Brass is a pain to make up for the 510 Whisper but once made it lasts a long long time. In fact, I've never worn out or cracked a case.
I use a harbor freight micro chop saw to do a rough trim on length then run them through the expander die to remove the taper like Dogtown noted above. After that I trim them on a good trimmer with a pilot to final length before using a neck turner to finish them up. Always check the length after turning the neck. Sometimes it will grow a bit especially if your turner bit is getting dull. If needed trim length again and do a final cut with the turner. Shoulders will be precise if the length is right. I was doing batches of a couple hundred at a time this way though I did cheat and set up my neck turner in the lathe chuck with a clamp to hold the cases in the tool post. Lots of kerosene for coolant/cutting fluid will make the cutter last longer and prevent the brass from building up on the cutter.
The GI bullets are great and have been cheap but they're not very accurate. Most have been pulled with less than careful methods and none of them were particularly match grade to begin with. The API will pop if you hit hard targets when subsonic but soft dirt or wood won't set it off. Tracers light up just fine and are great for a display of long range trajectory. Shooting them at 1000yds demonstrates what a suborbital flight would look like. M1 Incendiery bullets will pop on cardboard but many of them will pop in the bore too which can be hard on your suppressor. They have not been made since about 1943 so all of them have aged and become more sensitive. APIT will light up if they're good though they have a much smaller base and are harder to light. They will pop when they hit hard targets too. I've never tried raufoss projos because they cost more than they're worth and are tough to find.
New GI bullets will normally shoot about 1.5-2" groups if you're careful with the loading. New AMAX bullets will shoot sub MOA. Powder weight consistency is critical as it is with all subsonics. Neck tension is too so while most guys don't anneal the necks often it does help maintain consistent neck tension. With that done a taper crimp will help maintain consistent bullet pull.
I've never been a big fan of JD Jones but the 510 whisper is really one of his, as far as I can tell anyway. It is a nice subsonic round and a lot of fun to shoot. There are other guys using other cases out there but so far I've been most impressed with the consistency of the 510 W for this one. I've made up a lot of barrels for the Desert Tactical rifles and even a couple Mausers in the cal. Three of those were CZ Safari Mag rifles I made barrels for and they were sweet. For the Desert tacticals I used the 308 magazines with the spacer removed because the 338 lapua mags have the front pinched to catch the shoulder under recoil. Great idea but it means the huge 50 cal bullet won't fit. The 308 mags have the shoulder part farther forward so the bullet clears. You do have to use the follower and spring from the 338 mag and trim the feed lips a bit. With all that done they feed well with the long BMG bullets.
I trimmed the cases to 1.79" to make them legal for deer hunting in Indiana. I loaded them with 300 and 450 gr Barnes soft flat points. The 300s will run about 2300 fps and the 450s will do about 2000. In the CZ rifles it was quite a smack to the shoulder and I found that I needed to use some rosin on the scope rings to keep the scopes from sliding in the rings. The rifles were about 12 lb with a scope. One customer got his first deer in 35 years with the rifle because the suppressor got him 3 shots at the deer. He was a bit old and not a great shot....first shot went over the deer, second went under and the third knocked it down. He was over joyed. For the much shorter Barnes bullets the regular 338 lapua mag will work in the Desert tactical rifles.
Hope something there helps and shows that the 12.7 has been in the running for a long time. I built my first in about 2008 and it had been around before that.
Frank
