User Panel
User Panel
User Panel
|
Posted: 3/30/2008 9:52:20 AM EDT
I just zeroed the iron sights on my pair of M4gerys yesterday. Both carbines are identical in construction except one uses an RRA barrel with standard FSB and the other uses a CMMG barrel with F-marked FSB.
Both carbines are zeroed at 50 yards and both use a LaRue BUIS. Why is there such a difference in height between the two front sight posts? If anything, it seems the front sight post on the CMMG should be buried further down inside the FSB because the FSB is supposedly taller. It appears the opposite is true Should I go ahead and buy a taller front sight post for my CMMG barrel, or is the current height okay? Am I missing something? Thanks   
|
|
|
|
Posted: 3/30/2008 10:01:40 AM EDT
[#1]
You do know that the posts are adjustable for elevation, right?
|
|
|
|
Posted: 3/30/2008 10:07:59 AM EDT
[#2]
I think you may be confused here.  I'm using a LaRue back-up iron sight in the rear. This type of BUIS does NOT have elevation, thus the only way I can zero my carbines for elevation is through the front sight post All I'm trying to understand is why the elevation of my two front sight posts are so much different when they are both zeroed at 50 yards with the same rear BUIS. LaRue LT-103 BUIS |
|
|
|
|
Posted: 3/30/2008 12:22:36 PM EDT
[#4]
Why does it look like my front sight post needs adjusting? Both pictures are of ZEROED carbines. |
|
|
|
|
Posted: 3/30/2008 12:43:36 PM EDT
[#5]
Something's missing, somewhere.
The RRA looks about right. The flat part of the FSP is below the base of the FSB. I don't know why the CMMG would be so far off, but a taller FSP probably still won't help. It's only .04 inches taller. That looks like it is more than .04 inches above the base of the FSB. A couple questions: Did you zero with the Aimpoints removed from the rifle? If not, try it and see if it makes a difference. Are both LaRue's genuine?(There are some pretty good knock offs out there) Compare every detail including height. Assuming the Aimpoint is zeroed, where does the dot sit in relation to the FSP when looking through the irons with the Aimpoint on? It should sit very close to the top of the FSP. Did you buy the upper complete from CMMG? If so I would ask them about it and see if anyone else has had this kind of problem. |
|
|
|
Posted: 3/30/2008 12:55:02 PM EDT
[#6]
|
|
|
|
|
Posted: 3/30/2008 1:14:25 PM EDT
[#7]
No, for the first question. The glass wouldn't make any difference but the Aimpoint is partially in the way. You usually can't see the entire aperture circle looking through the irons with the 1/3 lower co witness. But it looks like you zeroed both rifles exactly the same so it shouldn't matter in this case. Don't worry about the LaRue thing if you bought them from LaRue Nothing else seems off base, but looking at the pictures it looks like they should be reversed. The top one should be the CMMG and the bottom one should be RRA. At least that's how I see it. Are you sure you didn't mix the barrels up? The FSP on me Sabre middy is sitting kind of high zeroed at 50 yards with my LaRue BUIS. But not that high. The wheel of the FSP is still inside the base of the FSB(about half way). You could try a taller FSP and see if it helps. Maybe the barrel is canted downward because the upper is out of spec. Just an idea. I wouldn't go as far as buying a new upper receiver yet. |
||
|
|
|
Posted: 3/30/2008 1:22:28 PM EDT
[#8]
Exactly! They definitely should be reversed, at least that's the way I understand it. No I didn't mix 'em up either. It almost seems like the RRA is really an F-marked FSB even though it isn't marked. Maybe the CMMG FSB ISN'T an F-marked FSB even though it is marked as such? Or maybe something else is out of spec like the upper or FSB itself. A taller front sight post will put the wrench flats of the front sight post a bit deeper into the FSB, and that's really all I'm uncomfortable with in this situation. I would be upset though to find out my CMMG FSB was really the culprit. I paid a premium to get a barrel with a real F-marked FSB. |
|
|
|
|
Posted: 3/30/2008 1:47:19 PM EDT
[#9]
You could try some measurements.
