Noticed that the AR10 bolt will re-headspace a cartridge.

[2aBaC̶a̶]

Foooook is that a light primer strike?

Just think, that headspace change happens every time the gun cycles. Wonder if with light neck tension does the bullet move in the case.

 

[little_scrapper]

Foooook is that a light primer strike?

Just think, that happens every time the gun cycles. Wonder if with light neck tension does the bullet move in the case.

Yes it does. I have seen pics of a police officer who had been chambering and unchambering the same round every day as they have to unload at end of shift. The bullet actually worked its way BACK into the case and released the powder all over his action. At least that what the thing said happened.

 

[little_scrapper]

I wonder if this was a "built" AR10 ?

Scrappy, who's your barrel manufacturer? This a factory gun or did you put it together?

Maybe he's mixing Armalite and DPMS components? Using a DPMS carrier with an Armalite extension or something ?

Someone way back said that I said I had a problem. Not true I never said I had a problem. I just had a realization and tried to prove it. Then asked about it.

It is 100% LaRue. NO DPMS lower either. Its supposed to be a M110 lower. Not sure if that makes you feel any better or not. LOL hehehe

How would I tell if it was mixed parts. I mean any knuckle head could get the wrong parts together and how would I know? What would I look for to prove or disprove a set of wrongly mixed parts? I can measure and photo anything. School me if there are doubts. I may be ignorant but I am one smart MFer. I figure sh|t out. That's literally what I do for a living. Build shit that hasnt been built before and I have to figure out how to do it. That's what I do!

Hell at work not only do we have access to Xray that can look right through many many inches of hardened steel we have a CT scanner to!

Ohh yea, this is a home built UU Kit from LaRue. I am confidant that it is assembled correctly and I have all my tools verified in the cal lab at work. I am extremely confidant that everything is torqued to proper spec. Seeing as I have a couple fire formed cartridges that measure 1.629"; I assume my chamber is AT LEAST 1.630".

Again I never said I had a problem. Just talking about what I saw and was looking to see what the community thought. I understand lot of folks just naturally go into diagnostic mode.

 

[maggitas]

out of curiosity if you reinsert a case that has already been pushed back by the force of closing the bolt does it keep reducing the headspace? If not you may want to load your rounds to that headspace.

 

[little_scrapper]

out of curiosity if you reinsert a case that has already been pushed back by the force of closing the bolt does it keep reducing the headspace? If not you may want to load your rounds to that headspace.

OMG I already opened a can of worms with my observation. Can you imaging the exploding heads if I told them subsequent chamberings reduced the shoulder even more! LOL

I would bet to a certain level it does. But I am not touching that one. You go right ahead. LOL

 

[LawnMM]

It's not likely with a factory gun. How certain are you the bullet isn't making contact with anything on the inside of that comparitor?

I have the same gauge for bullets, but use a Sinclair bump gauge for shoulder measurements.

One possibility would be the bullet making contact, if it were loaded long, and being seated further into the case by the rifling. Then measuring shorter in the comparitor. I'd think the comparitor would have to be making contact with the bullet in the comparitor though.

Easy enough to check, take a fired case and measure at the datum line, measure again after resizing, then seat a bullet with no powder and see what that tells you.

Ideally, we'll see a difference between the pre/post sizing measurements, and not after adding the bullet.

While you're at it, measure base to ogive before and after chambering and see if the rifling is interacting with the bullet at all. You could also examine a bullet after chambering and see if it's marked up at all on the jacket. It will look like straight lines on the jacket around the ogive.

 

[LawnMM]

Wonder if with light neck tension does the bullet move in the case.

It'll move out with insufficient tension, I've checked my rounds with .002" tension and they don't move, unless you're doing super light I wouldn't worry about it.

I would bet to a certain level it does. But I am not touching that one. You go right ahead.

Unless your chamber is shrinking that isn't possible. Who makes the caliper? Do you have one that isn't digital?

