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Page Armory » M-16
Posted: 4/20/2016 11:37:47 PM EDT
[Last Edit: 4/21/2016 12:36:00 AM EDT by Machineguntony]
I decided to build a temporary RDIAS host while I wait for my 300 BLK set up to be complete.

Last night, I purchased a Spikes lower and built it out with some spare parts.

Here is the project...



M16 parts.



The completed gun. It's mostly Magpul furniture. I had a spare silencer laying around, so I stuck it on there.





I shot the gun today and it ran fine after the second magazine. The first magazine had two stoppages.

Do these primers look light? To me they look a little shallow. Does this mean I need to move the RDIAS forward with a shim? Or do I need to dremel out some material to move the RDIAS back?



Here is video of the gun in action.

https://youtu.be/_xAD88bEU4o
Link Posted: 4/21/2016 3:45:24 AM EDT
Get out some drill bits and time your DIAS operation based on the bit shank size. Quarterbore's site has a DIAS timing guide on it, might be also in the stickies here.

Basic range is .080 (min) to .100 (max) - you want to fall in the middle of the range, and if shimming your DIAS will move you closer to the sweet spot, then fine.

Both early and late timing can lead to light strikes - early from hammer follow, and late from bolt (carrier) bounce.
Link Posted: 4/21/2016 8:48:08 AM EDT
Good looking build. I've always liked spikes offerings for lowers.
Link Posted: 4/21/2016 11:17:48 AM EDT
Is there a YouTube video that shows a walkthrough of Quarterbores instructional? The written instructions are not exactly easy to understand, if you've never timed a RDIAS before.
Link Posted: 4/21/2016 11:24:03 AM EDT
Oh so jealous...I keep thinking I should have traded my colt m16 for a steel RDIAS when I had the chance.
Link Posted: 4/22/2016 8:04:50 AM EDT
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Originally Posted By Machineguntony:
Is there a YouTube video that shows a walkthrough of Quarterbores instructional? The written instructions are not exactly easy to understand, if you've never timed a RDIAS before.
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It's pretty simple. You don't want the hammer to fall on the larger bit, and you do want it to fall on the smaller bit.

I have a Spike's lower that I used for a DIAS host until very recently and I had to lower the shelf and move it back a bit. It was not a 'drop in' for that lower.
Link Posted: 4/22/2016 8:06:34 AM EDT
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Originally Posted By david05111:
Oh so jealous...I keep thinking I should have traded my colt m16 for a steel RDIAS when I had the chance.
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These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.
Link Posted: 4/22/2016 8:06:34 AM EDT
[Last Edit: 4/22/2016 8:07:04 AM EDT by colt933]
double tap
Link Posted: 4/22/2016 11:06:22 AM EDT
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Originally Posted By colt933:


These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.
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Originally Posted By colt933:
Originally Posted By david05111:
Oh so jealous...I keep thinking I should have traded my colt m16 for a steel RDIAS when I had the chance.


These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.

Interesting, I did not know that.
Link Posted: 4/22/2016 11:08:18 AM EDT
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Originally Posted By Machineguntony:
Is there a YouTube video that shows a walkthrough of Quarterbores instructional? The written instructions are not exactly easy to understand, if you've never timed a RDIAS before.
View Quote


There isn't a youtube video that I am aware of.

Personally I have never been super concerned about "late" timing as if you have bolt bounce under control as long as the hammer reliably drops when set to full auto I have never really had an issue with timing being too late. (I actually have timed most of my RLL to drop extremely late as the later the hammer drops the less stress on the Link if it is only mechanically camming the disco back the minimum amount required to drop the hammer)

In regards to the quarterbore instructions, while they don't specify "how" you put the drill bit between the barrel extension and bolt carrier for timing measurement purposes, my impression was that they expect you to just stick a drill bit into the ejection port between the barrel extension and the carrier face. Its also possible to go up via the magwell as well.

When I first tried this years ago I got inconsistent readings at times as the upper receiver ejection port cutout can get in the way if the upper receiver ejection port cutout isn't cut exactly flush with where barrel extension begins. I also found it a pain is the ass to hold the gun, actuate the charging handle, and hold a drill bit inside the ejection port or up the magwell all at the same time.

I ended up making custom set of cut drill rod that fit on the bolt carrier itself to measure timing with. Its really pretty simple procedure but probably one of those things where a picture is worth 1000 words type deal.

I have not used them in years but can dig them out and try and take a picture for you this weekend on how I use them if you want to make your own. You are local to me as well so you are welcome to come by and either borrow them or use them at my place to measure your current timing.
Link Posted: 4/22/2016 11:24:12 AM EDT
It's not my imagination, right, those primers do look shallow?

I'm going to see if I can make a video following these instructions from Quarterbore. Then you can tell me what I'm doing wrong. Those instructions aren't really that simple or clear.

