New build, barrel length

[kugle]

I am new to the 300 Whisper; I am looking into building an AR upper.

I mainly want to shoot 220gr Sierras thought it with a suppressor.

What is the shortest barrel length I can have with a carbine length system and have it function reliably.

Thanks

[jjmcrowell]

I'm pretty new to the 300 whisper also, but you may really want to consider a barrel that has a pistol gas port location. This would allow you to go much shorter. I had one cut to 9" from a 16" barrel and it functions fine without opening the gas port up. I only shoot subsonics so I didn't get an adjustable gas block. I also use 220gr loads and have had luck with H110 at 9.2grs, it gets about 1025fps out of my barrel.

If you really want the carbine gas system, I think you could do it, just a little tricky when you get really short. If you went as short as 10.5" you could probably be ok with a little work. You most likely would have to drill out the gas port to make it function though. Maybe a port opening of .100, but I would start at the factory size and work up.

The suppressor will help the gas system function by adding some back pressure, so you got that going for you too.

When you use the carbine gas system, the distance between the end of the barrel and the gas port is really short and doesn't allow much room for the gas to do it's work.

This is a photo showing a 9" barrel with the pistol gas port location.
http://www.quarterbore.net/forums/photopost/data/535/DSC08080.JPG

[Spook]

That is about the best avatar I've ever seen...... good job!

[jjmcrowell]

That is about the best avatar I've ever seen...... good job!

Can't take credit for that. Saw it somewhere and saved it.

[pug]

jjmcrowell that is a nice looking upper also. I have a 300 whisper barrel ported in the pistol position in shipment to me now. The further you move the port back towards the chamber the lighter the bullet can be and still cycle the action. I was wondering if you (or anybody else with a pistol port) had gotten anything lighter than 180 grainers to cycle and still be subsonic?

[320pf]

Pug,

I have an AR15 with a 16 in. Olympic Arms barrel with the gas port in the pistol position. I have tried running several differnt 165 gr bullets at ~1000 fps (Nosler 165 gr BT Ballistic Tip ~1010 fps, Sierra 165 gr BTHP GameKing ~1090 fps). I am pushing both with 8.5 grs of AA#9.

I have also tried 180 Sierra BT GameKing at 1030 using 7.5 g AA#9.

I am very happy with the position of the gas port on my AR. I can also run the same 180 Sierra BT GameKing bullets at 1840 fps with 16.4 gr of W296. I do not have to adjust the gas port for any of these loads.

I have posted all of my loads on:

http://www.reloadersnest.com/frontpage.asp?CaliberID=135

My loads are the one listed under "Not yet verified user loads" with the exception of the ones that use the AD2205 powder

320pf

[pug]

320pf, I really appreciate it. Actually I have looked at your loads many times and didn't even realize there was one for 165 subsonic there. As you know its always helpful to have a starting point and I really liked the deviation you got as I wondered about that also. Would like to get similar results with the 150s since they are pretty cheap at bulk prices but I may be asking for too much. Got plenty of AA#9 on hand as well as H110 so I should be good to start. I usually use N330 with the 150 grain subsonics but that is for a blowback action and I am thinking its a little too fast for a gas system but we will see. Thanks again for pointing me back to your data and maybe later I will have something to share.

[kugle]

jjmcrowell:

That is a sweet upper. I was thinking of building mine along the same lines, but not going below 10.5. The reason I wanted a carbine lenth is to use the ARES Defense piston system seen here:
http://www.ar15.com/forums/topic.html?b=3&f=124&t=310274

[jjmcrowell]

jjmcrowell:

That is a sweet upper. I was thinking of building mine along the same lines, but not going below 10.5. The reason I wanted a carbine lenth is to use the ARES Defense piston system seen here:
http://www.ar15.com/forums/topic.html?b=3&f=124&t=310274

I have seen those, they look pretty interesting. That should help keep the receiver clean. From what I understand they are somewhat self regulating, so if you over gas the piston it bleeds off the excess gas so as not to bend the rod.

I think you could do 10.5"...

Hopefully someone has tried a 10.5" with the 300 whisper and tell you first hand. I think since your working with basically one load it will be easier to get it running. If you were trying to make it work across the board with a bunch of loads, you might be pulling your hair out.

I have 10.5" LMT receiver and it has never malfunctioned, so if it can be done with .223 you should be able to do it with 300 whisper, certainly one load.

I wonder if it posssible to modify the ARES piston system to fit a pistol gas system? I might be willing to try, but I think these are about $400.

[320pf]

Pug,

I just shot the 165 (Sierra and Nosler) and 125 data this weekend. So that is why you had not noticed them before. The 165 gr. subsonic loads were my first experience with the 300-221 fireball using subsonic loads. I have to admit it was pretty cool :). The report was a bit more than a 22LR and the recoil was nonexistant.

If I remember correctly, I think that someone on this board shoots 147 winchester bullets in front of 2400. I do not remember if the load is subsonic???

I think that you will get better results using faster powders than H110 for ~150 gr subsonic loads. I might be interested in 147 gr load at 1080 to 1100... I know that at that velocity I might be pushing super sonic but if I am going to run that load in competition I need to have a power factor of over 150. So if I come up with a load I will post it.

320pf

[Spook]

for some reason I have 8 grains of 2400 written down in a loadbook for 147's at 1050.. I think I was thinking pistol w/steel jacketed milsurp.

[pug]

Thanks guys for the info.

320pf I am curious about the 125 grain bullet data. Did you stop at 2240fps because of pressure signs or was that the most accurate load? I was thinking the 125s may do 2500fps but I also have heard people saying some of the data is really too hot and they are getting loose primer pockets.

[320pf]

Pug,

The Sierra and Hornaday reloading manuals list about 18.5 to 19.5 gr of H110 as max loads for 125 gr bullets. The pressure signs on the primers suggest that this is about max. I do not think that you can get 2500 fps without being way over pressure. The best loads that I have seen for a 16 in. barreled AR is about 2340 fps with 20.6 gr H110. These are listed on the site below. There is one load listed there that is hotter, but this is in a bolt action:

http://www.quarterbore.com/300whisper/supersonic.html



Good Luck and Have fun

320pf