Gunsmithing AR15 Loose Pin & Hammer Pin Fit - SunDevil

[Phil3]

Guys,

I am pretty bent out of shape right now. Got all I need to assemble my first AR15 and wanted to shoot it for Father's Day next weekend. But, project halted because of a SunDevil lower receiver and there is little I can do about it, but to replace it (I think), with another brand.

I started to install a Geissele Match trigger in the receiver and the first thing they say to do is make sure their pins are a light tap fit into the receiver, especially for the hammer. The fit with the SunDevil receiver is very loose. The Geissele instructions says if the fit is loose, to use the provided slightly oversize hammer pin for the hammer hole. That pin falls right through the hole! This receiver has never been used, so it is not worn. The oversize pin is .0005" bigger than the standard pin of .1558", which means it is .1563". That is verified since a 5/32" drill is .15625" and that falls right through the hole with no resistance at all.

It looks like the SunDevil receiver pin holes are just BIG. I can't tell how big the hole actually is. I checked my receiver against another SunDevil, which is just as bad as mine. The Geissele oversize pin would not fit with finger pressure in another receiver made by a another manufacturer.

I can't use KNS pins or JP Rifles oversize pins, as those are all SMALLER than the Geissele oversize pin. This thread says more.

http://www.ar15.com/forums/topic.html?b=3&f=118&t=393072

I don't expect the Geissele to operate optimally unless the trigger pins are sung. Given there are no larger pins available, the only apparent alternative is to scrap the receiver (which already has a most of the lower parts kit installed) and buy something else.

I have already sent an e-mail to SunDevil and Geissele requesting advice and comment.

- Phil

 

[Casey Simpson]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Shooter, there is nothing wrong with neither your Sun Devil reciever, which is the best, nor your trigger, which is the best. You simply got the wrong trigger. Gisselle sells two models; small pin and large pin. You got a small pin trigger. Don't sweat this; its fine. Get the right trigger and stick with Gisselle. I love mine. And Gisselle will call you back; he did me.

 

[Casey Simpson]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

John Holliger at White Oak Armament might swap your triggers, but also try the dealer who sold you the small-pin trigger for the large pin reciever.
You have the best parts available for your build

 

[Phil3]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Unfortunately, the SunDevil receiver IS a small pin receiver, and so is the trigger. The SunDevil hole is about .156" (about as best as it could be measured) and the pins are about .1555". The large pin type you are referring to is .169", normally found on Colt receivers.

- Phil

 

[Casey Simpson]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

I'm surprised by that problem and I would be intereted in how Sun Devil works it out with you.

 

[Glen Seekins]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

.156 is within spec, .155-.157 is what they call for on a small pin.

Our trigger pin holes are reamed .157 and after coating come in around .1555.

.0005 difference is not much at all and my feeling is that it will work fine. There isnt much of a difference between a hole that is strait and the pin falls thru VS a interference fit.

Have you tried it out to see? If there is only .0005 clearance i would bet you that your trigger will be tight enough and you need not worry

Just measured a DPMS lower i have laying around with a pin guage....156 falls thru and .157 wont go..

Also measured a DPMS trigger pin at .1545

A drill bit is NOT a good measuring device, They are quite often undersized. When you drill with a drill bit they cut oversize so they are often under by a little bit by design. If you want to use a drill bit to measure with you can, but first you need to use a micrometer on it so you know what you have. I bet that drill bit is under by .001"

 

[Phil3]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: heatseekins</div><div class="ubbcode-body">.156 is within spec, .155-.157 is what they call for on a small pin.

Our trigger pin holes are reamed .157 and after coating come in .1552-.1555.

.0005 difference is not much at all and my feeling is that it will work fine. There isnt much of a difference between a hole that is strait and the pin falls thru VS a interference fit.

Have you tried it out to see? If there is only .0005 clearance i would bet you that your trigger will be tight enough and you need not worry

Just measured a DPMS lower i have laying around with a pin guage....156 falls thru and .157 wont go.. </div></div>

Glen, thanks for your imformative reply. May I trouble you with a few other questions. First, I have no way to try and see how big the hole actually is. I can say this. With a 5/32" drill bit (.15625") pushed through both sides, I can visibly move the bit laterally sideways back and forth. Not much at all, but you can feel it, and just see it. The Geissele oversize pin is supposed to be .1563" and I can see and feel the same thing.

Secondly, how do loose pins affect trigger function? I have heard that without the trigger tightly located, trigger function can be impaired, but not sure how. Also, I can see how the trigger pan can not rotate with the hammer springs resting on it, but don't see anything other than friction fit in the receiver to stop the hammer pin from rotating.

Interesting that the DPMS receiver may have loose pins just like mine, but hard to say without actual fitment.

Thoughts?

- Phil

 

[Glen Seekins]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Honestly, The trigger pins that i have been measuring are all over the place. The reason their is a tolerance is so the parts can be manufactured within reason and the mating parts will fit without interference. Every part that mates wit another has a tolerance range for manufacturing.

On a lower pin hole, the hole is made a certain size to allow for coating build up. Mil spec coating is .0018 to .0022, that is a .0004 tolerance and will effect the outcome of your hole size.

