Initial loading issues

[jinx44]

I assembled an AR in .300 whisper with parts from a local dealer. I believe the barrel is a J&T. My dies finally came in yesterday and I started to load some rounds last night but encountered problems.

Dies are Redding FL (adjusted down to touch the shellholder), brass is .223 factory remington, case length trimmed to 1.355", bullets are 220MKs.

I started by loading the OAL so they would fit in a standard metal LE mag. Then I tried to chamber one and the bolt wouldn't close. I shortened the OAL, and after several tries, it finally chambered. I fired this round and it was super-sonic at 9.7gr of AA#9. The case didn't eject. It was easily pulled by manually ejecting the case. I am sure I felt the action cycle, and there seems to be a mark on the case head from the ejector trying to pull it out of the chamber.

I then took a sized case and cut 4 slits in the neck and inserted a bullet so I could find where it touched the lands (read about this trick on a 300 whisper page that was linked from this site). This case wouldn't chamber either. The bullet was loose enough in the case that it should have easily pushed back if needed. So then I tried to chamber a freshly sized, empty case and the bolt still wouldn't close. It required considerable force to get the bolt to close. When I extracted this case, there were marks on the shoulder where it seems the chamber was pushing back on the shoulder.

I compared this case, a loaded case, and the fired case. The neck on the fired case is MUCH longer than the neck on a sized case. .265" on the fired, .221 on the sized. The shoulder also appears to be pushed downward, but is extremely hard to measure because the shoulder of a sized case is not very pronounced.

Obviously, either my chamber is too short, or the dies are loading the case too long. It seems my reloading manuals disagree on dimensions. Where can I find the correct SAAMI specs?

Also, sized case neck OD is .333", loaded case is .334", and fired is .336". Is that correct or a little tight?

[amafrank]

There is no saami spec on this case yet and there is more than one set of specs. I chambered my barrels with a Dave Manson 300-221 reamer and most cases will fit fine using the CH4D dies. I tried some dummy rounds loaded by a friend with redding dies and they did not fit. There may be a die problem or a chamber problem depending on who's reamer, dies and cases you are using. One other problem very commonly encountered is the thick neck due to heavier walled brass in military cases. I've found a few different types that must be neck turned just to fit the chamber. For the most part I've decided to use only winchester or Lake city brass from now on. Both have been pretty consistant and require no special treatment. What your problem may be is exactly the thick neck and putting a bullet into the case prevents the neck from "squishing" enough for the bolt to close. I've had some of these heavy walled necks that even after sizing they still won't fit the chamber when there is no bullet in them. I've never tried hammering the bolt home as I don't want to have to hammer it open. If it doesn't fit it doesn't fit.

Good luck
Frank

[pug]

The necks on mine run about .330" loaded on average. I would say if the fired neck is .336" then that isn't the problem but worth trying some different brass anyway. If thats ok then maybe you can pick up another shellholder and have someone take .010" off the face of it. This will give a similar effect of using a small base sizer die as it will allow you to push the shoulder back a little farther and also size the body smaller. I would not think it was the dies. It may be the brass, barrel being short chambered or else your bolt could be out of spec. I had one of those where the cup in the bolt face was too shallow and caused the problem you describe. Depth of cup is .122" on one just measured if it helps. A headspace gauge would rule out the chamber and bolt instantly if you could get your hands on one.

[jinx44]

Well, I found part of my problems. The brass I started with was S&B .223 Remington. The case was obviously too thick. Last night I loaded some winchester brass and my loaded neck diameter was .331 instead of .335. Fired neck diameter was .334 instead of .336. The brass worked easier and the shoulder was pushed back to where it should be to chamber.

It seems I am hitting the lands at 2.112" OAL with the 220 MKs, so I am loading to 2.110. I tried 8.4gr of AA#9 and it has a supersonic crack. How heavy should I crimp the bullets? I am crimping by turning the seating die in 1/8th turn from when it touches the case. I pulled a couple bullets with an inertia puller and there were no marks on the bullet, but they required several solid blows to come out.

Now, my next problem is ejection of the fired cases. It seems the action is not going back far enough to eject the spent case. The case comes out, but not far enough to clear the breech and the action hangs. I am using a standard AR front sight/gas block, 16" barrel. Does it possibly not have enough pressure? As I said, they are still supersonic, so I know the problem will be worse when I load subsonic.

[interceptor]

Cycling: You have a few things you can try.

One, are you using a carbine or rifle length receiver extension tube? If a rifle length they you could try a carbine spring with your rifle buffer.

Two, if a carbine system then you might remove a coil at a time.

Three, reduce the weight in your buffer. (to get my rifle length to cycle properly I pulled the weights and replaced with aluminunm total buffer weight of 88 grams)

Four, pull the gas block and enlarge the port one number size drill at a time and replace with an adjustable block.

Five, you ain't gonna like this one, have a smith turn your carbine barrel port into a pistol length port. (more dwell time)

Six, try a different load. For instance, I'm using 11.8g AA1680 with 220g SMK.


These are a few options off the top of my head, none are guaranteed and use at your own risk. I did get my 16" carbine barrel (+ can) to cycle with subs by using a carbine spring and a reduced weight buffer. These are easy mods, and non permanent too. If you want to pursue the lightweight buffer thing, then a trip to your local hardware store for some 0.5" solid alum rod will get you started. IIRC, cut length was 4.625" for me.

[jinx44]

Interceptor, thanks for the info. All of the ARs I have had in the past were .223, so I have never had to deal with cycling issues.

I am using the rifle length extension tube. I believe I have a carbine length spring at the house as well. That will definetly be the cheapest way to try, so I will start with that.