2 Quick Questions - AR lower issues

[penguinofsleep]

So I put together a lower recently and ran into 2 minor problems:

1. Bolt Catch roll pin won't go all the way in - About 1mm sticking out, won't go in no matter what I try. I don't have a vise though (although this hasn't hindered me in the past). Seems to be in firmly and securely, but I don't like leaving it "half done". Trying to hammer it in with a punch or using vise grips or pliers (taped up) doesn't seem to help, the very end of the pin looks like it has actually mushroomed every so slightly because of it, so I stopped trying to force it in.

Any ideas? The roll pin for the bolt catch is the type where it looks like a coil (imagine someone rolled up a little sheet of metal), not the standard C type that looks like a round pin with a small line cut down the length of it, so I can't use a regular roll pin punch.

2. When the hammer is resting in the upwards position (after you pull the trigger), it rests against the bolt catch instead of barely clearing it and resting on the receiver. Hammer rests so that it applies enough pressure to the bolt catch to bind it up, but not so much that a firm push or smack on the bolt catch won't drop it back down.

I'm assuming its safe to grind/remove about 0.25-0.5mm off of the bottom part of the hammer so that it can clear the catch? There is a lot of excess material on the hammer in that location. I'd prefer to not change the trigger parts out as I got lucky with this trigger, it's really nice for a GI trigger.

Other comments:
- I have never encountered these issues before.
- LPK from G&R, trigger/hammer came from a DD lower parts kit.
- Bought all small parts at least a year ago before the current panic, so I imagine possible manufacturing issues due to the current rush would not be applicable here (although I realize production issues are always possible).

[kcstott]

Pull the pin and redrill to .097" and try again.

As per the hammer resting on the bolt catch it is supposed to do that.

Let me as you this. How would the hammer be in contact with the bolt catch if the bolt is back?? The hammer will be cocked and held back by the trigger.

Also you don't want the hammer to strike the receiver as it is much softer then the steel bolt catch.
Do not remove material from hammer you are defeating the purpose of the design.

[penguinofsleep]

Thanks. A quick check before I go on:

1. Original hole size is 0.09375" (3/32). I am drilling to 0.097" - what size drill bit is this? I see on a chart that #41 is 0.096" and #40 is 0.098 - guessing either one is close enough?
Also how do you drill the hole here - the hole is too close to the body of the receiver and I think the body of the drill would get in the way and keep me from drilling straight down?
Just thought of this: Would it be easier to figure out what brand roll pins may consistently use slightly little less material (ie C shaped pin that has a bigger cut in it) so that it is easier to fit in?


2. I've never had a single hammer that rested against the bolt catch so I wanted to check this - it was a bit curious to me. None of my other receivers exhibit any damage/wear in that area so I'm guessing that with a BCG/firing pin in place, it won't go far enough forward (or at least with sufficient force at that point) to where it makes contact. I also realize it usually won't make a difference when the hammer is cocked back nor will it make a difference when the bolt catch is doing it's job, but I'm wondering if it may make a difference at some other point?
i.e. possibly delaying the bolt hold open after the last shot in a few cases, maybe helping something stick if I have an issue after pulling the trigger, etc.

[penguinofsleep]

MODS: Would this go better in rifles instead of smithing? If so, could one of you please move it for me?

[uxo2]

I would have someone who knows what
they are doing assemble it instead of
"I think I KNOW"'

Next post will be.

I broke the tab on the trigger guard.

[Drew Eckhardt]

Also how do you drill the hole here - the hole is too close to the body of the receiver and I think the body of the drill would get in the way and keep me from drilling straight down?

Aircraft drill (6" long) from the buffer end (I don't know that a drill bit from the front would clear the magazine well lump centered on the catch pawl) so the chuck does not need to clear the receiver. If the drill bit touches the receiver you're not drilling straight.

A #41 is $2.12 from Enco.

http://www.use-enco.com/CGI/INSRIT?PMAKA=337-3013&PMPXNO=28074783&PARTPG=INLMK32

Shipping will probably be $7 so take the opportunity to replace any of your drill bits which have been misplaced, dulled, or damaged.

