AR10 headspace or my die?

[Dmilner]

I just finished this gun in .260 rem. I’m using a Hornady Comparator to measure base to shoulder. I’m using a Forester die.

Using a Fail Zero BCG and a Wilson Combat barrel.

My Forester will size my brass to 1.620 base to shoulder as measured with the Hornady comparator, no smaller, done deal. When I drop a sized case into the chamber and let the BCG slam into lock up it changes the brass length to 1.610. Yes, I’m caming over. I’ve also tried different shell plates, no change. Tonight I stopped by my LGS and measured a factory .260 cartridge and it measured 1.610. I don’t like the idea of my brass getting slam sized down .010. I’m a match shooter and just can’t deal with it

So what’s the fix? Relieve my lugs on the back side? Are all dies the same? Seems to me .010 is a whole lot of difference but why dis my BCG slam sized brass match the factory cartridges?

 

[nn8734]

To be clear, you are saying your chamber is pushing the shoulder back an addl .010 after sizing?

If yes, sounds like your cases are under sized by at least .010 relative to the chamber’s headspace.

Did you check headspace with a go/no go gauge and your bolt prior to assembly?

Have you fired any factory ammo?

If so, did you measure the base-shoulder of the fired cases using your comparator?

Sorry for all the questions, just trying to clarify

 

[Dmilner]

Good questions. No, headspace hasn’t been officially measured...
I’ve put three down the tube to check function. It cycles fine. I can also easily extract manually after I let the BCG slam home. Fired brass is about .008 longer than slammed brass. Slammed brass is about .010 shorter than sized brass. I don’t use factory ammo, ever I did measure a factory round at it matches my slammed dimension.

 

[nn8734]

i don’t use factory ammo either except to do initial barrel break in. For semi autos I f/l size my brass with a small base die to .001-.0015 of chamber to avoid having the brass expand too much.

If it were me, I’d pull the barrel off and check headspace by sizing your brass with different shoulder-head length dimensions in .001 increments starting with 1.620 and finishing with 1.610 (10 pieces total).

I’d write the dimension on each case then drop each one in the chamber, closing the bolt completely. Eventually, you get one that closes with very minimal to no resistance.

Whichever dimension that is, that’s the dimension you need to size to (or push it back .0005-.001 to avoid any risk of interference fit.

If you can’t push the shoulder back any further than 1.620 then there’s something amiss with your set up.

 

[Dmilner]

That’s my problem. I can’t get the die to size below 1.620. An AR10 BCG and buffer spring have plenty of energy to stash that extra .010 down but I don’t want that happening for several reasons.

 

[nn8734]

That’s my problem. I can’t get the die to size below 1.620. An AR10 BCG and buffer spring have plenty of energy to stash that extra .010 down but I don’t want that happening for several reasons.

Lol, no shit - you def don’t want the gun pulling double duty as a press

I don’t think you have a headspace issue beyond not knowing the specific dimension to which you should size the brass (have a feeling it’s 1.610-1.612 based on the above info).

Perhaps post a picture or two of your press set up so we can see if something looks obviously wrong and go from there.

 

[2aBaC̶a̶]

Could a stiff extractor cause the BCG to slam into the back of the brass hard enough to resize it? Are there any Mark's on the back of the brass?

Have you tried removing your bolt from the BCG and also the ejector from the bolt and put a sized case in the bolt and insert into the chamber by hand?

 

[Dmilner]

Ok, I know you guys don’t know me so let me give you some history so you know where I’m at. I started loading five years ago when I got in to match shooting and load for five rifles. Three AR’s, one 270 hunting rig and my 260 bench gun. I use a Lyman All American Turret for my match quality loads and a Hornady LNL AP for practice rounds. My match AR and my F class 260 are both 1/4 moa setups, everything else is under 1/2. Me personally, If you hooked me to a mechanical aptitude meter I’d peg the damn thing. As a kid I started as a machinist and am now a master electrician, 40 years in the field. So believe me, I can appreciate your concern about someone’s ability to set up a loading operation but lol, I’m not that guy.

I used an adjustable gas block because my brass is like gold to me. I spend a lot of time on brass prep so the first thing I looked for was marks on the brass. Nothing. No dents on the back and no extractor marks. All three test fires landed 5’ away at 4 o’clock.

