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Old 08-05-2010, 12:35 AM   #61
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Originally Posted by CHLChris View Post
What's a carrier key? Are you talking about the tube thing at the top that goes around the gas tube?

This is a carbine, so I suppose it is possible I should look at the buffer, itself.
Yeah, that's the carrier key or gas key. Part #2 in JD's picture shows it well. The two screws also pictured often work loose and allow gas to escape between the key and carrier body - often causing short stroking. This shouldn't happen in a new upper but you never know, someone could have been asleep at the wheel at the factory. Grab the key and carrier and twist a little to make sure nothing moves. As far as staking, the two screws should be very tight and metal from the key should be staked or MOACKed over the screws to prevent them from loosening.

Even if all is tight it's possible that the mating surfaces don't seal well and allow gas to leak but over time you'd see fouling there. Probably not an issue but might as well cover all bases until you get this sorted out.

And don't worry, Chris you will sort it out and have a better understanding of all this plus a great rifle! I had issues with my build but solved them all and wouldn't have it any other way.

Did you say you have a carbine buffer? (That means no H stamped on the buffer face...) Not really talking about a carbine vs. rifle here, just the standard carbine buffer or H (heavy) buffer.
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Old 08-05-2010, 01:28 AM   #62
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Yep, just took apart the stock and looked all over the buffer. No H. No writing of any sort.

BTW, would heavier mean more recoil is absorbed by the loss of inertia making the heavier buffer move, making the felt recoil less? And increase the chance of short-stroking? Or the opposite?

Thanks, Quentin, for reframing this whole discussion. Rather than see this hiccup as a pain in the rear, I should see it as an opportunity to get to know my rifle better. Chris, meet your upper. Upper, meet your master!

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Old 08-05-2010, 06:21 AM   #63
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Chris, yes the H buffer is a little heavier and slows down the recoil a little. With a midlength gas system firing weaker ammo sometimes the H buffer is too much because the middy has a softer recoil than a carbine length gas system in the first place. So the action doesn't go back far enough to strip off the next round in the magazine (short stroking). Also a heavier M16 style bolt carrier instead of an AR-15 carrier can do this in a marginal system. Odds are you'll want to stick with your carbine buffer while my ArmaLite middy likes its H buffer. Different rifles, same gas system length but different results I guess.

Yes, this definitely is an opportunity! Annoying when something doesn't work 100% at first but it can be fixed. You just have to play detective and eliminate all the suspects until you find the real culprit. Be methodical and you'll succeed. And we'll try to come up with more suspects, too!

Short stoking often is the gas system or excessive friction or binding. See how smooth the action is by operating it manually. And definitely check that carrier key.

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Old 08-07-2010, 02:50 AM   #64
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Any luck cleaning up the crime scene Detective Chris?

Want some more suspects...

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Old 08-07-2010, 07:47 AM   #65
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Nope. Right now I'm in a holding pattern waiting for the mags and different types of ammo.

However, I do have a holographic sight issue that I'm going to photograph and bring before the council sometime on Saturday. My flattop seems to be 1/2" too short for my BSA sight and YHM flip-up BUIS.

I'll photo it and ask for suggestions.

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Old 08-07-2010, 03:19 PM   #66
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Your iron sights should "cowitness" about 1/3 of the way up from the bottom of your red dot glass so they're close to the actual dot but slightly under it. If the irons are obscuring the dot then you can use a rail riser to raise up the red dot.

Bushmaster has one that raises the rail about 1/2". It's about $13.50 and you'll probably need two since they're short, only giving about 1 3/8" of taller rail. I find they're the perfect height for my cheap red dot and for an old scope I have. Very likely they'll be perfect for you as well. This is a common issue so no doubt there are other risers that'll work well.


ETA:
BTW, if you're in a hurry and have a Sportsmans Warehouse nearby you may find the Bushys there - the SW we have here in Boise sells them for $19.99.

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Old 08-07-2010, 06:17 PM   #67
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Nope, this photo will show you that the problem is not height, it is length of the rail vs. the sights that I am using.

The red dot can be installed and the sights do cowitness about a 1/3 up. So I am able to view the red dot through the sights if I wish.

Here's the problem:

The BSA sight is pretty darn long and only fits it I install it forward. This means that the lug (screw) that is used on picatinny rails to fit inside one of the cross slits (in the photo labeled "T12", etc.) is not seated in one of those slits. This would mean that in recoil it has a greater chance to walk fore or aft because of recoil. I'm sure I could really go to town making the screws tight, but I'd really like to seat it down into one of the slits.

Possible fixes:

-Get a riser like this (Yankee Hill Machine Picatinny-Style Scope Riser Mount 5-1/4" Length AR-15 Flattop Matte - MidwayUSA) that gives forward slots. But this ruins the cowitness, which means I might as well remove the rear BUIS and never mess with the riser to begin with. NAY!

-Use it without a slot being engaged, risking some walking.

-Have a machinist drill out a T13.5 slot, forward of the (unlabeled) T13 slot. This would give room for everything and keep the heights correct.

Thoughts?

p8070001.jpg  
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Old 08-07-2010, 06:24 PM   #68
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Add a quad rail hand guard that is slotted and matches the height of your upper receiver.

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Old 08-07-2010, 07:30 PM   #69
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Nope, not in the budget. Good thought, however. I wished it was in the budget. Not even $50 do I want to allot to a new handguard.

If I did that I could get and support hand grip, a bipod, and all sorts of tacticool items. But I want to stay away from most tacticool items for right now. I know a holographic sight sort of screams tacticool, I got a good deal.

Thanks for the idea. It would fix this issue, but not the way I see it going right now.

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Old 08-07-2010, 08:08 PM   #70
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Understood. In that case my vote is for having another slot machined into the receiver. The sight will cover up the raw aluminum and it will give you the solid mount you are after. If you were near me, I'd do it for you after work some evening. I'm sure someone nearby could hook you up reasonably cheap.

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