AR weird problem - sheared extractor pin

[KCJones]

So I went out again with the AR, still no heavier buffer or anything (vendor in question chastised in another thread)...

After a good cleaning, using brass, what I found is it will still malfunction on the first couple rounds in a full 30-rd magazine, presumably because the most spring tension?

It's ejecting fine, but on those first couple rounds, it fails to chamber the new round properly. If I look at the rounds, they have two distinct grooves along the top - at least I think it's the top, and the bullet is bent upward in that same direction. Pictures below.

The ejected casings show no unusual markings.

Still suspect the bolt is simply 'returning' too quickly and hoping heavier buffer helps. But open to ideas/suggestions.

IMG_20170308_090504018.jpgIMG_20170308_090539845.jpg

[danhr]

When you insert a full magazine...... Do you do it with the bolt closed?

[Gunsnwater]

Round hoped forward and caught on barrel extension and bolt lugs bent round.

[Gunsnwater]

Ejection clock: My built AR has a Wilson barrel that checks out as 1:8.5" (yes...8-1/2"...measured a dozen times) had a PITA characteristic of denting the brass as it bounced from the angled block * (can't think of the nomenclature) behind the ejection port. Since I reload, I tried a preventive measure. I glued a piece of inner tube rubber on that block. It totally stopped the denting and send the brass out to 1:30-2 o'clock. I don't remember where it went before the rubber was installed.

My Spikes Tactical is a 1:7, throws at appx 4:30 o'clock.

I mention the differences in twists to suggest: Wouldn't a faster twist create a heavier recoil than a slower one?

* Brass Deflector

Twist rate has zero influence over mass times speed. Feel is influenced by time of impulse, ie bolt vs auto and mass of the equal opposite half ie 6 pound gun vs 8.

[Hawk]

Pretty sure those marks are created by the lugs on the bolt and the bending is caused by the bolt closing on the un-chambered round. I also question as to if the full mag was inserted with the bolt closed? If so, then the mag was not seated which could cause the round to be stripped by side pressure on the case and not stripped via the bolt contacting the base of the round.

1. Load the mag to capacity and inset it with the bolt back. Drop the bolt and see if it properly strips and feeds the rounds.
2. Try other mag's
3. Try loading the 30 round mag to 28-29 rounds and test again.

I assume this is not a AR pistol? or an unusual barrel length or gas system? If not, then I don't think a heavier buffer will help with anything.

BTW, has this rifle run flawlessly up until the pin broke?

If you slowly manually ride the bolt closed (without a mag), does it fully close on it's own?
If you slowly pull back on the charging handle all the way, do you fell any resistance other than the buffer spring? You may feel a little caused by the hammer dragging on the bolt.

[KCJones]

Pretty sure those marks are created by the lugs on the bolt and the bending is caused by the bolt closing on the un-chambered round. I also question as to if the full mag was inserted with the bolt closed? If so, then the mag was not seated which could cause the round to be stripped by side pressure on the case and not stripped via the bolt contacting the base of the round.

1. Load the mag to capacity and inset it with the bolt back. Drop the bolt and see if it properly strips and feeds the rounds.
2. Try other mag's
3. Try loading the 30 round mag to 28-29 rounds and test again.

I assume this is not a AR pistol? or an unusual barrel length or gas system? If not, then I don't think a heavier buffer will help with anything.

BTW, has this rifle run flawlessly up until the pin broke?

If you slowly manually ride the bolt closed (without a mag), does it fully close on it's own?
If you slowly pull back on the charging handle all the way, do you fell any resistance other than the buffer spring? You may feel a little caused by the hammer dragging on the bolt.

