRTreedogs]

Mount a scope for load development then switch it back to a red dot.

 

[logem]

I just completed load development with .223/5.56 77 SMK and AR-Comp a week ago using my 14.5" AR-15 with a Aimpoint red dot sight. I highly recommend a chronograph to compare to a known load like MK 262 Mod 1 while going up the ladder. After reaching pressure signs, I backed down about 0.6 grain and ended up with the following results with 20 shot at 100 yards. If I can achieve this accuracy with a 14.5" barrel and red dot at 100 yards, I feel that I'm good for whatever I'd use the SBR for in the future. Next step is to shoot these through another of my AR's which is a 14.5 SBR with 1-6x variable scope to perform a more critical assessment of accuracy.

 

[Caseknife]

Find a different target that will allow you to be more precise with the red dot at 100 yds.

 

[Axlrod]

Just a fyi. Alliant lists a max of 22.1 gr of AR Comp w/ Sierra 77 gr. bullet.

 

[BigNate]

Barrel harmonics probably won't be affected much by changing the weight of a scope. Loose mounts will. Your example of the 300 stringing vertical and then horizontal doesn't prove much except the rifle still has issues.

I worked up loads for a 1:7 16", then shot them in a 1:8 16" and a 11.3" 1:7 to see if they remain useful. Not saying my way is perfect but it works for me.

My notes for a couple powders. Use at your own risk.

 

[logem]

Just a fyi. Alliant lists a max of 22.1 gr of AR Comp w/ Sierra 77 gr. bullet.

Thanks. Lyman lists 23.0 grain as max. I didn't see pressure signs until 23.4 gr. I settled on 22.8 grains going forward.

 

[logem]

Find a different target that will allow you to be more precise with the red dot at 100 yds.

What target would you suggest?

 

[Caseknife]

what kind of dot, how big of dot, what does it cover at 100 yds? Maybe something as simple as a big cross of black tape on a white piece of paper. Just so it is something that you can pick out/divide evenly to assure that you are holding at the same point each time. Much easier to install a scope for load development, which is what I do. I've got a SWFA 10x set up to go on a rail that I used for load development on two different AR pistols

 

[logem]

what kind of dot, how big of dot, what does it cover at 100 yds? Maybe something as simple as a big cross of black tape on a white piece of paper. Just so it is something that you can pick out/divide evenly to assure that you are holding at the same point each time. Much easier to install a scope for load development, which is what I do. I've got a SWFA 10x set up to go on a rail that I used for load development on two different AR pistols

It's an Aimpoint Comp-M3 with 2 moa dot, although I can dial it down to a very small (lessor sized) dot.

Thanks for the input. I can see how aiming for the center of a noticeable "cross" or large bulls-eye is much better than the perceived center of white piece of paper.

 

[Caseknife]

Or a target with black and white 2" squares in a checkerboard pattern. Lots of targets and patterns out there to see what works. Kind of what you have to do when you can't focus on handgun sights any longer, search for a target that is visible with aging eyes.