3 Issues Found During 1st Time Shooting new AA Grendel

[olinaz]

Took my new Grendel to the range for the first time Friday and found the following 3 issues:
1. 1st shot from a loaded (5 rounds in a 10 round mag) magazine would impact 1" to 1.5" inches higher than the rest of the group. Any ideas on why the first shot would impact higher than the others?
2. Bolt would not lock back when last round shot. (It did lock back on 6 of 8 groups)
3. The cases were new AA (Lapua) cases that measured 1.516" new. After shooting them, many of them measured 1.510". I'm not sure this is an issue or not but I have never heard of cases getting shorter when shot. I have a hard time believing this myself. How can cases get shorter when shot?

The upper is a new AA 24" Advanced Weapon System with a Shilen barrel.
The lower is Colt A2 that came with a Colt Match HBAR upper.
Ammo is reloads:
Nosler 120gr BalTip, AA (Lapua) Brass (1.516, COL of 2.230", CCI #41 Primers
AA2520 27.5gr (2480 fps av)
AA2520 28.0gr (2496 fps av)
AA2520 28.5gr (2531 fps av)
AA2520 29.0gr (2558 fps av)
AA2520 29.5gr (2597 fps av)
AA2520 30.0gr (2653 fps av)
All were shot at 50 Yards.

The picture below is the target:

[Taylormade]

How much time between each 5 shot group? Cold bore

[wheelguner]

I have owned several semi-auto rifles as well as hand guns that have shown this trait. I remember discussing this condition with several armorers at Parris Island over a 12 pack (supplied by me) while I was serving as a PMI on the Island. One of my duties was to be on the watch for recruits that exhibited exceptional shooting skills and I made sure to keep in good standing with the armorers so that I had access to "rifles with merit". Their analysis makes sense to me. The first round being chambered by hand is never seated with the force that the remainder of rounds from that magazine experience and causes the different point of impact. I'll yield to the the combined wisdom and experience of those guys. One of them, a truly salty Master Gunnery Sargent told what a PIA it used to be to get a Garand to put the first shot with the rest for the team shooters.

[babaganoush]

What a very intriguing thought. The confirmation could likely be made by single loading each of the five, and see if the group is consistently high, as his targets suggest.

[rickOshay]

wheelgunner - thanks for that insight. I am still curious as to why some autoloading rifles would do this and others not. What about the chamber or bolt makes this happen? Why always up? And that's a big shift in POI for 50 yards.

I've heard about this happening with garands. I just got mine from CMP and look forward to seeing if it suffers from this. I also bought a single shot SLED.

[LRRPF52]

What optics and mount...

[wheelguner]

I've seen it happen with iron sights, optics and dots.

[VASCAR2]

I know this is not a 6.5 Grendel but a Friend bought a blued newer version of an 18" Mini 14. The rifle consistently shot first round low left at 7 O clock. He did everything from adding a barrel strut, new thumb hole target stock properly mated to the rifle and a good trigger job. He contacted Ruger and they had him send it in where they replaced the bolt. The rifle is way better now but before the new bolt we tried everything we could think of including single loading, different bullets, powders, primers and scope. I guess it had to do with the way the bolt locked up but the new bolt pretty much eliminated the first shot flier.

[olinaz]

The mount is a LaRue LT158 QD. The scope is a Vortex Viper PST 6-24X50 FFP.

[LRRPF52]

Take your rifle and ensure it's cleared. While holding the pistol grip with one hand, grab the optic/mount combo with another, and attempt to move it forward and backward. If it moves, you need to tighten down the QD lever pivot points with the provided wrench.

I saw this on 2 AR15's w/ LaRue mounts during my Designated Marksman Course this past weekend. If your mount/optic combo is tight, check the scope rings to ensure that they are tight. The LaRue mounts are excellent QD systems, and will function beyond what most people will ever need performance-wise from them, however, they do need to be tightened down properly. The instructions explain that they work best when you meet significant resistance at 45 degrees when you start to close the QD levers.

If the optic/mount system is sound, what power were you shooting on? I'm interested to see what would happen at 100yds, but the fact that this was a consistent phenomena for 5/6 targets usually points to something equipment related.

[olinaz]

It does not move at all. I had to loosen the QD pivot points some originally just to get it on. They are still very tight and hard to lock in place. The scope ring screws are all tight. I checked them several times at the range just because it's a new setup.

I was shooting at 24X. I will try this again this Friday at 100 yards. I shot at 50 last Friday to sight it in and just get familiar with it.

[BjornF16]

Olinaz, what setup are you using to shoot from?...bipod, bags? I've seen this with my lightweight Grendel. I was shooting off bipod, on concrete, with a very light pull into the shoulder. The first shot out of a freshly loaded magazine was approx 2" high. The next 4 were grouped together. I guess I had a better pull into my shoulder after first shot. Putting down rug/sandbags to "pre-load" the bipod and using a firmer pull into shoulder eliminated the issue.

[LRRPF52]

24x is way overkill even at 200yds, let alone 50yds, but I think BjornF16 could have a point. Man-up on the gun in your position by settling it and loading-up on it before taking the shot. Self-loaders with reciprocating parts need to be driven a little harder.

[Tech09]

Definitely cold bore, mine fires 1 inch high and 1/2 inch right on cold bore shots

[LRRPF52]

Definitely cold bore, mine fires 1 inch high and 1/2 inch right on cold bore shots

There are consecutive groups that duplicate this phenomena well after the cold bore.