So I just finished my first 300 whisper build. Also I've figured out a really cool way to make whisper brass with a dillon trimmer and finally overcame the biggest issue which was the head of the case spinning(and getting torn up) when the cutter first came in contact with the .223 case neck. (I can talk about this more if anyone is interested.)
Here's a pic.
Here's the build spec.
-Noveske 300/221 Fireball 1/8" twist 16" bbl w/ pistol length gas system.
-Noveske BCG.
-Noveske KX3 (Until I get my can.)
-Noveske pinned low profile gas block
-Daniel Defense M4 12.0 Rail
-Tactical Inovations Billet deluxe lower (my first one was better than this one. (It's kinda wobbly even with the tension screw)
-White Oak parts kit.
- RRA 2-stage NM trigger.
-Magpul UBR stock and MIAD grip
-Stag carbine buffer and spring.
-Leupold 4.5-14x40 VX-III (Enough elevation out of all my cheapo scopes for zero.)
-Larue SPR-S mount. (10 MOA of forward cant)
Anyway. I'm feeling pretty good about this project. My first day out with it wasn't seriously disappointing, but I feel I could do better. My load was a bit anemic and not terribly accurate. I had started with a load my buddy had hoping to replicate his results. 9.1gr H110 pushing a 240gr SMK @ 1020ft/s For my build that same load only had them going @ 880ft/s (ES=35 SD=15) and it wasn't enough to lock back the bolt even though it fed all but 2 rounds. Oh yeah. Conditions. So I was roughly at 800ft elevation. Little to no humidity and the temperature was between 25-35 degrees Fahrenheit. Wind was kicking up to about 20 mph, but settled down to an average of about 5-10 mph.
Also, after looking through the photo thread, I noticed that I had loaded my rounds too long at .223 mag length. Since the bullets ogive changes the contour of the feeding geometry of the mag it looks as if it's better to seat them farther back so they don't cant inwards and jam up. (I'll have to do this.)
For my next set of loads, I was thinking I'd start at 11.0gr of H110 and work my way down to 9.5gr with the remainder of my 240gr SMKs. Then do the same with some 220gr SMK's starting at 12.0gr H110 down to 9.5gr. Sound like a good plan? (Looking at the whisper load data this seems all to be well in the safe margin.)
I'm really hoping to get it to function 100% and lock back on an empty mag in the subsonic range. Also, I'm thinking that the cold had a huge effect on the function of the rifle, velocity achieved and overall accuracy due to vertical stringing. H110 has been said to be temp sensitive, and I did notice velocity changes in my other friends AR when he cooked the rounds for too long.
Any advice would be appreciated.
Hybrid Mode
