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Noticed that the AR10 bolt will re-headspace a cartridge.
- Thread starter little_scrapper
- Start date
Improperly fitted how? This is something I am definitely not familiar with. I thought the barrel extension is simply threaded onto the barrel?
No it isn’t. It is threaded onto the barrel for minimum clearance between the bolt and the barrel. If there is too much clearance then the bolt will bottom out the round in the chamber and stop on the back of the case to rotate into battery. The system is designed to have the bolt hit the back of the barrel in order to rotate into battery. That way the round sits loosely in the chamber and is not resized by the bolt smashing it between the bolt face and the chamber shoulder.
Great info. Ok I understand this. That being said, if the round is moving forward at 10-15 MPH. Pushed by bolt. It will still impact the chamber shoulder. Also, being pushed in by the ejector. To me, this seems like it would be able to dent shoulders. The round. once in line with the bolt face, is being pushed by the ejector. Up until it slams home, the ejector is forked sidways and over the rin of the lip.
Apples and oranges I know. I measure the bolt clearance and bolt lugs. My bolt lugs are .310" long and the clearance inside the barrel extension is exactly .015".
I pressed the bolt until it stopped inside the extension and measured it. Then pulled it back until the back of the bolt lugs were resting against the inside of the barrel extension lugs. .015" of space in there for the bolt.
Is that a normal amount of clearance? I also noted that when a round is chambered the back of the carrier it exactly flush with the back of the upper receiver. Put a straight edge across them and I would be hard pressed to find daylight.
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The bolt does not strike the barrel. The case gets slammed into the chamber and stops, the bolt then continues moving forward rotating and locking.
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See this makes more sense. I know for fact that the ejector hits the back of the case and stuffs the case into the chamber, against the shoulder, before the bolt face ever does.
I think other factors like ejector angle, ejector spring stiffness, carrier/bolt weight, buffer and spring etc etc would all play a part in how much or little the force against the case shoulder.
So it then seems to be that if my measurement of .015" of slop in the extension is correct then my cases headspace must fall within that .015" otherwise if too short the bolt WOULD hit the barrel and then rotate. Like dropping bolt on empty chamber. Also if the case headspace were too long it wouldn't chamber at all obviously.
I think other factors like ejector angle, ejector spring stiffness, carrier/bolt weight, buffer and spring etc etc would all play a part in how much or little the force against the case shoulder.
So it then seems to be that if my measurement of .015" of slop in the extension is correct then my cases headspace must fall within that .015" otherwise if too short the bolt WOULD hit the barrel and then rotate. Like dropping bolt on empty chamber. Also if the case headspace were too long it wouldn't chamber at all obviously.
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I think the assumption that your chamber is at least 1.630" should be checked with a go-gauge. Considering that the bolt starts moving while the chamber is still under some pressure, I agree with those who wonder if the headspace measurements of fired cases are unreliable.
The case could easily be stretching a little due to bolt movement under pressure. And it won't be 60,000 psi.
Pressure will decrease as the bullet travels down the barrel, and when pressure reaches gas block, force is applied to the BCG. Back in the chamber, as soon as chamber pressure subsides far enough the case walls rebound off the chamber allowing extraction.
But my theory is, that this doesn't happen simultaneously, meaning that extraction begins as soon as 70% (or 80, 90, whatever) of the case has released enough that the extraction force defeats the friction force of the case against the chamber, causing some amount of stretch. This has to be true, unless the case walls only expand to the chamber initially, and have already completely rebounded before the bullet reaches the gas block. Seems unlikely, especially considering cases have tapered wall thickness.
Take the above with a grain of salt, I have no credentials in this subject and I don't even own an AR-10 (I do have small frame experience)
The case could easily be stretching a little due to bolt movement under pressure. And it won't be 60,000 psi.
Pressure will decrease as the bullet travels down the barrel, and when pressure reaches gas block, force is applied to the BCG. Back in the chamber, as soon as chamber pressure subsides far enough the case walls rebound off the chamber allowing extraction.
But my theory is, that this doesn't happen simultaneously, meaning that extraction begins as soon as 70% (or 80, 90, whatever) of the case has released enough that the extraction force defeats the friction force of the case against the chamber, causing some amount of stretch. This has to be true, unless the case walls only expand to the chamber initially, and have already completely rebounded before the bullet reaches the gas block. Seems unlikely, especially considering cases have tapered wall thickness.