I haven’t broke down the BCG because with no marks on the brass I didn’t see the need. I have numerous times locked back the bolt, dropped a case in the chamber and let the bolt fly closed. Perfect, not a mark on on the brass, no drag on extraction, just .010 shorter than it was before I let the bolt slam.

As for head space. I run tight in all my guns, .002 and below. I full length size everything I load because I think it’s the most consistent method over the long run.

it would make my day if another .260 guy who uses the Hornady comparator would tell me how far their die will size brass down but I usually don’t have that kind of luck.

i need another die for my lnl anyway so I’ll probably get a RCBS SBD set and see where that puts me.

 

[Yondering]

Good questions. No, headspace hasn’t been officially measured...
I’ve put three down the tube to check function. It cycles fine. I can also easily extract manually after I let the BCG slam home. Fired brass is about .008 longer than slammed brass. Slammed brass is about .010 shorter than sized brass. I don’t use factory ammo, ever I did measure a factory round at it matches my slammed dimension.

Sounds like a couple misunderstandings going on here.

#1 - You've fired three rounds, so compare your sizing die setting to that fired brass. That is your correct baseline, NOT that "slammed brass". Do not adjust your die to match the slammed brass. The fired brass dimensions may change slightly after another firing or two, but shouldn't be more than a thousandth or two different.

#2 - On the difference you're seeing after dropping the bolt on an empty case in the chamber - most ARs do this to some degree. .010" seems like a lot, but it depends on your brass and your barrel. It's a result of the clearance between the front of your bolt and the rear edge of the barrel around the chamber (not talking about the barrel extension here). On tightly fitted guns that may be only .002"-.003", but on a lot of factory barrels it can easily be .010" or more. When slamming the bolt closed like you're doing, the bolt is hammering the brass forward into the chamber, sometimes until the bolt stops against the barrel. (Heavier/stiffer/harder brass resists this more.)
You'll probably see different (lower) numbers when feeding a round out of the mag instead of slamming the carrier like you're doing.

#3 - On headspace measurements - you don't need the absolute value (like your 1.620" number in the OP). That's not a useful value, and is misleading if you try to compare it to someone else's comparator numbers. Instead, zero your caliper when taking this measurement on your fired brass (but remove the primer first). That is your most accurate reading of your chamber's headspace unless you resort to cerrosafe or something like that. From there, all your comparisons to sized brass will be relative measurements; i.e. the caliper may show -.003", meaning you've bumped the shoulder back .003".

#4 - Forster, not Forester.

 

[nn8734]

A small base die is a must for semi auto reloading IMO. I meant to say that i prefer Small Base dies for loading for semi auto platforms and shouldnt have implied they were somehow necessary.

Id still determine the correct shoulder-base dimension to within a thou or two based on the cartridge-chamber headspace on your Rifle and brass vs having someone give you a setting based on their rifle and chamber which is going to be different than yours.

As it is, the brass is undesized, just need to determine by how much.

Also I don’t know why you wouldn’t be able to adjust your current die to size the shoulder shorter than 1.620” other than perhaps its defective in some way (I’m assuming it’s set up correctly per your last post

Best of luck with it.

 

[Yondering]

A small base die is a must for semi auto reloading IMO.

No it really isn't, and it has nothing to do with the dimension the OP is talking about anyway.

A small base die can be necessary with a very tight chamber. It is not necessary with most AR barrels though. Adjusting the die correctly, on the other hand, is a big deal.

 

[nn8734]

No it really isn't, and it has nothing to do with the dimension the OP is talking about anyway.

A small base die can be necessary with a very tight chamber. It is not necessary with most AR barrels though. Adjusting the die correctly, on the other hand, is a big deal.

I guess we can agree to disagree on the first part but I like SB dies because they’re more consistent sizing the case overall, at least in my experience. I know it has nothing to do with the headspace issue. You may have misinterpreted where I was going with things by that first statement about the small base die (if so, no big deal).

he states that he can’t adjust it beyond 1.620 but who knows why....this is why he is using that number. We can’t say why he can’t size the shoulder further unless we know more about the set up, hence my request for pics.