Measure from the top of the barrel to the sight base. Like this:  Compare one to the other. If the CMMG is that far out of spec, then you should be able to tell. If it's not, it's up to you where you go from there. I wouldn't want you to tear down your rifle without someone elses opinion first You really can't leave the FSP up that high because vibrations will cause it to move on it's own. |
|
|
|
Posted: 3/30/2008 2:02:35 PM EDT
[#10]
THOSE MUTHA F*CKAS!
Yes, I'm officially upset. So much for a positive experience with CMMG.  I took out my handy Mitutoyo calipers and measured the FSB by placing the end of the caliper on the top shelf of the FSB and dropping the depth tool down to the top of the barrel. RRA "standard" FSB - 1.974" CMMG "F-marked" FSB - 1.943" Anyone care to speculate on what a call to CMMG might get me? Besides extra USPS postage and being without a barrel for weeks and weeks? Yes, a taller front sight post would solve my problem. I'm just really disappointed I didn't get what I paid for. |
|
|
|
Posted: 3/30/2008 2:24:06 PM EDT
[#11]
At least give them a chance to make it right. If you don't want to send the barrel back see if they'll send you a taller FSP on them. I have never done business with them because of a few other issues, so I don't know what to expect, customer service wise. |
|
|
|
|
Posted: 3/30/2008 2:54:43 PM EDT
[#12]
Glock 24, Pretty bad form to talk shit about a dealer without even contacting them first, especially when it is CMMG who has done nothing but go out of their way for me and a few others that I know of in the past. Shit, I've even traded firearms for parts at their wholesale prices with them. Sure they still made money off of the parts but if I would have sold straight out I couldnt have purchased the parts that I got from them. Find another vendor who would do that! Every company makes mistakes, its how they handle it that matters. Make sure you post the outcome of this. I am sure they will take care of you. |
||
|
|
|
Posted: 3/30/2008 3:05:55 PM EDT
[#13]
Maybe it's the angle or the lighting, but are your BUIS rear sights the same? Did you mic the rears for consistancy? Did you try switching them and see if the adjustments are different?
|
|
|
|
Posted: 3/30/2008 3:25:49 PM EDT
[#14]
So I don't have a right to be upset about this? I don't have a right to publicize my frustrations? Bullshit. I'm actually 0 for 2 with CMMG. The first time they incorrectly built my barrel to the specs I ordered. At least that time the wrong parts were obvious. And no, not every company makes mistakes. At least not like this, and at least not at the frequency I've encountered. I do tons of business with Midway USA, LaRue, Brownells, Bravo Company USA, Global Tactical, and even Model 1 Sales. They've all been 100%. Any by the way, what exactly was CMMG's mistake? It isn't like they omitted something, or mistakenly built me the wrong barrel again. I have a goddamn F-marked FSB that isn't an F-marked FSB. That's not a mistake, that's false advertising. Sure, I'll call 'em up first thing Monday morning and report back. Long story short, I'm not interested in sending them my barrel so they can fix it. I'm going to ask for a taller front sight post. We'll see . . . joker1 - No, I didn't measure my two LaRue BUISs, but I did swap them between carbines and the position of the Aimpoint red dots did not change at all. That's all I need for confirmation. |
|
|
|
|
Posted: 3/30/2008 3:35:21 PM EDT
[#15]
Hey glock24, I have a taller front sight post sitting here not being used. Email or IM me if you want it.
|
|
|
|
Posted: 3/30/2008 3:44:58 PM EDT
[#16]
long time lurker first time poster, I am going to give this a try. when I was researching my first ar purchase I ran into this site and i dont know if this will help you or not but you might give it a look.
http://forums.officer.com/forums/showthread.php?t=81462 hope this works Clint |
|
|
|
Posted: 3/30/2008 3:56:40 PM EDT
[#17]
I made it hot. forums.officer.com/forums/showthread.php?t=81462 The article seems to confirm my dilemma. Doesn't make me feel better, but at least I know I'm not crazy. Thanks |
|
|
|
|
Posted: 3/30/2008 4:00:21 PM EDT
[#18]
ok for some more info I just measured my FSB on my AR that I just got from CMMG, and it is not marked F and it measures at the short length of 1.94.
