View Full Version : 300 blk and gas system optimization
blasternank
12-04-11, 15:45
I'm looking at the 300 blk and will probably go with a 16" but my go smaller and go suppressed. If I go with a 16" is it better to go with a carbine or midlength gas system? Also, if I decide to use a suppressor on a 16" will that make a difference in the gas system I choose?
Thanks.
blasternank
12-04-11, 15:46
Also, what is the preferred twist rate?
Midlength gas will not work at all.
Your choices are carbine or pistol. Either one works fine, as long as the maker picked the correct has port size.
Also, what is the preferred twist rate?
1/8... Think of it as 1/7 for 5.56.
Why will the mid-length gas not work with the 300? Does the pressure drop off too much?
Yes. Carbine is the longest gas that works.
If I run a pistol gas system can I shoot both super and sub sonic?
I have couple of blanks. Who would you recomend to do the rest of the work on the 300?
Yes, provided you pick the right gas port size.
I am not sure who to recommend if you don't have drawings for the barrel you want.
Why will the mid-length gas not work with the 300? Does the pressure drop off too much?
Larger bore for the gas to expand into, with a smaller charge of faster burning powder.
I tried rifle length gas on a 20 inch barrel, and it did not work, even supersonic with a suppressor and a carbine buffer and with the gas port at 0.125.
So stick to carbine gas for barrels over 16 inches, carbine or pistol gas for barrels that are 16 inches, and pistol gas only for barrels in the 7.5 to 14.5 range.
I have been following the development of the blackout for a while now. This is the first time I have seen a choice of pistol or carbine for a 16" barrel. Coming from you I am sure it is correct. That is great news. Does that mean I can initally set up my 16" as a pistol length then if I decide to cut it down to 11" I am still good to go?
Yes, but you will have to enlarge the gas port if you cut it - which is simple to do.
Just note - my statement was not an endorsement of every 300 BLK 16" barrel with a pistol length gas system. There are certainly bad ones for sale. I meant that I know how to make a 16 inch barrel with a pistol length gas system which would be fine.
I still prefer carbine, just as I prefer mid-length gas on 16 inch 5.56mm rifles because it delays unlocking and has lower gas port erosion. I generally believe that the further you can move out the gas system and still remain within spec on cyclic rate, the better.
Rwatts62081
12-05-11, 22:51
I am building a 300blk with a 10" noveske barrel pistol gas... what would be the best buffer to use with this barrel? It will be run 100% unsuppressed
H buffer.
Wouldn't an A5 run even better ?:D
I like the A5 concept, but I am into the CTR or SOPMOD stock.
I like the A5 concept, but I am into the CTR or SOPMOD stock.
a5 tube springs & buffer with STR stock body. Best of both worlds!
Are you saying the tube is compatible with normal stocks? I thought it only worked with the Vltor stock.
Are you saying the tube is compatible with normal stocks? I thought it only worked with the Vltor stock.
Of course it is; that's the beauty of it. It's just that the CTR won't collapse completely to position 0. the STR should collapse to position 0, I'll tell you after X-MAS. :cool:
I don't know how it'll affect sub unsuppressed but for shooting supers unsuppressed it's very smooth. I'll do comparative test with some buddies in 2 weeks to compare my A5 with their C, H and H2 setup on my 110gr vmax handloads/Noveske 10".
You can use the A5 or rifle system, we test with a rifle system not just carbine.
Vltor makes two receiver extensions, one for longer stocks like the Emod and ACS to collapse all the way and one for standard length stocks that stop about 3/4" from fully collapsed.
Of those two - do both use the special long buffer and standard rifle spring?
How much, if any, additional travel is there in the buffer from full recoil to the bolt being closed?
http://img546.imageshack.us/img546/8825/buffertubecomparisonsma.jpg
http://img820.imageshack.us/img820/9268/buffercomparisonsmall.jpg
From these photos, it would appear that the A5 has the same amount of travel as a standard carbine stock, but is designed to work with a rifle spring. Is that the case?
They are the same length, the one designed for the Emod stock has an extra locking position.
Both use the A5 buffer and standard rifle spring. The A5 RE and buffer are extended the same length, so bolt travel remains the same as carbine.
Looking to get an upper that can shoot super w/a 13" barrel. What gas port and length should I use? Thanks
Is anyone following this thread anymore???
Is anyone following this thread anymore???
Who knows?
13" bbl - pistol-length gas
Who knows?
13" bbl - pistol-length gas
May I ask why? What are the benefits, etc? Why not mid or carbine length? Thanks
16" carbine gas 300BLK here. I have not had a single hiccup in this rifle. Vltor A5 kit should be here Friday, it should be just about perfect then.
I wouldn't go Pistol gas unless it is to be suppressed or a SBR/Pistol.