-Mags were loaded with bolt open, as is always my habit.
-Yes, I had two mags of the same make/model that day. Will test with others I have, just hadn't brought
-I did in fact, load them to 28 and no problem
-Yes, the bolt fully closes if ridden in manually
-No, the gun was not working ideally before the pin broke - at least in the sense it was ejecting around 1:00 and -occasionally if I had let it get pretty dirty - would stovepipe the outgoing casing (like 1/100 when dirty)
-It's not a pistol or unusual length barrel. But it is a "home build" with different lower & upper and god only knows what gas-block wise.
-I don't think I'm feeling any unusual drag pulling the charging handle, but will have to go do it with more attention to be sure
-I've already ordered the heavier buffer (arriving tonight in fact), so might as well at least try that first.

Thanks for all the feedback & ?'s

KC

PS - The truth is before having problems I wasn't being all that 'observant' of things... e.g. did one magazine brand vs. the other have the 'issues' etc. It was just 1/100 stovepipes when dirty (which means maybe 1/500 overall) and I just said "oh well"... Just saying "pre problems" I may not have robust answers about too much.

[Bang]

Try putting a witness on the cartridges using a Sharpie, and loading them witness at 12 o'clock. Then the marks made in the brass can be related to whatever causes them. Some magazines are poorly designed. You may have a couple. I have a variety. Some followers are really lame, some are like an elevator on tracks. If a mag binds cartridge # 29 and #30 I would either mark it 28 MAX or cut a coil off.

To evaluate the BCG by slow manipulation, replace the buffer spring with a light "test" spring. That will help with the feel for what's going on.

Also, try lubricating per military manual. Some call it running it wet.

[KCJones]

Try putting a witness on the cartridges using a Sharpie, and loading them witness at 12 o'clock. Then the marks made in the brass can be related to whatever causes them. Some magazines are poorly designed. You may have a couple. I have a variety. Some followers are really lame, some are like an elevator on tracks. If a mag binds cartridge # 29 and #30 I would either mark it 28 MAX or cut a coil off.

To evaluate the BCG by slow manipulation, replace the buffer spring with a light "test" spring. That will help with the feel for what's going on.

Also, try lubricating per military manual. Some call it running it wet.

Thanks, Bang. Good idea re: the sharpie. Will try that and also (if I can nail it down to that) cut some coils springs off "over eager" mags.

I tend to run pretty "damp", but maybe next go-round will try getting truly sodden... Maybe soak down all the internals in Ballistol AND put gun oil on all the 'moving/contact' parts too.

But do have to be a bit careful not to adjust too many variables at once, lest I not know what 'fixed' it. Would stink to soak it down, mess with magazines, add a heavier damper, etc. then wonder which one made it 'work right' and have to start working backward.

We'll get there one way or another, eventually. Given it's a $500 homebrew AR, I should probably just go buy a better/already-working-right one. But some have said I'm a bit stubborn...

KC

[Bang]

Do you belong to AR15.com or any of those AR-related sites? Can be helpful. Agree one change per session. Good plan.

BTW, when I was on the range Monday there were two guys with ARs who departed soon after my arrival. One of them did not pick up the once-fired brass that deposited in the grass at about 1:30-2 o'clock. Don't know what brand AR did it. Just sayin. (And I was happy to score good fresh brass.).

Oh, and I had a fail to fire. Well-hit CCI #41 primer. Looked just like every other struck #41 that fired. Second strike didn't set it off. Unusual to have a primer fail. But it happens.

[Hawk]

So, if the bolt is locked back, and you insert and seat a fully loaded mag, and drop the bolt, the 1st two rounds will look like the ones in your picture and the rest of the rounds feed fine?
If you manually ride the bolt closed on a full mag, do the first two rounds feed correctly?
What mag's are you using? Do you have any good old mil spec steel 30 rounder's you can try?

Try this:
Load up a full mag and insert it with the bolt open. Manually hold the bolt back with the charging handle and press the bolt release. Let the bolt come forward slowly, just enough to make contact with the first round. Take a close look at where the bolt touches the base of the first round. One of the bottom bolt lugs should be contacting the base of the round along the entire face of the lug. See pic below.

images (1).jpg

This is how it should look.