For example, how do I know when the hammer has dropped? When I hear the click and the sound of the hammer falling?

Also, do I insert the front of the drill bit or the chuck (back end) into the ejection port? Also when I insert the drill bit into the ejection port, would I have to hold the drill bit so that it is perfectly perpendicular to gun? Wouldn't easing the bolt into the drill bit cause the drill bit to become angled to the gun, thereby throwing the measurement into an approximation rather than an accurate measurement?

These Spikes lowers are not drop in. I've already had to dremel a bit out just to be able to close the rear pin.
Link Posted: 4/22/2016 11:51:44 AM EDT
The primers look perfectly fine to me.
Link Posted: 4/22/2016 12:03:04 PM EDT
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Originally Posted By Machineguntony:
It's not my imagination, right, those primers do look shallow?

I'm going to see if I can make a video following these instructions from Quarterbore. Then you can tell me what I'm doing wrong. Those instructions aren't really that simple or clear.


For example, how do I know when the hammer has dropped? When I hear the click and the sound of the hammer falling?

Yes, you go by the audible of the hammer dropping. You just ease the bolt down onto the drill bit and/or let the bolt ride home from maybe an inch out of battery. Don't try and drop the bolt from lock back on the drill bit as it may shatter..

Also, do I insert the front of the drill bit or the chuck (back end) into the ejection port?

You use the barrel of the drill bit, the part that is solid. Not the fluted/cutting end.

Also when I insert the drill bit into the ejection port, would I have to hold the drill bit so that it is perfectly perpendicular to gun?

Yes the drill bit sticks perpendicular out of the ejection port similar to a chamber flag.

Wouldn't easing the bolt into the drill bit cause the drill bit to become angled to the gun, thereby throwing the measurement into an approximation rather than an accurate measurement?

In my experience, just sticking the drill bit into the ejector port doesn't always give you a good measurement. For it to even be correct you need to remove the bolt from the carrier and stick the drill bit all the way across the barrel extension face and measure using just the carrier installed (sans bolt). The bolt has nothing to do with the carrier to autosear timing and just gets in the way. That said, if the ejection port isn't cut forward enough you will end up with the drill bit resetting against one side of the barrel extension inside the receiver and the other side against the ejection port cutout on the upper receiver making the drill bit not 100% perpendicular to the carrier or bolt extension face giving you a less than perfect reading (i.e. a larger gap than really exists).

These Spikes lowers are not drop in. I've already had to dremel a bit out just to be able to close the rear pin.
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Link Posted: 4/22/2016 1:17:48 PM EDT
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Originally Posted By colt933:


These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.
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Originally Posted By colt933:
Originally Posted By david05111:
Oh so jealous...I keep thinking I should have traded my colt m16 for a steel RDIAS when I had the chance.


These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.

Open bolt FCG? Huh?
Link Posted: 4/22/2016 1:45:10 PM EDT
[Last Edit: 4/22/2016 1:46:41 PM EDT by Machineguntony]
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Originally Posted By jbntex:

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Originally Posted By jbntex:
Originally Posted By Machineguntony:
It's not my imagination, right, those primers do look shallow?

I'm going to see if I can make a video following these instructions from Quarterbore. Then you can tell me what I'm doing wrong. Those instructions aren't really that simple or clear.


For example, how do I know when the hammer has dropped? When I hear the click and the sound of the hammer falling?

Yes, you go by the audible of the hammer dropping. You just ease the bolt down onto the drill bit and/or let the bolt ride home from maybe an inch out of battery. Don't try and drop the bolt from lock back on the drill bit as it may shatter..

Also, do I insert the front of the drill bit or the chuck (back end) into the ejection port?

You use the barrel of the drill bit, the part that is solid. Not the fluted/cutting end.

Also when I insert the drill bit into the ejection port, would I have to hold the drill bit so that it is perfectly perpendicular to gun?

Yes the drill bit sticks perpendicular out of the ejection port similar to a chamber flag.

Wouldn't easing the bolt into the drill bit cause the drill bit to become angled to the gun, thereby throwing the measurement into an approximation rather than an accurate measurement?

In my experience, just sticking the drill bit into the ejector port doesn't always give you a good measurement. For it to even be correct you need to remove the bolt from the carrier and stick the drill bit all the way across the barrel extension face and measure using just the carrier installed (sans bolt). The bolt has nothing to do with the carrier to autosear timing and just gets in the way. That said, if the ejection port isn't cut forward enough you will end up with the drill bit resetting against one side of the barrel extension inside the receiver and the other side against the ejection port cutout on the upper receiver making the drill bit not 100% perpendicular to the carrier or bolt extension face giving you a less than perfect reading (i.e. a larger gap than really exists).

These Spikes lowers are not drop in. I've already had to dremel a bit out just to be able to close the rear pin.