Take the above with a grain of salt, I have no credentials in this subject and I don't even own an AR-10 (I do have small frame experience)
Does not!
Well I agree that the bolt is cushioned by the ejector and extractor, but it is heavy and moving fast. It does hit the back of the barrel to rotate into battery. And then the bolt carrier hits the back of the barrel extension.
Come to think of it, it could be that the bolt carrier isn’t stopping on the barrel extension. What if it bottoms out on the bolt? And then you have the full weight of the bolt carrier hitting the case.
Check out the big brain on Brad!
Well I am just figuring it all out. Being very mechanically inclined helps. What is your opinion of having .015" of play for the bolt inside the barrel extension? Is that normal? Excessive?
Well I am just figuring it all out. Being very mechanically inclined helps. What is your opinion of having .015" of play for the bolt inside the barrel extension? Is that normal? Excessive?
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When the bolt lugs lock in on a round the carrier will still move on the bolt just a little bit.
Old adage: "One experiment is worth a thousand expert opinions" I want to know if that round that was chambered from locked back bolt and became shorter, (in the video) becomes shorter again if it is put through the same ordeal? And then try it again and again, measuring each time until it stops becoming shorter. Then try this with an empty case hand dropped into the chamber and let the bolt close on it again and again until this shortening stops happening. Inspect the shoulder on each of these cases for impact signs?
See post 33 - I tried to replicate the condition on my SR25 with factory AA11, AB39 and FGMM 175s; none of those rounds experienced resizing when chambered (thank God)
I just tried this on my mega maten. Yep just like you said I started with an empty with HS 1.636
After chambering it changed to 1.631. If I start with a case that's 1.631 then chambering does not affect HS
HS measument performed with the Hornady HS gauge. I zero the calipers using a GO headspace gauge (1.63000)
I think what's happening is the ejector is pushing the case against the chamber HS datum and when the bolt slams shut and dents the brass slightly. The shoulder is not actually pushed back. It's just deforms the brass a few mils
After chambering it changed to 1.631. If I start with a case that's 1.631 then chambering does not affect HS
HS measument performed with the Hornady HS gauge. I zero the calipers using a GO headspace gauge (1.63000)
I think what's happening is the ejector is pushing the case against the chamber HS datum and when the bolt slams shut and dents the brass slightly. The shoulder is not actually pushed back. It's just deforms the brass a few mils
You ever put any other size HS gauge (1.632-1.633, for example) into your chamber? If so, did it close completely on that gauge?
Its funny, three pages of posts not one that confirms or refutes the OP's claim.
Guess its easier to type a paragraph than drop a round on the chamber.
In my Mega Maten with a Noveske barrel and an Armalite bolt, new FC brass straight out of the bag gets shoulder bumped .003”
I dropped the case in the chamber and released the bolt from locked back position.
I messed around with an FAL once, it would move shoulders chambering rounds. In the area of .01 if I remember correctly.
I FL sized a FC case bumping the shoulder .002”
Dropped the bolt on it and the shoulder got bumped another .006”
Dropped the bolt on it and the shoulder got bumped another .006”
I took a strange FC case that had been fired out of another AR and FL sized it do that the shoulder length was .003” longer than my AR chamber. I dropped the bolt on it and that shoulder bumped it .007”
Yes whenm I first installed the barrel ( 22criterion SS) the no go (1.634 ) would not chamber. I experimented and convinced myself the HS was 1.633
BTW the OP 's method of measuring HS with the hornady tool is a little off the hornady cylinder has an bevel inside so the contact surface is below the top flat side by about 0.014. When he zeros the caliper (see the YouTube he attached) he is under measuring the HS by about 0.0145. You really need a reference object like a HS gauge to get correct results
I didn’t notice the bevel. The bushing that came in my kit doesn’t have it...I’ll rewatch the vid. For your rifle, basically any ammo with a cartridge headspace length larger than 1.633 would be resized upon chambering.
My SR25 has a length of 1.638, which matches a preponderance of my fired cases...It closes on 1.638-39 but not 1.640 gauge. All the AA11 and AB39 I have is 1.636 so it won’t resize when chambered. I measure any factory ammo (ie FGMM) before firing and set anything with 1.628 or less aside for disassembly. I’m ok with a one-time expansion of up to .010 but would never resize it back to that dimension for the second go-round.
