I posted a while back on my efforts to shoot subsonic ammo in my ar-15/458. I am using WC820 powder and magnum primers with a 600 grain cast bullet. Using about 20 grains of powder gives me 1070 fps with a stdev of only 6 fps. The bad part is that less than half the time does this load extract properly and pick up the next round from the magazine.

I guess I might have to think about biting the bullet and dropping big bucks for heavier jacketed bullets. I need a bullet that has an ogive less than .445" so that it does not engage the rifling when it chambers. The Lyman mold I uses casts a bullet like this, the jacketed bullets all chamber well too, but they do not extract at subsonic velocities.

I was told that using a CAR spring or a 9mm upper buffer/spring might help. I am still hesitant about drilling out the gas port to a larger diameter.

I also have an extra standard ar15 spring that I can cut down. I was thinking of just cutting it down an inch at a time until the spent brass extracts properly.

While I am very happy with the consistent performance of the WC820 powder, I am willing to try something else. Would a slower burning powder give me better extraction? Or a faster burning one? My upper has the 16" barrel with the gas port about 10" down. Thanks.


Ranb

order a box od remington 405gr flatpoints and repeat.

have you emailed marty for advice?

does it still work well with full house loads, as designed?

jeffe

My first post should read that I used 500 grain cast bullets, not 600 grain.

Full power loads work well.

I tried the 405 grain remington bullets in subsonic, they did not work as well as the 500 grain cast bullets.

Marty's advice was to use 500 grain bullets.

While the suppressor I made for it might help it cycle, I can not use it most of the time as I live in WA.

Ranb

I'm thinking of getting a 645 grain NEI mold. Would this bullet be too heavy to drive at 1050 fps without over-pressure?

Ranb

What twist on your barrel? I have just ordered two barrels from Pacnor, SS in 1-8. A gunsmith friend has made a few, and tried a lot. The 405's Jeffe is talking about work really well. Since we always install silenceres on theese babys, cast bullets are out of question.

Lil Gun and Rel-7 will provide 500 gr sub-sonic loads that cycle in my gun with the original Colt factory spring. The bullet is the Hornady Interbond.

If you have Marty's email he'll send you the tables.

Bent, mine uses a 1-14" twist to just barely stabilize the 500 gr bullet. This slow twist encourages tumblimg on impact. At 100 fps, the 500 gr bullets just don't expand well but tumbling does enough tissue damage to make up the difference.

Why are cast bullets not an option when using a suppressor? I use cast bullets in my 338 whisper. While they do blacken the baffles alot, I have not noticed any reduction in the baffle bores. The baffles clean off easy after shooting cast bullets. thanks

Ranb

Tigger,
Jupp, and that is not what we want over here, and spesialy if one wants to use any of the longer copper bullets. My gunsmith friend has made homogenous bullets to expand at sub velocity, and they work well. Still an interesting teory, good to know if someone insists on using a 14 twist.

RanB,
Yea, they sure do work, but because of the fouling we do not consider them as ideal.
In our part this is a leagal gun for big game hunting when supersonic, and legal for Roe-deer when going sub. As a hunting rig, bullet cost is not an issue.

Thanks,

The technique was also part of the original concept behind the 300 Whisper. It used the extra long 30 caliber 240 gr Sierra MatchKings precisely because it did so much damage when they tumbled.

But that was based on relatively soft-skinned game like hogs. It's illegal in most states to hunt native game like deer or bear with a supressor so most folks dropped the heavy bullet and went supersonic with lighter bullets.

Same for the SOCOM; can't hunt native game with it but you can do culling and other game management with one on exotic pastures.

I cut down my buffer spring (a spare) about 1.5 inches until the brass extracted and the bolt picked up the next round. The 500 grain cast subsonic load throws the empty brass between 2 and 6 feet back. I will try 405 grain jacketed bullets next. Shooting cast bullets in an ar15 gives new meaning to the words, "dirty rifle".

Ranb

Cutting the spring was not a good idea. Just cutting an inch off results in failure to chamber 10% of the time.

I finally got around to taking all of the lead weights out of the hollow buffer. That did the trick. The brass always extracts, and always picks up the next round. About 10% of the time the last round will not lock the bolt back, but I can live with this for now. I will have a separate buffer for my other uppers.

21 grains of WC820 and the jacketed remington 405 grain flat nose gives me 1055 fps with a 6 fps stdev. Very nice internal ballistics. This is good for 2-3" groups at 100 yards. The 500 grain lyman cast bullet gives slightly larger groups, and works just as well in the rifle.

After several months of load development, I have learned much. Subsonic loads using 748, WC844, WC846, 3031 and 4895 all leave too much fouling in the chamber and keep the bolt from closing fully after shooting about 5-10 rounds. This is made worse using cast bullets.

I am going to limit my load development to jacketed bullets only, like the 405 grain Remington soft points. Subsonic loads with WC820 (like H110) cycle the action well as long as I remove the lead weights from the buffer.

I read about problems with Starline brass being too short. After a few subsonic firings, my brass started chambering with difficulty unless I set the shoulder back a bit.

I think the Lee dies suck. The seating die barely seats down to 2.15†OAL and I needed to grind down the bottom of the sizer to be able to set the shoulder back.

Ranb