Adding a bipod mount to a TNW ASR or ASP barrel nut

[docnugent]

TNW may eventually offer a better solution, but this is my plan for the interim. It uses an Ironsighter rail adapter (model 624M) because I already had one left over from a previous project, and will require the ASR (or ASP) barrel nut to be milled with the dovetail grooves a 22LR barrel would have for sight mounting. Because the adapter is longer than I want, it will need to be cut and a new clamp screw hole will need to be drilled and tapped.

So why not just use the factory under-receiver rail? Because I'm old school (USAR, 1965-71) and that's where my left hand goes. Besides, a bipod does the most good when it's as far from the shooter's shoulder as possible.

Input is welcome as I won't get this to the machine shop for a couple of weeks.

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[Velzey]

I would cut off the whole dovetail mount and leave the picatinny rail and drill and counter bore a couple thru holes and then drill and tap the bbl shroud..

 

[docnugent]

I would cut off the whole dovetail mount and leave the picatinny rail and drill and counter bore a couple thru holes and then drill and tap the bbl shroud..

Thought about that (just using a standard rail, actually), but the back of a picatinny rail is usually flat, so it'd have to be milled to match the radius of the barrel nut for a non-rocking fit. Last time I talked to a machinist about making a rail bottom concave, he was less than enthusiastic as he'd have to by a new tool with the radius I'd want.

 

[Velzey]

Well I mill radius's daily and forgot to mention that! I just assumed to mill one in..

Brownells sells a low profile aluminum 3" rail with a radius already cut and a couple mounting holes already in it, that I bet will match close enough.. The rail is made by Yankee hill and runs about $17 item number 100-002-081wb ... Kinda defeats the purpose of using what you have tho..

 

[docnugent]

Well I mill radius's daily and forgot to mention that! I just assumed to mill one in..

Brownells sells a low profile aluminum 3" rail with a radius already cut and a couple mounting holes already in it, that I bet will match close enough.. The rail is made by Yankee hill and runs about $17 item number 100-002-081wb ... Kinda defeats the purpose of using what you have tho..

Thanks for the details - I looked into it, but even the 3" is 0.75" too long, so it'd still require cutting and drilling a new countersunk hole. They don't mention the backside being concave, but it sounds like you're familiar with them - is it around 1" diameter?

 

[SON*OF*LIBERTY]

I ike the ideal.

I see one problem, putting that much force on what is a detent held component may lend itsself to coming loose over time, even if it is a few degrees it is enough to damage the index interface at the barrel extension, which may intrun cause a burr that may stick the barrel in the receiver.

However, you could make an extended rail for the lower mount holes that extended out long enough to accomplish what you have in the drawing.

Just my two cents.

 

[Velzey]

Yep it is close to 1"

You could trim .375 or so from both ends I think and not need to redrill
And cb.. I will check when I get home for sure

 

[Velzey]

Ah wait it is a detent that holds it in place.. Hmmmmm liberty may be right

 

[SON*OF*LIBERTY]

Ah wait it is a detent that holds it in place.. Hmmmmm liberty may be right

You could still add an extended rail.

 

[docnugent]

You could still add an extended rail.

Rail floating over the barrel nut? Sounds like a knuckle slicer each time the barrel is removed/installed.

This brings up a couple questions about the detent, though. Is it customary for the detent pawl (or whatever it's called) to carve a narrow spiral groove across the nut's detent notches (about the width of a knife cut)? I bought a used ASR barrel with that pattern, so I'm wondering if I should expect my pistol barrel to develop that wear pattern, too.

And in a youtube, I'm pretty sure I saw you unscrew the barrel a bit (with the lower still attached) and then remove the cocking handle. Something in mine seems to keep the bolt carrier too far back to do that - is there a bolt carrier stop in the newer ones that wasn't present in the earliest ones?