 

[newguy2k3v2]

I found a bag of brass I had sized for a different rifle and my 6.5 creedmoor mws. It's a Noveske barrel so not the typical LMT. Measured a few pieces with the .375 insert and got measurements of 1.551-553". Insert them partially into the chamber, let the bcg go about 1" forward from the bolt catch and it gives me consistent measurements of 1.549" on ejected brass. No sticky extraction either which is a surprise.

It is possible

 

[2aBaC̶a̶]

I'm starting to load precisiin rounds for a 6.5 semi. I'll have to keep an eye on this.

I'm tuning the system to be gentile on brass.

 

[little_scrapper]

OMG I already opened a can of worms with my observation. Can you imaging the exploding heads if I told them subsequent chamberings reduced the shoulder even more! LOL

I would bet to a certain level it does. But I am not touching that one. You go right ahead. LOL

It's not likely with a factory gun. How certain are you the bullet isn't making contact with anything on the inside of that comparitor?


One possibility would be the bullet making contact, if it were loaded long, and being seated further into the case by the rifling. Then measuring shorter in the comparitor. I'd think the comparitor would have to be making contact with the bullet in the comparitor though.

Easy enough to check, take a fired case and measure at the datum line, measure again after resizing, then seat a bullet with no powder and see what that tells you.

Ideally, we'll see a difference between the pre/post sizing measurements, and not after adding the bullet.

While you're at it, measure base to ogive before and after chambering and see if the rifling is interacting with the bullet at all. You could also examine a bullet after chambering and see if it's marked up at all on the jacket. It will look like straight lines on the jacket around the ogive.

@Lawn Because the comparater is made long for those bullets to NOT hit.

Correct. Measurement off the case shoulder at the 400 datum line is completely independent of the bullet.

Not adding any bullets. These are factory Lake City M118LR rounds.

I will measure the base to Shoulder, Base to Ogive and OAL. Before and after chambering. However, Im out of my shop right now. I may do it later tonight or if not will do it tomorrow. But I will report back maybe another video showing all.

 

[little_scrapper]

How do i turn the video 90 degrees? NM Ill figure it out in short order.

EDIT: Ifgured it out. Rotated and re-uploaded to the tube.

 

[LawnMM]

Don't worry about it, we could see it. So clarify...

You're getting this setback on EVERY chambering regardless if first firing out of the box from lake city OR after resizing and reloading the rounds yourself? Or you've only tried it on the factory rounds?

If it's only factory ammo it could just be a short chamber. If it happens on factory ammo, and you're resizing those fired cases and loading them and it happens again something else is up.

 

[little_scrapper]

Tried it on Factory M118LR and Fire Formed M118LR. Have not tried it on resized, shoulder bumped M118LR. Seeing as Bumped shoulders are longer than factory and shorter then fire formed M118LR brass I will assume they will also change.

Factory M118LR = 1.621
Fireformed M118LR = 1.626
Bumped M118LR = 1.623

Again I have a couple that came out fireformed at 1.629" so chamber has got to be 1.630 at minimum. Ans If I recall correctly that is the SAMMI minimum. So doesnt appear to be a short chamber or anything like that. I think its just what happens and people dont realize it because who the hell would check that except a guy like me who does ship like this for a living????

OR? Maybe it isnt supposed to be happening and I just got a effed up kit. Let me know if this isnt supposed to happen and it indicates a fault.

However, I have been making several 1MOA groups that tend to indicate it is doing what it is supposed to be doing as long as I do what I am supposed to be doing.

 

[918v]

If you have too much clearance between the bolt and the barrel, the bolt will stop on the case and not on the barrel. Then it will rotate into battery. This is causing the change in shoulder length.

 

[little_scrapper]

So does this mean I am wrong? Have a problem? My ignorant understanding is that short cases aren't really an issue as much as too long is?

 

[LawnMM]

Tried it on Factory M118LR and Fire Formed M118LR. Have not tried it on resized, shoulder bumped M118LR. Seeing as Bumped shoulders are longer than factory and shorter then fire formed M118LR brass I will assume they will also change.

