300 whisper = pita

[800X]

This thread isn't meant to discourage anyone thinking about building a 300 nor is it meant to bash any vendors, but I have to share my problems with the hope of helping others if possible.

A buddy and I each decided to play with the 300 in an AR platform. We each bought uppers from M1S. Right off the bat we have had trouble with rounds chambering. We started with CorBon 220 subsonic and then loading our own with brass we bought off the web.

Our successful feed rate was maybe 2 in 5. During all of this we also were having terrible keyhole problems with anything heavier than 180gr.

After much frustration we checked the twist rate as best we could with a cleaning rod and we positive that our barrels were actually 1 in 10 not 1 in 8 as advertised. So the feed problems became secondary to getting new barrels.

I called M1S and explained my findings expecting to get some grief. Surprisingly they were not at all reluctant to offer new barrels. This made me think they were expecting calls of this nature. They assured me that we were the only complaint they have received on this matter. I guess it’s possible, however unlikely that we bought the only two 1 in 10 barrels out there.

It took quite some time to get the replacement barrels (months) but overall I think M1S was as helpful as they could be. This brought me back to the feed problem. We decided right off the bat to start fresh with 221 fireball and form it ourselves. This has worked extremely well. So we tried our formed 300 whisper brass purchased earlier and immediately had the same problems.

The brass bought from keith_davis is, as posted by him trimmed to 1.390. I believe this is our problem. The 221 formed by us usually ends up at only 1.350 - 1.355.

To Mr. Davis's credit, he has contacted us more than one telling us he is happy to help us with any problem that may be brass related. I think he is a stand up guy. At this time however I think that I will wrestle with this myself because the brass was received exactly as described.

I have a crappy Lee trimmer that requires I use deprimed brass to trim. I am trimming some tonight and will be function testing this weekend. I will post my results. I am afraid I will have to deprime the 900+ primed cases I bought so I can trim them, but it will be well worth it if this solves my problem.

FWIW, I have not had a cast of my chamber but I checked the neck diameter with a gauge pin and found both barrels to be .336" Both the 221 and 300 brass I have measures about .332 loaded. This is a fairly tight fit for an autoloader, but I think I am OK.

The moral of the story is that M1S barrels seem to require a trim length of 1.355 (all four of the barrels had this problem) and be sure to check the twist rate before you pull you hair out.