[Jules]

Trying to think of solutions to the accuracy issues reported with RDB rifles. Given that putting pressure on the handguard seems to be the biggest problem (especially with a bottom-attach bipod) I'm wondering if suspending the rifle from an over-bore bipod would be an improved way to support the rifle.

I'm wondering; if your rail is really rock-solid screwed-and-glued down, would an over-bore bipod mounted on the section right above the front attachment between rail and barrel, if this would lend itself to improved accuracy?

 

[RogueIV]

Not really. The main issue isnt the handguard its the fact that your basically putting pressure on the barrel. The rail would cause the same thing. Best option really is monopodding off of the magazine so you arent putting any pressure on the barrel.

 

[WolfWings]

Yeah, the handguard's primary attachment point is the gas block already, same as the rail, so you'd be applying the same forces.

And a lot have good luck with just using longer magazines as the forward brace point, but you can run into issues if your RDB doesn't like the added pressure from that particular magazine, etc.

Some kind of 'split bipod' akin to the SU16 attached using a replacement longer takedown pin on the forward spot and swinging down in front of or around the trigger assembly might be an option, but that'd still involve a lot of what-ifs.

The platform just doesn't lend itself to bipod/tripod prone use as well as others.

 

[Signe]

People who complain about the barrel pressure on the RDB dont understand why barrel pressure can cause point of impact shift in firearms.

On say, an AR15 that is not free floated, the rail ends at the barrel extension. Your handguard is attached to the barrel past the barrel extension. Meaning, if you put pressure in any direction on the handguard, it will bend the barrel away from the rail. Because the rail is all the way back on the receiver, behind the barrel extension, it does not bend with the handguard.

On the Kel Tec RDB, the barrel is attached to the scope rail and the handguard. The scope rail extends all the way to the front attach point on the gas block, where it is screwed down solidly, and the handguard is attached to the bottom. It even "floats" at the rear attach point of the handguard. In effect this means there is no place on which you can apply pressure to the handguard, and deflect the barrel from the scope rail. Anywhere you push on the handguard, you will push on the scope rail equally. There is no deflection.

The Kel Tec RDB is a bullpup. It is unfamiliar to many, and behaves differently than they would expect. The problem of a bipod applying pressure to the barrel causing accuracy issues, is a problem of either user error (they are doing something else that they dont recognize) or
assembly error (the screws on the rail are loose or torqued incorrectly, or the handguard is loose, i highly recommend Lucky Irishmans handguards for that reason). The bipod putting pressure on the handguard cannot cause the issues people expect.

People are far too eager to apply knowledge that they have from previous guns or from other fields where it just does not apply because the RDB is different. It's not free floated because its a bullpup, and bullpups dont need to be.

This was not to shoot down your idea, its a good one and would solve the problem of barrel deflection as the gun would just hang from the rail. But it would work for the same reason that this is normally not a problem for bullpups.

 

[odinforever2000]

Accuracy out of the RDB is fine. Bipod is extra weight anyways.

 

[dazed]

I'm sure ya'll have seen this already, but it's an interesting bit.

The part where they explain and then figure out a better way to over come the pressure flex is at about 6:05.

 

[Jules]

I'm sure ya'll have seen this already, but it's an interesting bit.

The part where they explain and then figure out a better way to over come the pressure flex is at about 6:05.

I haven't seen it so thank you

 

[gxer]

I had the idea of mounting the bipod on the trigger guard extension on the RDB-C, some modification is needed in order to properly mount a bipod there.

 

[BJK]

It's really not much different than any other gun that has a pencil barrel and the handguard or sling (when used for shooting) mounted to the barrel. Thin barrels bend. It's that simple. It's one reason I hated the M16A1. It had a sling, but it was for carrying only. Use it for shooting and it substantially changed POA.

In general there are a few things that can be done; free float the barrel, be gentle, move the bipod closer to the breech/action, get rid of the bipod all together and don't replace it with a shooting sling. A padded pack or a hat might also be better but that falls in line with being gentle.

 

[WolfWings]

I had the idea of mounting the bipod on the trigger guard extension on the RDB-C, some modification is needed in order to properly mount a bipod there.

Yeah I saw your thread about the idea, I thought it might be easier mechanically to get a replacement longer takedown pin made as the primary anchor point than relying on clamping to a non-structural plastic widget.

 

[Signe]

It's really not much different than any other gun that has a pencil barrel and the handguard or sling (when used for shooting) mounted to the barrel. Thin barrels bend. It's that simple. It's one reason I hated the M16A1. It had a sling, but it was for carrying only. Use it for shooting and it substantially changed POA.

In general there are a few things that can be done; free float the barrel, be gentle, move the bipod closer to the breech/action, get rid of the bipod all together and don't replace it with a shooting sling. A padded pack or a hat might also be better but that falls in line with being gentle.

It would be nice if that were true, unfortunately its not.

 

[BJK]

It would be nice if that were true, unfortunately its not.

By all means write less for full understanding.

 

[Signe]

I already wrote why its not. The barrel being mounted to both the end of the scope rail and the handguard on the RDB means you literally cannot push on the barrel by pushing on the handguard and deflect the scope rail from the barrel, like you can on an m16. You can keep saying "its that simple" all you want, the fact of the matter is in a kel tec rdb you should not be able to get that same deflection that you get on an M16, unless you have caused some form of user error. Usually, I think its not user error, but assembly error, such as screws being overtorqued, undertorqued, or just loose from the factory.