Agree that anyone with multiple platforms in a given chambering (e.g. 308 or 6.5CMoor) should have a headspace gauge set. Short of that, a Go/No Go set should be had at a minimum for basic HS checks.
I hadn't thought about this. However, its all relative. Using that same gauge I measured all my ejected brass and came up with 1.626 so I bump shoulders to 1.623. But you are saying my HS gauge is actually measuring around .014" short?
Then my chamber HS would be more like 1.642". Seems long?
I did an experiment. I stripped my bolt, took a piece of sized brass HS'ed at 1.625" and placed in chamber. Bolt closed on it no problem. I then cut a small circle of printer paper to match case head and placed it against the bolt face. Bolt would NOT close/lock with a .003" thick piece of paper behind it. My measured HS would then be something less then 1.628" measured with my Hornady HS gauge. Or possibly/realistically 1.642"?
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Scrapper,
1.642” is .002 over SAAMI max and is highly unlikely you have such a chamber...The right way to find your chamber’s headspace length is via a gauge set. Absent that, redo your experiment but this time, size brass pieces staring at 1.620” - 1.640” in .001 increments, marking each case’s hs length with your sharpie...Try to chamber each using your stripped bolt. The longest one that cleanly chambers will correspond to your headspace (or at least get you very close).
I suspect you have a minimum headspace chamber (1.630). It may be less (ie a short chamber).
You put this gun together from a LaRue UU Kit, right? 100% larue parts, including bolt?
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In the beginning you talked on and on about your credentials and how precise you are at work, why not carry that home with you?
You can stop all the guesswork and have a definitive answer to what you want.
Cast your chamber and your guesswork is over.
You can buy what you need for less than a happy meal and learn something new.
You can stop all the guesswork and have a definitive answer to what you want.
Cast your chamber and your guesswork is over.
You can buy what you need for less than a happy meal and learn something new.
Hornady's tool does not measure headspace. It is a comparator, it is used to compare pieces of brass. If you want to measure the actual size of the chamber, you need something else.
Are you telling me Des Draws is full of shit? Color me shocked. LOL
My comparator says my brass comes out at 1.626 so its gonna be hard to make it longer. My bolt closed on a 1.625 brass and does not if I put a .003" shim behind it. CLOSE ENOUGH! My comparator basically says keep it 1.625 or less.
I will bring my comparator and see if I can find some longer range brass and do exactly as you suggested and make a set of .001" increment brass. Im always looking for tools for the tool box to make life easier. Bonus if I dont have to buy them.
Yes 100% UU, including bolt, assembled myself. I have managed to get a fairly nice set of tools including all those specialized punches and a 200Lb adjustable clicker wrench that I ran through the cal lab before torquing the barrel nut. Used moly and did the 3x tight and loosen and tighten. ect ect.
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I would get fired if I started bringing things home from work.
Unlike rich people like you obviously are; I am a sole bread winner for a family and I work for a living. I cant afford to buy a happy meal. LOL
The stuff you need to do the job is less than $10@Midway
Learn something new and apply it.
The whole process can be done in less than 30 minutes in the comfort of your home.
It will certainly take the guesswork out of it.
Everything I've read so far is guesswork and selective reasoning.
Some good people have chimed in and gave you some damn good answers.
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Actually I ran across this the night before you mentioned it and I was definitely interested.
So how does this process work? Do you plug the barrel and fill the chamber? Then how to extract past the lugs. Please advise.
Google is your friend and there are a ton of YouTube videos on it,Midway has a few out as well.
Why would you worry about the lugs?
You are casting the chamber which will be a negative of a piece of brass.
Most casting materials will shrink giving you time to remove it.
Then as it cools it will expand to its original size.
It's magic.
Why would you worry about the lugs?
You are casting the chamber which will be a negative of a piece of brass.
Most casting materials will shrink giving you time to remove it.
Then as it cools it will expand to its original size.
It's magic.
