Yeah double your clicks for the carry handle 6/3 sights.
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Yeah double your clicks for the carry handle 6/3 sights.
rjacobs - I use the RBIZ all the time. It's good stuff. Carry handles are my thing, and I am preparing to put together a thread on the subject and my experiences.
With that said, I have never experienced this issue. In fact, using the RBIZ, I normally have to adjust the front sight up on 20" rifles. Some to the point where the front sight is over the ears of the base. Yes, this is with F Marked FSBs. Something is not right to have the front sight so low.
Let's start from the beginning. You started with a basic carry handle, square forge mark, loosened the elevation drum and moved it back 4 clicks so that 6/3-4 is now "Bottomed out" correct? So you put it on 6/3, and then rotate it counter clockwise 4 clicks for a 50 yard zero? It is then completely bottomed out? If so, that is correct.
Who made the barrel? Who made the front sight? Who made the actual sight post? Try measuring the actual front sight post itself and see if it is in spec. Perhaps it is too tall and causing you to have to screw the post in more than normal.
Are you sure it is F-height? With people blindly following the chart maybe someone is BSing? Measure it and see if it is correct. Most likely is, but it's best to eliminate variables.
In short, what you are experiencing is not normal.
Why do the loudest do the least?
Eurodriver, that is what I am saying.
The whole upper is from PSA. Its got one of the FN CHF, double chrome lined, high end barrels, just normal hand guards and an F marked front base. Windage was SPOT ON, like surprising, at mechanical zero. The gun shoots small groups(as small as I can shoot on iron sights, about 1.5" at 50 yards). I dont believe the barrel is damaged or installed weird or anything like that. It shoots better groups than my Daniel Defense IMO.
The carry handle is set so it bottoms out at 6/3-4(there is like a HALF a click until true bottom). That was where I started yesterday and was 12-14" LOW. The front sight post was real high, almost maxed out. I calculated 24 clicks for 50 yards to come up the 12". I think I only got to 16 or so...that was at the range yesterday using a punch and my pocket knife to turn the post before I couldnt really get anymore. Then I had to RAISE the rear sight ~10 clicks(it was dead on the 4 mark) to get to zero. So my initial thought of 24 clicks was close(needed 26).
Today I got 7 more clicks out of the front before its completely bottomed out. Used a punch and some pliers to turn the post. Then I lowered the rear 7 clicks also. So now the rear is at 6/3 -1, which should still be zero'd. I have not gone back out to test this.
FSB measures to 1.980 from the barrel which is spot on for an F marked FSB.
My setup for shooting yesterday was nothing spectacular. Concrete bench, used my normal Red Tac rear bag as a front bag, no rear bag, just my shoulder. Felt fairly stable. I had the bag back towards the back of the hand guard so I dont believe I was flexing the barrel much if at all, and if I was would have been flexing it UP, not down.
So no matter what I am doing with the marks on the drum, if it is bottomed out, I SHOULD be able to get a zero using JUST the front sight...presuming the front sight base is correct and presuming the front sight post is the correct height also(and not a TALL front sight post).
sight at 6/3
6/3-4(bottomed out)
Front sight post bottomed out
Front Sight Base. The forge mark on the other side is a circle with something in the middle(cant make it out) and 60(again I think).
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Is the barrel straight? I would check the barrel straightness. From what you are saying that you can't get it zeroed vertically without using what appears to be excessive adjustment of the sights.
Dan
Im guessing the barrel is straight considering it needed no windage adjustment from mechanical zero. I would find it VERY odd for a barrel to be bent and miraculously only in one direction, down. I would expect on a bent barrel(which I believe is exceedingly rare anyway) for it to be completely randomly bent.
Im guessing at things here, but if this carry handle was designed to use a non-F marked FSB, that is 004 shorter, thats not much, but could account for about 1 full turn of the post which would get me to basically where I needed to be.
Now that I am down 7 more clicks on the front(bottomed out), I am going to go back out and shoot it and bring some different targets with a much larger POA so I can get a more consistent hold.
With the tip of the front sight that low in the sight frame it looks like a dedicated 1000-yard upper.
Yup, something's goofy.
There are at least four different rear sight shelf heights that I know of which the bottom of the rear sight sits on top of (which the USAMU found out when they went from A2 to A4 uppers).
If you switch from a F marked to an unmarked front sight base, I believe there is 0.040" difference in height. This should raise the POA roughly 7 MOA at 100 yards or about 1-1/2 revolutions of the front sight. That would be fourteen 1/2 MOA clicks on a standard rear sight elevation wheel.
I would raise the front sight at least 2 turns from bottomed out, then raise the rear sight elevation to zero the rifle. After you have the weapon zeroed, take a set of feeler gauges and determine the gap between the bottom of the rear sight and the carry handle. If you should decide to install an unmarked FSB, the gap should close 0.040". If the gap is less than 0.060", I would leave the F marked FSB on the rifle.
FYI, when I want to verify if I have 1/4 MOA click or 1/2 MOA click elevation adjustments on a rear sight while at the work bench, I use feeler gauges. A 1/2 MOA click sight on a rifle will change roughly 0.003" for every click of the elevation wheel. I raise the rear sight 20 clicks from the bottom and measure the gap between the bottom of the rear sight and carry handle. A 1/2 MOA per click sight will give you a gap of 0.057" to 0.060". If the measurement is half that value, I know I have 1/4 MOA clicks.
Last edited by T2C; 06-08-16 at 23:54.
Train 2 Win
I think you're correct about the .04", but I also believe the difference between the two is found at the base of the shelf on the FSB. The actual FSB, measured to the top of the "ears", is the same height over bore. Now, I don't think that makes a difference in the end result you're implying; as the tip of the FSP, when sitting flush to the shelf on an A2, should still be lower than the same with an "F" Marked version. But I could be wrong.
For the OP, I'm not sure I'd jump to a non-F right away in your quest to fixing the problem. You could try a FSP that is shorter to begin with; which would essentially yield the same result as swapping for a non-f FSB. I bought a multi-pack from KNS Precision a while back, and a few of the Posts were noticeably shorter than a standard FSP. I might even have one I could send your way. It'd be a cheap and quick way to see if that's help fix your problem.
But, as others have stated, something seems to be off here that warrants a deeper dive. Just because it shoots nice groups doesn't necessarily mean the barrel/upper is installed correctly. I don't really have a great idea of what the issue might be, and feel others have provided more educated guesses than I could offer. I'm sure you'll end up getting it figured out one way or another.
The best advice I can provide is pick up a FSP tool. They're cheap, take up almost no space in a range bag, and make it remarkably more efficient to raise or lower a FSP.
Good luck brother!
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FSB differences.
F front sight base 01.jpg
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