Dont know if this helps but thats what I have oh yea my AR was a Bargin Bin rifle and I am real happy with the way it looks and feels for the money in fact there are no signs of "bulk storage" Cant wait to shoot it. Clint |
|
|
|
Posted: 3/30/2008 4:12:37 PM EDT
[#19]
You just need a taller front sight post........ Look here...
|
|
|
|
Posted: 3/30/2008 5:08:41 PM EDT
[#20]
Some of you aren't getting it, I think.
He doesn't need a taller post (well, he does, but that's because of the real problem). He's got an F marked FSB that's not the right height, and is the height of a non-F marked FSB. If he had a non-marked FSB that was the shorter height, yes, a taller post would do it, but the FSB should be the right height for the post he's got, except it's the wrong FSB. He's also got a non-marked FSB that's the same height as an F FSB, but that one's not causing a problem. Do I have that right? |
|
|
|
Posted: 3/30/2008 5:14:47 PM EDT
[#21]
|
|
|
|
Posted: 3/30/2008 5:32:01 PM EDT
[#22]
Agreed. |
|
|
|
|
Posted: 3/30/2008 6:43:57 PM EDT
[#23]
So if I understand correctly, the CMMG FSB is an F-marked FSB but is not the right height.
If that is the case, CMMG's supplier is at fault. I wouldn't expect CMMG to check every single FSB that goes through the place for compliance. Either way, relax. No one got hurt, everything is fine, just make a phone call in the morning. |
|
|
|
Posted: 3/30/2008 7:05:28 PM EDT
[#24]
I have almost the same problem with my CMMG middy. My FSB is F marked but looks to be a "little" low. Its zero'd at 50y with my Larue BUIS and the post is almost to the hight of the ears, but if i put it flat on a table the ears still protect the post enough to not send it back for a proper FSB and be without a barrel for a month
ETA: but WOW, looking back at your pics mine is not near as bad. Your "round thing" on the post is well above the FSB so how does it keep from turning and altering the zero? |
|
|
|
Posted: 3/30/2008 8:17:34 PM EDT
[#25]
I have a CMMG F marked 14.7 and it zeroes fine with my Matech BUIS.My carryhandle is set for IBZ and it works fine.They build barrels as they get the order so who ever made the FSB or machined it screwed it up, but where they take the time to assemble per order they should take the time to make sure the parts are to spec.Especialy when your dropping $310 shipped for a barrel only assembly.
You do have right to be frustrated and angry but CMMG also deserves a chance to make it right with you so slamming them right off I think was unecessary but to each his own.Call them ,let them know..theyll make it right You said you bought the barrel.You install it or someone else?for that post to be that high that means you had to seriously lower bullet impact so it was shooting high?This can happen when a barrel is pushed up while tourqing on.Its possible this happened when the barrel was installed. |
|
|
|
Posted: 3/30/2008 8:52:13 PM EDT
[#26]
I just checked my CMMG F marked FSB, and it's the correct 1.98 version. Sounds like a mis-marked on slipped through. Now to see how their customer service is.
|
|
|
|
Posted: 3/30/2008 9:00:47 PM EDT
[#27]
The SB is permanently fit a the factory and is a part of the barrel. It needs to be replaced at the factory.
|
|
|
|
Posted: 4/1/2008 7:22:52 AM EDT
[#28]
According to this pic, it sounds like both companies gave you the wrong FSB, according to your own measurements. |
|
|
|
|
Posted: 4/1/2008 7:24:43 AM EDT
[#29]
Or a bad supplier. 
|
|
|
|
|
Posted: 4/1/2008 7:39:49 AM EDT
[#30]
Tag for results
|
|
|
|
Posted: 4/1/2008 8:34:20 AM EDT
[#31]
That post is like all of ARFCOM AR Discussion Forum in one thread! |
||
|
|
|
Posted: 4/1/2008 8:34:58 AM EDT
[#32]
Hijack!
This has me thinking. Could you do me a favor and look HERE |
|
|
|
|
Posted: 4/1/2008 10:16:09 AM EDT
[#33]
SSDD with CMMG.