I’m only a few years late to this thread, but I did read it in it’s entirety. I’ve been reloading for about 4yrs now, (mostly for a 6.5CM bolt gun, but I’ve also loaded a bunch for an AR15 with 5.56 Chamber) & I THOUGHT I had a handle on Headspace UNTIL I read this thread, lol.Are you telling me Des Draws is full of shit? Color me shocked. LOL
My comparator says my brass comes out at 1.626 so its gonna be hard to make it longer. My bolt closed on a 1.625 brass and does not if I put a .003" shim behind it. CLOSE ENOUGH! My comparator basically says keep it 1.625 or less.
I will bring my comparator and see if I can find some longer range brass and do exactly as you suggested and make a set of .001" increment brass. Im always looking for tools for the tool box to make life easier. Bonus if I dont have to buy them.
Yes 100% UU, including bolt, assembled myself. I have managed to get a fairly nice set of tools including all those specialized punches and a 200Lb adjustable clicker wrench that I ran through the cal lab before torquing the barrel nut. Used moly and did the 3x tight and loosen and tighten. ect ect.
Bolt gun? No problem. Measure my fired deprimed 6.5 CM brass with Hornady 0.400 Datum HS comparator, subtracted 2 thou, & used Redding Competition Shell Holder Set to get FL Sized Case to read .002 less than fired. Shoots great. Same thing with AR15, except I use a Small Base Die, & FL Size to .004 shorter HS than fired deprimed brass. Shoots great also.
Unfortunately, I recently decided to start reloading for a piece of crap factory rifle DPMS Gen2 24” Bull AR10 with barrel stamped 7.62x51 1-10 Twist. I bought a small base RCBS .308 AR TC Die Set, and sat down at the bench with a pile of Hornady 168g ELDM brass previously fired through this rifle, & decided to get my feet wet in AR10 reloading world.
The majority of the Fired deprimed brass from the Gen2 Bull read 1.634 on the longest cases using the 0.400 Datum Hornady HS Comparator (For reference, the new unfired Factory Hornady 168g ELDM Ammo read 1.624 using the same comparator). Ok, this is easy enough, so I just set my SB FL Sizing Die up where I get a .004-.005 shoulder bump, & voila, I size all my brass to 1.629, which is obviously a little longer than the factory Ammo, but .005 shorter than my longest fired cases.
Everything seemed fine up to that point, but I like to chamber my resized cases to verify they fit with no issues, BEFORE I load them all, lol, and here’s where my mind got blown. I cleaned my bolt & chamber thoroughly, removed the rear takedown pin, dropped the Annealed & resized case in, & it kerplunked beautifully. I put the BCG in, pushed it in until the extractor and ejectors (dual VERY STIFF ejectors on this proprietary Gen2 garbage) met the case, pushed a little harder until the extractor snapped over the rim, & the bolt went fully into battery with no issues. Great! I ejected the case & re-checked the HS. Still the same at 1.629. Lovely! Then for whatever stupid reason, I put the upper/lower back together, locked the bolt back, threw the case in the chamber again, then pressed the bolt catch button, allowing the BCG to slam home. Pulled the case, & measured HS again. Holy crap… the case was now reading 1.624, 5 thou shorter. Thought it was a fluke, so I grabbed another resized case. Same thing, but this one read 1.623. Then I started repeating the bolt slam using the same case over & over, & the shoulder got set back incrementally with each bolt slam until it finally stopped shrinking at 1.618. Wutha heck!?!?
This is a factory rifle, so in theory, it shouldn’t be a component incompatibility issue. Since I didn’t build it, I never purchased Go/No Go gauges, so I don’t have that tool to trouble shoot with. I do know the rifle was initially over gassed bc it ejected everything I fed it at 1:00, so I eventually got an adjustable gas block for it, & toned it down to ejecting at 3:30 and barely locking back on empty mag suppressed. This gun shipped with an A2 Rifle Buffer/Gas System, so could it be when shooting suppressed, it’s unlocking early, & stretching my brass to give me a false indication my chamber is 1.634? This gun is stamped as 7.62x51 chamber, which should be slightly longer than a 308 Win chamber, so I’m not sure how repeated bolt slams on the same case would cause that case to go all the way down to 1.618? Could it be the stiff dual ejectors on the proprietary bolt, plus the friction forces encountered when the extractor has to overcome the lip of the cases combining to be enough to set the shoulders back on the soft annealed brass? Or, maybe I have excessive slop between my bolt lugs to receiver extension? I have no clue, but my mind is officially blown.
