So I just built a 6.5 Grendel, bought the complete upper from Grendel Hunter (18" Mid Length) and I've taken it out to the range 4 times now. Every single time out it's had problems cycling and feeding the ammunition and the accuracy has been really bad. Sometimes the bolt doesn't want to lock back on the last shot, it's getting stuck trying to pick up the next round and sometimes not picking it up at all. Groups are averaging 2.0 MOA at 100 yards.
My brass is getting absolutely ate up by this gun, it's causing major dents around the neck of each round making a "D" shape in the case necks. When I measured the brass with my headspace comparator it grew from 1.210" (new) to 1.222-1.226" (fired) on average and the loads that showed pressure signs grew to 1.228 - 1.230"!!!!!! I was concerned that it could be excessive headspace so I checked it with a Go/No Go Gauge and they both checked out fine.
I was also running an H2 buffer and thought it might be short stroking so I put a carbine buffer in and it still did not want to cycle. The upper came with an adjustable gas block so I might need to try tuning that next. I'm using an ASC mag right now and I just ordered an E-Lander mag to try and see if the cycling is a magazine issue.
As far as accuracy I thought the problem could be a scope issue so I put another scope on the gun and it shot just as bad so it's not a scope issue. My next move is to buy some factory ammunition and give that a try. 95 rounds down range so far and not a single group below 1 MOA. I Did ladder testing with AR-Comp and IMR 8208 from 26.3gr up to 28.5grs. It seems like I can't go above 28grs with AR-Comp without getting pressure signs. I was able to go a little higher with IMR 8208. The gun didn't shoot either of the powders, bullets or primers well. Going to back down the loads again to 26-27.5grs and re test after testing factory ammo first.
Results were as follows
Load 1
Brass - Lapua / Powder - IMR 8208 /Primer - CCI 450 /Bullet - Hornady ELDM 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
26.9 - 3.2
27.2 - 1.9
27.5 - 1.1
27.8 - 2.2
28.0 - 1.7
28.1 - 2.3
28.2 - 1.7
28.4 - 1.5
28.5 - 2.1
Average = 1.96 MOA
Load 2
Brass - Lapua /Powder - AR-Comp /Primer - CCI BR4 /Bullet - Hornady ELDM 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
28.0 - 3.2
28.1 - 1.4
28.2 - 1.6
28.4 - 1.2
Average - 1.85 MOA
Load 3
Brass - Lapua /Powder - AR-Comp /Primer - CCI BR4 /Bullet - Sierra Match King 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
27.5 - 2.3
27.8 - 2.2
28.0 - 2.3
28.1 - 1.6
Average - 2.1 MOA
Dented Case Necks
Ejector Marks on case head
Bulging case head (The one on the right is the best example)
Ring of brass I got after trying to resize those cases
Best I could get at 100yds (Red dots = 1/2")
My brass is getting absolutely ate up by this gun, it's causing major dents around the neck of each round making a "D" shape in the case necks. When I measured the brass with my headspace comparator it grew from 1.210" (new) to 1.222-1.226" (fired) on average and the loads that showed pressure signs grew to 1.228 - 1.230"!!!!!! I was concerned that it could be excessive headspace so I checked it with a Go/No Go Gauge and they both checked out fine.
I was also running an H2 buffer and thought it might be short stroking so I put a carbine buffer in and it still did not want to cycle. The upper came with an adjustable gas block so I might need to try tuning that next. I'm using an ASC mag right now and I just ordered an E-Lander mag to try and see if the cycling is a magazine issue.
As far as accuracy I thought the problem could be a scope issue so I put another scope on the gun and it shot just as bad so it's not a scope issue. My next move is to buy some factory ammunition and give that a try. 95 rounds down range so far and not a single group below 1 MOA. I Did ladder testing with AR-Comp and IMR 8208 from 26.3gr up to 28.5grs. It seems like I can't go above 28grs with AR-Comp without getting pressure signs. I was able to go a little higher with IMR 8208. The gun didn't shoot either of the powders, bullets or primers well. Going to back down the loads again to 26-27.5grs and re test after testing factory ammo first.
Results were as follows
Load 1
Brass - Lapua / Powder - IMR 8208 /Primer - CCI 450 /Bullet - Hornady ELDM 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
26.9 - 3.2
27.2 - 1.9
27.5 - 1.1
27.8 - 2.2
28.0 - 1.7
28.1 - 2.3
28.2 - 1.7
28.4 - 1.5
28.5 - 2.1
Average = 1.96 MOA
Load 2
Brass - Lapua /Powder - AR-Comp /Primer - CCI BR4 /Bullet - Hornady ELDM 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
28.0 - 3.2
28.1 - 1.4
28.2 - 1.6
28.4 - 1.2
Average - 1.85 MOA
Load 3
Brass - Lapua /Powder - AR-Comp /Primer - CCI BR4 /Bullet - Sierra Match King 123gr /COAL - 2.250"
Powder grains - 5 shot group (MOA)
27.5 - 2.3
27.8 - 2.2
28.0 - 2.3
28.1 - 1.6
Average - 2.1 MOA
Dented Case Necks
Ejector Marks on case head
Bulging case head (The one on the right is the best example)
Ring of brass I got after trying to resize those cases
Best I could get at 100yds (Red dots = 1/2")
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