I had the same deal with the upper I bought from them about two years ago. I had to use a taller front post that almost sticks up past the ears. It's ok because the post does not protrude past the ears, but if it did, that upper would have gone back. Couple that with the hard extraction problems I had, AND that the upper itself wore very quickly down to the metal and needed to replaced with a CMT, and that the CH BROKE after about a month of use, needless to say, CMMG is off my list. |
|
|
|
Posted: 4/1/2008 11:45:16 AM EDT
[#34]
Who installed, headspaced and torqued both barrels into your uppers of unknown origin?
|
|
|
|
Posted: 4/1/2008 1:46:20 PM EDT
[#35]
Since the F marking is just an industry convention, I'd say an unmarked FSB could likely be either size, but I'd certainly expect an F marked FSB to be the correct size. It's one of the problems with the extended AR industry - lots of vendors don't hold to the specs/conventions as well as they should. |
||
|
|
|
Posted: 4/1/2008 3:08:07 PM EDT
[#36]
Say what? Its a roll pin for the gas tube and a couple taper pins, then knock it off with a soft hammer. Piece of cake. Why the hell would you need a factory for that? Reinstall is just as easy. Lemme guess, you take your car to the dealer for an oil change because only the factory oil is going to work properly. You have taken something apart before correct? |
|
|
|
|
Posted: 4/1/2008 3:23:17 PM EDT
[#37]
Re-install is not just as easy. The pin holes need to be re-drilled as the old ones will probably never line up. Not to mention Taper pins can be a bitch to get out and not everyone has a backyard shop. Do you actually own a taper reamer? Please don't make snide remarks when someone asks a question. |
||
|
|
|
Posted: 4/1/2008 3:43:48 PM EDT
[#38]
I am guessing a suplier got a bunch of front sight blocks mixed up and stamped a bunch "F" that should not have been....
Now, are these from the bargin bucket? If so, then I personaly don't think anyone with the problem really has room to complain. Hell, I have been using the longer front sight pin on a number of my uppers for years and they will solve the problem for you and they work fine. Now, if you bought a complete gun or upper and it was a full retail gun, well then you have some room to complain but I still think it is a supplier/parts issue as I know dambed well CMMG would not stamp "F" onto an non-F block just to get bad publicity. I would just call CMMG and be nice and explain the situation... |
|
|
|
Posted: 4/1/2008 4:22:10 PM EDT
[#39]
Yeah, maybe thats why its in the bargain bin... F height unmarked and standard height unmarked units get sent to the bargain bin.
If this is a custom project they need to replace it for you, not send you a taller FS post since you paid for the F FSB to be installed. |
|
|
|
Posted: 4/3/2008 4:13:23 PM EDT
[#40]
I called CMMG Monday morning. After waiting around for my two voice mails and one e-mail to unanswered for 3 days, I decided to call them again on Thursday. This time I was able to speak to "the right person".
They acted like they never heard of me, but nonetheless were polite and responsive. They explained that somehow my FSB was mistakenly mis-marked and apologized for my inconvenience. They offered to fix the problem and even pay for shipping. I politely declined and explained that I could not be without my carbine. I asked for a taller front sight and they agreed to send me one immediately. I'm happy. My irons will be properly zeroed and my barrel won't be hacked apart and repaired. I'm sure aligning a new FSB isn't easy, and I also have a permanent A2 flash hider. I think my barrel is better left alone. Anyway, that's the end of this story. CMMG did right by me. |
|
|
|
Posted: 4/3/2008 4:43:32 PM EDT
[#41]
all this drama for a $5.50 part
|
|
|
|
Posted: 4/3/2008 4:51:57 PM EDT
[#42]
It is obviously over your head. |
|
|
|
|
Posted: 4/3/2008 5:34:07 PM EDT
[#43]
|
||
|
|
|
Posted: 4/4/2008 4:49:32 AM EDT
[#44]
.....other than shipping you the WRONG part in the first place. Your issue is "fixed", but it'll never be "right" unless you have them replace the front sight base or the entire barrel assembly. ETA: As long as you're satisfied, I guess that's all that really matters. Happy shooting.  |
|
|
|
|
Posted: 4/4/2008 1:45:50 PM EDT
[#45]
I'm really skeptical my barrel can be fixed properly. There are no specifications for the FSB alignment holes nor the blind hole used to attach my permanent A2. I'm really not interested in allowing CMMG to scab in three more holes in my barrel only to try and repair this problem and make me happy. It is kinda like the collision shop who rushes your car repair because of a deadline. What's done is done. A taller front sight post is the easiest way out for me. |
|
|
|
|
Posted: 4/4/2008 2:34:08 PM EDT
[#46]
So how are you going to put the new fSB on if the flash hider is perm attached ?
