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Posted: 3/22/2021 9:40:45 PM EDT
Most of my builds have a little resistance but a couple Aero Precision lowers are tight.  I mean hit with a rubber mallet tight or they won't budge only crack your nails. Should I try a different rear take down pin? It has been oiled and worked still crazy tight.  I don't think about it until I clean it or open it up. Just put a charging handle in it and tough.
Thanks
Link Posted: 3/22/2021 9:48:13 PM EDT
Tolerances
Finishes
Out of spec components
Link Posted: 3/22/2021 10:28:02 PM EDT
It could be the tension adjustment screw under the pistol grip needs to be loosened. If that's not it, you can polish up the lug holes with some Flitz and a bore mop chucked up in a drill. You can polish the pins, but it's a pain after they're installed.
Link Posted: 3/22/2021 11:19:23 PM EDT
Tolerance stacking
Link Posted: 3/23/2021 8:15:05 AM EDT
I will try to polish the hole. Get some 800 grit from work a few passes then some polish. Thanks
Link Posted: 3/23/2021 9:48:13 AM EDT
[Last Edit: 3/23/2021 9:58:13 AM EDT by greco]
If I get a rear pin that’s really bad, I snip a couple of coils off the little spring that fits through the rear. Then I thread the tiny hole and screw a little plug screw into it. Works every time.  For the front pin, I snip a few coils, push it in the little pin, then install the front cross pin. I’ve never had one that didn’t retain the pin well.
Link Posted: 3/23/2021 10:10:40 AM EDT
I have one lower (PSA complete) that the pins are hard to push even without an upper. I assume it is related to the detent, once they start to move then they move easy.
Link Posted: 3/30/2021 3:52:25 PM EDT
Put your thumb on rail and index finger under the tang and squeeze the upper and lower together as you work the pin in and out a dozen times. Squeezing the upper and lower together makes it easier fir the pin to move. Then go shoot the gun 100 rounds. It will be much easier to open and close.
Link Posted: 3/30/2021 4:21:36 PM EDT
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Originally Posted By 64tinc:
I will try to polish the hole. Get some 800 grit from work a few passes then some polish. Thanks
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I would sand the pin. Always modify the cheaper part if possible.
Link Posted: 3/30/2021 5:15:27 PM EDT
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Originally Posted By nottooslow:

I would sand the pin. Always modify the cheaper part if possible.
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Unless you swap uppers and the issue follows the upper.
Link Posted: 3/30/2021 5:55:50 PM EDT
Friction is the answer.
Link Posted: 3/31/2021 7:55:33 AM EDT
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Originally Posted By WIZZO_ARAKM14:
Unless you swap uppers and the issue follows the upper.
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Originally Posted By WIZZO_ARAKM14:
Originally Posted By nottooslow:

I would sand the pin. Always modify the cheaper part if possible.
Unless you swap uppers and the issue follows the upper.
It may and it may not dependent of tolerance stacking.  A different upper on the now sanded pin lower may now be sloppy as well, then again maybe not.

Link Posted: 3/31/2021 9:00:50 AM EDT
I like them tight to start
Like said above a little use and some rounds through it and they will loosen up

Link Posted: 3/31/2021 9:20:15 AM EDT
I've had new ones that were damn near impossible to move the pin(s).

I sat there at the bench and beat it back and forth, over and over, till it broke in some.  I assumed, at the time, it was a combination of the angle/length of the points on the pins and the shape/depth of the groove in the take down pins.  They got easier over time.

Others were/are most likely a size/dimension thing.  I have a couple that are really tough to push the back pin out first.  However, if I push out the front pin first (which is easier on those guns) the back pin is then pretty easy to push out.  Same thing going back together.  If I put the receiver halves together, then push the back pin in the front pin is easy.  If I push the front pin in first the back pin can be pretty tough to push in.

Maybe that's taking the lazy way out, but it works for me.
Link Posted: 3/31/2021 11:12:27 AM EDT
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Originally Posted By CryptoKnight:
Friction is the answer.
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OP needs a treadmill.
Link Posted: 3/31/2021 12:01:25 PM EDT
I had this issue with my Bootleg upper who's home is a Stag lower. That upper worked with my other assembled lowers. That lower worked with my other uppers. The pins were from a Stag LPK. I begrudgingly accepted it for the time being.

Then one day my order of enhanced CMMG, AD, and FCD pins arrived. I tried both the CMMG and AD, still the same tightness. I tried a Schmid Tool pin set, still the same. Then I decided to install the FCD pins because still tight or not, the extra length would make taking it apart not as painful. To my surprise, it was no longer super tight that only a mallet with a roll pin punch could move.