They ship most things to California from their Nevada warehouse so you usually get next-day delivery for ground rates.

[nastyhabts26]

Before drilling any thing out I would try a different approach which does not require removing metal from your lower.
Pull the roll pin out and get another new roll pin.
Slightly bevel the leading end of the roll pin with a grinder or dremel tool or just a file, dont take much off, just bevel it a bit.
Then oil up the roll pin and oil up the lower where the pin goes and see if it doesnt go in nicely.
Roll pins are cheap but lowers are expensive if damaged.

[kcstott]

Thanks. A quick check before I go on:

1. Original hole size is 0.09375" (3/32). I am drilling to 0.097" - what size drill bit is this? I see on a chart that #41 is 0.096" and #40 is 0.098 - guessing either one is close enough?

Read the print. drill to .093" +.003" A #41 works just fine.

Also how do you drill the hole here - the hole is too close to the body of the receiver and I think the body of the drill would get in the way and keep me from drilling straight down?

10% smarter then what you are working on. 6" aircraft drills

Just thought of this: Would it be easier to figure out what brand roll pins may consistently use slightly little less material (ie C shaped pin that has a bigger cut in it) so that it is easier to fit in?

Really?? you think you know more about roll pin fit then the manufacture of the pins?? Sorry slight jab there. but in reality there is not enough difference between manufactures of roll pins to make a difference. The real trick is get a lower with a taped bolt catch hole and special set screw.

2. I've never had a single hammer that rested against the bolt catch so I wanted to check this - it was a bit curious to me. None of my other receivers exhibit any damage/wear in that area so I'm guessing that with a BCG/firing pin in place, it won't go far enough forward (or at least with sufficient force at that point) to where it makes contact. I also realize it usually won't make a difference when the hammer is cocked back nor will it make a difference when the bolt catch is doing it's job, but I'm wondering if it may make a difference at some other point?
i.e. possibly delaying the bolt hold open after the last shot in a few cases, maybe helping something stick if I have an issue after pulling the trigger, etc.

Every Mils spec FCG I 've installed the hammer rested on the bolt catch and very close or also on the receiver. The point is the bolt catch is in position to take the punishment for a trigger being pulled when the weapon is hinged open.
You're not getting it. How can the hammer touch the bolt catch on the last round fired to delay it in working?? Last round fired the bolt retracts cocks the hammer and then the bolt catch comes up.
There can be no interference from the hammer on the last round. the BCG is holding the hammer back

I'm not trying to belittle you but you really need to learn how your weapon works. How things interact with the weapon hinged open is not exactly how they work when closed.

[penguinofsleep]

Did not know 6" drill bits were called aircraft drills. I didn't think they would make a drill bit this long for these small diameter bits but I'm glad I was wrong. Thanks guys.
And nastyhabits yes, I'll probably do that in the future. I'm probably just going to pop the pin out this weekend and taper it down a tiny bit on the ends where it seems to be getting stuck (it was much harder to get in than a normal pin, but pushing it in once it got started was only equally difficult).

kcscott:
-Didn't see anything about +.003". Guessing that is machining tolerance I don't know about (I'm not super familiar with machining or machining capabilities)) or I looked at a different chart that left those off.

-How did you get me knowing more about manufacturers out of that? I figured that since there are probably many shops making these little pins, it is likely that there will be a normal (or some other type) of distribution for spec vs finished product. It may also be somewhat reasonable to assume that X or Y company may consistently sit towards one of the tail ends of said distribution. I.e. how sometimes people will say "oh company x's parts are always a little tight at first or company y's parts usually need some fitting when used in conjunction with company z's parts.

- Yes, I know how it works. Like I said, I was more curious than anything. Since weirder things have happened to people before, I figured I may as well ask (since I've never had a hammer like this) to see if everyone would say "nah nothing will happen." which is what I was hoping for and wouldn't surprise me knowing how the AR works. i just didn't want to type it all out, but i know a bolt isn't going to magically be able to fly back if the hammer isn't going to be able to go down w/ it after the gas pushes back on the gas key. and if the hammer is down, it isn't going to touch the bolt catch, which the user would presumably manipulate at this point if required.

