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Discussion Starter #1
Ok guys I put together a lightweight PSA carbine to run my D740 NV scope on a couple of years ago. From day 1 I was having issues with it running. It would stove pipe, and not fully extract the spent case. I had another proven upper and lower receiver so I swapped parts around until I came to the conclusion that it had to be the BCG. I talked with PSA and they sent me another BCG. well it did the same types of things, it would bind up as it was trying to chamber a round. So they sent me another BCG. I test fired it a few rounds and it seemed to run. But I had kept the proven BCG in the rifle with the NV and it has been running flawlessly. Well today I go to test fire some handloads in both rifles and low and behold the PSA BCG they sent me starts short stroking in a completely proven Bison upper and a proven lower that I assembled. it will fire the chambered round then not feed another round into the chamber. it will also not lock back on an empty mag. When I put the proven (I think white oak) BCG both rifles run flawlessly with the handloads and various factory loads. Its just the PSA BCG that seems to be having issues. The PSA is coated (can't remember what the coating is, but it is a brushed silver looking coating) and the proven one is not coated (just standard black BCG). I'm almost positive it's not a gas issue because both rifles run fine with the proven BCG and the other BCGs from PSA have all acted differently. I just don't get why all 3 of the PSA BCGs would give problems. I have built probably a dozen other PSA builds in 556 and never had any issues with any of them.

Now let me say that PSA has treated me very well each and every time, they say no problem, send it in and we will get a new one out to you, and have always had a new BCG arrive in a few days. I am just saying that I am getting frustrated with it and want it fixed to run reliably. The carrier key seems tight and everything seems to be ok to the naked eye. what should I try to see if I can make this bolt run without sending it back in?

thanks
 

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If it is short stroking the only thing I could think of with the BCG that would cause it is broken or missing gas rings. Unless of course there is something binding in the receiver.
 

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If it is short stroking the only thing I could think of with the BCG that would cause it is broken or missing gas rings. Unless of course there is something binding in the receiver.
or something with the gas key/staking/sealing....what are you swaping, the carrier only, the bolt only, or the whole BCG?
 

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Discussion Starter #4 (Edited)
I took the bolt out of both carriers and both seemed to have the same pressure by the gas rings, and both sets of gas rings measured the same OD. So i switched the proven bolt into the PSA carrier and the PSA bolt into the proven carrier.

The PSA carrier and proven bolt was short stroking from the get go and the proven carrier with the PSA bolt ran perfect for 10 or so rounds fired rapidly.

So I'm guessing something on the PSA carrier is dragging/binding in the upper?? Or it could be something still with the gas key.
 

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I took the bolt out of both carriers and both seemed to have the same pressure by the gas rings, and both sets of gas rings measured the same OD. So i switched the proven bolt into the PSA carrier and the PSA bolt into the proven carrier.

The PSA carrier and proven bolt was short stroking from the get go and the proven carrier with the PSA bolt ran perfect for 10 or so rounds fired rapidly.

So I'm guessing something on the PSA carrier is dragging/binding in the upper??
check the gas key to make sure it is tight and also staked properly....open the rifle and cycle the bad carrier by hand to see if its binding anywhere


I had a carrier that was nib coated that was too tight in an upper before. I took it to a buffing wheel and smoothed the outside with a little buffing compound and it worked fine after that. Just for that reason I do not like nib coated carriers anymore
 

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Discussion Starter #6
The gas key feels tight when trying to move it bare handed. The staking looks fine to me. I will try the hand cycling really slow to see if i can feel a bind or resistance.

So you just buffed the whole outside with a buffer and compound?
 

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So you just buffed the whole outside with a buffer and compound?
Look inside the upper to see of you can see any wear/rub marks.

Yes I just used a buffing wheel (open cotton type) with buffing compound...then I cleaned it and oiled it well, reinstalled, cycled by hand a while, then shot it and it seemed to work fine.

I know the NIB coating is supposed to be thin,but they do put it on over a milspec ccarrier , which adds some thickness....if you have a tight upper and "oversize" carrier (all within specs of course) it creates tolerance stacking and can cause issues

All I can say is to try it and see what happens
 

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Discussion Starter #8 (Edited)
I cleaned the whole bcg and then colored it with a sharpie and hand cycled it a dozen or so times and didn't really see any kind of obvious rub marks in the marker. And i rechecked and compared the gas key and staking to the functional bcg and it was tight and looked the same.

Is there something i am missing/not checking?

I looked inside the upper and did not see any obvious wear marks, but this bcg has probably not been fired more than 50 or so shots, and when hand cycling i don't notice any really obvious resistance
 

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Compare the machining on the undersides of the two carriers you have. Compare the good one to the bad one I think I remember someone having an issue where the slope on the bottom of the carrier was more abrupt on the one he had and did not have a nice slope or it may have been a shelf and a slope and it was slowing down the carrier when it was cycling back. I can't think of where I saw it or I would link to the thread so you could see what I was talking about.
 

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Compare the machining on the undersides of the two carriers you have. Compare the good one to the bad one I think I remember someone having an issue where the slope on the bottom of the carrier was more abrupt on the one he had and did not have a nice slope or it may have been a shelf and a slope and it was slowing down the carrier when it was cycling back. I can't think of where I saw it or I would link to the thread so you could see what I was talking about.
You talking about buddy's? Posted this pic in post #12 of his thread.



http://68forums.com/forums/showthread.php?57492-full-auto-bcg/page2&highlight=spec
 

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Chances of 3 BCGs all having the same issue are slim to none. I would be looking somewhere else.
 

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All of the BCGs with issues come from one source so if the BCG supplier to that vendor messed up then it is possible that they could all be messed up. Not saying that is the issue but something is not right with the BCGs. I just happened to remember that and if the issue moves with them then why not eliminate it as a potential cause.
 

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A agree but why do both rifles run fine with one bcg and neither run with the others?

I am not so sure now that the difference in angle on the bottom of my bcg was the cause of my problems. I thought it was slightly hanging up on the hammer but when I dry fired and then worked the bcg I did not notice the obvious bump, there was at that point no obvious difference in the way it felt when I hand cycled it. However, the psa bcg was the problem. I replaced it with a new complete bcg from ironworks tactical and it has been running good ever since. At the time they were on sale and they might still be.
 

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It just seems like with as many PSA rifles, uppers and bcgs I sell a year, if there was a run of bad ones I would have known about it. Maybe not. Just seems odd to me.
 

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It just seems like with as many PSA rifles, uppers and bcgs I sell a year, if there was a run of bad ones I would have known about it. Maybe not. Just seems odd to me.

I wouldn't bet the farm on it but it did seem to do the trick. If it makes a difference I have had this bcg for at least a year. I purchased it as a complete bcg with 6120 (I think that was the number) 5.56 bolt. If I get time, and I probably won't, I will try the psa bcg again one of these days and see how it does. Now that it has more rounds through it maybe it will function better.
 

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I'm not saying it isn't possible or even likely that you could get an out of spec bolt carrier. Just saying to get three in a row seems awfully unlikely.
 

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How about the cam pin and cam slot? If they are a little funky or slightly out of spec, it could slow the bolt down. Maybe try swapping bolts between carriers, then cam pins, etc to see if any one of those things makes the other known good unit not function or vice versa.


-Alexander
 
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