Model 1 Sales 300 whisper upper function problems

[MMA10mm]

I too bought a Model 1 Sales 300/221 kit w/ assembled upper, and have had the same experiences.

I've read about the opened-up port in the standard shorty location, but that seems like a marginal fix to me. It will probably work with subsonic, and to get best success, use a chrome-plated AR-style (lighter-weight) bolt carrier, a lighter weight buffer spring, and don't plan on shortening the barrel any...

I want my lower to work with other uppers, without changing out the buffer spring, so that's out. I want to be able to utilize a heavier bolt carrier and shorter barrel, so now we're back to marginal operations...

In my opinion, if you're going through all the trouble to modify it, make it as close to the SSK upper as possible: TIG weld the gas port under the front sight, drill a new port at the pistol position (7-8" depending on whose gas tube you use), and for best operation, get an adjustable gas block.

This is more involved than just drilling out the port, but it will be the most flexible in terms of working with the widest selection of loads, and with the least amount of fiddling with the lower and bolt. Theoretically, these modifications should keep the 300 upper modular, as the whole AR system is meant to be, meaning you can swap out bolt/bolt carriers, and put the upper on different lowers with a high probability of it working...

Lastly, there have been some posts here in this thread which show the downfall of the JP gas block. (the allen wrench) To be fair, the JP block was designed for use on target guns at the match ranges, where mis-laying an allen wrench or leaving it at home will not get you killed. But, if you have a 300 for field use, I would think you'd want an adjustment device that is always attached. Again, I look back to the SSK upper, and note that they install a large knob with a coin slot that shows up through one of the holes in the upper handguard. I will be working on something that will work similarly with the JP gas block on mine...

My next problem to overcome is how to work the adjustment device around a solid 4-rail handguard without cutting holes through the Picatinny rails... When I get it all sorted out, I'll post some pictures here.

[Cornholio]

Sounds interesting! I need a fix for my gas block/tube set-up, so I'm eager to see how yours comes out!

[jripper]

I agree that moving the gas port to the pistol position would be the best way to go. I do not have a problem with my AA 1680 load with subsonics, with either a full butt stock, or car, using stock springs and bolt carrier. However, as previously noted, it will not work with faster powders. This is adequate for my uses. However, if you want it to function with any subsonic loads, you had probably better move the port.

Joel

[MMA10mm]

Well, before modification, Cor-Bon 220gr Subsonics won't work, but my handloads with 150gr FMJs and 17.5grs of W-680 (Surplus from Jeff Bartlett) worked just fine... Cycled every time!

Also was able to make hot loads with H-110 work, but they were about 1.0gr overload. (They were right at the suggested max load from SSK, and I was using more voluminous Rem. 221 brass vs. the re-formed mil. brass that SSK uses, but they were still hot...)

Anyway, at least I could get the thing to shoot semi-automatically before modification... I'll probably shoot it some more and then do the mods when the weather gets bad.

[TerroristHunter]

Just put together my M1S barrel on a CMMG upper with an Adams Arms Piston kit. Haven't tried the AA1680, but H110 and Reloader 7 haven't cycled yet. After drilling out my barrel to the same size as the gas block hole (.155) it will at least eject. I have also cut 1/4 off of the buffer spring (and stretched it out), and removed one of the weights from my buffer. The Adams Arms is a heavy Bolt carrier, but there is an option of just installing a key on a regular carrier. (Maybe chrome lightweight) Will keep you posted...

[TerroristHunter]

By the way, M1S will turn the barrel down to install a pistol position gas block, but it costs an extra $100.00

[mak91]

I got a m1s 300 whisper barrel back in 2004. Did the same thing, drilled out the port, cut the buffer spring, tried a bunch of different loads with Reloader7, Accurate 9, and Hodgdon335. Got some loads to cycle most of the time but never got 100% reliability. I also wanted to shoot some non subsonic loads some time and this setup would not work for the higher pressures. I finally figured out something to try, a double gas port configuration. I had tp555 make me a custom gas block. The adjustable gas block has 3 settings, off, pistol gas port and carbine gas port. In pistol gas port position the carbine port is blocked and gas only flows back to the bolt from the pistol port, same goes for the carbine port position, gas only flows from the carbine port to the bolt, the pistol port is blocked. This gives me the best of both worlds. Since I had already drilled out the carbine port to a larger size trying to get it to work in the original configuration I now have to use an adjustable gas tube to get the pressure right.