If he wants to buy another die, that’s his prerogative but I was curious to see if we can figure out how to help him fix/use his current set up.

Reread my posts and yours - we’re both telling him the same thing: he has a cartridge headspace issue. He knows this but can’t do anything about it because either a) his set up is flawed in some way, b) hes not adjusting it right (as you suspect) or c) his die is defective.

 

[Dmilner]

Sounds like a couple misunderstandings going on here.

#1 - You've fired three rounds, so compare your sizing die setting to that fired brass. That is your correct baseline, NOT that "slammed brass". Do not adjust your die to match the slammed brass. The fired brass dimensions may change slightly after another firing or two, but shouldn't be more than a thousandth or two different.

#2 - On the difference you're seeing after dropping the bolt on an empty case in the chamber - most ARs do this to some degree. .010" seems like a lot, but it depends on your brass and your barrel. It's a result of the clearance between the front of your bolt and the rear edge of the barrel around the chamber (not talking about the barrel extension here). On tightly fitted guns that may be only .002"-.003", but on a lot of factory barrels it can easily be .010" or more. When slamming the bolt closed like you're doing, the bolt is hammering the brass forward into the chamber, sometimes until the bolt stops against the barrel. (Heavier/stiffer/harder brass resists this more.)
You'll probably see different (lower) numbers when feeding a round out of the mag instead of slamming the carrier like you're doing.

#3 - On headspace measurements - you don't need the absolute value (like your 1.620" number in the OP). That's not a useful value, and is misleading if you try to compare it to someone else's comparator numbers. Instead, zero your caliper when taking this measurement on your fired brass (but remove the primer first). That is your most accurate reading of your chamber's headspace unless you resort to cerrosafe or something like that. From there, all your comparisons to sized brass will be relative measurements; i.e. the caliper may show -.003", meaning you've bumped the shoulder back .003".

#4 - Forster, not Forester.

Good info, understood. This is good to here. My fired brass is a couple thousandth longer than sized. Also I am testing with soft brass (R-P) so I’ll compare it to some Lapua I have. Thanks for the insight.

 

[zeroz]

If it does turn out that you have tight headspace on your gun and need to size smaller than your die will go you have a couple options. 1) take .010 off the bottom of the die yourself 2) send the die and a case to forster and they'll do it. 3) get a .010 thicker shell plate. All those things will get you the .010 that you POTENTIALLY need.

It sounds like you may only need .003-.004 though. I would be looking to see what my 2x fired bras size was and then size .002-,003 down from that. As mentioned, chambering by hand and hammering the bolt home is going to change some measurements. .010 does sound like a lot, must be some pretty damn soft brass. Interested to hear what happens when you switch lots/brands.

 

[Steel head]

OP
Measure your fired brass and size it down 2-4 thousandths for a gasser.

Does the bolt close on your sized cases it you ease it closed?

slamming the bolt closed on a case monkeys the case every time.

 

[redneckbmxer24]

If you're going to check headspace that way you should size a piece of brass a little below SAAMI minimum, remove the extractor from your bolt, and use small pieces of scotch tape on the shoulder at the datum line to build up a layer at a time until the bolt no longer goes into battery. Make sure your chamber is squeaky when doing this. It's best to do it before installing the barrel into the receiver and working the bolt by your hand out of the carrier. Or just buy a set of go/no go gauges. Or a go gauge at minimum.

If it's sizing your brass back .010" then it's actually tighter than that because brass has bring back. Dropping a piece of brass in and slamming the carrier home IS NOT the way to check if headspace is safe.

 

[Yondering]

I guess we can agree to disagree on the first part but I like SB dies because they’re more consistent sizing the case overall, at least in my experience. I know it has nothing to do with the headspace issue. You may have misinterpreted where I was going with things by that first statement about the small base die (if so, no big deal).

he states that he can’t adjust it beyond 1.620 but who knows why....this is why he is using that number. We can’t say why he can’t size the shoulder further unless we know more about the set up, hence my request for pics.

If he wants to buy another die, that’s his prerogative but I was curious to see if we can figure out how to help him fix/use his current set up.

