yet another question on 240 SMK, M1S 16", and cycling

[andy b.]

i only recently received my Model 1 Sales 16" .300 upper (a week ago, of course it was ordered in November). it has the gas port at 7.5" (the Carbine location). all i want to fire are subsonic rounds, and preferably only bullets over 200gr. i have a suppressor, and plan on doing at least 90% of my shooting with it attached.

reloading info is somewhat, uh, unorganized for the .300, at least as far as i can tell. oh, there is plenty of info out there, but trying to find it all and make sense of it is a project.

right now i am experimenting with the 240gr SMK bullets and started with some AA #9 powder. i worked up loads from 8.9gr to 9.8gr and none will fully cycle my AR. i am using pre-fired .223 brass (i form the brass and then fire it in a .300 Whisper bolt rifle and then re-size and trim it).

so my question is, at this point does it sound like i need to open my gas port, or should i increase the powder charge, or should i try some other powders? i haven't pulled out my chrono to check velocities (it is in storage, but i want to get it out for this project), but the round still sounds subsonic. the brass shows no signs of overpressure. if the answer is to keep increasing the powder charge or try another powder someone has experience with, that is preferable to opening the gas port. i have the tools to adjust the gas port if that is what i need to do though.

what i really was trying to find was a listing of all minimum powder charges that cycle the 240SMK bullets in a 16" barrel with the carbine gas port location, as well as the gas port size, if known. anyone every come across such a listing or something close?

i apologize for asking this question as similar versions have been posted previously. i just haven't come across an answer that matches my situation.

thanks,

andy b.

[Pitt300]

Don't use that powder so cannot help w/that side of equation.
If the gun is brand new you need to wear it in some.
Either load up a bunch of supers & blast away or sit in front of the tv one night & drive your family crazy by cycling the action over & over.
I polished a few areas of my hammer where it would catch on my bolt carrier & I installed a CAR buffer spring.
Mine will not hold open after last round but otherwise functions flawlessly w/subs or supers.
As I recall you must have a can on to get enough back pressure w/subs to get it to cycle .

[andy b.]

ah, that could be it. i only have 50 rounds through it. :)

i do have a bunch of lighter bullets (also CHEAPER), so i guess i'll load up 100 or so and run them through the rifle to start getting the upper broken in. it is a completely new upper (new bolt and carrier and everything else). the rifle has a collapsible Rock River Arms stock, and i'm using the buffer and spring that came with the stock.

i have started compiling every bit of reloading data i can find on the 200+ grain bullets, so if i can put it in some sort of sensible spreadsheet, i'll post it here.

andy b.

[andy b.]

i figured today i would try some new powder as well as load some ammo just to run some rounds through to cycle the action. i did some more reading last night and this morning and found one bit of advice that i previously missed. when running a gas port in the carbine position, a slower powder should be used. Accurate #9 is relatively fast, but i have some IMR 4227 on hand, and that was a bit slower. loaded some up on the low end of the scale, and what do you know, the action cycled every time!!!

so it appears at least from that end i now have a bit more understanding of how this cartridge works. i don't know how many people are actually going to read this post, but if you do and you post load data, i'd say it would be helpful to include the gas port position on your rifle.

now i have to chrono some loads and see just where i am on the speed scale. my intention is to only run subsonic loads through the AR. i unpacked my chrono so hopefully it still works.

andy b.

[kdiver58]

Their are a few of us that have done quite a bit of testing and I've found that 1680 works the best for me. Cycles every time, locks the bolt back and I didn't have to move the gas port or lighten the springs.
Here is an old video with a load .. BTW this load works the gun suppressor or not ..

http://www.youtube.com/watch?v=ilNf6OiHd5c


320pf has also posted load data

[JimM44]

kdiver58,

I watched the video, is that a supersonic load, it still sounds loud and I can see the recoil from your shots?

[Pitt300]

http://www.silencerresearch.com/sshoot2008.wmv

link to video of Longview Silencer Shoot from 2008.
I’m @ 5:24 w/M4-1000 & 762SD on a .223 & @ 8:02 w/whisper (quite as a .22 suppressed)

140 db is considered ear safe

[Fudmottin]

140 db is considered ear safe? I shoot suppressed 223 with plugs because I find the action noise too loud. But then my right ear is pretty much next to it.

My very heavy barrel target 223 (24" barrel one inch to gas block and then 0.930 to muzzle, standard length gas system) will recoil about two inches with the AWC Raider when fired with 55gr and 69gr ammunition. And even though I feel more recoil with the action on, shutting off the gas port doesn't seem to change the recoil on video. It sure makes the rifle quieter though. At least it does to my ear.

Action cycling is loud!

I still haven't popped the cherry on my 300-221 :(

Haven't had time to get some rounds loaded and the gun to the range. I don't have a 30 caliber suppressor yet. I gotta get my Form-1 in too.

When I do get my stamp and can made, I would love to be able to break below 110db with the gas block closed. From my research, that is a threshold no one has gotten below even with .22LR. The really quiet guns can make it down to a bit below 115db.

I don't have a reliable way to measure SPL. So I will be happy if I can hear the hammer drop when firing.

[interceptor]

Buy a SPL meter. Good ones aren't but about a grand, new mikes for 'em are cheap too. (I was 8 years lead tech at a big car audio shop, way too many sound-offs in my past)


Check out a local car stereo store, see if they have one. One of the guys in the shop may wanna do some trade out in exchange for getting to shoot a supressed gun. High end vehicles in db drag racing will hit in the 160's range, so shooting a supressed .300 within 6' won't kill it.

[Fudmottin]

You mean my radio shack SPL meter isn't good enough? :(