"Do all" 10.5" barrel?

[AlcoholicusMaximus]

Yes..... the holy grail of .300 whisper barrels... I want to have a 10.5" .300/221 barrel that will cycle 220gr. subsonic smk's and 180 gr. supersonic game kings in an AR15, without an adjustable gas block.
I am willing to do load development until California falls into the Ocean. Is this even feasible, Or should I wait until John perfects his Switchblock? As of right now, I am going to put a .080 gas port at the pistol position after the barrel comes back , chopped to 10.5". Just need to know If anyone is cycling the action with both sub & supersonic ammo and this barrel config. .......

[Ron458]

LMK what you find out. I just finished an 11" from a PacNor poly & figured I would need to make an adjustable gas block. It would be nice to have a DO ALL brl. Ron

[TheAlmightyBob]

I've got a 10.5" noveske that has cycles everything from 130 soft points, to 220gr mk. One good thing I think about this lenth I have found is that the 220gr pills only dropped an inch under the 130gr pills at 100 yards. I think that maybe because the barrel is so short, that its not burning all the powder in supersonic loads with while is enough to get them going supersonic, its just barely enough burn time to get them there.

[pug]

For your stated weights it will certainly cycle with a fixed gas block. In fact for 220 grain subs and 180gr supers I might would put a .070" pistol port first and see what happens. You can always go larger if needed but not vice versa.

[Ron458]

TheAlmightyBob, what gas port do you have? Inquireing minds want to know. Thanks, Ron

[TheAlmightyBob]

well, I'm not sure if this is going to help at all. I don't have any precision measuring equipment for such a small hole. The best I could think to do is use drill bits and see what would fit in the hole. Here is my findings.

3/32 bit wouldn't fit, but it was damn close. (3/32 = .09375)
5/64 would fit with room to spare. (5/64 = .07812)

So I tried to do some math to see what the middle point is and I came up with .08593. So I guess the best guess I could make is that its near .086" but seems closer to .090"

[Ron458]

Thanks I owe you one. Compiling gas port sizes for difernt brl lengths/manufacturers. Sounds like.090 I will start smaller to be sure but this realy helps. Ron

[AlcoholicusMaximus]

My stamped form 1 showed up, so I asked Model 1 Sales to make a 10.5" barrel with a .082 dia. gas port @ the pistol position. 8 days & $275 later,testing commenced.
8.5gr alliant 2400 & 220 smk cci450 - did not cycle
8.6gr AA#9 & 220 smk cci450 - did not cycle
Opened gas port to .086 using #44 bit, and have been off to the races ever since. Almost all test loads are cycling, subsonic & super.So far, this setup seems to"DO All".All loads were tested with a suppressor. See the "loads that cycle a 10.5" upper" thread in the reloading section where I will post results shortly.
Think I'll have a beer.

[Pitt300]

What kind of velocities are you getting from full power loads (supersonic) w/125g bullets out of 10.5" barrel?
I'm getting around 2160 fps & 1/2" groups w/16" M1S & either 125g Nos BT or 125g Sierra SPT w/18.4g H-110.

[JFettig]

I did some short load development on 125gr TNTs, My max of that day was 2000fps out of my 10.5" barrel. The next .5gr was too hot.
18.0gr of H110 was my max, 18.5 was too hot. I might be able to go back and work it up in smaller increments but I'm worried that when it warms up, hot will be too hot.

-edit- just went and looked at the data I have for it, 17.5gr shot 1950 average, 18 shot 2020 one shot, and 1950 average for the next 4.

Jon