That’s when I went online & found this thread, and I’m more than curious if the OP ever got any resolution on his issue. If not, does anyone have any ideas on what I’m seeing?
Some AR-10 rifles are way over gassed and ejected cases can show datum length farther out than the actual chamber. I have a GAP 10 that shows a fired datum of 1.634-35". There's no way that 308 chamber was headspaced to those numbers. I have a very early SR-25 that has a very tight chamber and gives measurements of 1.631-32" on fired cases. For both of those Rifles, I set my F/L die to size @ 1.630" so they can be fired from both rifles.
I have a friend with a Les Baer AR-10. He gives me his once fired Federal GMM cases. They measure 1.640". There's no way that Rifle has a 1.638+" chamber. All of the regular manufacturers are chambering with 308 Win. specs. My Remington 40XBKS that has a factory barrel marked "7.62 NATO" has a chamber length of 1.632".
M-14's are notorious for this, more than AR-10's.
If you need to know what your chamber measures, use headspace gauges or make some dummy rounds with varying shoulder bump lengths to see what will chamber and just size off of that. The Rifle is not going to chamber a case on the shoulder that isn't sized back enough. It's tough to get actual, precise fired shoulder lengths in gas guns.
There's a lot of back and forth in this thread with guys that don't understand how a comparator like the Hornady tool works. It is not set to give precise headspace measurements. It's a Comparator.
I have two of the Hornady .400" inserts. One measures 1.611" on a 1.630" Go gauge and the other measures 1.622" on the same Go gauge. One has a .019" chamfer, the other one, a .008" chamfer.
If you want a tool that's set to zero off of SAAMI measurements, The RCBS Precision Mic and the Whidden case gauge will do that.
I reload for 2- AR-10's, 2-M1-A's and a bunch of AR-15's.
I have a friend with a Les Baer AR-10. He gives me his once fired Federal GMM cases. They measure 1.640". There's no way that Rifle has a 1.638+" chamber. All of the regular manufacturers are chambering with 308 Win. specs. My Remington 40XBKS that has a factory barrel marked "7.62 NATO" has a chamber length of 1.632".
M-14's are notorious for this, more than AR-10's.
If you need to know what your chamber measures, use headspace gauges or make some dummy rounds with varying shoulder bump lengths to see what will chamber and just size off of that. The Rifle is not going to chamber a case on the shoulder that isn't sized back enough. It's tough to get actual, precise fired shoulder lengths in gas guns.
There's a lot of back and forth in this thread with guys that don't understand how a comparator like the Hornady tool works. It is not set to give precise headspace measurements. It's a Comparator.
I have two of the Hornady .400" inserts. One measures 1.611" on a 1.630" Go gauge and the other measures 1.622" on the same Go gauge. One has a .019" chamfer, the other one, a .008" chamfer.
If you want a tool that's set to zero off of SAAMI measurements, The RCBS Precision Mic and the Whidden case gauge will do that.
I reload for 2- AR-10's, 2-M1-A's and a bunch of AR-15's.
Follow up:I’m only a few years late to this thread, but I did read it in it’s entirety. I’ve been reloading for about 4yrs now, (mostly for a 6.5CM bolt gun, but I’ve also loaded a bunch for an AR15 with 5.56 Chamber) & I THOUGHT I had a handle on Headspace UNTIL I read this thread, lol.
Bolt gun? No problem. Measure my fired deprimed 6.5 CM brass with Hornady 0.400 Datum HS comparator, subtracted 2 thou, & used Redding Competition Shell Holder Set to get FL Sized Case to read .002 less than fired. Shoots great. Same thing with AR15, except I use a Small Base Die, & FL Size to .004 shorter HS than fired deprimed brass. Shoots great also.
Unfortunately, I recently decided to start reloading for a piece of crap factory rifle DPMS Gen2 24” Bull AR10 with barrel stamped 7.62x51 1-10 Twist. I bought a small base RCBS .308 AR TC Die Set, and sat down at the bench with a pile of Hornady 168g ELDM brass previously fired through this rifle, & decided to get my feet wet in AR10 reloading world.
