I got my TD vertical grip today and I could use some advice on the best way to get it to fit on my ARMS SIR 50.  As most of you probably know the bottom rail is not mil-spec but the TD vertical grip will only fit mil-spec rails.  Is there anywhere that I can purchase a true 1913 mil-spec rail that will fit on the ARMS SIR or do I modify the vert. grip?

The bottom rail as are all the other selective rails are 100 percent mil spec. Every thing out there in service fits and ARMS developed what became the mil std. dovetail rail dim's way back in the 80's.  The plastic maker is at fault by having too much material on the top, not the angles. Just place the plastic on a belt or circular sander and remove some of it.
Good shootin, Jack

So the fact that the grip fits every other rail system except the SIR is the fault of the plastic maker?

The bottom rail sits a little closer to the handguard than on other systems.  The rail itself is milspec except for the neck height, it is just the nature of a removeable rail and making it as low profile and stable as possible.  Here is a link to the first TD grip post:  [url=http://www.ar15.com/forums/topic.html?b=3&f=12&t=167569&page=1]TD Forward Grip[/url],  It tells of the problem half way through the thread and how to take care of it.  Good luck.

My grip is still in the mail and my AR is about 200 miles away, but I have something in mind.  I went to Lowes and purchased some small washers that I can use to shim the lower rail a fraction of an inch.  If it's stable enough that way, I'll be happy as hell.  If not, there isn't much of a choice but to grind off a little plastic.

Well, mine arrived yesterday, and slipped right on the bottom rail of my M4 RAS. The dual lock bars are a PITA, but very stable locked in position!

I got mine in the mail about 20 minutes ago, and it slid right on my SIR lower rail... I dunno what the deal is, but I didn't have to force it or anything.

-Cap'n

The plsastic on that pitol grip varies a little from one to the next, depending how they trim them.
Good shootin, Jack

i had a forward grip that didn't fit on my SIR rails.  it fit on the A3 upper rail.  i ended up selling it out of frustration.

if it fits other rails and not the SIR rail..i would say the SIR rail is not quite to spec.

I have three SIRS, I have locked various ARMS products on them and all have locked up tight with no movement what so ever. Usually if the mount is new, it will be alittle tight on the first few mounts.

A new SIR rail spec TD grip might be in production to meet certain oversea military requirement.

That's good news!  But why doesn TD make a replacement rail for the SIR bottom rail?  Wouldn't that save on confusion?  I would hate to mix up a grip or have the wrong grip sent to me and have a loose grip on my RAS.

Gentlemen,

Here are the facts.

Our grip was designed to accept the U.S. Mil-Std 1913 rail. Our grip fits every rail system as purchased and accepted by the U.S. Military. With every grip, we furnish a copy of the Mil-Std 1913 drawing as supplied to us from Crane Naval Surface Warefare Center. This allows quick reference to see which commercially offered rail systems TRULY comply with Mil-Std 1913.

As previously established on this board and elsewhere, the ARMS SIR system does not have a Mil-Std 1913 compliant rail at the 6:00 position. This rail lacks the required standoff to allow installation of our grip. We use the standoff to support 2 additional surfaces in our grip housing that enable it to take enormous side loads of force without deforming or outright separation from the host weapon.
There are other dimensional variations in the ARMS rail that fall outside Mil-Std 1913 as well.

We will offer in the very near future a Mil-Std 1913 rail for the ARMS SIR at the 6:00 position. This is the only way to properly install our grip.

Any other method of modification as suggested elsewhere in the above thread will produce a loose grip/rail fit and sacrifice the inherent strength of our product.  

We hope this eliminates any confusion. Any further questions may be addressed directly to me via email at: [email protected]

Sincerely,

Jeffrey M. Cahill
President
TangoDown LLC

If you would, sir, describe, "very near future".[;)]

So a whole new rail, and don't touch my TD FPG huh?

OK, will standby.

/S2

Well, I'm going to go get the FFRAS gun in a little bit to check and see if the TD grip will be loose on that or not. Out of the box though, with NO mods, it fit on my SIR #58 and my SIR #50.

-Cap'n

Am I the only one who thinks it is sad that ARMS wont produce milspec rails for the SIR?  Why does Tango Down have to provide this?  Why is ARMS not providing full spec rails to those who want them instead of forcing non-spec rails to reduce the profile of the forearm?

All the rails are mil spec 1913 on the SIR's. This particular fairly new pistol grip is the only thing that seems to have a problem, but all the other mil spec items in service do fit perfectly. This kind of reminds me of RRA when they said they were to spec., but were not. The vertical wall on all the selective rails I have measured were right to spec. and if they wern't the general issue items already out there for years wouldn't fit. The vertical wall above the 45 degree angle can be higher to a vague max if they choose in the overall design, and there is a min. which the selective rails meet to keep it slim line I presume. This particular pistol grip needs to be changed like they are saying they are going to do, and that will be in the area that I suggested needed to be ground back so it doesn't hit where no other mil spec products do.
Jack

Well, not only does my TD grip fit on both SIRS, it also fits on a FFRAS, a RAS2, an OLY FIRSH, and 8 different Colt upper receivers.