Reread my posts and yours - we’re both telling him the same thing: he has a cartridge headspace issue. He knows this but can’t do anything about it because either a) his set up is flawed in some way, b) hes not adjusting it right (as you suspect) or c) his die is defective.

You can disagree all you want but it's still wrong. Small base dies are not "more consistent" either. The die is a fixed set of dimensions and is as consistent as any other fixed object.

Small base dies exist to size the base of the cartridge smaller (the was a clue in the name...) near the case head; that has nothing to do with consistency or with the OP's measurements.

You're trying to suggest solutions to the OP without even understanding if there is a problem. Time to slow down and figure out if a problem even exists before throwing out random fixes. We are definitely NOT both telling him the same thing; you don't seem to understand what's going on in his post or what I said above.

 

[knuckleballz]

Are you familiar with Reddings competition shell holder sets? I had a similar problem where I couldnt get my brass to size down far enough to fit my chamber with the sizing die bottoming out on the shell holder. The competition shell holders vary in height .002 so you can select the correct shell holder. It would be like putting a shim on your shell holder underneath your case head that puts your brass higher up in the sizing die.

 

[knuckleballz]

The other option would be to machine off material from the bottom of your sizing die

 

[Dmilner]

Are you familiar with Reddings competition shell holder sets? I had a similar problem where I couldnt get my brass to size down far enough to fit my chamber with the sizing die bottoming out on the shell holder. The competition shell holders vary in height .002 so you can select the correct shell holder. It would be like putting a shim on your shell holder underneath your case head that puts your brass higher up in the sizing die.

I have a set but don’t they add length?

 

[Dmilner]

The other option would be to machine off material from the bottom of your sizing die

I’ve talked to my gun smith about tiis. He says he could do it easy enough on his lathe. Won’t be the Forster though, that die is for my bench gun. I’ve only got three shots through this AR10 so I’ve still got a lot of data to gather. My plan is to load for this gun on my progressive Hornady so if any changes are made it’ll have to be to the die.

 

[padom]

A small base die is a must for semi auto reloading IMO.

It is not. Ive never used or owned a small base die for any AR15, AR10 or bolt gun. Never have I had an issue. Forster FL Sizing die is all you need for problem free sizing.

 

[nn8734]

It is not. Ive never used or owned a small base die for any AR15, AR10 or bolt gun. Never have I had an issue. Forster FL Sizing die is all you need for problem free sizing.

I wasn’t clear in my message and should have said I prefer them for semi autos like m14, ARs, not that they are required or any more beneficial, which is how the post reads. I can edit it to avoid any further confusion.

 

[padom]

Ok, Ive tried to stay out of this thread but there is so much crap going on I cant resist anymore.

What are you doing basing all your frustration and questioning on "slammed home" and/or "virgin" brass? Thats not how you begin to size brass for your rifle. IF your are so concerned about headspace (which I am sure is fine) then get a Go and No-Go set, remove your ejector and check your rifle. Other than that, move on to learning to properly sizing your brass for that gun.

You need to fire 10rd in that gun, if you dont have known 308 gasser loads from years of experience then go buy 1 box of ammo. 308 Bolt gun ammo has been hot in gassers in my experience. Not all, but some. Fire 10rds and save that brass. Go home, deprime and clean the brass. Now, measure those 10 pieces of brass with your case comparator and write down each of those measurements. Find the avg of those 10 and record that number. Thats your fired case headspace, period. Thats how you find it. Nothing else matters. That number NEVER changes unless you change your BCG and/or barrel. Now take that final avg number you wrote down and subtract 0.003". Thats what EVERY CASE SHOULD BE SIZED TO! Period. Done. No more discussion. You want to go 0.005" go ahead. None of this has anything to do with slam fire or virgin brass.

Now go screw your sizing die down into your press till it touches then back it off 1/2 turn. Now, lube up those 10 pieces of brass. Take 1 piece and size it, wipe it clean and measure it again with your case comparator, it most likely will be larger than your avg above - 0.003". Wipe some more lube on that same case, turn your die down another 1/4 turn and size that case again. Wipe it off and measure again. Rinse and repeat until your sized case measures your above fired 10 case avg minus 0.003". Once you hit that number, lock that die down. Its set for that rifle, its done. Size all your cases and worry about other things.