What does fire formed mean to you?

Resize a piece .003" under whatever it measures coming out of the gun and try it again.

 

[little_scrapper]

It means fired in my chamber. Look up to post #63. I list all the lengths from head to shoulder.

It ejects after being fired at 1.626 about 90%. Some are longer. I have a couple that ejected from my rifle (fire formed) at 1.629". Maybe I am not using the correct vocabulary.
?

 

[nn8734]

If you have too much clearance between the bolt and the barrel, the bolt will stop on the case and not on the barrel. Then it will rotate into battery. This is causing the change in shoulder length.

Is this a condition you can detect by very carefully chambering a round into the chamber?
Perhaps it may hang up or otherwise feel different vs a rifle with a bolt/barrel clearance within spec?

Also wondering if it can be spotted visually in some way.

 

[918v]

So does this mean I am wrong? Have a problem? My ignorant understanding is that short cases aren't really an issue as much as too long is?

Yes. But they can’t be too short either. There is a difference between Armalite and DPMS pattern bolts. Maybe you have a mismatch.

 

[918v]

Is this a condition you can detect by very carefully chambering a round into the chamber?
Perhaps it may hang up or otherwise feel different vs a rifle with a bolt/barrel clearance within spec?

Also wondering if it can be spotted visually in some way.

No. You have to pull the barrel and put it in a cradle, then insert the bolt into the extension and see.

 

[little_scrapper]

No. You have to pull the barrel and put it in a cradle, then insert the bolt into the extension and see.

And see what? how would I identify an Armalite bcg and barrel extension vs a DPMS pattern? I see lots of google hits on the subject with none telling me what specs to measure. I will keep looking.

So how do i tell the difference?

 

[918v]

See if you have too much clearance. Meaning that the bolt is rotating on the case and not against the barrel.

 

[LawnMM]

So, this only happens on a fired case that hasn't been resized?

You gave us all the impression this was happening on all your brass, new, "fire formed" and resized, you said you believe it would happen every time you did it. I asked if you resized .003 and you said yes.

Then you just now said you haven't tried it on resized brass...

You're firing factory ammo, putting a case that hasn't been resized, but has been reloaded ? back in the gun to fire again? Those are the rounds you're seeing headspace issues with?

Am I getting this right?

 

[nn8734]

See if you have too much clearance. Meaning that the bolt is rotating on the case and not against the barrel.

Sounds like addl machining will be required to correct the condition if that’s the problem unless it’s literally just an issue with a DPMS when it needs an Armalite bolt or vice versa

Saw this on AR15.com....seems to explain the chambering, barrel extension and dialing in the correct amount of clearance between bolt/barrel to spec.

How to chamber an AR barrel and fit a barrel extension - my method - AR15.COM

Firearm Discussion and Resources from AR-15, AK-47, Handguns and more! Buy, Sell, and Trade your Firearms and Gear.

www.ar15.com

 

[918v]

When I put together my Mega Maten I went with an Armalite setup and I have maybe .010” of clearance between the barrel and the bolt while locked in battery.

 

[918v]

So, this only happens on a fired case that hasn't been resized?

You gave us all the impression this was happening on all your brass, new, "fire formed" and resized, you said you believe it would happen every time you did it. I asked if you resized .003 and you said yes.

Then you just now said you haven't tried it on resized brass...

You're firing factory ammo, putting a case that hasn't been resized, but has been reloaded ? back in the gun to fire again? Those are the rounds you're seeing headspace issues with?

Am I getting this right?

In Post#20 he did it to a factory round and it changed the shoulder length.

 

[little_scrapper]

I asked if you resized .003 and you said yes.

Where did I say that? I said I did not drop bolt on cases with bumped shoulders and seeing as they are in between factory and fired cases I assumed they would also get shorter.

This whole thing started because I found a couple fired cases that were 1.629". This lead me to believe that I may be able to bump my shoulders less. in fact 90% of my cases were coming out .003 less than those two cases.