I dunno if it's a fluke or what. It fits tight on all rails tested.

-Cap'n

hey crunch,
must be a fluke or some non-std SIR rails [:P]
i don't want to rehash what we went over in the SIR vs. predator rail thread about the SIR rails and the mil-std 1913 rail drawing, so i recommend that anyone who hasn't read that thread please do so, examine the drawing carefully, and draw their own conclusions about whose rail profile (SIR or TD grip) meets the spec. this is just something that some of us will have to agree to disagree about.
off-topic - hope everyone and their familiy has a merry xmas and ya'll get lots of gun goodies for presents! [:D]
cheers,
MM

I would be interested in a pic of a caliper which is reading the height of the neck and rail combined on a SIR rail that the TD grip wont fit on and the picture of the milspec right next to it.  Seems like that would clear it up right away.

I probably know less about official military specs than anyone on the board, so I dont claim to speak with any authority on the matter. However, I do believe the picture of the rail spec in the Predator vs SIR thread was a picture of what the flat top on the upper reciever needed to be. I am not sure that other rails, that are not on the upper, need to meet those specs. I swear I read that, probably in a 3rdtk post, but I cant be sure.



Stay on topic jerky! [:P]

haha, sorry new-arguy, i'll stay on topic from now on [:P]
as mentioned in the title "military standard - dimensioning of accessory mounting rail for small arms weapons", the mil-std-1913 spec provides the rail profile dimensions for a rail, wherever it may be.  if a rail does not meet the requirements on the drawing (it can be the flat top or rail system), it's not a 1913 rail, and cannot be claimed to be.  just like the .223 case has specified dimensions. if you manufacture your own .223 case and change any of those dimensions outside of the specified tolerances, you no longer have what is defined as a .223 case.
quoting from section 3 (definitions) of mil-std-1913:
3.1 - Accessory. In this document, accessory refers to items which can be attached to the accessory mounting rails such as laser pointers, fire control devices, night vision devices, grenade launchers, optics, thermal weapon sights etc.
3.2 - Accessory mounting rail. A grooved dovetail feature that serves as a mounting platform used to mount accessories."

it's clear that the accessory rails refer to any rail used to mount accessories, not only the flat top. that'd be one helluva place for the grenade launcher!
i don't have calipers on hand at home or else i'd take that pic for ya, DevL.  but anyone can refer to the drawing and make his own measurements.
cheers,
MM

I think you are probably right that the height was not specified for any rails other than the top rail of the flattop.  However, it seems that it is common practice for everyone, except ARMS, to spec the side and bottom rails as well as the top handguard rail to the flattop neck height.  This provides for more uniformity thrughout the system.  I don't have the specs, so i can't answer whether or not it was or was not specified.

The SIR raises the rail higher than the flattop receiver.  The lower rail is of a shorter height than the rails of their competitors.  Even the bilevel rail is slightly higher than the flattop.  Does this mean it is not to spec?  Maybe not because maybe the height of the rails weren't specified for the handguard rail systems.  If anyone has the original specs, maybe they can ansewer that question.

However, it doesn't follow the uniformity of other entries into the RIS/RIS II programs.  Is it innovative?  I don't see how not matching the rail heights would in any way be innovative.  It was probably more a necessity of the design to meet what ARMS expected of it rather than what the DOD expected of it.  I don't necesarily feel this is bad.  It works withmost things, the TD grip being the first thing that hasn't worked with the SIR.

The TD grip was made to be ultra stable and ultra tight on the current RIS and RAS systems currently in official adoption.  To make it looser in tolerances to fit any variances that other manufacturers might come up with would have made it fit loosely on the RAS and RIS systems and thus defeating one of the goals of the grip's design.  

I'm sorry if anyone took offense to my stating a variance in the SIR design.  It just gets me angry that 3rdtk won't acknkowledge that the SIR uses a diffeent neck height than Knights, LMT, and DD in their rails.  Instead, he bashed TD, stating first that the grip has "too much plastic" and then stating in a second post that it "varies depemnding on how they trim them".  His obvious bias toward ARMS is fine, we all have products we prefer, but the fact that it caused him to bash a good company like Tango Down and their product gets me a little fired up.

The SIR may not be my cup of tea, but I don't hate it.  I wouldn't mind having one or two, or several.  However, it seems some are not willing to acknowledge any flaws/variances/differences to industry standards that it might have.  Some of the differences are innovative, some not.  It has strenghts and it has weaknesses.

