Thread size on Picatinny rails versus sling studs?

[JimGnitecki]

I am trying to add an Accu-Shot monopod to my PGW M15 XRS which (as the model name implies) comes with an MDT XRS chassis. That chassis comes with a rear sling stud.

However, Accu-Shot tells me that their models that mount to the sling stud won't work on my XRS chassis, because the bottom of the XRS's stock is flat for 1/2 inch of its width before rounding to blend into the vertical surfaces of the stock. Apparently, the Accupod sling stud mount monopods need a rounded surface to mount to, even though the website and even the installation instructions never say that.

So, I bought an MDT 2.5" Picatinny rail which will (supposedly) mount right up to the TWO pre-existing sling stud threaded holes in the stock (one of which is currently occupied by the existing sling stud).

That MTD Picatinny rail even comes with 2 sets of 2 bolts of different lengths.

However . . .

Neither of those 2 sets of 2 bolts will thread into the stud holes!

So, I am guessing that the "standard" Picatinny mounting bolts are a different thread than "standard" sling studs.

So, I guess I need to find out what the "standard" threads are for a sling stud, and find 2 bolts at a hardware store that match that standard. And of course to add to the festivities and further opportunities for setbacks, I will need to get bolts that have the correct thread but also (a) have tapered heads to recess into the Picatinny rail, and (b) have a hex or torx head because the heads need to be recessed into the Picatinny rail so as to not interfere with mounting the monopod!

I have no idea if sling stud mounting holes are metric or inches . . .

So . . . . can anyone tell me what the standard threads are for a sling stud? (I am dangerously assuming there IS a standard)

It's the darn little things that create big obstacles to progress . . .

Jim G

 

[SGW Gunsmith]

Common rail mounting screws can be of #6-48,or #8-40, for even better strength in steel. Some will use a slightly courser thread (#6-40) for aluminum. Using other threads, other than what are considered to be "gun threads" may later in life confuse a future owner.
These threads are not normally found at ACE Hardware, but are an "on the shelf" item at most gunsmith shops or Brownells.

 

[JimGnitecki]

Now it gets REALLY interesting. I actually took the sling stud out of the rifle, took it to a local hardware store, and used the store's hardware thread testing array to find out what thread it actually uses.

Surprise!

It's a METRIC thread: 5mm x 0.8 thread x 16mm length.

The threads on the bolts that came with the picatinny rail are SAE!

So, I needed to find 5mm x 0.8 x 16mm bolts to replace the ones that came with the Picatinny rail, and that meant finding this combination:
- 5mm x 0.8 x 16mm
- Countersunk head
- Either hex or Torx (I'm not stupid enough to try to use a flatblade head or Philips head - been there, done that, and regretted it)
- In a steel grade that is strong enough to resist the potential leverage loads inherent in a monopod.

This combination is remarkably rare, even here in Canada where we went metric decades ago. I tried 3 hardware stores and an auto supply store and no luck. I finally had to order online from Amazon, and with COVID era shipping, I wa alerted that it could be up to 17 days before I receive the bolts.

It compleyely baffles me why a shooting sling stud would use a metric thread while a Picatinny mounting bolt would be SAE, but the firearms industry has often been surprising.

Jim G

 

[JimGnitecki]

Common rail mounting screws can be of #6-48,or #8-40, for even better strength in steel. Some will use a slightly courser thread (#6-40) for aluminum. Using other threads, other than what are considered to be "gun threads" may later in life confuse a future owner.
These threads are not normally found at ACE Hardware, but are an "on the shelf" item at most gunsmith shops or Brownells.

Yes, as I said above, the specific combination of features needed in my case is apaprently fairly uncommon. Since I am in Canada, it takes Brownells 21 to 30 days under COVID era mail service for anyhting from Brownells to get to me on Vancouver Island, Canada (BOTH USPS and Canada Post are involved and neither is swift). I currently have 2 orders coming from Brownells. One has apparently decided to vacation on USPS truck somewhere since May 6, and the other has also not updated its tracking location since April 23rd (Today is May 16). Sigh.

We shooters need professional procurement assistance during the COVID supply line disruptions! (The Accu-shot website fails to even mention that a thread difference exists)

Jim G

 

[a5werkes]

This may give you some ideas for your situation; however, I just modified a Rogers SuperSToc that has a QD sling socket that I fit with a bushing with a 0.25" internal diameter that allows a common 1/4-20 fastener to fit thru; the other point of fixation is a simple radius slot fit to the 8-32 fastener of the LaRue Prone Optimization Device (POD) that has picatinny rail mount. The Accu-shot is either secured to the picatinny or use a lever QD mount for the accu-shot-POD attachment.
Sometimes you just have to tinker with the parts until a solution occurs. Here is a LaRue OBR with a Accu-shot & Am. Defense QD picatinny system and a Knights Armament
with a M-Lok rail for attachment of the Accushot.



your

 

[JimGnitecki]

A5werkes, your setup ended up looking pretty clean. But you obviously have both skills and machines I don't have! I have put together the following solution from "store bought" parts that are on their way to me or already here:
- Accu-Shot BT12-QK monopod for Picatinny rail
- 2.5" Picatinny rail whose bolt holes are spaced to perfectly match the distance between the 2 slink stud holes
- 5mm x 0.8 threads x 20mm long, grade 10.9, black oxide coated steel bolts with countersunk heads that tighten via 3mm recessed hex driver heads

The above setup minimizes the height of the assembly so that I can minimize bipod extension and thus optimize bipod rigidity.

I think I will be happy with the results. I just wish it had been a lot easier! Having to order from 3 different suppliers for a simple monopod solution seems excessive and too costly.

When I mentioned the thread incompatibility of the original setup I was advised to do, the local gunsmith, who is apparently used to such illogical realities, simply said "Yeah". He says he buys a LOT of hardware from a local hydraulic fittings supplier. Evidently, the hydraulics industry has some of the same issues.

Jim G

 

[SGW Gunsmith]

What brand of sling swivel studs are you using, if I might ask?

 

[JimGnitecki]

What brand of sling swivel studs are you using, if I might ask?

I have no way of knowing. The sling stud came installed as stabdard equipment in the brand new rifle, and there are no manufacturer identifying markings on the stud.

Someone told me that sling studs and other accessories on rifles can be metric or SAE, and that SOMETIMES (apparently not always) it depends upon what country the rifle was built in. I live in Canada, which went metric decades ago, so that MAY be why the sling stud is metric. A European rifle, like a Tikka, Sako, or Anschutz MAY come with metric studs as well? AR15s on the other hand?

Jim G