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Discussion Starter #1
I'm using a V7 titanium takedown pin in a new build. I have not yet installed the spring and detent. The pin fits PERFECTLY through the lower only and through the upper only. With the upper in place, the pin is VERY tight. With moderate force, I can push it about 1/4 the way. Any recommendations on what to do here?

Would you recommend I take some fine grit sand paper to the pin and lightly sand until it fits or try to slightly enlarge the hole in the upper???

My lightweight build is almost complete!

Thanks,

Garland in VA
 

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It sounds like there may be a slight misalignment between the two bores in the receivers. Do you have a spare standard pin to compare the OD dimension of the Ti pin to verify they are the same? I would measure everything else to rule out as many possibilities before messing with the receivers. Can you install the rear pin with out the from pin in?<o:p></o:p>
 

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Titanium is very "sticky" for lack of a better word. It is possible for your new pins to be the same diameter as the old steel ones and yet still be harder to insert. I think I would polish the pin before removing the protective anodizing from the receivers' through holes.
 

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Discussion Starter #5
The fit is close... I just tried another complete lower with steel pins and they fit...they are VERY tight but they fit. I worked the steel pin in and out a few times and see marks on the bottom of the hole. I'm guessing that is where hole in the upper could be slightly enlarged. I will measure the pin diameter in a few minutes.
 

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The fit is close... I just tried another complete lower with steel pins and they fit...they are VERY tight but they fit. I worked the steel pin in and out a few times and see marks on the bottom of the hole. I'm guessing that is where hole in the upper could be slightly enlarged. I will measure the pin diameter in a few minutes.

By marks do you mean two lines left by the groove for the detent in the pin? If you plan on using a specific lower i would check it with that one.
 

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It is not that uncommon for an upper and lower to not mate perfectly. There is nothing wrong with a little "fitting" on the holes in the upper to make it match up. A chainsaw file actually works pretty good for this.
 

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Discussion Starter #8
No, wear marks from running the steel pin in and out of the upper. I see a small mark at the bottom of the hole.

I just measured the pin diameters. Unbelievably, they are the same; about .249" in diameter.

So what do you think, sand the pin or the hole....or both, slightly?

I have the takedown pin spring secured with a set screw, so dis-assembly won't be difficult.

Garland
 

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No, wear marks from running the steel pin in and out of the upper. I see a small mark at the bottom of the hole.

I just measured the pin diameters. Unbelievably, they are the same; about .249" in diameter.

So what do you think, sand the pin or the hole....or both, slightly?

I have the takedown pin spring secured with a set screw, so dis-assembly won't be difficult.

Garland
Just what Woodstock said if there was nothing wierd going on with the Ti pin dimensions just do some minor fitting. To the upper pin bore not the pin.
 

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BTW, this is a coated upper/lower set from Wilson Combat. Their coating is Armor-tuff.
In that case you might try working the pin in and out to smooth the coating down a bit and with any luck you won’t have to remove any material or coating. I talked to the Wilson rep awhile back about the coating they use and was told it shouldn’t interfere with tolerances much if at all. <o:p></o:p>
 

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Discussion Starter #14
I will work the pin back and forth but a dowel will be required to remove it the first few times! After getting the light just right on it, I see that the pin is raking across the bottom of the hole in the upper take-down pin hole.

I want the upper/lower to mated as tight as possible but I still want to remove the take-down pin for regular cleaning and lube without using tools. If exercising the take-down pin doesn't work I will take a bit off the bottom of the hole until it does fit.

Thanks for your help,

Garland in VA
 

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I will work the pin back and forth but a dowel will be required to remove it the first few times! After getting the light just right on it, I see that the pin is raking across the bottom of the hole in the upper take-down pin hole.

I want the upper/lower to mated as tight as possible but I still want to remove the take-down pin for regular cleaning and lube without using tools. If exercising the take-down pin doesn't work I will take a bit off the bottom of the hole until it does fit.

Thanks for your help,

Garland in VA
I have RRA 5.56 that is a dead nuts fit with zero movement between the receivers and a Wilson barreled upper in a Vltor receiver that fits the lower the same. The pins go in and out easily on both and a small bump is needed on the back end to separate the halves when unpinned. Does the close fit make them more accurate? I cant say for sure as the Wilson Matched billet set I have has play in it but shoots just as well.
 

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I don't understand the recommendation to file on an upper when even a stripped upper will cost twice what the titanium takedown pin costs. Chainsaw files are for sharpening chainsaws.

Grease the pin and exercise it. I have a RRA that I had to use a plastic mallet on when I first got it, but the parts eventually lapped in place and now I can take down the rifle with finger pressure alone. Tight is definitely better than a fit that rattles, although it makes no difference as far as accuracy is concerned.
 

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I don't understand the recommendation to file on an upper when even a stripped upper will cost twice what the titanium takedown pin costs. Chainsaw files are for sharpening chainsaws.

Grease the pin and exercise it. I have a RRA that I had to use a plastic mallet on when I first got it, but the parts eventually lapped in place and now I can take down the rifle with finger pressure alone. Tight is definitely better than a fit that rattles, although it makes no difference as far as accuracy is concerned.
Fitting is required with many parts on many guns. What is the big deal with some light filing to match up the holes? Gunsmiths have been filing on gun parts for many many years. It's not like you're going to ruin the upper or anything. Just do it judiciously and check your progress regularly.
 

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Fitting is required with many parts on many guns. What is the big deal with some light filing to match up the holes? Gunsmiths have been filing on gun parts for many many years. It's not like you're going to ruin the upper or anything. Just do it judiciously and check your progress regularly.
The rule for home gunsmithing is to always alter the cheapest and most easily replaced part. The difference between a perfect fit and one that's sloppy can be as little as one or two file strokes.

You also have to look at resale value. If I found file marks inside a used AR that I was thinking about purchasing, I'd close it up and look elsewhere not knowing what else had been altered.

Some of us on these forums have been doing home gunsmithing for many years without an issue. The problem is that gun guys tend to fix something that ain't broke until it is.
 

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Fitting is required with many parts on many guns. What is the big deal with some light filing to match up the holes? Gunsmiths have been filing on gun parts for many many years. It's not like you're going to ruin the upper or anything. Just do it judiciously and check your progress regularly.
Couldn't agree with you more Woodstock, look at the high end 1911 makers the difference between high volume parts cranked out on CNC machines and meticuously hand fitted custom guns built one at a time. Custom craftsmanship versus economical pricing and performance.
 
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