Magpul UBR on Bushmaster 450 Carbine

[Siringo]

I tried the Endine Rifle buffer. Didn't work for me.

[Hoot]

Not having empirical data, I can't say for sure. However, my physics sense tells me that having the weight in the bolt carrier impacts the unlock impulse timing differently, albeit not a lot, than having the same amount of weight back in the buffer.

I've seen two different pictures of the CWS. One picture show a fairly thin flange



and another shows a more substantial flange.



I wonder if the thinner one was first revision and was abandoned because it could not hold its shape after repeated cycling or whether it is a newer revision intended to minimize it impeding opening up the action.

Hoot

[Siringo]

I have the thinner flange. Action still must be opened by pulling both pins.

I was shooting 400 grain bullets at velocities in the 1400 to 1600 fps range. I had noticed that the rims on my brass where being pulled back -- as the action was trying to open while there was still pressure in the barrel. This has to do with the speed of the bullet/timing. The heavy buffer system slowed the opening enough to alleviate the problem.

However, as always, if you are shooting factory loads or hand loads to those velocities -- this system may not be needed. A side benefit of this is it slows the return to battery enough to minimize bullet jump -- gentler chambering. In fact it cut it nearly in half. From .005 inch jump to .003 inches. i wrote about this test on another thread.

[SoulHunter]

However, as always, if you are shooting factory loads or hand loads to those velocities -- this system may not be needed. A side benefit of this is it slows the return to battery enough to minimize bullet jump -- gentler chambering.

Thanks to all for the great feedback. One additional question about the CWS--do you think that the rifle would still cycle properly with the CWS installed at factory load pressures? Could it cause the gun to short cycle? Even though it isn't necessary, I like the idea of a slower cycle rate.

[Hoot]

If you're not fussy about modding your weapons, here's an affordable solution, assuming all carriers are a similar ID to mine. (Is there a spec on that somewhere?)

1) Run a 5/8" (or 16mm) tap it up into the back of the carrier.
2) Take a 5/8" (or 16mm) threaded steel bolt, cut the head off and slot the end for a screwdriver with a Dremel cut-off wheel.
3) Screw it into the back of the carrier so it is flush with the end.
4) Back it out, dress it up, degrease it and the inside of the carrier and loc-tite it in.
5) Presto! no hang-up opening the action on your now slower-cycling rifle.

You're only removing approximately .020-.030" worth of metal from the inside of the rear of the carrier, so it won't effect its function adversely.

Options:

If you want, you can use a socket cap head bolt and turn down the head OD smaller than the threaded portion of the bolt. You could then use an Allen wrench to screw it in and out, skipping the slotting step.

If you want, you can wrap the bolt with a layer or two of teflon plumbers tape and probably get away with skipping the loc-tite.

Hoot

-Revised-

[YoteAddict]

Anybody tried a hydraulic buffer?

Yes. I still use it. I bought my first 450 carbine as a complete rifle. Before switching the stock from the A2 stock to the 6 position stock, I asked Bushmaster what they would recommend for a buffer and spring for this application. For my 16 inch carbine, Bushmaster recommended the use of the Enidine hydraulic buffer (carbine version) when using their 6 position collapsible stock in combination with the spring that came with the 6 position stock. The rifle functions correctly in this configuration. The notable difference is that it is more difficult to lock the action open due to the resistance of the hydraulic buffer when holding the action open with the charging handle. If you have one, you know what I'm referring to.

[Siringo]

Just to clarify -- my endine rifle buffer has the piston on the front end, not the back end like the carbine version. The piston was very easy to move. I suspect is was broken -- it slammed pretty hard. I sent it back to Endine a year ago and have not heard since. There went a 90 dollar experiment.

[Hoot]

Before you plop down your hard-earned $58.00 + S/H for that CWS...

Having done some actual research and in defense of CWS' price. Pure tungsten rod is god awful expensive. I'm sure the lion's share of the price is a reflection of the cost of the tungsten insert. It is heavier by volume than depleted uranium. Using a plain steel rod or worse, threaded bolt, gives up quite a lot of mass. Better off buying a tungsten rod toleranced precisely to the ID of the carrier and loc-titing it in. An alternate method would be to heat the carrier, freeze the rod and press it in quickly.
Hoot