Hello all,
I am working to diagnose an issue that is likely shooter error, but maybe more. I will appreciate any advice.
I have been trying to help a buddy develop a load for his 6.5 cm larue upper with a 22” stainless barrel. Honestly, I am struggling. I am not an ar-10 expert and most of my experience is with a bolt gun. I have an old OBR and have spent a lot of time behind SR-25’s and M110s, so I think I have realistic performance expectations, and a sense that something isn't right with this rifle.
My buddy was running .260 with average results. Swapped to his 6.5 cm barrel yesterday. Barrel nut torqued to spec, along with foregrip bolts. Used geissele reaction rod and quality torque wrench with the larue barrel nut tool.
When we went to the range, the rifle grouped about 2 moa with factory hornady amax for most five shot groups. None smaller than 1.6 moa, and some up to 3 moa at 100m. Similar results with 140 gr amax, newer hornady 140 eld, and with my loads… lap 136 scenar-L with 41, 42, and 42.5 gr h4350 loaded 2.84 coal (same setup as for my match bolt gun, just backed off charge a bit and worked up).
swapped scopes to a leupold mk-6 3-18. No change to groups.
swapped bags and shooters. No change
swapped ammo. No change.
with hornady factory ammo (not my reloads), we were blowing primers. For the rounds that didnt, had very flat primers and significant bolt-type ejector swipes (again, not an ar-10 expert). I threw them in a wilson case gauge and they look way long. Maybe .010” + beyond max saami and noticeably longer than rounds that come from my match gun, or even my cheap savage. If it matters i can pull better measurements... Not sure if this is normal for ar platforms. I think if so it might explain the lost primers instead of pressure. But we were shooting factory hornady. With magnetospeed this ammo gave approx 2620fps mv, so nothing crazy.
Fired brass was weird. Lots of dimples on the shoulder of fired brass. Not initially, but after maybe 20 rounds brass coming out of the gun looked mangled in the shoulder. Remained across different loads. I thought maybe lubricant in the chamber or maybe dirt until I borescoped it. I will borescope again after I clean the rifle, but this seems excessive, crazily so for 100 rounds total.
what seems extra weird to me is that the grooves of the rifling extend into the throat, and the shoulder looks like hammered dogshit. This is a new barrel with less than a hundred rounds total fired.
Is this normal? I am gonna clean and rescope, but I am worried that the grooves in the throat might be allowing gas/carbon directly into the shoulder area of the case causing rapid heavy fouling right at the shoulder.
I have still not ruled out user error either. But 2 moa seems excessive, especially with two experienced shooters behind the gun, across multiple loads, swapping between quality scopes, and retorquing everything to spec. Shot from prone with a rear bag and bipod in good conditions. Should be moa or slightly better all day long. Absent advice otherwise I am leaning towards an issue with the weapon. Either the barrel-action connection, or a defect in the chamber/barrel (most likely imho). Still possible we had a few shit rounds that fouled the chamber, or that we screwed something else up, but I am skeptical. just dont have a warm fuzzy that this is how things should be.
please help…
I am working to diagnose an issue that is likely shooter error, but maybe more. I will appreciate any advice.
I have been trying to help a buddy develop a load for his 6.5 cm larue upper with a 22” stainless barrel. Honestly, I am struggling. I am not an ar-10 expert and most of my experience is with a bolt gun. I have an old OBR and have spent a lot of time behind SR-25’s and M110s, so I think I have realistic performance expectations, and a sense that something isn't right with this rifle.
My buddy was running .260 with average results. Swapped to his 6.5 cm barrel yesterday. Barrel nut torqued to spec, along with foregrip bolts. Used geissele reaction rod and quality torque wrench with the larue barrel nut tool.
When we went to the range, the rifle grouped about 2 moa with factory hornady amax for most five shot groups. None smaller than 1.6 moa, and some up to 3 moa at 100m. Similar results with 140 gr amax, newer hornady 140 eld, and with my loads… lap 136 scenar-L with 41, 42, and 42.5 gr h4350 loaded 2.84 coal (same setup as for my match bolt gun, just backed off charge a bit and worked up).
swapped scopes to a leupold mk-6 3-18. No change to groups.
swapped bags and shooters. No change
swapped ammo. No change.
with hornady factory ammo (not my reloads), we were blowing primers. For the rounds that didnt, had very flat primers and significant bolt-type ejector swipes (again, not an ar-10 expert). I threw them in a wilson case gauge and they look way long. Maybe .010” + beyond max saami and noticeably longer than rounds that come from my match gun, or even my cheap savage. If it matters i can pull better measurements... Not sure if this is normal for ar platforms. I think if so it might explain the lost primers instead of pressure. But we were shooting factory hornady. With magnetospeed this ammo gave approx 2620fps mv, so nothing crazy.
Fired brass was weird. Lots of dimples on the shoulder of fired brass. Not initially, but after maybe 20 rounds brass coming out of the gun looked mangled in the shoulder. Remained across different loads. I thought maybe lubricant in the chamber or maybe dirt until I borescoped it. I will borescope again after I clean the rifle, but this seems excessive, crazily so for 100 rounds total.
what seems extra weird to me is that the grooves of the rifling extend into the throat, and the shoulder looks like hammered dogshit. This is a new barrel with less than a hundred rounds total fired.
Is this normal? I am gonna clean and rescope, but I am worried that the grooves in the throat might be allowing gas/carbon directly into the shoulder area of the case causing rapid heavy fouling right at the shoulder.
I have still not ruled out user error either. But 2 moa seems excessive, especially with two experienced shooters behind the gun, across multiple loads, swapping between quality scopes, and retorquing everything to spec. Shot from prone with a rear bag and bipod in good conditions. Should be moa or slightly better all day long. Absent advice otherwise I am leaning towards an issue with the weapon. Either the barrel-action connection, or a defect in the chamber/barrel (most likely imho). Still possible we had a few shit rounds that fouled the chamber, or that we screwed something else up, but I am skeptical. just dont have a warm fuzzy that this is how things should be.
please help…
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