Page 1 of 2 1 2 LastLast
Results 1 to 10 of 16

Thread: Please help, my front barrel trunnion is missing holes?

  1. #1
    Gunco Rookie calebl's Avatar
    Join Date
    Feb 2013
    Posts
    7
    Feedback Score
    0

    Default Please help, my front barrel trunnion is missing holes?

    Hey Guys,

    So first post here, after getting a kit, 80% receiver, etc -- getting ready to start my build this week.

    So at first, I was super excited thinking this was gonna be a breeze -- I just finished an 80% AR-15 lower and got this parts kit, was going through the steps, and was excited because I only had to demill like one rivet in the rear trunnion to prepare this thing ...

    Then I got to looking at the front trunnion and WOW! There's almost no holes! (Please see the attached pic.) It appears that:

    1. there are no holes for the rivets to attach to the receiver (missing 4)
    2. there are the two rear rivet holes at the bottom
    3. The barrel pin hole is "started" but it's not 100% drilled through?

    At this point, after searching for terms related to drilling the front trunnion (and only finding info on drilling the receiver attached to front trunnion) I'm asking for help:

    1. Can anyone point me to a diagram ... OR ... give me "coordinates" as to where these four holes should be?

    I don't want to "eye ball" it lol. If I had another kit or aK here I could just measure and mark mine but I don't. any help?

    2. What size hole should I drill? I know the screw kits come in 10-32 but that's the thread size ... not the drill bit/hole size right?

    2. Also this steel (iron?) looks VERY tough. I'm going to have to drill this thing with my drill press -- will a carbide drill bit set like this one work if I go slow and use lots of lube (insert "that's what she said" joke here)???

    Bosch CO18 18-Piece Cobalt Twist Drill Bit Assortment in Plastic Case - Amazon.com

    Please excuse any ignorance on my part, I thought I was prepared!!

    P.S. any idea how I got a front barrel trunnion without these holes? lol I thought this was a used parts kit? Did it just never get used? Anyone else experience this?
    Attached Images Attached Images

  2. #2
    Gunco Regular Ken3030's Avatar
    Join Date
    Sep 2011
    Location
    South Central Louisiana
    Posts
    639
    Feedback Score
    0

    Default

    Welcome to Gunco!

    Looks like someone sold you a missed-matched parts kit with a virgin front trunnion. What kind of kit is it? Where did you get it?

    If this helps any, I measured a couple of Romanian trunnions I have. The rivet holes are 4mm. (same size as the lower hole you have) You could probably use a 5/32" drill. Thats what I usually drill my receivers with for rivets.

    A 10-32 thread calls for a #21 drill, .159" if you're using screws like you mentioned.

    The rivet holes you are missing measuring from the front of the trunnion, are 10mm and 27mm from the front.

    As far as drilling the trunnion, its softer and easier to drill than you would think.

    On the barrel pin hole, what I would do is drill that after headspacing the barrel in. I would use a 1/4" center cutting end milll and drill about half way thru and finish with a drill bit, then ream to 7mm. THATS what I would do, there's probably some more ways to skin that cat.

    I am sure some other more experienced members will chime in on this.
    “The very atmosphere of firearms anywhere and everywhere restrains evil interference- they deserve a place of honor with all that is good.” George Washington

    "A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
    George Washington

  3. #3
    Gunco Rookie calebl's Avatar
    Join Date
    Feb 2013
    Posts
    7
    Feedback Score
    0

    Default

    Ken3030!

    Thank you so much my man! That helps a LOT!

    yes after going through even more tutorials this morning, I found one on a build CD I bought where the guy referenced what size bit fit to drill his receiver front trunnion holes and it was around #23 he said -- so that makes sense what you're saying for size.

    My kit is one I got off gunbroker, I don't have a link for you as the posting is now expired. I got it from "mrnva". I don't even think the description said what type of kit it was (no foregrip, it came with a flat, don't think it was bulgy as the flash hider was the slanted type, not sure if any of that matters).

    Overall I'm pretty happy with the kit, just this trunnion issue threw me.

    Thanks so much with helping me locate where the rivet holes are.

    " measuring from the front of the trunnion, are 10mm and 27mm from the front. "
    That helps a LOT!

    1. Do you know how far DOWN from the top of it I should start these holes?

    2. And thank God it's going to be easy to drill, I thought I was effed as it looks like iron or some type of hard steel (my only experience drilling any firearms at this point was my aluminum 80% AR lower and looking at this stamped steel receiver I'm comparing it to, got me all scared!)

