I got a DPMS .300 WSM; it was a standard .308, i had rechambered to .300 WSM.  It has a gas issue i can not get figured out, and have done just about everything i can think of to fix it.  I think that if someone wanted to (and had the time and place to do it) they could probably get it worked out.  From the get go, i have been able to fire any where from 1 to 5 rounds, and then i have a fail to eject (the brass does not eject completly out of the ejection port, causing the next round to not feed).  At one point i ran 40 rounds thru it, with out any kind of failure (dont know why it went back to the failures, but it did) so i truly believe it can be worked out (i just dont have the time or place or patience to spend working on it anymore).

I decided to go with a standard .308; i am going to go with an 18" barrel and get a different FF tube (although i really like the SWS tube i have, it will be to long for the 18" barrel).  Where is a good place to by a ready to install .308 barrel and bolt?

I guess i will see if anyone is interested in the .300 WSM barrel and bolt and the SWS FF tube, or do you think i would have better luck selling the whole upper, and just getting a new one?

Thanks,
Mack

How far do the rounds that do eject come out?  It sounds like intermittent under gassing.  Have you tried opening the gas port by a couple or three thousandths?  If you were to go into an over gassed situation then you can always install an adjustable gas block or put a set screw in the side of yours to reduce gas flow.  
A change in powder burn rate might perk things up also, either slower or faster.  Assuming you reload that is.  The .300 WSM was not intended as a semi auto round so the gas curve for the LR-308 might be wrong with the powder being used either by yourself or factory loads.
Before selling and taking a loss on the barrel, I'd try changing powders first, one step faster, one step slower and see if there is any improvement.  If you don't reload, start.  If not willing to do that try enlarging the gas port by one drill bit size.  Let's say the port in there slip fits a number 32 bit, open it up with a number 31.  Most number changes are between  .001 and .003 inch difference.

If you single load rounds in the mag, will the bolt consistently lock back?  If so, your gas is probably ok.  Extractor tension can be the issue.  If the extractor does not hold on to the case long enough, the empty case gets jammed forward and you get the empty case/full round double feed.

Things to try:

O rings, I use two on the extractor.  They are cheap and easy to find at any hardware store.  1/4" OD  - 1/8" ID.  I think #6.  I stack two like so:

Yes its hard to get the pin back in, but worth it.  Make sure the spring is good too.

A heavier buffer, like swap 3 or 4 weights for tungsten.  That increases dwell time, and smooths the cycle.


More info:
Armalite tech note

Hello,
how much are you asking for the upper ? drop  me a im i dont reload for the  300 WSM
but i do for the 308 i have only shot handloads in my LR308 , im in Carroll county myself 65 miles ne of KC.MO. anyway if i can help you tune that let me know i would really like to shoot that upper to see if i want to add one for mine ,, i could try to  trade you out of it to

TS2

I have an enlarged gas port, with an adjustable gas block and adjustable gas tube; i also have a haevy ejector spring, and i have a rate ruducing buffer to slow the system down. And the bolt does lock back 90% of the time.

I dont relaod and dont want to start (i dont have time to hardly shoot, much less reload and shoot); i have ran Winchester 150 gr supreme ballistic tips thru it mostly, but i tried one box of 180 gr ballistic tips, and one box of Black Hills gold 170 gr.  It is constant thru out all the different loads.

Thanks for the info guys, i appreciate it
Mack

My 300 WSM is not a DPMS but I did have the ejection port enlarged by about 18 thousandths to ensure the larger case cleared the receiver.  Otherwise it was being deflected back into the path of the BCA.

Quoted: I have an enlarged gas port, with an adjustable gas block and adjustable gas tube; where do you have them adjusted?  if they are full open, and you still not locking back, then they not helping-- actually hurting-- thats for BOTH the adjustable block and adjustable tube.  The adjustment part cuts some of the gas.  They are only necessary when you need to LIMIT gas.  It seems you are not getting enough, so throw on a normal block and tube. i also have a haevy ejector spring, and i have a rate ruducing buffer to slow the system down. So far as I can tell, the MGI rate reducing buffer is only available for ar-15, but there is an adapter for 308.  I'd try a normal buffer just for ease of testing. And the bolt does lock back 90% of the time. This should be 100%++, anything less says that you are not getting full cycling, which means too little gas, or too much buffer/spring/etc.  getting in the way. I dont relaod and dont want to start (i dont have time to hardly shoot, much less reload and shoot); i have ran Winchester 150 gr supreme ballistic tips thru it mostly, but i tried one box of 180 gr ballistic tips, and one box of Black Hills gold 170 gr.  It is constant thru out all the different loads. Thanks for the info guys, i appreciate it Mack

I dont know what brand of Gas block you have, but here is a snip from the JP site

Gas Block Setup The main purpose of our adjustable gas block is to allow you to adjust the port pressure to the operating system, thereby fine-tuning the bolt velocity, which will result in a smoother shooting rifle especially if you already have a JP Recoil Eliminator. Additionally, the JP Gas Block is also useful in obtaining optimum port pressure on otherwise difficult to run setups, such as suppressed weapons, short-barreleled weapons, or unusual chamberings for nonstandard cartriges. Most rifles cycle faster than necessary and the resulting “bolt slamming” effect is a noticeable part of the recoil impulse. To adjust for your load, turn the gas adjustment screw in all the way to close it off. Then, back it out about two full turns, and load one round in the magazine and fire. If the bolt holds open, the gas block is set. If the bolt does not stay open, it is short-stroking and the valve should be opened about another half turn. Continue backing the gas adjustment screw out until the bolt holds open consistently on last round lock back. Test this again with one round in the magazine. Remember, if you change ammo, the rifle may not cycle reliably and should be tested again with any ammunition that you intend to use in actual competition. If you must use untried ammo, back out the valve several turns to ensure full cycling. You may want to Loctite the valve screw. It is also possible to shut the valve completely if you want to cycle the rifle manually for any reason. If your rifle is used for law enforcement or military purposes, we recommend the full open setting so as not to compromise reliability. A new rifle or bolt assembly will have a great deal of friction between the gas rings and carrier and may require a break-in period during which the gas block must be run wide open for complete cycle. As the path through our gas block is a bit longer than a standard front sight manifold, it is a bit less efficient initially, and a new rifle with an extremely stiff bolt may not cycle completely until broken in. It helps to polish the bore of the carrier on a new bolt to reduce friction and mate the parts.

Trust me guys, I know this upper inside and out

Even spoken at length with Randall about it.  By all appearances it is OVERgassed, not undergassed.  The port was sized for .308 and with the higher pressure and larger gas volume of the 300 WSM, it is getting too much oomph.

I have fired 180 BT without issue, but have seen it do the intermittent thing.  We tried just the adjustable gas tube, but it had no effect.  Just the adjustable gas block had no effect so we left them in combined.  Added the MGI RR buffer with 308 kit to make it work.  Still no joy.  Lapped the key into the carrier as we originally thought it was undergassed as well.  Chrome carrier.  Ejection port is enlarged for the larger round.

EVERY possible combination has been tried, Mack has been patient (like angelic) and worked with us, but he is at the end of his rope.  The upper will likely SING in the hands of a handloader who finds the right load for it.  Mack just wants a reliable rig and we have tried everything possible.

sounds like a upper i need to spend some time with on the bench

has this upper seen any handloads at all or just factory rounds ?

TS2

Quoted: sounds like a upper i need to spend some time with on the bench has this upper seen any handloads at all or just factory rounds ? TS2

At the shop only factory loads and from what Mack told me, only factory loads as well.