 

[padom]

I wasn’t clear in my message and should have said I prefer them for semi autos like m14, ARs, not that they are required or any more beneficial, which is how the post reads. I can edit it to avoid any further confusion.

That makes more sense.. Required vs preferring is a big difference...

 

[Yondering]

I’ve talked to my gun smith about tiis. He says he could do it easy enough on his lathe. Won’t be the Forster though, that die is for my bench gun. I’ve only got three shots through this AR10 so I’ve still got a lot of data to gather. My plan is to load for this gun on my progressive Hornady so if any changes are made it’ll have to be to the die.

Padom and I are trying to help you with correct information here. Don't go off on some tangent modifying your sizing die, at this point you don't even know if you have a problem yet. None of the information you've given actually tells us anything about whether you have a problem with sizing or not.

The fact that you're able to load and fire rounds indicates you probably don't have an issue at this point.

Learn what you're doing first before looking for problems. Padom's post is a good tutorial on how to set up your sizing die. Stop wasting time with this "slammed brass" stuff, it is completely meaningless.

 

[LANCER]

I would get a competition shell holder set to force the brass into the die more at given measurements. Or get a small base die if running a gas gun.

 

[Yondering]

I would get a competition shell holder set to force the brass into the die more at given measurements. Or get a small base die if running a gas gun.

That'd be a big negative to both.

Why do people try to give advice like this without having any understanding of the problem or their proposed solutions?

 

[Dolomite_Supafly]

I use SB dies when I initially size brass of an unknown origin. After that I use regular dies. There is no need to own a SB die as long as you have good brass. The reason is some unknown brass will have a larger base diameter from being fired from machine guns or guns that are extremely over gassed.

If the die is touching the shell holder when sizing a case and the case is measuring different than a chambered round then something is wrong.

Is the brass being made from another caliber? Sometimes the dimension in the neck/shoulder junction can be off a little, not enough to notice, when making brass. It will fix itself after firing.

I would take a piece of sized brass, sharpie the neck and past the shoulder then chamber. That will tell you where the problem is. If it is the shoulder then the easiest, and cheapest, thing to fix is the shell holder. You can do it yourself with a sandpaper pack from Walmart. Measure, sand, measure, sand until you get the dimension you want.

 

[Dmilner]

I just finished this gun in .260 rem. I’m using a Hornady Comparator to measure base to shoulder. I’m using a Forester die.

Using a Fail Zero BCG and a Wilson Combat barrel.

My Forester will size my brass to 1.620 base to shoulder as measured with the Hornady comparator, no smaller, done deal. When I drop a sized case into the chamber and let the BCG slam into lock up it changes the brass length to 1.610. Yes, I’m caming over. I’ve also tried different shell plates, no change. Tonight I stopped by my LGS and measured a factory .260 cartridge and it measured 1.610. I don’t like the idea of my brass getting slam sized down .010. I’m a match shooter and just can’t deal with it

So what’s the fix? Relieve my lugs on the back side? Are all dies the same? Seems to me .010 is a whole lot of difference but why dis my BCG slam sized brass match the factory cartridges?

Update: Turns out the chamber didn't get a finish hone.

I just finished this gun in .260 rem. I’m using a Hornady Comparator to measure base to shoulder. I’m using a Forester die.

Using a Fail Zero BCG and a Wilson Combat barrel.

My Forester will size my brass to 1.620 base to shoulder as measured with the Hornady comparator, no smaller, done deal. When I drop a sized case into the chamber and let the BCG slam into lock up it changes the brass length to 1.610. Yes, I’m caming over. I’ve also tried different shell plates, no change. Tonight I stopped by my LGS and measured a factory .260 cartridge and it measured 1.610. I don’t like the idea of my brass getting slam sized down .010. I’m a match shooter and just can’t deal with it

So what’s the fix? Relieve my lugs on the back side? Are all dies the same? Seems to me .010 is a whole lot of difference but why dis my BCG slam sized brass match the factory cartridges?

Update: turns out the chamber didn't get finish honed. Wilson Combat's customer service was great to work with and replaced the barrel. Problem solved.