RAP4 M4 carbine buttstock for MR

RAP4 M4 carbine buttstock for MR series breakout

I just got this buttstock through this forum, painted by the seller. I've noted my discussions about RAP4 buttstocks, so I've decided to break this one apart. Of note is that RAP4 makes many models and I was not able to locate this one, but in respect to other discussions, it looks like this is the regular air-trough that could use mounting adapter. Judging by the description, this one is the closest option:
Spyder Flexi Air Buttstock

With the RAP4 Flexi-Air system for the Spyder you have the option of connecting a remote line directly in the back of the stock and have it completely out of your way to add the most realistic look and feel to your Spyder…and out-gun your opponent at the same time. The RAP4 Flexi-Air system for the Spyder features an enormous 1.5 oz air expansion chamber. With this expansion chamber, which is conveniently hidden inside the collapsible stock, you can expect your Spyder to be consistent like never before. Your shots will be more consistent and reliable, and thus more accurate, as your Spyder feeds continuously from this enormous reservoir. For winter play, your CO2 won't freeze up in your marker again!

Interestingly, when you go to the page for Spyder Flexi-Air Line and Adapter, you will see following warning:

Please note: The flexi-air system is made to be used with a macro line, which is designed to be used with compressed air. It is not recommended for CO2. If CO2 is used, the line may become brittle and burst.

With all respect to RAP4, I found some of their products a bit too pricey, and all of them very poorly described. You have to search out of their website to get a better idea how some part works.

This model fits into velocity adjuster hole. You have to remove velocity adjuster together with its mount, remove adjuster from mount, stick on the spring and insert it into hole, in front end of the buttstock mount. Then you use field strip pin to secure it in place.

On this pic you can see all parts that make this assembly:


1. Allen wrench, regular size for velocity adjuster
2. Intermittent velocity adjuster screw, headless
3. Mount, with plug for expansion chamber and macroline swivel fitting
4. Intermittent velocity adjuster cover
5. Intermittent velocity adjuster cover screw
6. Expansion chamber with two QD one-way nipples
7. Hex screw, prevents unscrewing of the chamber from mount
8. Extendable buttstock
9. Pin screw and spring
10. Release lever
11. Nut for pin 9

This is the front part of the mount, next to original MR1 velocity adjuster and MR1:

Remove velocity adjuster from its mount, stick it on the spring and insert it into buttstock mount hole:


Velocity adjustment is very clumsy. There is a small headless screw that is supposed to push velocity adjuster, but it is very short and I do not see how can you make adjustments over wide ranges. More importantly, you need to have Allen wrench with very short end, as my regular sized will not fit adjusting opening, lets not speak how to fit it into the screw. I'll replace this screw with a regular screw with hexagonal head, in order to use regular wrench.

There is a small cover that fits over intermittent velocity adjuster screw. Needs medium sized Allen wrench.

There is a significant free play in the buttstock mount:

But, it does look good when mounted:


(NOTE: pics on RAP4 website depict some sort of adapter that fits between buttstock and marker. I do not have any info about that, like is it delivered in original buttstock packaging? But, it looks that it could be ordered separately.)

On a good side, mounting into velocity adjuster hole provides better viewing over marker and gives you one built-in macroline and two remote hose fittings.
On the bad side, opening for original buttstock is left open. Macroline fitting is too tall, and I do not see the real need for a swiveling fitting on this location. Remote hose nipple on the buttstock rear end protrudes from the buttstock when fully collapsed.
The "enormous 1.5 oz air expansion chamber" may be a nice addition, but is it of any real use when it is connected with MR using long and narrow macroline? In my opinion, in just adds weight and swallows 1.5 oz of air. Then they say "your CO2 won't freeze up", but you cannot connect braided hose, and you cannot use CO2 with regular macroline.
It should be much better if chamber was made out of plastic and rear QD is connected to the front part with braided hose or steel pipe. MR series is heavy out of the box, and I'm not all that keen to add extra weight to it.

I got mine for a fair price, and I cannot complain too much. But if I were to order a brand new one - I guess I will not be all to happy with my investment. My major complaints go toward "enormous 1.5 oz air expansion chamber", tall macroline fitting (will be replaced asap) and free play.

Other than that, it’s a great addition to MR, especially because I really like the design of this particular buttstock, way more then any other design. I'll keep it and I'll fit single trigger frame on MR1 as soon as it arrives.

[slim and shady]

nice posr very informative