Similarly, does the lower have to be removed for the barrel nut to be screwed in all the way? I've heard in the youtubes there's a click when it's seated, but mine doesn't seem to do that (it just won't turn any further).

I sure appreciate being able to tap into the experience you two share!

 

[SON*OF*LIBERTY]

If the anodize was not etched down far enough , the detent hole may be out of spec, if the person was not watching for this during assembly then it woul cause the detent to bind and the line to be scratched in the barrel nut.

In the earlier videos I was showing a prototype, which did not have a bolt stop.

You do have to remove the lower to remove the bcg.

I did unscrew the barrel nut a bit to pull the cocking handle out easier. Unscrew untill the handle aligns with the relief in the slot.

Hope this helps.

 

[docnugent]

This phone pic doesn't show it well, but the 'knife cuts' I referred to are alongside the two rows of shiny spots (I drew one pair in the middle in green). The real question, of course is does this indicate a problem that makes the nut and/or receiver unsafe, or is it 'normal?'

And I don't think I got an answer to this one:
". . . does the lower have to be removed for the barrel nut to be screwed in all the way? I've heard in the youtubes there's a click when it's seated, but mine doesn't seem to do that (it just won't turn any further)."

 

[docnugent]

ARRRGGGH!

I was having trouble getting my laser/LED combo to stay on the ASP's lower rail, and I just found out why. MIL-STD-1913 specifies a 0.835" (-.005") rail width. My ASP's top rail is 0.800" wide (apparently close enough), but my ASP's lower rail is only 0.750" wide - nowhere near wide enough for any of the several accessories I tried to mount on it.

If I buy another lower rail from TNW, will the replacement be the correct width, or are they all the same?

Put another way, is my best bet to locate some shims . . . ?

 

[SON*OF*LIBERTY]

This phone pic doesn't show it well, but the 'knife cuts' I referred to are alongside the two rows of shiny spots (I drew one pair in the middle in green). The real question, of course is does this indicate a problem that makes the nut and/or receiver unsafe, or is it 'normal?'View attachment 84996

And I don't think I got an answer to this one:
". . . does the lower have to be removed for the barrel nut to be screwed in all the way? I've heard in the youtubes there's a click when it's seated, but mine doesn't seem to do that (it just won't turn any further)."

1) the marks are from a stuck detent during production and will ussualy free up. As long as it is clicking, not neccesarily audibly, during lock down, safety should not be an issue. There is no "finaly click" of any kind. "just not turning any further" is the the norm.

2)the lower does not need to be removed for the barrel to lock lock in.

 

[SON*OF*LIBERTY]

ARRRGGGH!

I was having trouble getting my laser/LED combo to stay on the ASP's lower rail, and I just found out why. MIL-STD-1913 specifies a 0.835" (-.005") rail width. My ASP's top rail is 0.800" wide (apparently close enough), but my ASP's lower rail is only 0.750" wide - nowhere near wide enough for any of the several accessories I tried to mount on it.

If I buy another lower rail from TNW, will the replacement be the correct width, or are they all the same?

Put another way, is my best bet to locate some shims . . . ?

In my time, the rails were in house and holding to the mil-std-1913 rail standard was always my goal. Ofcourse, I can not speak for the current methods being used for QC. That said, you might get a good rail if you contact the factory. I do not know for sure.

The factory aside, shims would be a guaranateed workable solution.

 

[SON*OF*LIBERTY]

This phone pic doesn't show it well, but the 'knife cuts' I referred to are alongside the two rows of shiny spots (I drew one pair in the middle in green). The real question, of course is does this indicate a problem that makes the nut and/or receiver unsafe, or is it 'normal?'View attachment 84996

And I don't think I got an answer to this one:
". . . does the lower have to be removed for the barrel nut to be screwed in all the way? I've heard in the youtubes there's a click when it's seated, but mine doesn't seem to do that (it just won't turn any further)."

oh, the lines you see, not the spots with anodize worn, are a detent guide and are a factory feature of the barrel nut....