Been buildin AR's for a week or two and have decided to build myself a blackout to play with and get a feel for the platform.
I have 3 really nice Rock Creek Barrel blanks laying on my bench and a bag of barrel extensions.......and the chamber reamers just came in.
I'm gonna build a 1:10 barrel as that is what I have on the shelf and the first is primarilt to play with gas por size and functioning.....just wondering what ya'll thought would be the best way to configure it (carbine or Pistol gas system) and what load would be best to run through it.
While 90% of my expertise is in building DI pistol caliber stuff.....I have had a lot of past sucess with 1;10 twist and .308 bullets......
Any input will be appreciated.
Rudy
R.N. Koester
Certified Master Engine Machinist
Cpt US Army (dis)
1-10" twist is gonna keep you accurate with the lighter bullets, 170ish and lower maybe. The 1-10 wont stabilize those bigger subs us blk fans love. Thats why savage scrapped their 300aac project. If possible go with 1-8 twist. It will stabilize the big boys AND if u r wanting to play with gas port size thats only necessary when tweaking ur rifle for subs. Sooooo, with that being said, if you want a supersonic plinker it will be fun...but if you want to play with the entire gammet of blackout accessories get a 1-8 or 1-7 twist barrel....BTW i believe the 1-7 is the new blackout rifle twist preference. 1-8 will still get your 220-240grainers flying steady
318lll1927 wrote:1-10" twist is gonna keep you accurate with the lighter bullets, 170ish and lower maybe. The 1-10 wont stabilize those bigger subs us blk fans love. Thats why savage scrapped their 300aac project. If possible go with 1-8 twist. It will stabilize the big boys AND if u r wanting to play with gas port size thats only necessary when tweaking ur rifle for subs. Sooooo, with that being said, if you want a supersonic plinker it will be fun...but if you want to play with the entire gammet of blackout accessories get a 1-8 or 1-7 twist barrel....BTW i believe the 1-7 is the new blackout rifle twist preference. 1-8 will still get your 220-240grainers flying steady
Thanks, Looks like I am the proud owner of a 300 Blackout high speed plinker.....LOL....and guess I'll be ordering a 1:8 barrel monday....Green mountian has a nice blank that'll make a 16 and a SBR barrel for around $50.00.
On the gas system.....how Keep it pistol length or since the upper is being made to shoot lighter bullet supersonic loads.....will a carbine tube work?
R.N. Koester
Certified Master Engine Machinist
Cpt US Army (dis)
Pistol length will run the subs more reliably, but mine is a carbine and works great. Pistol length tube for pistol gas system and carbine gas tube for carbine barrel...FYI some carbine barrels will have pistol systems. If you are making your own though i would use pistol length.
I didnt mean anything by it being a plinker, but 1-10 is gonna be best with supersonics. with 1-7 or 1-8 you can shoot a helluva variety of bullets! $50 barrel blanks you cant go wrong. Shooting subs is fun, but those 115 umc's can host a really good time too
No offense taken on the plinker comment....It is actually probably gonna be a pig killer.....I'll wait till my 02 SOT is in place before I mess with the subsonics......planning an integrally supressed at that time.....
R.N. Koester
Certified Master Engine Machinist
Cpt US Army (dis)
I am in the process og having a 10 twist gun built.
I have done a lot of subsonic stuff with the 7.62x25 Tokarev as the case. I have fired 180 grain Sierra SP bullets in a 10 5/8 twist barrels with great success. And when I ran those numbers in the Miller formula and compared them to some haviner bullets in 10 twist I found out this. A 10 twist will stabilize 200 grain VLD bullets or 220 grain hunting bullets. Both os those showed higher stability numbers than a combination I KNOW worked.
The barrel I used measured 10.625 twist. I know it is a odd twist rate but I think it was supposed to be 11 twist but because it was a Numrich $33 barrel blank I think the maker knew the twist was messed up and sold them CHEAP.
With this barrel I would shoot 180 grain soft point Sierras (2150). Those bullets remained stabile and were actually 1/2 MOA capable at least to 100 yards when fired at ~1,050 fps. Because I planned on only shooting subsonic the Tokarev case worked fine. I did some testing using several different twist rates until I got the bullet just stable enough to be accurate yet unstable enough to tumble when it hit something, this is where the 10.625" twist was perfect. I got it to where the subsonic bullet would reliably tumble between 6" and 10" of water.
According the the JBM bullet stability calculator the stability using the 180 grain Sierra SP with a 10.625 twist was 1.795 at 1,050 fps and 90 degrees.
Now I am building Savage in 300 BLK. The barrel I decided to use is a 10 twist rather than the common 8 twist for the caliber. I am going to be shooting a cast bullet that is 230 grains and 1.363" long. I am planning on shooting them at 1,050 fps as well. But according to the calculations this load will have a stability of 1.88 which is greater than my Tokarev load that was stabile to 100 yards.
Also, the stability should not be below 1.4 for the bullet to remain stabile throughout its flight.
I have spoken to several people and they are saying that 10 twist will not stabilize these bullets or any jacketed bullets over 200 grains. But it has to do with bullet length and not weight. It will not stabilize 210 grain SMK's but according to the calulations it should stabilize 200 SMK's, just barely. It will stabilize 220 grain Sierra SP's according to the calculations because they are shorter vs weight than the SMK's. And all of these seem to corrolate to all the Tokarev data I gather over the course of a couple of years of testing.
One more thing, before the BLK became popular the Whisper was king and there are a lot of successful 10 twist Whispers out there shooting heavy subsonics.
I also have a 8 twist AR barrel coming. It is a Shilen with a pistol length gas port so I can shoot subs reliably.
I know there are people who think the 10 twist will not work with anything beyond 170 but I know they will because I have shot heavier bullets with a slower twist.
If you willing or want to try cast bullets you can go even heavier with the slower twist. A 200 gr from a 12 twist AR with no trouble at all and have shot 220 gr from a 10 twist bolt gun at sub speeds
and have decided to build myself a blackout to play with and get a feel for the platform.
