300 Fireball Cycling issues

[JimM44]

Here's my question, I was told via an email that the M1S barrel won't cycle subsonic with a can? Is this true I thought is was designed subsonic.

I was planning on shoting the 240grain Sierra matchking bullets because I want to hunt with them. Decided this after reading a lot of opinions about how they tumble from a quarter away shot ot hitting bone here on this site.

I don't have my barrel and won't for a while with the backorders.

I ordered the 16" threaded with low profile gas block from M1S and have a Gemtech HVT can on order too.

It will probably be at least 4 months before I have the stuff and can put it together. I have also ordered some brass but nothing else for it yet.

So any advice on what dies, primmers, powder and loads for this would be great too.

New to this site found because of the 300 but you can find my handle on plenty of other sites. More of an AK kit builder than an AR man.

It took me a lot of years to buy an AR after the M16s we had in Vietnam.

[pomofo]

I just tested a whole bunch of heavy loads this weekend trying to get subsonic. Not sure if I made it or not, since it's an indoor range, but they sure were quiet compared to the known supersonic loads, not to mention easy on the shoulder. My M1S upper has a short throat, so I have to load deeper.

220 Hornady RNSP - COAL 2.000"
Loaded w/ AA 1680, from 11.6 down to 9.4 grains in 0.2 grain increments. All loads ejected brass, 11.2 grains locked the bolt, 11.0 and below didn't.

220 Sierra MatchKing - COAL 2.145"
Loaded w/ AA 1680, loaded 12.6, 12.3, 12.0, 11.7 grains, then from 11.4 to 9.4 in 0.2 grain increments. Only 12.6 and 10.6 locked the bolt, all other loads ejected but no BHO.

240 Sierra MatchKing - COAL 2.145"
Loaded w/ AA 1680, loaded 10.7, 10.4, 10.1, 9.8, then from 9.6 to 9.0 in 0.1 grain increments. All loads ejected, but none engaged BHO.

Quickload measures that 10.7 grain 240 SMK load at 50208 PSI and 1235 fps out of a 16" barrel, although my experience from my limited analysis of loading manual data is that QL often overestimates the pressures and velocities of loads using 1680. I may work up a little, very carefully, to see if I can get the bolt to lock back on that loading. It seems odd that a true 50K load would fail to generate enough gas at the port to lock the bolt back, even if it is in the carbine position. I suppose an adjustable gas block might alleviate any BHO problems.

[Colohunter]

I was able to get subsonics with AA1680 to cycle the action and lock the bolt back with 220gr Sierra HPBTs. It is in a M1S upper, but I don't have a suppressor.

[Gpz1100]

mine cycled better with the can

[320pf]

Originally Posted by JimM44

Here's my question, I was told via an email that the M1S barrel won't cycle subsonic with a can? Is this true I thought is was designed subsonic.

Jim,

If it was my e-mail, sorry it seems that I was a bit unclear about the M1S barrels.

"If you are getting one from Model-1 have them put the gas port in the pistol position. The is particularly important if you are going to be shooting sub-sonic loads. I am using a 0.083" gas port with a fixed gas block. I am able to shoot both super and sub-sonic loads. "

You can get rifles with the gas port in the carbine position to run subsonic ammo but it is going to take more development effort than a rifle with the gas port in the pistol position. In addition, a rifle built with the gas port in the pistol position will also be able to shoot the lighter bullets at subsonic velocities than a gun built with the gas port in the carbine position.


Because the gas port is further down the barrel and the pressures at the carbine position are lower, when compared to the pistol position. The slower burning powders like A1680 are usually the go to powders with guns ported in the carbine position.

Installing a can will help an AR15 run subsonic loads as well because a can will increase the gas pressures and lengthens the pressure pulse. This basically increases the amount of gas that can work the action.

Sorry about any miss understanding. I hope this helps.

320pf

[Fudmottin]

I agree the can should improve cycling reliability. At worst, it won't make any difference.