The majority of the Fired deprimed brass from the Gen2 Bull read 1.634 on the longest cases using the 0.400 Datum Hornady HS Comparator (For reference, the new unfired Factory Hornady 168g ELDM Ammo read 1.624 using the same comparator). Ok, this is easy enough, so I just set my SB FL Sizing Die up where I get a .004-.005 shoulder bump, & voila, I size all my brass to 1.629, which is obviously a little longer than the factory Ammo, but .005 shorter than my longest fired cases.
Everything seemed fine up to that point, but I like to chamber my resized cases to verify they fit with no issues, BEFORE I load them all, lol, and here’s where my mind got blown. I cleaned my bolt & chamber thoroughly, removed the rear takedown pin, dropped the Annealed & resized case in, & it kerplunked beautifully. I put the BCG in, pushed it in until the extractor and ejectors (dual VERY STIFF ejectors on this proprietary Gen2 garbage) met the case, pushed a little harder until the extractor snapped over the rim, & the bolt went fully into battery with no issues. Great! I ejected the case & re-checked the HS. Still the same at 1.629. Lovely! Then for whatever stupid reason, I put the upper/lower back together, locked the bolt back, threw the case in the chamber again, then pressed the bolt catch button, allowing the BCG to slam home. Pulled the case, & measured HS again. Holy crap… the case was now reading 1.624, 5 thou shorter. Thought it was a fluke, so I grabbed another resized case. Same thing, but this one read 1.623. Then I started repeating the bolt slam using the same case over & over, & the shoulder got set back incrementally with each bolt slam until it finally stopped shrinking at 1.618. Wutha heck!?!?
This is a factory rifle, so in theory, it shouldn’t be a component incompatibility issue. Since I didn’t build it, I never purchased Go/No Go gauges, so I don’t have that tool to trouble shoot with. I do know the rifle was initially over gassed bc it ejected everything I fed it at 1:00, so I eventually got an adjustable gas block for it, & toned it down to ejecting at 3:30 and barely locking back on empty mag suppressed. This gun shipped with an A2 Rifle Buffer/Gas System, so could it be when shooting suppressed, it’s unlocking early, & stretching my brass to give me a false indication my chamber is 1.634? This gun is stamped as 7.62x51 chamber, which should be slightly longer than a 308 Win chamber, so I’m not sure how repeated bolt slams on the same case would cause that case to go all the way down to 1.618? Could it be the stiff dual ejectors on the proprietary bolt, plus the friction forces encountered when the extractor has to overcome the lip of the cases combining to be enough to set the shoulders back on the soft annealed brass? Or, maybe I have excessive slop between my bolt lugs to receiver extension? I have no clue, but my mind is officially blown.
That’s when I went online & found this thread, and I’m more than curious if the OP ever got any resolution on his issue. If not, does anyone have any ideas on what I’m seeing?
Additional testing performed to rule out dual ejectors & extractor:
Stripped bolt of both ejectors & the extractor. Took a resized piece of brass at 1.629 HS, plunked case into chamber, then slid bolt into battery by finger with no issues. Took same piece of brass, added a layer of clear packing tape to the bottom of the case, rolled case head around on hard marble countertop to score tape edges, stripped away excess tape, then repeated test, one layer of tape at a time, measuring the HS each time, until the stripped bolt would no longer go into battery by pushing the BCG in by finger/hand. That last case measured 1.637 HS with the .400 Datum Comparator, which I am calling my NO GO case. That makes sense to me if my longest fired cases were reading 1.634 (accounting for brass spring back). Soooo, next, I took a different piece of fired, annealed, sized, trimmed, chamfered/deburred ready to go case that was sized to 1.629 HS, seated a 168g ELDM bullet to 2.800 COL (No powder/primer), loaded the dummy round into a magazine, manually locked the bolt back on the bolt catch, inserted the magazine, and pressed the bolt catch allow the stripped bolt to slam into battery. No issues. Removed the BCG, tipped rifle up, bumped the butt, & the dummy round fell right out. Measured the HS on that round, and it measured 1.623… which is 0.014 shorter than my impromptu home made NO GO case, & .006 shorter than where I originally set the shoulder… with a stripped bolt that had no dual ejectors or extractor!
