Back from a day shooting on my property

[1911man]

So I have been slowly but surely loading up rounds to shoot out of my Grendel in case I get some free time to do some load testing and low and behold I found a day off to drive out to my property and do some shooting. All shooting was done laying prone in the back of my truck shooting off of a front and rear bag. My barrel is a 18" BHW 1x9 twist. I shot several loads but some were not even worth talking about. The two that have the most promise are these:

28.3 gr XBR 8208 120SMk CCI 450 primer 2.230 OAL. This load shot a 1.1" 5 shot group but the first 4 were .662" and I had the last round land low center. I want to blame myself but I was really shooting well. I had just shot a .389" 5 shot group out of my other rifle. I also shoot enough to be able to tell if I made mistake while shooting. Although I will admit I have a little more trouble telling in the AR platform and with this rifle being so light. I may very well be the problem.

I shot a second group and it was basically the same thing 4 shots around 3/4 MOA then a 1 low center. Velocities were:
1.2419 2.2436 3.2450 4. 2461 5. 2439
1. 2456 2. 2455 3. 2450 4.2455 5.2452

As you can see the first group had a huge spread where as the second group was really consistent. Does this data tell anyone anything?

My next load was the same thing only with 28.5 gr of XBR. I had 4 shots go into .552" and 1 low center again, opened it up to 1.056". Velocities were as follows:
1.2498 2. 2474 3.2482 4.2477 5.2507

I have also attached a picture of one of my targets and the brass. The larger group of brass is my 28.3 XBR and the smaller one is 28.5. Do you guys see any pressure signs? I cant tell.

I plan on loading up some more of each and playing with the overall length a little bit. I have heard these bullets like to jump the lands a little bit.The problem I have on the Match Kings is the tips of the bullets give me inaccurate readings when I am measuring the final length when loading.

EDIT: I attached one more picture than I thought. The picture of 4 pieces of brass is a CFE load. It was 31.5 grains this load felt very hot and had noticeable added recoil.

[LRRPF52]

Lookin' good. Can't really see excessive pressure signs from brass unless it's really excessive, and a gas gun will often exhibit flattening of primers when the pressures are still well below MAP.

Chronograph is the better pressure indicator for the layman.

Getting a lightweight rifle to shoot well is very difficult without a heavy bag that clamps to the fore end, and a rear bag. You're doing very well shooting off a truck bed.

28.5gr of 8208XBR is the ceiling with 120/123gr.

That load with the 6fps ES looks promising if you ever want to shoot distance with it.

[1911man]

Thanks, I actually find shooting out of my truck bed one of the most comfortable positions I shoot in. The benches at my local range are lousy and I feel very stable in this position. I really do need to invest in a nice shooting rest but the large sand bag I use for my front rest has been getting the job done for years. I also have an Atlas Bipod that I shoot off of from time to time. I am going to load up 20 rounds of both and play around a little more with it. I am also not crimping them, so I might add a light crimp.

[Savage Shooter]

Was it the last round in both groups that was low center? So you had a great 4 shot group going and then mysteriously "blew" the last shot - hmm, bet that happens to most of us at one time or another. While the gun was likely a little hotter and a little more fouled on the 5th round, so that the last shot walked a little, it's also very possible that the excitement/pressure of getting that last shot to group tight caused you to rush the shot and throw it off. Even though you shot a very tight group with you other gun, you are likely much more familiar with it and the load in it, so "no pressure", LOL.

[1911man]

I am not sure if it was the last round or not. I am using a fixed 10x Bushnell scope and my eyes are not what they used to be. I actually cannot see my hits through the scope anymore, I have to walk up to the target after I am done to check. Sometimes I know right off the bat if I pulled one or not. I felt really good about my pulls on all of these shots. I was in a stable position, my pulse was consistent, and my trigger squeeze felt good. One thing I have learned is that with any rifle I own I have to kind of break myself into each gun and load. I will practice over and over again until I have a great feel for the combo of me, the rifle, the scope, and the ammo. It helps down the road when I am hunting because I know exactly where my shots will land in a given situation. I also practice from several positions. The thing is that since this is an AR and i am using the exactl same stock, trigger, and lower that I use on my other ARs I should already have plenty of muscle memory built in.