|
|
|
|
Posted: 4/4/2008 3:14:02 PM EDT
[#47]
Damn people, time to spend some more time over in the "Build it Yourself" forum. First of all . . . I'm not going to put any new FSB on my barrel. Read it again dude. If I was however . . . any permanent flash hider is attached with a pin that protrudes into the bottom of the barrel and the other end of the pin is then welded over. The pin can be accessed with grinder, or the flash hider can be cut and vertically split in two which allows removal. Once removed, the the old FSB can be slid off the barrel. Once a new FSB is installed, a new flash hider would then be screwed on, pinned, and welded over. Unfortunately it is highly probable that both the two holes for the new FSB and the hole for the new flash hider will not align with the old ones. That's why I don't want it done, because I'll end up with six holes, or at least three scabbed up ones when it is all over. |
|
|
|
|
Posted: 4/18/2008 12:55:03 PM EDT
[#48]
I had problems having to unscrew my FSP too far to get a 50 yd zero also. The rifle is a CMMG BB 18" SPR running a LaRue BUIS. Front sight base is "F" marked. I was able to use a taller Bushy FSP which now has my rifle zeroed and the base of the post is slightly below flush, and the tip is still below the ears. I finally got around to digging out the caliper: FSB is 1.956. Got it fixed and as was stated, I shouldn't bitch too much considering the price, but it still sucks that a batch of mis-marked parts got out.
|
|
|
|
Posted: 4/20/2008 11:55:10 AM EDT
[#49]
I am happy to see that there are so many guys I could make happy buy selling you junk at prem prices. send it back and get what you ordered.
|
|
|
|
Posted: 6/2/2008 6:58:16 PM EDT
[#50]
Thanks for this thread.
I bought a CMMG 14.7 upper in January but wasn't able to take it to the range until the end of May. After sighting it in I noticed I had the front sight post backed out way too much, more than a millimeter above the sight socket. The front sight/gasblock was marked "F". But from reading posts like the OP and others previously I thought it might be mismarked. This thread confirmed both the proper measurements for the "F" height front sight and the fact CMMG received a batch of mismarked front sights from one of their suppliers. I measured my sight and it was 1.955 above the bore. So definitely wrong. I called CMMG after reading this thread. I talked to Garson and described the problem. He told me to send it in. They e-mailed me a UPS label that day and told me to return it. I dropped it off and it got to them a week later. They had it about a week and sent it back to me with a new front sight block. I received it today. Most of the time was eaten up in shipping, no biggie. It measures the proper 1.985" above the bore and the gas block looks like better quality. The weld spot for the permanent hider looks a little different. So it looks to me like they replaced the entire barrel assembly, which makes sense because of the drill holes for the pins and alignment. So overall I am completely happy and satisfied. They took responsibility for their product, and fixed it quickly and properly. They paid the two-way shipping and made it easy for their customer to get it shipped. They didn't try to do a shoddy half ass repair by fitting a new gasblock on an already drilled barrel. They didn't simply install a longer front sight post. I understand we are humans and sometimes things go wrong. It's how the company handles the situation that makes all the difference. I'm not sure where some of the "history" comments regarding CMMG come from, and I can't dispute anyone else's experience, but my experience was all positive. +1 
|
|
|
AR15.COM is the world's largest firearm community and is a gathering place for firearm enthusiasts of all types.
From hunters and military members, to competition shooters and general firearm enthusiasts, we welcome anyone who values and respects the way of the firearm.
Subscribe to our monthly Newsletter to receive firearm news, product discounts from your favorite Industry Partners, and more.
Copyright © 1996-2024 AR15.COM LLC. All Rights Reserved.
Any use of this content without express written consent is prohibited.
AR15.Com reserves the right to overwrite or replace any affiliate, commercial, or monetizable links, posted by users, with our own.