Link Posted: 3/31/2021 5:34:27 PM EDT
Originally Posted By 64tinc:
What makes take down pins on some lowers hard to push to separate upper and lower?
Thanks
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Well made detents and well made pins . . . .
Link Posted: 4/1/2021 5:53:12 PM EDT
The specific dimensions of the upper and lower have almost everything to do with this.

From a reliable maker, uppers and lowers should be snug at first.  It’s almost certainly not something to do with the pins, unless you go with fancy - and not necessarily standard sized - pins.  But as the receivers get broken in, everything gets much easier to connect and separate.

I once bought a Rock River complete upper and a RR complete lower to go with it.  When new it took some serious “tapping” to get the upper and lower to close, and more tapping to get the takedown pin all the way in.

After a number of cycles, my build settled down into a perfect fit.  Rock River (at least used to) mills their uppers and lowers for a near-interference fit at the lugs - on purpose.  That allows the parts to wear into each other, and after that, it’s like butter to put them together or take them apart.

It’s OK to need a bit of tool help to get the takedown pin started out on a brand new rifle, or a new build.  Give it time and it should be much easier to manipulate.
Link Posted: 4/10/2021 6:56:23 PM EDT
just keep pushing it in and out. It will loosen up.
Link Posted: 4/10/2021 7:01:45 PM EDT
Poor dimensioning
Poor process capability
Worn our tools
Link Posted: 4/10/2021 7:08:36 PM EDT
[Last Edit: 4/10/2021 7:14:58 PM EDT by WIZZO_ARAKM14]
All depends how tight is tight.

I just traded into a sopmod configured upper and the lug was super wide for 6 of my complete lowers, the take town pin was impossible to push through on 4 of them as well. All were assembled with Colt, FN, RRA, CMT (continental machine and tool), and PSA uppers without issue.

I took the problem upper out and narrowed the takedown pin lug by .02" and chamfered the front and rear of it more. The pin bore was still to high, so a rat tail file was used to open the bore on the bottom. It now fits the 80% it was destined for and has no abnormal slop on the other in-spec lowers.

Sometimes, stuff is out of spec. Out of the 30+ uppers that have come through my hands, this was the only that actually needed real filing to make it drop in like it should.
Link Posted: 4/10/2021 7:39:54 PM EDT
tolerance stack up
Link Posted: 4/12/2021 3:33:04 PM EDT
This lower pins hard to push in out without an upper.  Will try changing pins.
Link Posted: 4/12/2021 10:14:24 PM EDT
Which LPK did you use? Check the pin fit without the springs and detents. The takedown is easy to check, and if you're using the 4-40, the spring may need to be trimmed.
Link Posted: 4/15/2021 8:48:06 AM EDT
I found another pin and spring removed the problem parts put in new pin and spring that looked just like the parts pulled out. Now pin goes in and out like it should. 2 small parts works wonders. Worked front pin until I can push it out better.
Link Posted: 4/24/2021 6:56:19 AM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By 64tinc:
This lower pins hard to push in out without an upper.  Will try changing pins.
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I had this issue with one of mine, turned out the new pin right from the package was ever so slightly bent. I put in another new pin and it functioned perfectly.
Link Posted: 4/24/2021 7:18:00 AM EDT
The detent pin can be too pointy and dig into the front pin slots detent

you can give them a brief deburr on a sheet of 800 grit
Link Posted: 4/24/2021 1:47:38 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By doc_Zox:
The detent pin can be too pointy and dig into the front pin slots detent

you can give them a brief deburr on a sheet of 800 grit
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This is an important “oversight” with some detent pins.  The end of the slot in the takedown pin is drilled through, and if the detent is just a little less than round, it can catch that hole.

Along with putting my pins and springs in a little “oil bath” before assembly, I check for burs, points and such when I unpack the parts.  Pre-oiled parts go together smoother (especially things like bolt catches and detents), and doing the pre-oiling makes it easy to inspect the parts before you start assembling.
Link Posted: 5/5/2021 5:41:31 PM EDT
Sometimes the “just shoot it and it’ll loosen up” or “push ‘em in & out a bunch and they’ll loosen up” isn’t actually true.

I have a Range Tool lower that I’d Form 1’d a few years ago. I had to use a hammer & punch on that bastard. Didn’t matter what pins, detents, springs, uppers, etc. Didn’t matter that I’d shot thousands of rounds through it. Didn’t matter how many times I opened & closed....

Finally got some JP undersized pins and it’s  great. They go in & out easily/correctly and look good too.
Link Posted: 5/5/2021 5:59:55 PM EDT
Sand the pins down.  If you really want to know what’s wrong mike the parts.
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