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Posted: 5/15/2010 4:40:03 PM EDT
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Went to try out the lapping tool from brownells today. It goes in then stops about 2.5 inches short of the head. Inside of the receiver is too tight. Don't have another upper to try. Any suggestions on what to do? Thought I'd check with the hive before I ended up doing something I later regret :-)
ETA: yes, I did apply a liberal dose of CLP. |
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I have only one upper it will not fit, and that is a Rock River upper. I don't know if all RR uppers are on the small side but this one is. Solution, try the build without lapping and then if the barrel is not centered in the forend or the sites will not zero properly, give RR a call. Mine turned out OK without lapping but this is the only AR upper that I have that is not lapped.
I had some ideas about freezing the lapping tool and heating the upper but what happens when the temp of the upper cools and the lapper heats up and you are still lapping? Better to just try it without lapping and see what happens. |
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It is but the tool goes inside the upper receiver so that it keeps the lapping surface perpendicular to the axis of the bore. If the hole cut in the upper is too small the lapping tool will not go in, ergo you cannot lap the front of the receiver threads to square them up.
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upper is from DSA, cardinal forge. Overall seems like a nice uper. I'm building a medium to long range SAM-R/SPR hybrid so I thought it would be good excuse to expand my tool collection by 1 
So as sugguested I'll just put it together and see what kind of results I get. |
| I've had two uppers that had the same problem. One problem I found was having the receiver block too tight in the vise. Even then, they had a tight spot. one was at the forward side of the ejection port and the other was just aft of the port. Used a light motor oil and a drill and worked it in. Being tight, it will get hot so go slow and don't get too hot (withdraw the tool and let it cool and start over again). Also don't force it and get it stuck. It will remove the anodizing, but everything will be square and in line. I have had no problems with the bare spots for about 3yrs. I guess it just depends on what makes you warm and fuzzy feeling inside. |
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Quoted:
upper is from DSA, cardinal forge. Overall seems like a nice uper. I'm building a medium to long range SAM-R/SPR hybrid so I thought it would be good excuse to expand my tool collection by 1
So as sugguested I'll just put it together and see what kind of results I get. My buddy got TWO DSA UPPERS that were tight, to the point where the fucking BCG's wouldnt even slide freely. Send the fucker back and make them replace it with one that is in spec. |
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Do nothing, it won't fit Whose receiver is too tight 458 Have two side chargers sitting here ( AA, Rainer [MEGA] ) and decided to see if the lapping tool would fit. Nope. Both carriers ( Young? ) fit though. I'm thinking either make a new lapping tool or forgo lapping these two. 458 |
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The CLP soaking in overnight seemed to help. I could now seat the tool all the way in. Applied some outers gun oil and started turning. Things started to loosen up. Now I applied the compound and started lapping by hand. Worked pretty good. Stopped once to check progress.
But now take a look at this .... 
Looks like the anodizing is flaking off. It's much worse than what it looks like here. I degreased with non-clorinated brake cleaner, which I've used before and never had this happen. Can't be the grinding compound because the lapping tool wouldn't touch were this photo shows, and some of these specks are on the outside of the receiver too and along outer edges. Just not too the same degree. I don't think I can return this to DSA, I've had it for probably 2 years, plus I've just hit it with lapping compound! |
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Might be just me. What am I looking at? The lapping will remove the finish 458 It's not suppose to remove the finish INSIDE the upper-the tool is supposed to square the face of the upper. Yeah, until you look real close, it kind of looks like a spray paint-like splattering. |
| I wouldn't sweat the little specs you're seeing on the inside of the receiver. They're just high spots in the anodizing that the BCG may or may not have worn down anyway. Unless you're using this weapon in an extreme environment a properly lubed rifle will prevent those specs from ever being issues that will impact the performance of the weapon. I've seen similar spots on the end of the receiver where the tool contacts the receiver while lapping. They kind of look like little bubbles. |
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