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Posted: 1/2/2017 10:19:31 PM EDT
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I recently installed a free float hand guard and new gas block as well as 45 degree buis. The rifle is a lefthand Stag in 5.56/.223.
When I use the scope, it functions correctly, zeroes fine and shoots 1" (Mark 1 mod 2 eyeball measure) 100 yard groups. Since I'm a lefty, I put the backup sights on the left (ejection port) side on the handguard. If the scope fails or the target is too close, I can roll the rifle clockwise and use the backups. When I do so, about 30% of the rounds keyhole. The first one I saw at 50 yards looked like a tear from a ricochet. When I pulled it back, the bullet hit exactly 90 degrees off long axis, directly side on. The barrel is Original Stag 1/8 twist 5.56/.223, less than 600 rounds downrange. When I got it home, I cleaned it and didn't find any damage to the gas tube, and it ejected in either straight up or 45 off axis positions. I would appreciate help in solving the problem. Thanks, Kevin |
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Keying holing most of the time, if the bullet striking inside of the Brake or FS on the way out of the bore before it goes down range.
So on that note, you could check the bore to inside of the FS with say a cleaning rod, but is not going to show if you over tightened the FS and caused the last inch of barrel to be canted off axis isntead. Hence, just pull the FS/Brake off the barrel, and shoot the barrel without it to determine if the problem is the FS/brake to begin with (bullet strikes to the inside of it). As for the bullet striking the target differently with the scope mounted on top, then side sights, kind of normal, since the two may not be looking at the same POI down range. Also, when you installed the float tube, may have either gotten crap between the lip of the barrel extension shoulder and the barrel socket front lip to cause the barrel to be canted off center line of the upper receiver, or worse and over torqued the barrel nut to really cant the entire upper barrel socket off the center line of the upper receiver instead. |
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Thank you sir.
I will check to see if there is any interference in the barrel at the end and at the gas tube. I used a reliable torque wrench to reinstall the barrel at 35 ft/lbs. The flash hider was installed with the crush washer in the same orientation and lined up properly but may be tilted. Since it has only keyholed when using the iron sights, and all bullet holes are perfect on scoped shots, it is confusing. The FS stands for front sight? It doesn't have a triangular Standard AR sight with gas tube on the barrel. The buis are on the free float hand guard and should have no noticeable effect. There are no impact marks on the rear end of the gas tube indicating misalignment. There are no marks on the gas receiver/bolt interface. The flash hider is relieved so it will have to be significantly canted to allow a bullet strike. However, this is my first AR and I'll check more closely. Thank you again, Kevin |
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Do your targets look like this? This is textbook keyholing. The bullets are going through the target sideways.
I don't see how turning a rifle on its side would have any effect on keyholing. Bad barrels or worn out barrels cause keyholing unless the bullet is striking the flash hider or such. 
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Yes, my point exactly. The rounds on the scope-only sight-in target
were perfect circles in a 1" group. The rounds on the iron sight only sight-in target had about 30 percent keyholed rounds of varying lengths. The first one looked like a die cut profile of a bullet. Very perplexing. When I finished, I had half a magazine left and I called over a lefty young kid who had been shooting a RH bolt action with his dad. I asked him if he wanted to shoot a LH rifle. He shot a 11 or 12 round scope-only 2" group lined up on the Bullseye. No keyholes, great group for someone shooting a new-to-them rifle sighted in by an old man. I think I made his day. I know his dad's grin when he saw the kid's target made my day. Thank you, Kevin |
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Might be ammo but I've never shot steel cased ammo of any brand. I checked my mag's and I had GECO
(Swiss) 55 grain and American Eagle 62 grain at the range. I don't think I shot any of the 62 grain and I think a 1 in 8 twist should stabilize 62 grain bullets. I'll test that theory next range trip. I examined the barrel to flash hider attachment and as noted, the internal diameter of the,flash hider is significantly large than barrel caliber. So it's not hitting there. I still have to remove the gas tube to check if there is something blocking it but it ejects each and every time. Thanks, Kevin |
| I don't see how whether you look through the scope or transition sights would matter. It's all an interaction between the bullet and barrel. If it becomes a problem with good ammo, you probably have a defective or worn barrel. That's what caused my keyholing in the above picture. Even with just 1400 rounds. Barrel manufacturer replaced the barrel. |
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Thanks,
I'll take it to the range another time and see if I had 62grain bullets loaded...though I don't think so, it might have happened. However, as noted, I've got less than 500 rounds through it in slow fire I can't see why it would do this either, that's why I put this out for help. I'm enjoying the assistance and am grateful. I may have to send the bbl back. Cordially, Kevin |
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