My barreled upper should be on route to me today or tomorrow. It needs a bit of break in due to a minor issue with the gas port having a burr. It was discovered during testing and removed. As a result, I have a slightly larger port. Should make cycling more reliable.

Porting is in the pistol position with a three way block.

I can fire form some of the brass I got from 320pf at the same time I test out the barrel. I've got some old 220s. I don't know if I have anything lighter lying around.

I've also got a bunch of 240s. My big fear is that I will enjoy shooting them more than 69s in 223. They are more expensive even though they use less powder :-p

[ranger dave]

you should never and i mean never fire super sonic loads in a rifle with a pistol gas tube too much preasure try 8g of 2400 with a 147g to 150 g bullet it will stay sub sonic and work fine in a model 1 upper

[320pf]

Originally Posted by ranger dave

you should never and i mean never fire super sonic loads in a rifle with a pistol gas tube too much pressure try 8g of 2400 with a 147g to 150 g bullet it will stay sub sonic and work fine in a model 1 upper

I think that this needs some clarification. You can shoot super sonic loads in 300-221 Fireball/300 Whisper provided that the gas system has been set-up correctly for these conditions.

For example there are several companies that offer AR15 pistols that shoot standard 223/5.56 ammo. The port pressure for these pistols is about 45000 to 50000 psi. The cycling of the action is controlled by the port diameter, buffer weight, and recoil spring tension. There also numerous carbine length rifles with "carbine" length gas systems. The port pressure at the "carbine" position is about 30000 to 35000 psi. These rifle have "carbine" buffers and are designed to operate at these pressures. The standard rifle length gas system operates at pressures of about 15000 to 20000 psi.

In the 300-221 Fireball/300 Whisper, super sonic loads produce about 18000 psi at the pistol port position (~5in, from chamber) and about 10000 to 12000 psi at the carbine port position ~8in. from chamber). See QuikLoad data output here:

http://www.quarterbore.net/forums/ph....php?photo=371

I have built rifles with gas ports in both the pistol and carbine position. They all use standard rifle weight buffers and recoil springs without the need of an adjustable gas port. The trade off for this is that rifles with a carbine gas port require slow powders and heavy bullets to reliably run sub sonic ammo. But you will be able to push the 125gr bullets about 30 to 80 fps faster than a rifle with a pistol position gas port.

On the other hand, rifles with the gas port in the pistol position can shoot the lighter bullets like 150gr at sub sonic velocities with much less load development. You can still push 125gr bullets but your max loads will be about 30 to 80 fps slower than a rifle with a carbine position gas port.

So if you are considering building a 300-221 Fireball/300 Whisper you need to decide if you are more interested in super sonic loads or sub sonic loads. If you want to mostly shoot super sonic with an occasional sub sonic load go with the carbine position gas port. If you are mostly interested in sub sonic shooting and occasional super sonic loads go with the pistol position gas port. Both will work but each has it's unique advantages and disadvantages.


320pf

[mooster1223]

Originally Posted by Fudmottin

I've also got a bunch of 240s. My big fear is that I will enjoy shooting them more than 69s in 223. They are more expensive even though they use less powder :-p

I think you'll find that shooting any weight subsonic is more enjoyable

Jim

[Fudmottin]

An adjustable gas port at the pistol position can be helpful. Of course that is added complexity. Being able to shut of the gas entirely is an added option you get with the right gas block. Cutting out the action noise makes quite a difference. However, manually cycling with the standard charging handle is a nuisance. But you get the added option of firing loads that would not allow reliable cycling.

Port diameter regulates how much gas pressure can get into the tube. Only so much fluid can go through a given sized hole no matter what the pressure is. The gas port is like a resister in an electrical circuit. The gas pressure is like the voltage.

Thanks for the numbers, 320pf. It's always nice to have numbers. I had an engineering professor who said, "If you can't put a number on it, you don't know it."