I wondered if those fired cases would fit back in the chamber as is. So i measured them. dropped a couple in the chamber without resizing and they seemed to go in just fine. I ejected them and re-measured them and noticed that they were several thou shorter at the shoulder.

The rest is history. I tried it with factory ammo and they also got shorter at the shoulder. \

Here we are now. Whats next? Some have said that I may have a mismatched bolt and/or barrel extension. you can look at the video and clearly see I have an AR10 pattern upper/lower. If someone can tell me how to measure the barrel extension and bolt to verify armalite vs DPMS I will do it.

That being said i never said i had any issue. But maybe I possibly do have a DPMS barrel extension or BCG. How would I verify because everything I ordered was AR10 pattern and NO DPMS pattern anything. So school me. what do I measure.

 

[LawnMM]

Are you FL sizing the cases, scrapper? How much are you bumping the shoulders?

I FL resize with .003" bump. Originally I was finding all my fire-formed cases coming out 1.626". Lately I am noticing more and more at 1.628 and a couple at 1.629". My factory M118LR is head spaced at about 1.621-1.623ish".

Now that I am finding cartridges around 1.629"; I am wondering if I should FL resize the 1.626's with ZERO bump? However, 90%, or more, are all coming out fire formed at 1.626". I may try a couple small batches and see how they fair for reliability. By the numbers it doesnt sound unreasonable.

So far I am limited on COAL by the magazine; which is about 2.870". Even then I may be dragging tips. with 175SMK's I need to seat head to Ogive at about 2.260". By the numbers I am jumping about .020" give or take already.

From there on we went down the rabbit hole. If cases come out at 1.629 then bumping them to 1.626 is correct.

If you don't bump the case at all, and load it up without sizing, the fit between case and chamber is going to be super tight.

It might catch on the sidewall of the chamber, might be right up against the inside of the chamber with .001 or less clearance.

There's your problem. "Fire formed" is not typically used in this context. They're just fired. They're also a cunt hair smaller than the chamber and reloading them without sizing in an auto loader is bound to cause a whole range of problems.

Not every case is the same, they also work harden and spring back less with use. That's why at first you saw 1.626 and then you're seeing some jump out after firing at 1.629.

That's assuming they were resized and reused. Factory ammo is notoriously inconsistent with these measurements to the third decimal place.

That a fired case, unsized and rechambered is acting weird is no surprise at all.

Measure ten fired cases, size to .003 below the measurement of the fired cases and you'll be fine. I'll also bet you money after you size a case bumping the shoulder back .003 from the fired measurement will solve whatever's going on with your headspace measurements. If you size a case under the fired measurement by .003 and drop the bolt the headspace won't move.

You're getting inconsistent measurements because you're measuring brass and how it's chambering without sizing the case. You're mashing something that's barely smaller than the chamber into it and while I still doubt it's bumping the shoulder it certainly explains the inconsistency of the measurements.

 

[little_scrapper]

That original statement was simply "what I do when reloading". FL resize with a .003 shoulder bump to 1.623. Those are (so far) 100% reliable in cycling.

The fact that I found a couple at 1.629" leads me to believe my chamber is 1.630" (or more).

I measure EVERY SINGLE CASE. Without exception. 90%+ come out at 1.626". Some at 1.627 and 1.628 and a couple at 1.629". Seems like you aren't really reading what I have said in several posts in this thread. I have stated this several times. Just sayin.

How do you figure I am getting inconsistent reading? I will bet you that after bumping the shoulder back .003" to 1.623" it is still LONGER than most factory M118LR which are mostly 1.621". I dont understand how you think that a case that is 2 thou longer than the factory M118LR wont get bumped when a case that is 5 thou longer does.

The shorter M118LR is getting bumped. Video proved it. The fired cases being 1.626" ARE being bumped. Not following how one would think that a case that measures in the middle of those two lengths would not get bumped?

At this point it feels like you may or may not have read what I posted but are certainly NOT actually thinking about what I am explaining.

 

[nn8734]

Where did I say that? I said I did not drop bolt on cases with bumped shoulders and seeing as they are in between factory and fired cases I assumed they would also get shorter.

This whole thing started because I found a couple fired cases that were 1.629". This lead me to believe that I may be able to bump my shoulders less. in fact 90% of my cases were coming out .003 less than those two cases.

I wondered if those fired cases would fit back in the chamber as is. So i measured them. dropped a couple in the chamber without resizing and they seemed to go in just fine. I ejected them and re-measured them and noticed that they were several thou shorter at the shoulder.

The rest is history. I tried it with factory ammo and they also got shorter at the shoulder. \

Here we are now. Whats next? Some have said that I may have a mismatched bolt and/or barrel extension. you can look at the video and clearly see I have an AR10 pattern upper/lower. If someone can tell me how to measure the barrel extension and bolt to verify armalite vs DPMS I will do it.

That being said i never said i had any issue. But maybe I possibly do have a DPMS barrel extension or BCG. How would I verify because everything I ordered was AR10 pattern and NO DPMS pattern anything. So school me. what do I measure.

I believe the gun may have an issue, given its “resizing” factory ammo where the brass is sized at the factory within SAAMI lengths for 308win. That’s clearly not normal, as you know. hence why you started the thread. You may have a short chamber but if your fired cases are measuring 1.630 or more before any re-sizing, that’s probably not the cause. It may or may not have to come apart (if 918v is right about the bolt-barrel clearance issue, it will need to).

Hope you get it figured out.

 

[little_scrapper]

I believe the gun may have an issue, given its “resizing” factory ammo where the brass is sized at the factory within SAAMI lengths for 308win. That’s clearly not normal, as you know. hence why you started the thread. You may have a short chamber but if your fired cases are measuring 1.630 or more before any re-sizing, that’s probably not the cause. It may or may not have to come apart (if 918v is right about the bolt-barrel clearance issue, it will need to).

Hope you get it figured out.

Whether its normal or an issue or not I am still wondering. Some say they thought everyone already knew this happened. Like its normal.

However, mismatched bolt vs barrel extension does ring true as something to look into. Still waiting for someone to show me armalite vs DPMS specs because hell if I can find them.

 

[whatsupdoc]

Bolt carrier velocity is around 10 MPH, so the loaded round's "shoulder" (regardless of shoulder datum to base length) is slamming into the chamber shoulder at around 10 MPH causing the brass to move. Very Plausible.

Many statements made here are just not correct.

 

[nn8734]

Still waiting for someone to show me armalite vs DPMS specs because hell if I can find them.

Feel your pain, I don’t know either. Never build my own large frame AR no have I owned any DPMS AR10. Had an Armalite Super SASS like 10 years ago, lol. It shot okay. Besides it may not even be the case of mismatched bolts/extensions, just mis machined extension or something else entirely.

That’s why I suspect it needs to come apart and be fully gone through (bolt-barrel clearance measurements, headspace gauges, visual inspection, etc).

 

[little_scrapper]

Thank you. Feels like people are just trying to convince themselves that I have a problem; and they don't even know if their hardware does it or not.

That being said I will look into the bolt vs extension specs. If I can find them I will measure and put this to bed. Hell, maybe I do have a mismatch.

That all being said, I would like to think that a company like LaRue would be able to give me the right matched set of parts. No?

 

[nn8734]

I would like to think that a company like LaRue would be able to give me the right matched set of parts. No?

Odd as it may sound, I don’t assume anything even with large companies. Manufacturing is prone to defects as you know and sometimes things slip through.

Don’t lose too much sleep over it. Call Larue tomorrow and see what they say. The may want to have you send it in for a look-see.

 

[918v]

DPMS bolt lugs are .314” thick. I can’t get to my a Armalite because the battery in my safe lock just died and I can’t find a 9 volt. Dammit

 

[918v]

OK, Armalite measures .312” so that’s not it. It’s got to be an improperly fitted barrel extension.

 

[Ravenworks]

OP
I suggest you go to Brownells or Midway and spend the $10 to buy the stuff to slug your chamber.
Read up on how simple it is.
Spend a few hours properly obtaining the dimensions of your chamber.
You could have cast the slug,measured it and had the gun back together in the time you've been fucking around here

 

[LawnMM]

How do you figure I am getting inconsistent reading? I will bet you that after bumping the shoulder back .003" to 1.623" it is still LONGER than most factory M118LR which are mostly 1.621". I dont understand how you think that a case that is 2 thou longer than the factory M118LR wont get bumped when a case that is 5 thou longer does.

Because you still don't get it. If your chamber is 1.630 (hypothetically) and your fired cases (90% by your measurements) come out at 1.626 then your chamber is at least 1.626 long, possibly 1.630.

The farther away from that chambers shoulder you get, the less chance of making contact. A case shorter than the chamber CAN'T be bumped by a chamber shoulder it never touches.

I'm not even sure why we're still discussing this. If 90% of your cases come out at 1.626 and you already bump to 1.623 with 100% reliability the discussion is over.

You want to know if it's worth not bumping 90% of cases that measure 1.626 because less than 10% come out at 1.628 and 1.629? The answer is no, it's not worth risking feeding problems with 90% of your cases to avoid overworking less than 10% by an additional .003

So 10% measure longer? Who cares? If the die is set to bump everything .003 under the 1.626" 90% of your cases measure on ejection, those 10% will get sized a little extra, and they'll all run 100% reliably in the gun.

Why risk malfunctions 90% of the time to benefit 10% of your cases?

Your chamber isn't growing longer. Perhaps the brass is springing back less, who knows. If sizing .003 under whatever the majority of ejected cases measure (1.626 right?) runs reliably why would you change anything?

 

[Mordamer]

Because you still don't get it. If your chamber is 1.630 (hypothetically) and your fired cases (90% by your measurements) come out at 1.626 then your chamber is at least 1.626 long, possibly 1.630.

The farther away from that chambers shoulder you get, the less chance of making contact. A case shorter than the chamber CAN'T be bumped by a chamber shoulder it never touches.

I'm not even sure why we're still discussing this. If 90% of your cases come out at 1.626 and you already bump to 1.623 with 100% reliability the discussion is over.

You want to know if it's worth not bumping 90% of cases that measure 1.626 because less than 10% come out at 1.628 and 1.629? The answer is no, it's not worth risking feeding problems with 90% of your cases to avoid overworking less than 10% by an additional .003

So 10% measure longer? Who cares? If the die is set to bump everything .003 under the 1.626" 90% of your cases measure on ejection, those 10% will get sized a little extra, and they'll all run 100% reliably in the gun.

Why risk malfunctions 90% of the time to benefit 10% of your cases?

Your chamber isn't growing longer. Perhaps the brass is springing back less, who knows. If sizing .003 under whatever the majority of ejected cases measure (1.626 right?) runs reliably why would you change anything?

I read through most of this thread and I believe you are wrong about something. If his chamber is 1.630" long when measured from a fired case, then that measurement is from when the bolt lugs are pushed hard against the extension lugs. When the bolt drops the bolt head can actually move all the way forward until it contacts the face of the barrel. Usually the bolt face to barrel face clearance is .010 to .015". This explains how his brass can be set back slightly by sending the bolt home. Chamber length (1.630) minus bolt face clearance (.015" for example) would be 1.615" which is in the ball park of what the OP is seeing. The bolt and buffer are like a 2 lb hammer moving pretty fast. A piece of nice soft thin brass can certainly be squashed a couple thou by that mass.

I think the OP fully proved that what he claims is actually happening.

 

[LawnMM]

I read through most of this thread and I believe you are wrong about something. If his chamber is 1.630" long when measured from a fired case, then that measurement is from when the bolt lugs are pushed hard against the extension lugs. When the bolt drops the bolt head can actually move all the way forward until it contacts the face of the barrel. Usually the bolt face to barrel face clearance is .010 to .015". This explains how his brass can be set back slightly by sending the bolt home. Chamber length (1.630) minus bolt face clearance (.015" for example) would be 1.615" which is in the ball park of what the OP is seeing. The bolt and buffer are like a 2 lb hammer moving pretty fast. A piece of nice soft thin brass can certainly be squashed a couple thou by that mass.

I think the OP fully proved that what he claims is actually happening.

Excellent point. Love the responses that provoke thought and discussion.

My issue with your suggestions is for that to work we would have to assume part of the case, .010"-.015" is unsupported by the chamber while under pressure. I'd think that would cause a rupture but perhaps I'm wrong.

Might need a few Smith's to weigh in on that. I think it's more likely the case swells and sticks as is without the rearward movement or that headspace is chambered minus that lug clearance so the case CANT slide back and allow a portion of the case to remain unsupported during ignition.

Should be testable though.

 

[little_scrapper]

I appreciate the responses guys. Especially like the last few that are discussing possibilities vs negative nancies.

One more question on the mechanics: When/how does the bolt ejector on the AR10 get over the cases ejector lip?

It looks to me that when the bolt slams the round into the chamber, the ejector is forced out and over the ejector lip. Unlike my pistol, where the ejector lip of the case rises up behind the ejector automatically.

If this is true, the AR ejector must be pushing the case hard into the shoulder of the chamber. That is until the force of the ejector spring is overcome and the ejector hook clears the case rim. I think this is Contributing to bumping shoulders if not fully causing what is happening.

Or, I have a mismatched bolt and barrel extension and have more slop in the system then I am supposed to. If thats how it works. Still cant find specs on lugs and extensions.

 

[Shoots 700's]

I don’t see how it could be bumping the shoulder. Unless you are lubing every case they would get stuck.

 

[whatsupdoc]

The measured headspace of the fired round has nothing to do with the shoulder being pushed back.

The round is stripped from the magazine and fed into the chamber by the bolt face, the round comes to a complete stop when the case shoulder meets the chamber shoulder then the extractor snaps over the the head of the case allowing the breech to lock.

If you slowly ride the charging handle forward cambering a round, the cartridge will end up fully chambered (case shoulder to chamber shoulder) but the extractor will not snap over the case head preventing the bolt from locking and setting the headspace.

 

[little_scrapper]

I don’t see how it could be bumping the shoulder. Unless you are lubing every case they would get stuck.

Did you watch the video? last post on page one.

 

[supercorndogs]

The ejector never goes into the extractor grove, or pops over the rim of the case.

 

[whatsupdoc]

The ejector never goes into the extractor grove, or pops over the rim of the case.

Correct I meant the extractor but had a brain fart and typed ejector, fixed it.

 

[918v]

I appreciate the responses guys. Especially like the last few that are discussing possibilities vs negative nancies.

One more question on the mechanics: When/how does the bolt ejector on the AR10 get over the cases ejector lip?

It looks to me that when the bolt slams the round into the chamber, the ejector is forced out and over the ejector lip. Unlike my pistol, where the ejector lip of the case rises up behind the ejector automatically.

If this is true, the AR ejector must be pushing the case hard into the shoulder of the chamber. That is until the force of the ejector spring is overcome and the ejector hook clears the case rim. I think this is Contributing to bumping shoulders if not fully causing what is happening.

Or, I have a mismatched bolt and barrel extension and have more slop in the system then I am supposed to. If thats how it works. Still cant find specs on lugs and extensions.

After measuring a DPMS and Armalite bolts, it’s not a mismatch. It’s a badly fitted barrel extension.

You said you assembled the rifle from a kit. And it’s 100% Larue. So call them and show them the video. You’ll prolly get a new barrel and bolt.

 

[supercorndogs]

I don’t see how it could be bumping the shoulder. Unless you are lubing every case they would get stuck.

Its not the shoulder that gets stuck in an FL die, its the body.

 

[Tictac]

There is no chance a proud primer is being re-seated?