Having said all that, I feel it’s pretty safe to say I can rule out the dual ejectors and extractor, but what else is there? My fired brass & homemade NO GO case both correlate; therefore, I feel my HS is legitimately somewhere close to 1.634 +/- a couple thou. The Bolt Carrier is making contact & stopping, yet there is a decent amount of play between the Bolt itself’s Lugs and the Receiver Extension’s lugs. I haven’t thought much on how I can accurately measure that slop yet, but it appears to be almost 1/32 of an inch eyeballing it. My eye’s aren’t that calibrated, but there definitely is slop there.
Houston, I guess I have a problem, but I’m out of ideas. It just seems wrong & unsafe to shoot a rifle when u can clearly prove the rounds that you chamber are getting pushed back 14 thou shorter than your measured HS! Bout ready to chunk this rifle!
Thank you for the advice. Yep, I do realize the comparator is all relative & not in any way reflective of the actual true chamber measurement dimensions, but it me gives something to go by, & something is better than nothing. IMHO, I think too many ppl just crank down their sizing dies till they hit their shell holder, then turn in another turn so they get cam over, & never even measure the effects of how much they are setting their shoulders back. It works, but I like to try my best to not overwork my brass. Each to their own. I will definitely be getting a set of GO/No Go gauges, & probably the Whidden as well. Thank you again!
I think you're getting too wrapped up over the chambering a cartridge over and over and getting shorter shoulder measurements. That's not an issue. The issue is for you to find the minimum datum measurement that will chamber in your Rifle. Just set your F/L die to -.003" from that and use that for the brass resizing.
I did this with my Rifles by using dummy rounds with varying shoulder bump lengths. Noted that measurement in the binder I have for each Rifle so I have numbers i can go off of. This can be done with the Hornady comparator.
I've gotten 8-10 firings off of brass this way. These gas guns are hard on brass and if they're over gassed, they beat the shit out of the brass. M-1A's are worse on brass than the AR-10's.
I did this with my Rifles by using dummy rounds with varying shoulder bump lengths. Noted that measurement in the binder I have for each Rifle so I have numbers i can go off of. This can be done with the Hornady comparator.
I've gotten 8-10 firings off of brass this way. These gas guns are hard on brass and if they're over gassed, they beat the shit out of the brass. M-1A's are worse on brass than the AR-10's.
Yeah, I was definitely hung up on that, & was concerned there might be a mechanical issue with the rifle when it kept bumping the shoulders incrementally every time I let the bolt slam into battery on the same case. I suppose it won’t be much of a safety issue, so long as I’m not unloading & loading the same round countless numbers of times like some LE/Mil entities may have to do when clearing their weapon at the end of each shift. It’s only bumping them a couple thou shorter than factory Horn 168gELDM rounds I measured, so I guess I’ll keep setting them at 1.629, & just run with it.
For chamber headspace, the bolt indexes in the barrel extension when the rear of the bolt lugs are mated to the front of the barrel extension lugs. There is a gap between the front of the bolt lugs and the barrel tenon. You probably found out what your rifles gap is by slamming the BCG home on the case until the front of the bolt contacted the barrel tenon. Just FYI in case you didn't already know, SAAMI cartridge spec for commercial ammo is 1.634" (-0.007") base to datum.
That confirms what I was seeing, & makes more sense to me now. Thank u for explaining. So, if I’m understanding this correctly, it appears my chamber headspace may be within tolerance (jury still out until I can get Go/No Gauges to verify) from chamber shoulder datum to bolt face when the bolt is in battery, as the ejectors are applying force to the cartridge, pressing it’s shoulders forward into the chamber, which forces the bolt lugs rearward into the front side of the receiver extension’s lugs. However, the slop that exists between the front of the bolt’s lugs & the barrel’s tenon is what is allowing the front face of the bolt’s lugs to continue moving forward by the inertia of the buffer spring, the buffer weight, & the weight of the BCG when chambering a round, and that little bit of slop is what is causing my case shoulders to get pushed back.
If my understanding is correct, I should be able to quantify an estimate of the amount slop by taking my comparator estimated HS reading of 1.634, and then subtracting the comparator HS reading I got when the cases finally quit getting bumped back after numerous repeated bolt slams, which was 1.618, equaling .016. Not sure if there is a spec for that, if it’s safe, unsafe, or perfectly normal, but I don’t wanna run into a worst case scenario situation where I eject an unfired at the range or after hunting, re-chamber it 0.016 shorter, then grenade the rifle. Should I be overly concerned or roll on?
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