Let me make sure we are talking about the same thing.

This is the carrier, and this is the bolt? See picture I made. So I can do this timing measurement by just removing the bolt and just using the carrier? That's what I get from reading your description.

More confusion, in that case. Am I better off using sticking the drill bit UP the magwell? I've been to Lowes a lot, and I've never seen a drill bit that long.

If I remove the bolt, what do I rest the drill bit on? The carrier face? Wouldn't it make a big difference whether I rested the drill bit on the carrier face (front) without the bolt or the bolt)?



I thought this whole BCG was just collectively and colloquially known as a 'bolt'.
Link Posted: 4/22/2016 3:37:27 PM EDT
[Last Edit: 4/22/2016 3:40:11 PM EDT by Circuits]
You use the shank (back) of the drill bit. I've always gone in through the magwell. If you're careful about the placement, you don't need to remove the bolt, but removing the bolt can make the measurements a bit easier, since the drill bit can lay across the entire face of the barrel extension.

As jbntex posted, you can hear when the auto sear releases the hammer. You don't even have to keep the trigger pressed back if you don't want to, though the sound of the hammer flying fully forward is easier to hear than the hammer dropping off the auto sear onto the trigger nose.
Link Posted: 4/22/2016 6:19:00 PM EDT
[Last Edit: 4/22/2016 8:50:30 PM EDT by jbntex]
I took some pics when I got home from work today with a carrier and barrel (with the upper receiver removed) to give you a better idea of what you are attempting to measure.

This is the distance you are trying to measure in relation to the hammer dropping. In general it should be 0.1 or less for proper timing. If this gap is too big when the hammer falls, the hammer can "catch up" to the bolt carrier prior to it closing this distance resulting in a less than 100% clean strike on the firing pin.



Here is how it is effectively being measured via inserting a drill bit.



Here is the issue I am talking about when trying to insert a drill bit through the ejection port or the magwell as there can be material in the way keeping you from getting a good measurement.

In both cases the drill bit is going to be shimmed against the upper receiver vs. be sandwiched flat between the carrier and barrel extension. How "off" the gap measurement is varies from upper to upper. However it generally gives you a false high reading. i.e. you put a 0.09 drill bit in the ejection port and the hammer wont fall because the drill bit is resting on the ejection port making the gap measurement 0.011







I made a set of short rods in varying diameters (0.125", 0.11", 0.9", 0.07", 0.06).

I then use a rubber band held into the carrier via the cotter pin to hold the shim to the carrier.





You can then put the carrier into the upper, reattach the upper to the gun, and cycle the charging handle to confirm if the hammer will fall with the varying diameter shims.

edited to add when reattaching the upper to test you need to do the "RLL upper receiver install" method to the lower where you remove both the front and rear lower receiver takedown pins and guide the upper receiver rear lug into the lower first, then lower the front of the upper onto the lower and reinsert both upper and lower take down pins. The reason being is that the bolt carrier will be slight slightly sticking out the back of the upper because of the shim so you cant just pivot the upper closed as you normally would.

If the hammer falls on the 0.125 or the 0.11 shim you know the sear is timed to early and the hammer is dropping before the carrier is closed enough. The other smaller rods can be used to confirm the actual timing of the gun. Ideal would be to be to close on the 0.11 and not have the hammer fall but close on the 0.09 rod/shim and have the hammer fall.

I have personally never really had an issue with a hammer falling too late as long as bolt bounce is properly controlled. However with a DIAS you can shim it to be right in the perfect range as needed.

In regards to light primer strikes there can be a bunch of other reasons for light primer strikes other than sear timing. Headspace, bolt bounce, hammer spring power, etc. My first thought on an M16 with a suppressor that is getting less than 100% primer strikes is bolt bounce. However, it certainly cant hurt to confirm you DIAS timing as well. If you have a dremel tool you can cut down some drill bits from home depot and then all you need is a rubber band (and a bent paperclip to hook it and pull it out the front of the carrier)

If you have any other questions please let me know.

Hope this helps

Link Posted: 4/22/2016 7:20:01 PM EDT
[Last Edit: 4/22/2016 11:42:07 PM EDT by Machineguntony]
So awesome.

Doing it. Now it makes sense.

Many thanks.

MGT
Link Posted: 4/23/2016 9:30:25 AM EDT
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Originally Posted By peekay:

Open bolt FCG? Huh?
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Originally Posted By peekay:
Originally Posted By colt933:
Originally Posted By david05111:
Oh so jealous...I keep thinking I should have traded my colt m16 for a steel RDIAS when I had the chance.


These days, the registered lower only has one advantage over the RDIAS: you can only use an open bolt FCG with the lower, not with the RDIAS. I recently acquired an AM15 with open bolt FCG, and installed all on the Colt lower. Glad I kept it. I had considered selling it when got the RDIAS a few years ago.