Lets assume you want a hole to come out at .155 after coating. You need to ream your hole .002 oversize (.157) and allow coating to finish sizing it for you. You shoot for the middle ground on coating thickness (.002). Now, you also have to understand that there is no exact anything in manufacturing. There is always a tolerance. As your reamer dulls it will cut a different size by a few ten thousandths .0002. That also needs to be in your calculation.....also, when they anodize they etch your parts and that removes a few tenths from the hole making it just a touch larger again...Thus .155-.157 is the tolerance zone you need to work with and have a half way easy time making the part. I have done some holes within .0005, but if they are to be anodized afterward you can forget it!

About the trigger pin hole size and what it does for you...Tighter is always better in theory, but then again your going to have they guy that says his is too tight...

My DPMS has had a few different trigger in it including factory with just aftermarket springs, a jewel that i tried out, a timiny (awesome BTW) and now wears a defensive edge trigger that i custom fit. Every one of them worked perfect and all of them were way looser fit than what you have (pin size .1545 and hole size pushing .157)

I guess the trigger could walk around, but you also have springs holding it in place and putting force on it all the time. You wouldnt want your trigger to rock when you pull it as you would feel it creep, but honestly i would put it together and try it out and see. I never had a problem with my sloppy one.

If your pin was .00015 larger than your hole you wouldnt get it in without quite a bit of effort just to put some perspective to the sizing

 

[Phil3]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Glen, thank you. I understand about tolerances, and apparently, SunDevil has intentionally opted to go with the higher end of the tolerance range. I found one writing where SunDevil had problems with holes too small and opened them up.

Noting your emphasis on tolerances and how a tiny bit can make a difference, I wanted to find out just how big the hole was. So, I painted the end of a drill bit, dried it on the gas stove, and tried to fit it in the receiver. Still loose, so another coat, and now it would not fit. I used steel wool to slowly shrink the diameter until it was a press fit with my fingers with some pressure. The fit was not so tight so as to peel paint.

Geissele says there standard pin is .1558" +/- .0001". My mic says they are .1554", so assume my mic reads .0004" low. The painted drill bit is .1567 to .1570" in diameter (not exactly round. If my mic is .0004" low, actual diameter of the bit is .1571" to .1575". It would appear then that SunDevil is at the upper limit of the spec for this hole. I guess I can't really fault them for that, except that oversize pins are routinely .1555" or .1560", which would appear to still fall through the SunDevil holes. Seems like other makers are using smaller holes.

I just installed the trigger, but no hammer (no hammer springs on trigger pivot pin). Operating the trigger this way causes the trigger pivot pin to rotate in the receiver. Not what I want, but with hammer installed, the trigger rotation did stop. Was not assembled enough to test for hammer pin rotation.

I will see on Monday what Geissele has to say about this.

This thread was interesting.

http://www.calguns.net/calgunforum/showpost.php?p=2513914&postcount=11

- Phil

 

[Phil3]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Update: Don't know why I didn't think of it before, but I have a Noveske N6 308 lower receiver sitting here waiting on parts. Why not see how the Rock River Arms lower parts kit, Geissele standard, and Geissele oversize pins all fit vs the fit in the SunDevil receiver.

I was surprised. All the above pins go right through the Noveske pin holes with no resistance. The amount of wiggle you can get out of a pin when it sits in one hole (not through to the other side) is less on the Noveske, vs the SunDevil, indicating the SunDevil does have bigger holes. But, even with the largish standard (.1558) and oversize (.1563) pins from Geissele, the pin fit is still loose in two brands of receivers.

My visit to the dealer yesterday showed another brand receiver accepting all pins as well, without interference, except the Geissele oversize pin.

Of the three receivers, the SunDevil is the loosest.

- Phil

 

[Phil3]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

SunDevil says my original receiver had oversize holes, and sent me a replacement receiver. Unfortunately, the holes in the new receiver appear just as loose as the original. On top of that, this receiver has some minor marks on it the original didn't. I spent a month for SunDevil to rectify this and they sent me back a product that is functionally no different than what I originally had (which they admitted was not right), and cosmetically, it is not as nice as the original. I have had it with SunDevil. I'll call them and complain, and maybe they will eventually fix this. Their customer service has been weak, the delays long, and the end result unsatisfactory. I don't know what other receiver to use that has tight pin holes, but would welcome any suggestions.

- Phil

 

[Scottmilk9]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Anti-walk pins will solve the pins from walking out.

 

[Criver600]

Re: AR15 Loose Pin & Hammer Pin Fit - SunDevil

Like Glenn Seekins is saying, trigger pin holes are all over the place. I have been building a few rifles on Predator(Sabre Defence), Mega-machine, and Seekins. I had originally purchased some JP .156 anti-walk pins and they would not fit in anything I had. Got some KNS .1555 pins and a .1555 chucking reamer and all is well. Anodizing does not build up perfectly and it seems like some of the trigger pin holes had high spots in the middle. The pin fit to the trigger is more important than the fit to the receiver. The .1555 chucking reamer did a great job uniforming the trigger pin holes (no bare aluminum) but it might not be the tool for everyone. You could easily ruin a lower.