Klem Wrote:OK it sounds like most things are in order as much as I can tell from what you have written. Things like lose mounts and rings would certainly blow the groups out but vertical stringing is more specific. Thin barrels heat up quickly, especially when shooting more than 1rd/min (which usually happens in auto loaders). This leads to vertical stringing.

I note you are using some new cases and some fired. Different neck tensions here mean different velocities. The result on the target will be vertical spread.

The AR is a difficult platform to shoot as well as a bolt-gun. It's purpose light weight doesn't lend itself to being stable so you have to lock it in. Other things like returning the gun to exactly the same position on the rest after it has recoiled will reduce stringing. Some shooters use a mechanical stop on the underside of their handguard like a barrier stop. Push the gun forward after recoil until the stop comes up against the rest before the next shot.

If the length of the loads are touching the lands or close to it then the difference between jump and no-jump will definitely result in vertical stringing. Or maybe a high impact and low impact. Loosely held bullets in the neck can shift forward on being loaded into the chamber and come up against the lands. If some do and some don't then you will get stringing.

These are some mechanical possibilities but potentially the easiest fix is to lock that gun in and fire it at exactly the same position and hold on the rest.

Retro Wrote:OK the gun is built on an Anderson 80% lower with Anderson upper. 20" Odinworks barrel, bolt and carrier, non-adjustable gas block, rifle length gas tube, Odin foregrip, Rock River 2 stage NM trigger, H2 buffer weight with carbine length buffer spring. I just installed an Odin Atlas 6.5 compensator as well. Glass is a Primary Arms 4 -16 x 44 with Primary Arms cantilever scope mount. All of the ammunition is hand loaded and today they were all variations of Hornady 123 Amax. Powders used were H335, CFE 223 with a little bit of IMR 8208 for good measures. The brass was either new or once used Hornady and the primers were CCI 450. All of the loads came straight out of the 2nd edition Grendel book or off of Ammoguide.com. Scope mounts are tight and so are the scope clamps. The temperature was at a balmy 38* with a light breeze from behind. I was shooting on a 100yd range. I was shooting benchrest with with Caldwell bags for support front and rear. On one group I managed to put five rounds into a 1" square. Most of the groups had at least two rounds touching. I only started shooting about a year ago so my skills still aren't the best. I appreciate any and all help the Horde can give.

LRRPF52 Wrote:One of the biggest things that can help shooting off a bench or even prone is a large rear bag.

That will eliminate a lot of the vertical stringing.

Retro Wrote:I have one of the Caldwell bags with the two ears on it. I usually place the rear of the stock in it then squeeze the ears for more or less elevation. As I said earlier, shooting is a new sport for me. I had never shot an AR style rifle before I built my first one. I've built four of them now and they all shoot very well. The Grendel became my new favorite round the first time out.

Klem Wrote:I disagree with the bipod being better than a front bag. My experience is that bags and rests beat bipods for accuracy. Bipods however are field expedient.

I agree with the fixed-stock choice for best accuracy in an AR. I also use automatic alignment where you settle the gun in the rest and bags point at the target and then suddenly relax. See how far the gun moves off aim and readjust and try to minimise this. Do this a few times prior to shooting and each time there will be less movement when you release tension as you realise how much you are putting pressure on the gun from various angles. Make sure it can track smoothly in the recoil by pushing it forwards and backwards, slightly. These are relatively light guns so you have to lock them in to prevent jump.