|
Forum Rules | Firearms Safety | Firearms Photos | Links | Library | Lost Password | Email Changes |
Register | FAQ | Calendar | Search | Today's Posts | Mark Forums Read |
|
Thread Tools | Search this Thread |
April 1, 2012, 09:22 PM | #1 |
Member
Join Date: August 30, 2009
Location: Georgetown, CA
Posts: 30
|
Anyone interested in tighter-fitting AR takedown pins?
I am building an AR rifle with a BCM upper and Aero Precision lower. I bought a Spikes Tactical lower parts kit and decided to test fit the upper and lower before I built the lower. I notice a little slop in the fit between my upper and lower if I use the takedown pins in the kit. Nothing abnormal, like some cheapo rifles I've played with, but noticeable. I measured the diameters of these pins (the right way, with a micrometer) and they both measure .2482". The holes in my lower and upper are between .2505" and .2510" (measured with gage pins). I imagine the pins in most kits are intentionally made on the small side so that they will fit any rifle out there, no matter what. I'm a bit fussy about things that fit together, being a machinist for 34 years, but that's just the way my brain works. I haven't put the detents in the lower yet, so I substituted a pair of 1/4" steel dowel pins (.2502" dia.) for the takedown pins and the slop is GONE. They slide in and out like a dream. This is how I want my rifle to feel. I scoured the internet for someone who makes precision takedown pins of a slightly larger size and all I can find are removable ones with push buttons or huge heads, but neither manufacturer states the actual diameter of the pins. Also, I want to retain the detents so the pins stay with the rifle and neither of these pins do this. My intent is to manufacture some custom pins with the same design as the stock pins, but with a larger diameter, say .2490-.2498". I own a small machine shop, so this is do-able, but I'm wondering if this would be worth making several sets and offering them for sale, since it appears that no one else makes them. I would probably make them out of 17-4PH stainless steel that is pre-hardened to Rockwell C45 and bead-blast the exposed areas so they aren’t reflective. I have a couple of friends with ARs who would like a set, but I was curious if anyone else out there would be interested in something like this.
|
April 2, 2012, 03:17 AM | #2 |
Senior Member
Join Date: November 13, 2006
Posts: 8,276
|
I made my own already.The ones I was finding ran about .245.Minimum material condition!
I used mold core pins.They are H-13 and come in two different hardnesses,one is in the low to mid 40's on the "C" scale.They are through hard and a few 10ths over nominal. I would not try mold ejector pins,they are usuallt .0004 to .0007 under nominal,but they are nitrided harder than a woodpecker's lips!!They do not machine well |
April 2, 2012, 06:42 AM | #3 |
Senior Member
Join Date: October 17, 2007
Location: Cowtown of course!
Posts: 1,747
|
Here's the solution I used on my last build:
http://www.brownells.com/.aspx/pid=7...TENSIONING-PIN Granted, the pin doesn't just pop out any longer, but the upper sure is kept tight to the lower.
__________________
NRA Chief Range Safety Officer, Home Firearms Safety, Pistol and Rifle Instructor “Today, we need a nation of Minutemen, citizens who are not only prepared to take arms, but citizens who regard the preservation of freedom as the basic purpose of their daily life......” President John F. Kennedy |
April 2, 2012, 08:43 AM | #4 | |
Senior Member
Join Date: November 2, 2007
Location: Northern Orygun
Posts: 4,923
|
Quote:
Would you offer custom sizing, or just a standard .2502? The problem would be dealing with people that have no clue on how to do a precision measurement. Asking people to measure to a ten-thousandth when most have a problem with a hundredth or even a tenth. On my uppers that had a sloppy fit it is normally from a oversize takedown pin hole. I have made inserts for these to tighten them back up. |
|
April 2, 2012, 11:47 AM | #5 |
Member
Join Date: August 30, 2009
Location: Georgetown, CA
Posts: 30
|
Madcratebuilder, you have a point there. Without any reference size gage, the customer would have no way to determine what size he needs. The only thing out there that is commonly available would be steel dowel pins which are .2502". Most good hardware stores have these. If that does the trick, as in my case, then there’s your size. I have a machining drawing for an AR lower and the takedown pin holes are dimensioned .251±.001, so they can be as large as .252, perhaps larger if they are already worn out. In order to offer custom sizing, I would have to keep several sizes in stock and offer an opportunity to exchange them for a different size if they didn’t fit the first time. Sounds like more of a pain than it’s worth. Definitely not a money-maker. Maybe I’ll just offer a .2495-.2500” size for those with new or near new rifles. Anything’s better than the pins that come in the kits. Thanks for the insight.
|
April 4, 2012, 03:03 AM | #6 |
Senior Member
Join Date: August 24, 2001
Location: LC, Ca
Posts: 1,917
|
|
April 4, 2012, 10:24 AM | #7 |
Senior Member
Join Date: November 2, 2007
Location: Northern Orygun
Posts: 4,923
|
Yup, those are +.001 and should be .2495.
I would love to get my hands on a box of 50 and mic them to see what the tolerance is. Can they mass produce at +/-.00025? |
April 5, 2012, 08:14 PM | #8 |
Member
Join Date: August 30, 2009
Location: Georgetown, CA
Posts: 30
|
Thanks DnPRK! $20 sounds worth it to me.
|
April 5, 2012, 08:21 PM | #9 | |
Senior Member
Join Date: January 27, 2010
Location: Norfolk, VA
Posts: 2,905
|
Quote:
|
|
Thread Tools | Search this Thread |
|
|