Was mostly making sure someone wouldn't say "yeah if A or B odd thing enabled by C (this) situation happens while X or Y occurs, Z malfunction/damage/failure may occur". This kind of stuff only happens a small percentage of the time, even when it is seemingly unexpected, but I'm sure we've all heard seen or have heard of weird stories that follow some kind of succession like the above that we would never normally expect.

and no worries, i know you weren't trying to belittle me, but i think you were missing the point of my 2nd question - double checking, not inquiring.

[kcstott]

kcscott:
-Didn't see anything about +.003". Guessing that is machining tolerance I don't know about (I'm not super familiar with machining or machining capabilities)) or I looked at a different chart that left those off.

It's on the print for the lower. Both the commercial print and the ordinance print.

-How did you get me knowing more about manufacturers out of that? I figured that since there are probably many shops making these little pins, it is likely that there will be a normal (or some other type) of distribution for spec vs finished product. It may also be somewhat reasonable to assume that X or Y company may consistently sit towards one of the tail ends of said distribution. I.e. how sometimes people will say "oh company x's parts are always a little tight at first or company y's parts usually need some fitting when used in conjunction with company z's parts.

Roll pins are roll pins. and they usually come from a handful of manufacturers despite what the box says. Roll pins are designed to have .003" to .015 compression depending on size of the pin. Measure a .093" roll pin and you will see it's near .100" thats a hell of a press fit for a little pin but it will compress

- Yes, I know how it works. but i know a bolt isn't going to magically be able to fly back if the hammer isn't going to be able to go down w/ it after the gas pushes back on the gas key. and if the hammer is down, it isn't going to touch the bolt catch, which the user would presumably manipulate at this point if required.

WTF??? I can't make heads or tails of that statement.??

Here's the deal. You are concerned with the hammer hitting the bolt catch? Correct??
The hammer CAN NOT touch the bolt catch when the BCG is in the weapon and the weapon is closed regardless of BCG position.
The hammer will either be held back and down by the BCG when the last round is fired or if say for instance your magazine fails to lift the bolt catch upon firing the last round. The hammer will still be in the cocked position either held by the sear or disconnector depending on the position of your trigger finger.

Tell me at what point can the hammer be in the fired position (straight up) with a empty mag in the well and the bolt forward, without dropping the bolt by the use of the bolt catch and without pulling the trigger on an empty chamber??

Check this out and see if you can figure it out.

http://www.bushmaster.com/anatomy_bushmaster.asp

and no worries, i know you weren't trying to belittle me, but i think you were missing the point of my 2nd question - double checking, not inquiring.

Seriously man we're just trying to help.

[penguinofsleep]

ok so long story short you are saying there is no way for a weird unexpected interaction to occur in a rare situation. exactly what i was looking for.

as for my statement that didn't make sense, i made a typo. delete "but". all it means is that i know that at any likely or reasonable point where the user actually needs to manipulate the catch the cycling of everything will result in the hammer being held back (not resting on the catch), but like i said, i've seen weirder things happen before where one would not reasonably expect them to, never hurts to ask, even if i think i already know the answer is "its fine". better if i don't ask in a way that already implies what i think the answer is and to prod into answers (prevent biasing from responders).

[kcstott]

I think you went the opposite direction. I think you unintentionally misdirected the question and created the appearance of ignorance on your part. Deleting "But" doesn't fix the statement I quoted. It appears that you either don't understand the order in which things happen in your rifle or you can not express how things happen in your rifle properly.


but i know a bolt isn't going to magically be able to fly back if the hammer isn't going to be able to go down w/ it after the gas pushes back on the gas key.
See I'm not sure if you mean fly forward (into battery) or backwards ( out of battery)


and if the hammer is down, it isn't going to touch the bolt catch, which the user would presumably manipulate at this point if required. Again this just seems like you expect that somehow the bolt is going to be locked back by the bolt catch yet the hammer could be forward (up in the fired position) A mechanically impossible situation???
I still think, And I'm sorry to say, that you have no clue how the FCG and the cycle of operation works on this rifle