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New to the community - LR308 forward assist issue


Beergut

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Hello, thank you for building this forum. This is my first LR308 build. I read through the intro sticky and used the search function (with "forward assist" and did not see my issue posted previously). I have an Aero Precision M5 upper. The forward assist slides in and out nicely and the spring does its job when testing fitment and articulation of the push rod....until I try to add the threaded roll pin. There is only one way to put the forward assist into the upper and have the pin slide in to where the threads of the pin and upper meet. However, as soon as I get any thread engagement, the forward assist is held in place by the side pressure of the roll pin and can no longer slide in and out without force. I called Aero and they were surprisingly not surprised by this. The tech on the phone said that it was simply an issue of tolerance stacking and that the Aero parts kit that I used was outsourced and not made by them. (good to know actually before for my next purchase) They took my address and quickly sent me out not just a new threaded roll pin, but a new spring and forward assist as well. Well, unfortunately with all new parts and every combination of the old and the new parts tried, the exact issue remains. There is really not a lot to this set up. Pretty simple mechanically. Has anyone ever heard of the actual roll pin hole itself being drilled wrong and being off by a couple thousandths or so, or even crooked? That is really the only other thing I can think of. I know I could possibly grind the tiniest amount off of the flat on my forward assist to "make it function properly" but, just no. Is this a common thing with the M5? I have several AR15s (all Aero uppers on  those as well) and built every one of them myself with no issues. All forwards assists work flawlessly using the exact same methods tried here. I will be contacting Aero Precision again when they open tomorrow, but I was hoping to get lucky and find a functional answer tonight if anyone else has experienced this so that I can complete this build if possible. I know I can run without a forward assist, but after what I just spent on this pile of parts, I want everything working as it should without compromise.

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Shave the flat in the Forward Assist.  That'll fix it. The threaded pin-portion is a larger diameter, where it threads.  That's hitting the flat portion of the forward assist, where a roll would clear - then you need to clearance that flat on the forward assist.  That's your bind.

Simple fix.  Get the Dremel and sanding wheel out, and fix the part that's causing the problem.  :thumbup:

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9 hours ago, edgecrusher said:

I don’t have an m5 but I also have never had a threaded forward assist roll pin. Is it possible to use a conventional pin? Just throwing it out there 

Thank you for your response edgecrusher. I have not seen every style and brand of m5 upper, but at least on the Aero version, it is a one-sided hole. The internal dimension of the hole where the pin stops is standard pin width it seems (I really cant verify) but where the pin hole opening is, it is a wider hole to accept the fatter portion of the pin where the threads are. I cant see using a standard pin here. If I did manage to shove a pin in that hole and made it flush so it was not an eye sore, I would never get it out. Good luck drilling a steel pin out of an aluminum surround without destroying the aluminum around it. If I shoved an extra long pin in there so that I had something to grab to remove the pin in the future, I would be forever pissed that I am Mickey Mousing brand new parts that are supposed to be legendary for quality control. I appreciate the thought but I refuse to let Aero off the hook by damaging this upper if I can help it. 

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9 hours ago, 98Z5V said:

Shave the flat in the Forward Assist.  That'll fix it. The threaded pin-portion is a larger diameter, where it threads.  That's hitting the flat portion of the forward assist, where a roll would clear - then you need to clearance that flat on the forward assist.  That's your bind.

Simple fix.  Get the Dremel and sanding wheel out, and fix the part that's causing the problem.  :thumbup:

Thank you for your response 98Z5V. This was a first instinct of mine, but I wanted to see if anyone else has done this and its no big deal, or I was going to get flamed by people saying that was the dumbest idea in the world to remove material and compromise the integrity of the weapon. I am still a tad bitter about the thought of having to grind same brand parts to make them fit together properly. I will try one more time with Aero to see if they will swap out my upper. Otherwise I will have no choice but to grind the flat enough for proper movement of the forward assist. Thanks again for your time!  

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11 minutes ago, Beergut said:

Thank you for your response 98Z5V. This was a first instinct of mine, but I wanted to see if anyone else has done this and its no big deal, or I was going to get flamed by people saying that was the dumbest idea in the world to remove material and compromise the integrity of the weapon. I am still a tad bitter about the thought of having to grind same brand parts to make them fit together properly. I will try one more time with Aero to see if they will swap out my upper. Otherwise I will have no choice but to grind the flat enough for proper movement of the forward assist. Thanks again for your time!  

Right on man! I get it’s not optimal but it’s not too big a deal. No real compromise on integrity of the weapon or part

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Thanks to everyone for the kind and insightful responses I received. Just a quick update. I did contact Aero Precision again to follow up with this issue. They were incredibly nice on the phone at every level of person I talked to. I told the person in the warranty/repair department about my issue, and also mentioned the suggestions that all of you offered. I was happy with both of the guy's answers. I expressed how long it took for all of these parts to arrive for my build and I was apprehensive to send my upper back for repair or replacement. I was concerned that it would take 6+ months to get anything back and was concerned I would miss out on my clubs events or any other competing I wanted to get involved with this spring. He totally understood and gave me 2 options. He first confirmed that you guys were correct and that I would not harm anything by using a Dremel to grind away just enough for the forward assist to work with the threaded roll pin. He did however recommend that I use a file of the proper width to make a nicer/flatter surface. I can see his point, but the Dremel is faster. Maybe I combine everyone's advice, and Dremel the majority of the material for speed, and then finish with a file for flatness....I digress. The other option was for me to send my upper back for inspection/repair/replacement. Taking my time concerns into consideration, he explained that Aero keeps an un-publicized amount of Aero parts in stock for warranty issues just like mine. He said the average turn around for a case like mine is under 10 days. I thanked them for such great customer service. Since they sent me all new parts to see if it was a tolerance stacking issue, they recommended I try grinding one of the extra forward assists they sent me since I have it already, and see if that works for me. That way I have no down time other than what it takes to do this minor fitment adjustment. I doubt any of you are sitting by the keyboard waiting on the resolution of this cliffhanger, but I wanted to tell everyone thanks for their time in answering this post and let you all know the end result. My take away is that even though I had this annoying issue with my Aero upper, the customer service and willingness to help me out will keep me coming back and telling people I know about my personal experience with that company. I hope I can be of help to someone else in the future.

 

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