AR-15 Piston upper-bolt does not lock back on last round

[mikeinla]

I am using a Ferfrans gas piston upper and the bolt will not lock back on the LAST round. The rifles cycles the next round but it just does not lock the bolt back on the last round. I have tried .223 PMC gold, Hornady and a few other rounds and it still does not lock back. I have tried two different complete lowers with no help. Does a piston upper need a different buffer or buffer spring????

link to my upper....http://www.armsunlimited.com/FERFRAN...oar-p-14.5.htm

spring and buffer I am using.....

[damndave]

Just a few basic questions.

Does it lock back when you insert an empty mag and pull the CH all the way back?
Have you tried different mags?
Do you have an adjustable gas block?

[HappyCamper781]

What mags do you use?

Have you tried other brands of mags?

[mikeinla]

[QUOTE=AlliedArmory;11540810]Just a few basic questions.

Does it lock back when you insert an empty mag and pull the CH all the way back? Yes
Have you tried different mags? Yes
Do you have an adjustable gas block? Pistons do not have an adjustable gas block. The Ferfrans has 4 different settings.
9:00 o'clock position to disassemble
12:00 o'clock normal shooting
1:00 o'clock suppressed
3:00 o'clock single shot

I was shooting at 12:00 position

[mikeinla]

What mags do you use?

Have you tried other brands of mags?

20 and 30 round Magpul mags. Gen 2 and Gen 3 mags.

[mn82388]

I had the same problem I was using magpul mags but once i broke it in it was fine

[mikeinla]

I had the same problem I was using magpul mags but once i broke it in it was fine

100 rounds through it and it still does not lock the bolt back on the last round.

I cleaned upper last night and I tried running it REALLY wet today with no change.

[MrPlink]

So the gas block isn't adjustable but it has two settings, got it! I dont think I would have learned that if you didn't use large bold text.

[mikeinla]

So the gas block isn't adjustable but it has two settings, got it! I dont think I would have learned that if you didn't use large bold text.

The large TYPE was to be able to separate it from his questions.
It is NOT an adjustable gas block.

Thanks for your insightful post!!! I really learned a lot from it


Ps. it has 4 settings, got it?
None of which lock the bolt back.

[Merc1138]

The large TYPE was to be able to separate it from his questions.
It is NOT an adjustable gas block.

Thanks for your insightful post!!! I really learned a lot from it


Ps. it has 4 settings, got it?
None of which lock the bolt back.

So your gas block, that is not adjustable... has settings to adjust it's operation.

Riiiiight...

So what's that adjustment knob on the front of the gas block for again? Also since you know so much about the adjustments that your gas block supports, what buffer tube are you using(since I'm not seeing this listed anywhere).

[mikeinla]

So your gas block, that is not adjustable... has settings to adjust it's operation.

Riiiiight...

So what's that adjustment knob on the front of the gas block for again? Also since you know so much about the adjustments that your gas block supports, what buffer tube are you using(since I'm not seeing this listed anywhere).

a PISTON upper does not have an adjustable gas block like a DI upper does. A DI gas block can be adjusted for each load you are using. A PISTON upper has ONE setting to shoot at UNLESS you are using a suppressor or want to shoot SINGLE shot.
I posted a picture of the spring and buffer next to a tape measure. So you must realize that that spring and buffer will not function in a positional Buffer tube for an adjustable stock??
here is the one on it...

http://www.brownells.com/rifle-parts/stock-forend-parts/buffer-tube-parts/buffer-tubes/receiver-extension-tube-prod24086.aspx

[PHOSCHEKER]

Im not trying to hijack this thread, but I am having the same problem as the OP with a DI. Wont lock back on last round, gen 1 and 2 pmags, 62 grain green tips 5.56. doesent matter how clean or wet it is. Must be the buffer spring?

[HappyCamper781]

Yeah, the buffer isn't letting bolt cycle far enough back to lock is all I can think of. Try a different weight buffer? More compressable spring? Different gas block setting?

[Merc1138]

a PISTON upper does not have an adjustable gas block like a DI upper does. A DI gas block can be adjusted for each load you are using. A PISTON upper has ONE setting to shoot at UNLESS you are using a suppressor or want to shoot SINGLE shot.

So basically what you're saying is, that your gas block is adjustable.

I posted a picture of the spring and buffer next to a tape measure.

Yes.

So you must realize that that spring and buffer will not function in a positional Buffer tube for an adjustable stock??
here is the one on it...
http://www.brownells.com/rifle-parts...prod24086.aspx

Well it's not like we could be sure whether or not you knew that since you're telling us that your adjustable gas block isn't adjustable.

[MrPlink]

I really dont think you understand how your firearm works if you think that isn't an adjustable gas block.