Open bolt FCG? Huh?


Yes, the AM15 upper requires an open bolt fire control group to function. The firing pin is made into the bolt face, so the hammer does not strike the back of the firing pin. The AM15 open bolt FCG is included with the AM15 and it is based off of the Colt LMG open bolt fire control group, but with 2 less pieces. The AM15 will not fire with a regular M16 FCG.

With the COLT LMG FCG, the hammer, when cocked, engages a recess in the bottom of the carrier. When you let off the trigger, the hammer in the cocked position, engages this recess in the bottom of the carrier and holds the carrier in the open position. Pulling the trigger lowers the hammer (yes, lowers it) so that it no longer holds the carrier back. The carrier now flies forward, stripping a round, As the bolt goes into battery, a different part of the open bolt FCG is tripped by the carrier, and lets the hammer fly forward to strike the firing pin (similar in concept to the regular M16 sear, but totally different parts/linkage). This allows only safe and full-auto. No semi-auto position is available.

The AM15 open bolt FCG includes all of the COLT LMG open bolt FCG parts, except for the part that releases the hammer when the bolt goes into battery, and the pin that holds this part in place. The AM15 setup also allows for safe and full-auto only. So with this setup, the hammer's only purpose is to hold the bolt open and to release the bolt when the trigger is pulled. The hammer is never tripped like in the Colt LMG setup. The hammer never strikes the back of the carrier or firing pin. The hammer only moves up (to stop firing) and down (to release the bolt and fire). Again, the firing pin is fixed to the bolt face, like almost any open bolt submachine gun would be.

This open bolt FCG requires removal of all components of the M16 FCG, including the sear. Part of the linkage is installed into the sear pin holes in the registered machine gun lower receiver. We have tried to engineer a linkage that would be compatible with a RDIAS instead of a registered receiver, but have been unsuccessful in doing so. Because of this, the registered receiver M16 is required for open bolt operation. I know of no system that would allow open bolt operation with a RDIAS, but if I could get that to work, I could sell my M16 lower - and get another RDIAS.


Link Posted: 4/23/2016 9:31:31 AM EDT
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Originally Posted By jbntex:
I took some pics when I got home from work today with a carrier and barrel (with the upper receiver removed) to give you a better idea of what you are attempting to measure.

This is the distance you are trying to measure in relation to the hammer dropping. In general it should be 0.1 or less for proper timing. If this gap is too big when the hammer falls, the hammer can "catch up" to the bolt carrier prior to it closing this distance resulting in a less than 100% clean strike on the firing pin.

Here is how it is effectively being measured via inserting a drill bit.

Here is the issue I am talking about when trying to insert a drill bit through the ejection port or the magwell as there can be material in the way keeping you from getting a good measurement.

In both cases the drill bit is going to be shimmed against the upper receiver vs. be sandwiched flat between the carrier and barrel extension. How "off" the gap measurement is varies from upper to upper. However it generally gives you a false high reading. i.e. you put a 0.09 drill bit in the ejection port and the hammer wont fall because the drill bit is resting on the ejection port making the gap measurement 0.011

I made a set of short rods in varying diameters (0.125", 0.11", 0.9", 0.07", 0.06).

I then use a rubber band held into the carrier via the cotter pin to hold the shim to the carrier.

You can then put the carrier into the upper, reattach the upper to the gun, and cycle the charging handle to confirm if the hammer will fall with the varying diameter shims.

edited to add when reattaching the upper to test you need to do the "RLL upper receiver install" method to the lower where you remove both the front and rear lower receiver takedown pins and guide the upper receiver rear lug into the lower first, then lower the front of the upper onto the lower and reinsert both upper and lower take down pins. The reason being is that the bolt carrier will be slight slightly sticking out the back of the upper because of the shim so you cant just pivot the upper closed as you normally would.

If the hammer falls on the 0.125 or the 0.11 shim you know the sear is timed to early and the hammer is dropping before the carrier is closed enough. The other smaller rods can be used to confirm the actual timing of the gun. Ideal would be to be to close on the 0.11 and not have the hammer fall but close on the 0.09 rod/shim and have the hammer fall.

I have personally never really had an issue with a hammer falling too late as long as bolt bounce is properly controlled. However with a DIAS you can shim it to be right in the perfect range as needed.

In regards to light primer strikes there can be a bunch of other reasons for light primer strikes other than sear timing. Headspace, bolt bounce, hammer spring power, etc. My first thought on an M16 with a suppressor that is getting less than 100% primer strikes is bolt bounce. However, it certainly cant hurt to confirm you DIAS timing as well. If you have a dremel tool you can cut down some drill bits from home depot and then all you need is a rubber band (and a bent paperclip to hook it and pull it out the front of the carrier)

If you have any other questions please let me know.

Hope this helps

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Great write-up. Thank you sir!
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