BAD groups----need help

[One Shot]

I've got a AR in .300 Whisper and can't get good groups. I was shooting Matchking 220 gr with 9.1 gr H110. I bought some Nosler spitzer in 200 gr and tried 9 gr H110. I'm still getting 6-8 inch groups. Any ideas?
Thanks

[i8asquirrel]

What is your barrel twist rate? I have found better accuracy with 1680 powder and 4227..

[One Shot]

I think it's a 8

[Hoser]

Is your can on tight?

Have you tried shooting any groups without the can?

I am assuming you have some sort of muzzle device.

[One Shot]

I haven't tried it without the can.

[buffetdestroyer]

If using any sort of sighting device or optic, check that first to make sure that it is on tight.

Clean the weapon thoroughly and take the suppressor off. Tighten down any sighting systems (base, rings, etc.). See what kind of accuracy you are getting after this.

If you are getting good accuracy with the suppressor off, then you may have misaligned threads and you may be getting baffle strikes.

If accuracy is still crappy, inspect the rifling and crown for burrs and visible imperfections. If after all this, and you still are nowhere, try 150-175 grain bullets to see if it is a twist rate issue.

I would say that if you are getting 2-3 MOA, it is likely a load problem, but with 6-8 inch groups, it is likely something functionally wrong with the weapon (assuming a capable shooter in a benchrest situation and a reasonable sighting system).
________
Hero honda hunk specifications

[One Shot]

Some progress. I shot 3 rounds of 125 gr and 3 of 168 gr at super sonic speed and had 1 in groups. I'll try some 168"s with less powder and see what happens.
Thanks for the help. I'll keep you posted.
Doc

[LouBoyd]

Also confirm muzzle velocity, Preferable with a chronograph (buy or borrow). Measure EACH shot of at least a 5 shot carefully aimed group at 100 yards and note the point of impact and velocity of each of those shots. Preferably post a photo of the target with each shot and it's velocity marked. Take the velocities with the chronograph set about 10 feet in front of the muzzle. Most bullets will be more stable at 1000 fps than in the range of 1050 to 1300. So far no one as mentioned bullet velocity, velocity dispersion, or the shape of the groups. That's not to say faster velocities can't be used. Some bullets can have suffieient stablity across the entire transoinc range.

Before even doing shootnig test I'd have made sure my bullets are seated on or within .01"- of the lands, then worked up the the loads to give 1000 fps before doing any accuracy tests. I'd also have loaded ammo with its neck diameter between 0.002 and 0.005 of my chamber's neck.

If there is a lot of velocity variation and vertical stringing then you've probably got a problem with bullet seating depth and/or the fit of your cartridge to the chamber. If you loads are faster than 1050 fps but have uniform velocities then I'd expect a bullet stability problem. Groups could be any shape. Barrel twist and the specific bullet designs matter. Bullet weight an shape aren't the whole story. The interall mass distribution in jacketed bullets matters too. You can't determine a bullet's stability by looking at it ( though it is an indicator).

I agree on checking the barrel twist rate. (use a cleaning rod with a brush or tight patch. Mark the rod. measure to the mark, pull the rod for 1 turn of the mark, measure again to the mark and subtract. Be careful the brush or patch isn't slipping over the lands.

Also note the elevation, temperature, and barometric pressure when you do the tests. (air density is calculated from that those. Along with air density spin rate and velocity determines the stability for a particular bullet.

Please give the name and model of each bullet you use. Bullet weight and nose shape affect stability but they don't define it. Even the internal mass ditribution affects bullet stabity. The suggestion of using 220 grain Sierra matchkings isn't that they're more stable than other bullets, just that they're well known to give good performance. Other bullets may be more stable but not seat near the lands.

8 inch groups at 100 yards is terrible. It's not a subtle problem and the answer will be a head slapper when you find it.

[dick]

I had a problem like that. I was only shooting sub loads that had worked in other rifles. After I shot several strings of super-sonic loads of 150gr doing about 2000fps, basically breaking in the barrel. My sub groups are where they should be.

[One Shot]

Tried new stuff today. As my volocitys go down, my groups get wider. I was shooting smk 190 gr hpbt. First with 16 gr AA 1680 and shot 1/2 in groups. Then 14 gr, with 3/4 in groups. Then 12 gr with 1 1/2 in groups. My chrono didn't work, but all were supersonic. I'm going to try 10 gr tomorrow. The gunsmith who built this for me said it is a 1in8 twist.