Now as to why this is the case;

M16
Imagine you're holding the receiver on an M16 in a vice. You can push up on the gas block of the m16, and doing so will bend the barrel. The problem that causes, is it deflects the path of the bullet coming out of the barrel, from the straight line of the scope rail on the receiver. This causes point of impact shift, which is generally undesirable.

RDB
Now do the same for the Kel Tec RDB. Hold the rear upper and lower receivers in a vice. Now push up on the gas block. Pushing up on the gas block pulls the scope rail, and handguard along with it. You cannot apply force to the kel tec RDB's handguard in such a way as to cause point of impact shift, because the handguard, barrel, and scope rail all deflect together.

Point of impact shift occurs because the scope rail, or the barrel deflect in a different way. This causes them to go out of alignment, and you hit somewhere else than where your sights predict. If they deflect together, nothing happens, because your scope or sight and barrel are still pointed in the same direction. If someone is having issues with deflection while using a bipod, as I said in the previous post (#4 in this thread), try to retighten the scope rail screws, or replace the handguard with something that mounts more solidly, such as a lucky irishmans handguard.

 

[WolfWings]

RDB
Now do the same for the Kel Tec RDB. Hold the rear upper and lower receivers in a vice. Now push up on the gas block. Pushing up on the gas block pulls the scope rail, and handguard along with it. You cannot apply force to the kel tec RDB's handguard in such a way as to cause point of impact shift, because the handguard, barrel, and scope rail all deflect together.

Except that's very much not how the RDB is assembled.

Going from the front, the four screws on the rail are:

• Gas Block
• Gas Block
• Recoil Lug
• Recoil Lug

Then at the rear of the rail it continues:

• Bolt Stop
• Grip Mount via spring-tension washer

Of those only the gas block and grip mounts are on the barrel, and only the gas block is rigidly locked to the barrel. The spring washer has a degree-plus of flex that the rail-to-barrel is allowed at the rear by itself. The bolt stop and recoil lug are held up against the rail and just act as protrusions/stops for the reciprocating mechanisms there.

So the rail very much can flex differently than the barrel, and if everything is tightened down enough to stop that (or the spring-tension washer is removed) then you end up with differential thermal expansion causing drift instead.

The RDB Survival Manual, page 25 of the PDF (24 in print) shows the assembly pretty well along with labels on the next page.

 

[Signe]

-snip-

Try to think of just the gas block, scope rail, front recoil lug for the scope rail, and barrel together, along with all the screws and stuff. Hold the barrel extension of the RDB in a vice, and push up under the gas block, as a bipod would do. At best (or worst i suppose), what you could do is bend the barrel in between the barrel extension and the gas block. Doing so would still leave the rest of the barrel past the gas block going straight out of the gas block, and the scope rail points where the gas block points. No deflection occurs.

Now, the only other thing that interacts with these three major parts, is part 160 on the diagram you shared. Part 160 is mounted with the washer in a loose mounting to the scope rail, and the barrel should be able to move a bit there too. So unless you're really loading the bipod to such an extent that the screw bottoms out on that little slot it has, or using up all of that free travel it has, you're not going to be able to cause deflection with that either.

What I think might have caused the results from the people in the video above, is genuine barrel deflection. But it's likely caused by the recoil lug on the rear of part 160 interfering with the scope rail, and preventing scope rail from moving relatively freely with respect to part 160. Because if the problem is caused by the rear recoil lug pinching the scope rail in between the gas block and part 160, loading the bipod in the other direction, like they did when they pulled it into their shoulder, would alleviate the problem, because it would pull part 160 away from the recoil lug.

It is the only part that can cause that kind of behavior, and honestly, I would actually be interested to see if the problem could be reproduced with that part removed, or untorqued, moved back as far as itll go in the mounting hole, and retorqued. I struggle to see how any moderate amount of bipod loading could lead to barrel deflection.

But feel free to insist that people should make a free floated barrel assembly, I just think that for me personally, it would not be worth the time. Especially given the extremely short harmonic length that the RDB has is very conducive to accuracy, even with a very lightweight barrel. A free floated barrel would ruin that.

(This post was previously much more snarky. It has been de-snarked)

 

[Jules]

I realized my suggestion for the bipod in the original post would bring the RDB to look in some ways similar to the WA 2000, which I learned similarly does not have a free float barrel:

 

[odinforever2000]

I dont really see any accuracy issues. Really depends on what you think the gun is supposed to do accuracy wise.

 

[RogueIV]

WA2000 has the barrel incredibly locked down unlike the RDB and wasn't really intended to large volumes of fire so thermal expansion wasn't their primary concern.

 

[BlastRadius]

Sorry for resurrecting this thread... Has anyone tried mounting the bipod at the rearmost part of the forend, closet to the trigger guard? Seems any pressure would be taken by the rear action pins/screws rather than the gas block pin where there would be more leverage/pressure on the barrel. Of course keeping steady would be harder since the fulcrum is closer and minor movements in aiming would be amplified.

 

[odinforever2000]

Sorry for resurrecting this thread... Has anyone tried mounting the bipod at the rearmost part of the forend, closet to the trigger guard? Seems any pressure would be taken by the rear action pins/screws rather than the gas block pin where there would be more leverage/pressure on the barrel. Of course keeping steady would be harder since the fulcrum is closer and minor movements in aiming would be amplified.

When I'm shooting at a bench that is where I rest my rifle, right in front of the triggergaurd..Since I like it light (while I do have several) I dont have a bipod on any rifle I own.

The Rdb is not a precision rifle but it does have decent accuracy.The alluminum handgaurds are a bit stiffer than the Polyer variants.