Stuck Rear Take down pin

[CSNeoM4A1]

I installed my LPK on my DPMS receiver in anticipation of receiving my armalite upper in the mail.

Only thing is, the rear take down pin is extremely stiff. So stiff in fact, that once it is locked in the out (or the in) position, it will not budge. I had to take out the spring and detent pin just to get the rear take down pin to move again.

I reinstalled the rear take down pin and again tried to move it from in to out, and it still is stuck. I think the spring is putting too much pressure on the detent pin, or the detent pin itself fits in the detent so well that it doesn't come out...

Any suggestions on how to loosen it up a bit...

PS. This is my first time installing a LPK on a stripped receiver.

Once I install the upper, will having the rear take down pin locked be a problem?

[Akita]

Make sure you dont have the pin reversed (some are 1 way) and if its correct just trim a round or 2 off the spring to lighten the pressure.

[Skintop911]

If it's retained, it's oriented correctly.

Who manufactured the LPK? Sounds like you have stacking tolerances.

Find a known-good receiver and pin, and swap components between them to see where the problem goes.

Remember that the pin is harder than the receiver.

Don't cut coils off the spring.

If the pin is on the high side, fit that part to the receiver, not vice versa.

[CSNeoM4A1]

I have my upper now...will it be ok to put them together or should I wait until I have this issue completely worked out?

[Akita]

If it's retained, it's oriented correctly.

Not necessarily so. Different manufacturers make different shaped pins. MOST are milspec, but not all.

Why wouldnt you want to reduce spring tension by removing coils? I have seen it done may times by people wanting less pressure on the selector.

Go ahead with upper to lower. Just minimize the times you take it apart until you decide on a course of action. Tho this is a very easy fix imo.

[USMC79to83]

I'd closely examine the pin for burs or mis-manufacturing in the detent and lock channel, compare it to the front pin which, I'll guess, is working properly.

A little molly-grease and some use may help "wear" the parts in, if you don't see any glaring irregularities.

Like Skintop' said "Find a known-good receiver and pin, and swap components between them to see where the problem goes."

You can always replace the pin and plunger, they shouldn't be too expensive.

[Skintop911]

Not necessarily so. Different manufacturers make different shaped pins. MOST are milspec, but not all.

I've not seen a takedown pin with additional machining sufficient to confuse the assembler, but still enage the detent such that it would still be retained. Do you have an example you can post or link to?

Why wouldnt you want to reduce spring tension by removing coils? I have seen it done may times by people wanting less pressure on the selector.

There's no need to. By removing coils, that spring might have insufficient pressure to engage the pin positively, and then he'll be back with a different problem.

He hasn't even finished diagnosis of the problem, and should not be making corrections yet.

Go ahead with upper to lower. Just minimize the times you take it apart until you decide on a course of action. Tho this is a very easy fix imo.

No, he needs to follow the instructions he's been given, before he adds more variables.

[Akita]

I've not seen a takedown pin with additional machining sufficient to confuse the assembler, but still enage the detent such that it would still be retained. Do you have an example you can post or link to?

There's no need to. By removing coils, that spring might have insufficient pressure to engage the pin positively, and then he'll be back with a different problem.

He hasn't even finished diagnosis of the problem, and should not be making corrections yet.

No, he needs to follow the instructions he's been given, before he adds more variables.
-I'm not in the slightest motivated to find you a link. If youve only seen one type, hang around and youll see others as you gain more experience

-Springs are like 50 cents each. I fail to see the problem in snipping off a round at a time until perfect function is obtained.

-It absolutely amazes me that I've even had to answer my origional post.
I've seen this problem.
This fixes it.
Period.
If you dont believe me, I no longer give a rats ass. This really isnt rocket science as some would have you believe.

[CSNeoM4A1]

In my fooling around, I accomplished the following:

Bent the front take down pin spring and subseqently snipped off the bent part. It was maybe three coils. It still works just fine.

I then switch the front and rear take down detent pins with eachother, to see if they would work any better if they were just switched around.

After switching them, they both now work fine. I guess my receiver was a little picky about them.

[Skintop911]

-I'm not in the slightest motivated to find you a link. If youve only seen one type, hang around and youll see others as you gain more experience

I have some experience, thanks.

My request was out of genuine interest. I have seen a wide variety of pins, but none likely to create the conditions described yet provide the level of function they did. Further, none likely to be included in a basic LPK. Other than the GI type, of course. If you had a pointer, great, it would be useful since we might see them again.

-Springs are like 50 cents each. I fail to see the problem in snipping off a round at a time until perfect function is obtained.

Why not try a proper diagnosis of the problem, through some established troubleshooting techniques, before skipping to a Bubba fix?

-It absolutely amazes me that I've even had to answer my origional post.

When you say silly things, it shouldn't be amazing that you're asked about them.

I've seen this problem.
This fixes it.
Period.

More correctly, it masked an underlying problem.

If you dont believe me, I no longer give a rats ass.

Awfully defensive and testy.

This really isnt rocket science as some would have you believe.

This isn't just putting together legos, as some would have you believe.

It isn't rocket science, but there's something to it. Especially in the troubleshooting and diagnosis.