I am hearing great thing about the 12.5" barrel and the longer suppressors, shortcoming is no IR LASER with the dual BDC ability.
Sounds like 200 yards with subs and 500 yards with supers.
With carbine length buffers.
May I ask why? What are the benefits, etc? Why not mid or carbine length? Thanks
If you go back and read the thread from the beginning, you'll see why not a middy
If you go back and read the thread from the beginning, you'll see why not a middy
This.
The 5.56 has a longer pressure curve than 6.8, which is longer than 300BLK.
The faster the pressure drops off, the larger the gas port needs to be.
If the gas port needs to be bigger than the max (.125), the gas system needs to be shortened to get enough gas drive.
If you go back and read the thread from the beginning, you'll see why not a middy
I've read it from the beginning but man you guys really get into the details. Just tell something around the lines of, "small boom go short, big boom go long" or something like that.
This.
The 5.56 has a longer pressure curve than 6.8, which is longer than 300BLK.
The faster the pressure drops off, the larger the gas port needs to be.
If the gas port needs to be bigger than the max (.125), the gas system needs to be shortened to get enough gas drive.
So guessing mid is too long due to the bullet taking up most of the brass' room. Say I want to shoot up to but not limited to 500-600 yds with super, is carbine length capable?
Judging from Onyx Z:
16" carbine gas 300BLK here. I have not had a single hiccup in this rifle. Vltor A5 kit should be here Friday, it should be just about perfect then.
I wouldn't go Pistol gas unless it is to be suppressed or a SBR/Pistol.
...seems like the way to go. And Onyx what is the gas port size you have for your upper?
So guessing mid is too long due to the bullet taking up most of the brass' room. Say I want to shoot up to but not limited to 500-600 yds with super, is carbine length capable?
Judging from Onyx Z:
...seems like the way to go. And Onyx what is the gas port size you have for your upper?
No idea on the gas port size, but I can check when I get home. It's a 16" DD 300BLK S2W barrel.
Generally, gas length has nothing to do with effective range of a rifle. It only has to do with the action, which you feel as recoil.
If you are looking for 500+ yds with a .30 cal bullet, I would definitely turn my attention to a larger caliber cartridge, not a 300BLK. There just isn't enough room in the case for the powder to get the bullet travelling at proper the velocity.
No idea on the gas port size, but I can check when I get home. It's a 16" DD 300BLK S2W barrel.
Generally, gas length has nothing to do with effective range of a rifle. It only has to do with the action, which you feel as recoil.
If you are looking for 500+ yds with a .30 cal bullet, I would definitely turn my attention to a larger caliber cartridge, not a 300BLK. There just isn't enough room in the case for the powder to get the bullet travelling at proper the velocity.
Thanks, I'll hold you to that. I'm planning on getting an upper from Arsenal Democracy, and when I get it, want to zero in at 300 yds; 500-600 yds is just for kicks in case I feel like or have to shoot that far with 300blk. Also, a barrel change and maybe buffer group will do fine if I want to go back to 556.
May I ask why? What are the benefits, etc? Why not mid or carbine length? Thanks
If you roll your own ammo and want to shoot subsonic rounds there are some powders that will cycle in a pistol length gas system but not a longer system.
My experience so far has been good with a carbine length gas system though- there is a decent array of powders that are reliable in a carbine for subsonics.
If you roll your own ammo and want to shoot subsonic rounds there are some powders that will cycle in a pistol length gas system but not a longer system.
My experience so far has been good with a carbine length gas system though- there is a decent array of powders that are reliable in a carbine for subsonics.
This is nice to know, if I get into 300blk, I would definitely want to roll my own.
Thanks, I'll hold you to that. I'm planning on getting an upper from Arsenal Democracy, and when I get it, want to zero in at 300 yds; 500-600 yds is just for kicks in case I feel like or have to shoot that far with 300blk. Also, a barrel change and maybe buffer group will do fine if I want to go back to 556.
My gas port is .118. I'm willing to bet DD tuned it to this size for the carbine gas.
In terms of gas port for carbine gas, bigger is better. In fact, running a gas port at .125 seems to have no detrimental effect in terms of overgassing even with super ammo, and seems to significantly help reliability with subs. It is good to hear that DD made the gas port fairly large on their 16" barrel.
Personally, given the 300 BLK's intended use, I would personally always choose a pistol gas even if I was going with a 16" barrel. This is for maximum reliability with subs and more latitude to play with powders. Also, if you are zeroing at 300 yds, you are missing the point of this cartridge. From my calcs, a 300 yd zero puts you nearly a foot over POA at 150 yds.
hotrodder636
08-25-13, 08:33
Midlength gas will not work at all.
Your choices are carbine or pistol. Either one works fine, as long as the maker picked the correct has port size.
I have a LMT MRP barrel in 300BLK from LMT and it has a pistol length gas system. Works just fine so far.
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