Hi, I am new to this site and need help.

I purchased a new Bushmaster Predator .223/5.56 a few weeks ago. Last week I bought a new Olympic 6.8 upper. It's a 20" SS barrel 1/10 twist SPC II chamber. Everything fit well and on the first day at the range, I experienced a double fire. It double fired 3 more times, each after 4 or 5 single rounds. I am firing Rimington 6.8 115 gr SPC ammo. It also happened with Hornady 110 gr.

I am wondering if the buffer and spring is the problem. I did replace the fixed stock with a Magpul collapsible stock (my gum shop order the parts - spring, buffer, etc.) I have not had any other problems with the Predator other than a few jams using the 223/5.56 lower ( I assume that the Winchester 5.56 ammo or the mag. is that problem)

I replaced the original fixed stock and fire about 20 more 6.8 round and did not experience any double fire or other malfunctions. However, I am still leery and don't know if this could happen again. ANY IDEAS

What is the fix to be able to use the Magpul stock if this is indeed the problem.

Has the worst reputation out there

^Thanks for clearing that up....

The only doubling problems I have encountered stemmed from a bad trigger polish job. And that was releasing the hammer when slowly letting off the trigger after the previous shot. Not sure the receiver extension has any relation to trigger problems but who knows.

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I did not mention that using the .223/5.56 bushmaster lower, I have not had any firing issues.

Well, welcome.
Anything else you may have left out ?
Send the Oly back.  Far from the best but not the worst.That belongs to vulcan

SIG is right. Never rule out "chicken finger"

I can only imagine a disconnector, stuck firing pin or broken/trigger hammer pin problem. Most likely it is in the FCG. Does the firing pin move freely through the bolt and carrier?

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I agree with you on the Oly. But I wonted a 20" SS barrel and Bushmaster did not offer one in 6.8. Also for what it's worth, I got this upper at the right price.( Maybe) Even if I need to send it back for repairs. My problem is, sense it's different manufactures and I don't won't to get into the "he said, she said". Right now I don't know if it's a upper or lower problem. Or the thorough cleaning solved the problem.

As for as the firing pin sticking, I never thought of that. Like I said it did not double fire the last time I was at the range. However, I really cleaned it well before I went.

Does any one think the buffer and spring could be the problem? If not, I would like to put the Magpul collapsable stock back on. Maybe I should leave it along for a few more trips to the range. I don't think I will load more that 4 or 5 rounds in my mag at a time.

As for any thing else that I did not mention. Other than in the .223/5.56 mode it occusionally jams by trying to load two rounds at the same time. I think that's the Winchester 5.56 ammo or the mag. However, I changed to a .223 ammo and so far have not had a problem. Other than that the AR is sweet.

The buffer and spring should not affect doubling.

Are you sure you aren't just bump firing it?
With the extra 6.8 recoil and the Predator 3 1/2 lb trigger pull?

Your doubling problem does not lie in the upper although the extra recoil of the 6.8 may make the problem more likely to happen.  It's a Fire Control Group (your lower) problem and/or possibly the FCG operator.(you)  Try following through on your trigger pull.  And try another trigger group if you can.

ETA Oh and IBT atf is gonna bust down your door for owning an automatic weapon crowd.

You said your lower was bought new, a complete bushmaster. I would suspect that is not the problem. I would bet that you are not used to the increased recoil of the 6.8 upper and you may be bumpfiring the thing. One way to eliminate that is to let someone else shoot your setup.

Thanks all. Good info

Do you know how to do a function check? Do one in slow motion on the trigger release step. After a few dozen tries can you get the hammer to fall while releasing the trigger? If you can then you have a bad trigger-hammer interface.

Also, try swapping the bolt carriers between uppers, changing the bolts of course. The 6.8 and 5.56 rifles use the same bolt carrier, maybe there is an issue with the olympic carrier?

That rifle comes with the Bushy 2 stage trigger.

I'm also thinking that it is trigger follow through and recoil since it works fine with the 5.56 upper.





Good Luck
Bill