The SIR cools better than any other system, but it has a larger footprint than any other system and raises the top rail height/heights.  While it is heavier, it balances its weight better than any other system, thus making it seem lighter than most other systems.  Its removelable rails save on weight and bulk, but anything that is removeable can be lost.  It has strenghts, but has to give in to its weaknesses to gain those strengths, but so does the RAS and others.  

The SIR is not the be all/end all perfect system, nothing is.  However, it seems a lot of people tout its strenghts and do not acknowledge its weaknesses.  At least that is how it has seemed recently.  Maybe because its the latest toy.  I'm not a SIR basher, nor am I a SIR supporter.  I just don't like it when people bash other products and companies for the sake of the SIR and ARMS.

Oops, MM got his post in before I finished typing.  I guess the accessory specs could be interpreted that way.  However, if it deosn't specifically word the document in such a way as to say the handguard rails have to meet the same specs as the receiver rail, it could be interpreted differently or protested (such as the recent RIS II protest).  

Even as a SIR fan, I can see each and every point you make Knightone. Agree 100%. It never does much good for people to become monolithic about things. We've all seen it... Is there a Pony or a Snake on the side of your lower? Is there a Swan or a Helmet on the side of your rail? I think it is entirely true that the advantages touted by one system are at the expense of something else. Its only when these disadvantages are balanced equally with corresponding and connected advantages that a design is really great. If not, its just a waste....

One would think it woudl be easy for ARMS to mold the [s]plastic[/s] I meant polymer lower in such a manner to incorporate a conventional (read: like everyone elses interpretation) dimensioned rail...

I love a lot of ARMS products, the SIR's are just not some of those...

yep, the document doesn't differentiate between receiver or handguard rails (it's meant to provide a standard PROFILE for ALL accessory rails though). no one HAS to adhere to mil-std-1913 for receiver or handguard rails - they're free to modify them the way they see fit (and take the risk that some mil-std-1913 compliant accessories may not fit).  but when they do so they are no longer free to call them mil-std-1913 compliant if they are not.  whether a rail does or doesn't meet mil-std-1913 is not open to interpretation. in the govt's eyes, it either meets spec or it doesn't.  the only variation allowed is in the specified tolerances on the drawing. if ANY dimension on the drawing is not met within the specified tolerances, the rail is NOT considered compliant. period. for the past 12 years at work i've dealt with the Navy, Air Force and other US military representatives (read: watchdogs) whose only job is to ensure that the products we build meet the required specs and they are VERY clear that specifications are to be adhered to 100%.  approval for any out-of-spec item takes an act of God and it's usually easier to redo something than request a approval for deviation.
as for the TD grip 1913 groove, instead of it being molded as part of the plastic molding process (which *might* have some variability in it, if any), it is machined into the grip by a cutter made to 1913 specs to ensure that if there was any variance in the molding process, the groove would NOT be affected and would be guarranteed to fit on any 1913 compliant rail.
cheers,
MM

I've thought the same thing Kevin... Maybe if they mold a channel in the underside of the "synthetic" (is that a safe word?) so that the rail can be sunk in the bottom of the handgaurd a little?

Damn, now  gotta shark some TD grips out of Chen...

Dang... 5 posts to this thread in one minute! Its like were all hanging out! Maybe in Vegas?

Definetly in Vegas...
probably have to be in a Internet Cafe though [;D]

Well, it's official, my grip is a fluke. It fits on four SIRs, a Midlength (too long) FFRAS, a RAS II, RAS, DD FFRAS (Full length), OLY FIRSH, eight Colt Uppers, 2 Bushy upper, 2 RRA uppers, and countless other rails and setups. It didn't fit on my POF rail, or my FOBUS M33 though? It was loose on the POF rail (VERY loose) and too tight to get on the M33. I dunno if I should be happy, or what?

-Cap'n

cap'n, if it fits, don't worry, be happy. dang, with all that crap, how can one NOT be happy? (slaps cap'n upside the head - thwack!).
cheers,
MM

I would love to get together with everyone at the Shot show next year.  I will be on site from Friday to Sunday.  Like Kevin said, we will have to bring our laptops since we might have difficulties actually speaking to each other in person. Doh!!!

I definitely can see the SIR rail to the mil-spec required for the rail but as Armor stated the stand off area is too short to support the TD grip.  

Curtsey of Bigger hammer.

[img]http://www.biggerhammer.net/picatinny/recoilgroove_1.gif[/img]

TD will be producing a SIR 6 o'clock rail for a minimum fee.  This will be the same exact rail on the SIR but it will have the standoff space allow for the TD grip to be mounted.

Great post!  Could'nt have said it better!