    So like a regular carbide coated drill bit set or something? Go slow, use cutting fluid?

  4. #4
    GuncoHolic Sprat's Avatar
    Join Date
    Feb 2005
    Location
    Florida
    Posts
    3,710
    Feedback Score
    5 (100%)

    Default

    I have several of those trunnions they were common to see polish 47 trunnions that were virgin this allows the builder toplace the holes where they want also a indication that they are virgin

    follow the above advice and as always read the old threads and tutorials there are hundreds

    yep someone threw that trunnion in probably cause the did a scew build or they f*cked up the original or it was missing and this is a mutt kit assembled from several kits? who knows??
    Sprat and sprat1 are one and the same.

  5. #5
    Gunco Rookie calebl's Avatar
    Join Date
    Feb 2013
    Posts
    7
    Feedback Score
    0

    Default

    Ok great, thanks for the clarification Sprat.

    So by your comment ...

    this allows the builder toplace the holes where they want
    That makes me think that the actual location as far as how far down they are or back or whatever, is not SUPER specific/important?

    I can kind of eyeball how far down and use the measurements given me above to figure out where I want them?

    Thanks!

  6. #6
    Gunco Regular Ken3030's Avatar
    Join Date
    Sep 2011
    Location
    South Central Louisiana
    Posts
    639
    Feedback Score
    0

    Default

    1. Do you know how far DOWN from the top of it I should start these holes?

    It's kinda hard to measure but the holes on the two trunnions I have are both spaced different. One of them is different from side to side too! I dont think its that critical.

    One of them is about .020" below the centerline of the flat part where the hole goes and the other one is about .040" below the centerline.

    Sticking a drill bit thru the trunnion and looking at the front of trunnion on both of them the drill is below the centerline of the bore.

    Hope all that makes sense and helps you out.

    Like Sprat said, read all the old threads, there is tons of info there.
    “The very atmosphere of firearms anywhere and everywhere restrains evil interference- they deserve a place of honor with all that is good.” George Washington

    "A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
    George Washington

  7. #7
    Gunco Good ole boy tanvil's Avatar
    Join Date
    Feb 2007
    Posts
    5,353
    Feedback Score
    20 (100%)

    Default

    I haven't worked with one of these yet.

    Please forgive me. But,,,,

    Is there a recess milled on the inside to allow space for backside of the crushed rivet so that the barrel doesn't gall on the way in?

    If so, wouldn't you need to drill into those recesses?

    Take a pic from the inside, if you would.

  8. #8
    Gunco Rookie calebl's Avatar
    Join Date
    Feb 2013
    Posts
    7
    Feedback Score
    0

    Default

    Ken3030: Great help! Thanks for the measurements And yup that makes sense.

    Tanvil: that makes sense too!

    What I'll do is use the measurements from Ken3030 above, and make sure that where the recess is milled on the inside of the trunnion -- that's where the holes go (it make sense that they have to at least hit those spots because that's why those little recess are there -- to allow space for the rivets).

  9. #9
    Gunco Regular Ken3030's Avatar
    Join Date
    Sep 2011
    Location
    South Central Louisiana
    Posts
    639
    Feedback Score
    0

    Default

    Cool!
    Show us some pics of the build!
    “The very atmosphere of firearms anywhere and everywhere restrains evil interference- they deserve a place of honor with all that is good.” George Washington

    "A free people ought not only to be armed and disciplined, but they should have sufficient arms and ammunition to maintain a status of independence from any who might attempt to abuse them, which would include their own government."
    George Washington

  10. #10
    3/6 Infantry mtdew's Avatar
    Join Date
    Jul 2005
    Location
    Benton,AR
    Posts
    2,934
    Feedback Score
    3 (100%)

    Default

    Many times I wished I had a virgin trunion to use. It would be easier to drill the bbl pin hole after headspacing with a virgin trunion. And I beleive I could clamp the rec to the trunion and drill thru both rec and trunion at the same time. No more "egging" the rec holes!
    "NA BEAN DON CHAT GUN LAMHAINN"
    Clan MacPherson
    "CREAG DHUBH"!

Page 1 of 2 1 2 LastLast

Search tags for this page

There are currently no search engine referrals.
Click on a term to search our site for related topics.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •