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

[little_scrapper]

I loaded a couple cases that were fire formed to 1.626". After I dropped the bolt from locked back position; I re-measured the headspace on the cartridges. First one measured 1.623" & the second measured 1.618".

What do you all think of that re-headspacing on bolt drop.

 

[LawnMM]

 

[LawnMM]

Okay, nobody else is taking this so I'll throw you a bone, here goes: I don't know why you're getting those measurements, but what you're describing is impossible.

Let's pretend your chamber measures 1.630. Your fireformed cases measure 1.626. Why? Because brass springs back. If it had dimensions equal to your chamber you wouldn't be able to extract the case.

If you are bumping the shoulders back, and you should be doing .003 or .004 on a gas gun, you're literally moving the shoulder back towards the base of the case.

Following so far? If the shoulder doesn't even make contact with the shoulder area of the chamber, because it's .004 smaller in our example, your chamber can't bump the shoulder, can it?

A sizing die is a hunk of steel with a chamber cut in it with a reamer just like how a barrel is chambered.

If you aren't resizing the cases, and you're attempting to *just* necksize and load the case again I'll concede the case may be getting shoved around by the gun, but frankly I don't think the leverage is there with a simple buffer spring to do it.

So in summary: no idea what's going on with your measurements unless you aren't full length sizing the case.

If you aren't, start, especially with a gas gun. Heard of a small base die? It sizes even more of the case to minimum dimensions than regular dies.

It usually comes up in gas gun discussions because, frankly, they can be picky about feeding.

 

[2aBaC̶a̶]

 

[LawnMM]

 

[Ryridesmotox]

One time I got my brass mixed up and was pulling from my bolt action pile. Loaded it in my ar mag, pulled that charging handle back, let it go and literally nothing happened. Wouldn't chamber. The springs aren't stiff enough to re-headspace a cartridge, at least in my experience. I worked the action a few more times before I realized what I had done. They all had some scuffs on the shoulder but the brass didnt move around much at all.

I normally FL size, but I was messing around with my loading process on my bolt action at the time and was just neck sizing. So it was over spec by quite a bit. I normally FL size.

 

[little_scrapper]

Hey, I'm just saying, the though occurred to me "I wonder if the bolt drop would slam the case and change the measurement". So I tried it on two cases. Both cases measured 1.626 when I started and after dropping the bolt on them, the headspace measured .003" & .008" shorter respectively.

That just happened! Regardless whether you think it could or would; it did. I was just asking what y'all thought of that. Not trying stir a pot or anything and I am certainly NOT trying to headspace rounds with a bolt. that's LOL.

 

[1911hombre]

This is a common phenomenon that I thought more people knew about. Try it a home, kiddies.
On edit: I missread OP and thought he was talking about cartridge OAL. Which can and will change after racking a slide on a semi-auto pistol or sending a bolt home from lock on a gas gun.

 

[LawnMM]

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

 

[little_scrapper]

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.

 

[LawnMM]

If you measure fired cases at 1.626" you should be bumping to 1.623"

Your cases will not come out larger than the chamber. Your chamber ain't 1.621"-1.623"

 

[918v]

Could be his AR is overgassed and is stretching the brass, so that will throw the measurements off. I always check my AR chamber by incrementally sizing a case and trying to close the bolt on it with the upper off the lower. I never trust fired AR brass for headspace measurement.

 

[LawnMM]

Not being argumentative, but I don't see how too much gas is going to stretch his case.

The case takes, what? 30k-50k psi to expand against the chamber wall? Then springs back before extraction.

If he's overgassed it might be unlocking early, in which case it'll tear up his casehead, and eject a lot farther than necessary, but that'd be about it.

If he's overworking his brass it might be springing back to dimensions smaller than intended. That's an issue with how his dies are set up.

I don't think the little bit of gas necessary to drive the buffer and carrier rearward is going to be sufficient to stretch the case before it springs back enough to eject.

If it were unlocking that early I think his headstamps would look like cottage cheese from the ejector and he'd get cycling errors where the bolt would either fail to cycle or break the extractor claw from trying to extract a case still stuck to the chamber wall.

I suppose anything's possible, but given his answers here and explanation of what's going on, not to mention he's got another thread where he broke an RCBS Supreme press, I think there's a simpler explanation.

 

[whatsupdoc]

@little_scrapper

What does a fired case with the primer removed measure?

 

[little_scrapper]

If you measure fired cases at 1.626" you should be bumping to 1.623"

Your cases will not come out larger than the chamber. Your chamber ain't 1.621"-1.623"

That is what I do bump head-space to. Exactly 1.623" with perfect reliably. No of course chamber is not 1.621; that is what the Factor M118LR straight outta LC are head-spaced at.

Could be his AR is overgassed and is stretching the brass, so that will throw the measurements off. I always check my AR chamber by incrementally sizing a case and trying to close the bolt on it with the upper off the lower. I never trust fired AR brass for headspace measurement.

I have been thinking about trying this incremental brass just to find out I assume my chamber is more like 1.630ish and I dont think its overgassed. The lightest loads have had intermittent failure to fully cycle. I ran some 125gr that werent going overly fast and had several that failed to strip out of the mag. The video looked like bolt didnt fully cycle rearward. ie under gassed on those light loads. However, gun was new at the time and maybe not as smooth as a well worked and oiled machine. Just a theory.

The Chucker breaking is a completely separate issue. Not relevant to this thread. I think some are looking for a problem that doesn't exist, and I never said a problem existed because of the bolt slamming the brass. I just never thought about it before, and when I did think about it, I tested it to prove or disprove a theory. It made sense that a bolt slamming home on a round would stuff it a bit, and turns out it does. Also, it appears most people already know this but I did not. Now I do.

 

[little_scrapper]

@little_scrapper

What does a fired case with the primer removed measure?

90%+ measure 1.626". Some longer with a total sample of 2x measuring 1.629". That leads me to believe my chamber must be more like 1.630".

BTW' I'm not lost. I am just inexperienced having only been reloading for 6 months or so. I believe I have a solid bead on what numbers I need to be hitting for headspace, head to Ogive and COAL. Based on a bunch, not most or remotely close to most, but many cases coming out at 1.628 I am thinking of heading spacing a batch at 1.625" and see how they fair in terms of cycling reliably. Thats only .002" longer than what I currently do with 100% reliability (so far).

Again, I never said I had a problem. I just figured something that I dont recall anyone ever talking about. That being said, to me it makes perfect sense that the cases shoulder being slammed, by a bolt, into the chamber, WOULD move. **shrug**

 

[LawnMM]

You're overlooking the leverage involved in doing it on a press versus a spring that pushes the carrier forward. The force isn't there.

I'm not saying you aren't getting different measurements, I'm saying the hypothesis for why is incorrect.

Could be the wrong or incorrectly produced bump gauge, maybe the caliper is off, maybe the cases are different amounts work hardened, maybe dies aren't set right. Could be a lot of things, what it isn't: is the buffer spring moving the shoulder on your brass.

 

[little_scrapper]

You are right. The spring is only pushing the large chunk of hardened steel (bolt) forward very quickly. Which hits the back of the case and pushes case forward until the case should hits the shoulder of the chamber.

Have you tried it? I am guessing you have not.

Measure the headspace on a case, drop that case into the chamber, and from a fully locked back position, hit the bolt release and drop the bolt letting it slam home into the case. Now remove and remeasure the case.

I'll wait.

 

[nn8734]

This thread reminds me of another one a couple months back, started by a complete fucking idiot, asking about “slammed brass” on live rounds relative to his rifle changing the shoulder, complicating his efforts to find his head space.

Not saying little_scrapper is an idiot as it seems his experiment was simply borne out of curiosity based on an observation...but the discussion is eerily similar.

I always check my AR chamber by incrementally sizing a case and trying to close the bolt on it with the upper off the lower. I never trust fired AR brass for headspace measurement.

I do the same thing with a new barrel, prior to installing it (or on a freshly purchased rifle).

I remove and Disassemble the bolt (lose the extractor, ejector) then back the die way off. I start sizing, bumping a thou or two at a time until I can completely close the bolt into battery, recording the base-shoulder length.

Then I bump it back an additional .004-005 put everything together and go fire it...I’ll compare the fired cases to my reference case and most of the time they are within a thou or so of each other. Once done I’ll index my die body and lock ring with a sharpie to keep track. I have a separate sizing and seating die for each rifle.

 

[little_scrapper]

I just did it again on a LC M118LR round. Measured headspace at 1.623" at the 400 datum line. Hornady headspace checker and caliper. Placed round in mag, insert mag into AR10, hit bolt release. Eject round and re-measure. Round now measures 1.619" at the 400 datum line. The round is now .004" shorter at the 400 datum of the shoulder

**shrug** just saying.

I may be ignorant but stupit (sic) isn't something I am. Ignorance is simply educated away. Dumb is just... dumb. No cure for dumb. Now, I am not saying nn8734 IS dumb. But maybe if he used a "smarter" word than idiot, like imbecile or obtuse; I may not think he IS.

EDIT: Just for background I work in an engineering lab where we build prototype hardware. I build things off the cuff and run hardware on the bleeding edge to test it. The things we make have to operate with 100% reliability from -65C to +75C and everything in between or the military wont buy it from us. Running high tolerance hardware in extreme environments is what I do.

 

[nn8734]

I just did it again on a LC M118LR round. Measured headspace at 1.623" at the 400 datum line. Hornady headspace checker and caliper. Placed round in mag, insert mag into AR10, hit bolt release. Eject round and re-measure. Round now measures 1.619" at the 400 datum line.

**shrug** just saying.

I may be ignorant but stupit (sic) isn't something I am. Ignorance is simply educated away. Dumb is just... dumb. No cure for dumb. Now, I am not saying nn8734 is dumb. But maybe if he used a "smarter" word than idiot, like imbecile or obtuse; I may not think he IS.

Lol, you think I was calling you an idiot?

I wasn’t, thought that would have been clear by simply reading that portion of my post. A few others thought you’re completely lost but I wasn’t one of them.

Am I wrong? Tell me, if so and I’ll stand corrected.

I say what I mean and mean what I say. If I wanted to use “obtuse” or imbicile (synonym for “idiot” ) then I would have.

 

[little_scrapper]

Lol, you think I was calling you an idiot?

I wasn’t, thought that would have been clear by simply reading that portion of my post. A few others thought you’re completely lost but I wasn’t one of them.

Am I wrong? Tell me, if so and I’ll stand corrected.

I say what I mean and mean what I say. If I wanted to use “obtuse” or imbicile (synonym for “idiot” ) then I would have.

Taking it too literal. Hence the 3x smilies. Trust me I got what you say and I was just messin with ya. Having fun. Hence the three smilies. AFAIK we are cool. Next time Ill tone it down a tad.

My apologies if it came off too harsh. Wasn't meant to.

L_S

 

[newguy2k3v2]

I've noticed this with a 6.5cm barrel in my mws recently. Confirming fit and sizing die adjustment and imagine my surprise when they came out shorter as measured with Hornady comparator. Annealed Hornady 6.5 brass.

It does have a slash xh buffer and may have something to do with it.

 

[little_scrapper]

I just have a LaRue. I still have to find and prove a charge or two that works well with 175 and 168 SMK. Havent even gotten into lighter rounds yet. I still have lots of work to do and lots to learn.

Problem is my chucker broke. Not sure how. Maybe there was some cachingus that I didnt see. All I know is when I felt tension I quickly cammed it down and it snapped. I should have been going slower. I may have realized something wasnt right.

 

[LawnMM]

Yeah, you're right. A bolt carrier and buffer driven by a spring, magically have the same level of force generated by the compound leverage of reloading press linkage AND are somehow able to bump a shoulder back that's already sized shorter than the chamber that's supposedly bumping it ? ?

 

[nn8734]

Taking it too literal. Hence the 3x smilies. Trust me I got what you say and I was just messin with ya. Having fun. Hence the three smilies. AFAIK we are cool. Next time Ill tone it down a tad.

My apologies if it came off too harsh. Wasn't meant to.

L_S

no worries; my feels aren’t hurt haha....I also wouldn’t worry too much about the chamber resizing your brass, either. Just get the sizing die set up correctly (once you get a new press) and you will be fine. Your bolt won’t go fully into battery and gun won’t fire if it’s undersized...over sizing can result in excessive stretch and case head sep in extreme cases...watch your charge weights for pressure.

 

[little_scrapper]

@LawnMM I see the flaw in your statement. The force of a press being power power power! powered by my huge arm is WAY more then the kenetic force of the bolt powered by the spring. However, If the force of a press, powered by my 26" pythons were not STOPPED by hitting the bottom, I could bump that shoulder back to the primer.

Here is whats happening. Physics: The BCG moving at relatively high velocity, is pushing a round into the chamber. Even if the bolt face stops, the cartridge itself is still moving at velocity. It will continue to move at velocity until it is stopped by something. When does it stop? Does it stop when the shoulder hits inside the chamber? Probably. It hits with force. mv^2. the mass is the case, powder, primer and even the bullet itself being held by the static friction of the neck tension. All that mass being concentrated on the shoulder of the case, I say, is enough to "Dent" the should back a few thou.

Experiment you can do in your own neighborhood. Measure the length of your car. Its shorter than the distance to the nearest tree. Now floor your car and run it into the tree. Now remeasure your car. I bet it is shorter afterwards. Same thing. Also, your car will likely be wider. Just like the case is likely wider. That .004" doesn't just vanish.

Now quit arguing it and go try it. Measure a round then drop the bolt on it and measure it again. Just go do it.

 

[whatsupdoc]

LOL, so have any of the non believers just taken a round and tried it for the hell of it?

 

[1911hombre]

Now quit arguing it and go try it. Measure a round then drop the bolt on it and measure it again. Just go do it.

Nah, too easy to sit and argue. And argue. And argue.

 

[little_scrapper]

^^^^^ Yes this!

Some people just want to argue with you. *shakes head* Its like talking to my wife. Even if you state a definitive fact she will still say "No!" that's wrong. Some times she will argue for the sake of arguing.

 

[LawnMM]

The BCG moving at relatively high velocity, is pushing a round into the chamber. Even if the bolt face stops, the cartridge itself is still moving at velocity. It will continue to move at velocity until it is stopped by something. When does it stop?

Trying to get this fella to water but he just won't drink.

Scrappy, your bolt has an extractor, it's clipped around the case rim. It stops when the carrier, holding the bolt, hits the breech and stops. The end.

The cartridge, whose case is already shorter than the chamber on extraction, and sized another .003-.005 under the size when it ejected by your reloading die, doesn't go flying forward into the chamber wall. It stops when the bolt stops and rotates into battery.

You have a good grasp of the physics so riddle me this.

If the static friction produced by .003" of neck tension is enough to keep the bullet from slipping out of the neck and shooting down the barrel unaided by powder...

...how is is that same massive spring force (which can't unseat a bullet) enough to bump a shoulder back EVEN IF we pretended the case was long enough to contact the chamber at the datum line, which it isn't????

*Edited to add: better question: Let's pretend the sorcery you claim is at work in your chamber is true, what's the solution?

I guess we're all fucked right?! Anybody with a gas gun is getting their rounds reheadspaced on bolt release. Doesn't matter how far you bump the shoulder, right? Cause the whole cartridge flies forward until the chamber wall ahead of the shoulder stops it! Cause physics!

We should all just throw our dies away because if what you describe actually happened, there would be no way to stop it.

Maybe we can invent a rubber bumper for the chambers so the cases don't get the shoulder bumped back when they hit the chamber wall propelled, unrestricted by a bolt and extractor, by massive spring force sufficient to move the shoulder on a piece of brass.

I'll buy seven, let me know when the patent is awarded. I'm out. I tried, this horse won't drink.

 

[little_scrapper]

^^^^^ I introduce. My Wife!

Honey? I love you but have you actually tried it yet? Is the space between your ejector and the rim LESS than the spacial difference between case and chamber? I dont know I am asking. If you have a better explaination I am all ears. If you are saying it isnt happening; I must wholly disagree. After bolt drop, the distance from head to datum on the shoulder IS less.

 

[nn8734]

I still have to find and prove a charge or two that works well with 175 and 168 SMK.

Try 40-40.5g IMR4064. I’ve had good luck with both bullets with the same charge weight (40.3g) using fed brass and a 210M primer.

Its getting ready to rain here and I’m bored so just pulled a round of FGMM 175 and measured the case head to shoulder datum using the Hornady case gauge/D400 bushing.

I’m getting 3.6335. Loaded the round into my SR25 slammed it home. Same measurement.

measured a round of M118LR and got 3.636. Loaded it, removed it and still 1.636.

Measured a round of Mk316 mod 0 and it read 3.637. loaded/extracted the round and measures 3.637.

Perhaps it would be worth it to post a quick video of what you doing and seeing in your before/after measurements, assuming you have a means to support the camera/phone or an assistant willing to film.

 

[LawnMM]

I’m getting 3.6335. Loaded the round into my Sand slammed it home. Same measurement.

measured a round of M118LR and got 3.636. Loaded it, removed it and still 1.636.

Measured a round of Mk316 mod 0 and it read 3.637. loaded/extracted the round and measures 3.637.

 

[nn8734]

Haha, perhaps a pic would help

Point was I didn’t see any resizing/shoulder bump after loading relative to before.

3.6” would be something, lol

 

[little_scrapper]

LOL I didnt know M118LR measures over three inches. Damn! I mean I get my M118LR STRAIGHT FROM LC. No middle man no nothing. I want some of them larger M118LR. Where do i get those?

 

[nn8734]

LOL I didnt know M118LR measures over three inches. Damn! I mean I get my M118LR STRAIGHT FROM LC. No middle man no nothing. I want some of them larger M118LR. Where do i get those?

You have to know the secret hand shake. I’m supersonic to 3000 with those rounds!

 

[LawnMM]

He's just not subtracting the comparator length, on the other hand... the laws of physics appear different at his house

 

[nn8734]

He's just not subtracting the comparator length, on the other hand... the laws of physics appear different at his house

very different

 

[LawnMM]

Obviously your cartridges aren't slamming into the chamber with the same force, cause f=ma, so I can clearly deduce you have an inferior weighted buffer spring, you should probably replace it @nn8734 as it's clearly worn out!

Perhaps your carrier is just lighter, that would take care of the "m" component of the equation ?

Or, maybe... it's something ELSE.

 

[little_scrapper]

Try 40-40.5g IMR4064. I’ve had good luck with both bullets with the same charge weight (40.3g) using fed brass and a 210M primer.

I get it BTW, cant just zero a dial caliper. For me and 175gr SMK 40.5 and 41.4 gr of Hodgdon 4895 are looking like sweet spots. I have a POI shift down, over 40.5 gr, and then back up at 41.4gr. I am lookin at 41.4 for 175's. bit higher and lower to prove that the group isnt a fluke and then vary the jump to fine tune. At least that my plan. May try same at 40.5.

For 168 SMK my sweet spot is looking like 41.0. 40.9 and 41.1 both charges produced a 1MOA group and above and below the group opened up quite a bit.

I have, but havent loaded yet with 4064. Have several unopened.

BTW what is a "sand" is that a gun?

 

[nn8734]

LOL I didnt know M118LR measures over three inches. Damn! I mean I get my M118LR STRAIGHT FROM LC. No middle man no nothing. I want some of them larger M118LR. Where do i get those?

have you run a go-gauge into your chamber? If so did the bolt close on it normally?

 

[nn8734]

Obviously your cartridges aren't slamming into the chamber with the same force, cause f=ma, so I can clearly deduce you have an inferior weighted buffer spring, you should probably replace it @nn8734 as it's clearly worn out!

Perhaps your carrier is just lighter, that would take care of the "m" component of the equation ?

Or, maybe... it's something ELSE.

no the three inch M118LR I use is simply indestructible

 

[nn8734]

BTW what is a "sand" is that a gun?

Lol, No it’s my piece of shit iPhone auto correct in action.

Should have read “SR25”.

 

[LawnMM]

have you run a go-gauge into your chamber? If so did the bolt close on it normally?

Excellent question, pro tip Scrappy, don't drop the bolt on a gauge, it's harder steel than the chamber and if it wasn't fucked up before, it will be after you do that. Finger pressure only with the upper off the lower receiver.

 

[nn8734]

Excellent question, pro tip Scrappy, don't drop the bolt on a gauge, it's harder steel than the chamber and if it wasn't fucked up before, it will be after you do that. Finger pressure only with the upper off the lower receiver.

Assuming he isnt totally messing something up with his measurements (becoming less and less likely the more info he provides), I’m beginning to suspect he may have a short chamber which is creating an interference fit with his cartridge headspace. SAAMI min is 1.630. My Forster gauge set goes form 1.630 to 1.640 and I use that set to determine head space on my 308s once I get them in or rebarrel.

 

[LawnMM]

Except that saami specs are for factory ammo. Even if some yayhoo Smith cut his chamber short, it shouldn't have been able to load any factory ammo. Any ammo that did chamber and fire, once bumped back from the fired size, should chamber and fire normally thereafter.

As I understand it he's taking fired rounds, bumping them back below fired length, and he's still claiming the rounds are too long.

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 ?

 

[918v]

How much wiggle room do you have in the barrel extension between the bolt and the barrel?

 

[nn8734]

Except that saami specs are for factory ammo. Even if some yayhoo Smith cut his chamber short, it shouldn't have been able to load any factory ammo. Any ammo that did chamber and fire, once bumped back from the fired size, should chamber and fire normally thereafter.

As I understand it he's taking fired rounds, bumping them back below fired length, and he's still claiming the rounds are too long.

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 ?

Yea I would think that, absent any chamber “resizing” it wouldn’t go into battery.

He also mentioned this was happening with unfired M118LR (post 20). He mentions having a LaRue (post 24) thus my thinking his chamber may be short relative to SAAMI, unless LaRue doesn’t follow SAAMI spec when cutting their chambers (I know very little of their rifles).

AR10 builds are tricky and unless you really know what will go with what, I generally don’t recommend doing them as a DYI.

 

[little_scrapper]

Video