Impact on accuracy with headspace too long

[jelenko]

I don't understand what you've got going on here. Earlier you spoke of a COAL 2.235" but now you say it's just primed brass? Can't be both.

Right. Right now it's just cases.

Someone else expressed concern about the bullets jamming in the lands. The load I use, when making rounds, is 69SMK's at 2.235.

 

[fkimble@charter.net]

I remember this brass problem from the match forum! Yes the shoulder/headspace will get set back by the bolts force upon closing. The bolt slows down at the last bit when the extractor has to force it's way over the rim. The case/bullet will not be jammed in different ways destroying accuracy. If anything bullet/case fit will be better. I've noticed over my 20 years XTC with an AR that over the life of a bolt/barrel combo that headspace will grow. The bolt lugs wear and I imagine there is also wear on their mating surface. After chambering an empty case, how much does the shoulder set back? Getting a good feel for AR headspace is difficult due to the way an AR operates. It can shorten headspace on bolt close and then stretch the shoulder out upon firing and also on extraction while case is still under pressure. Don't need a small base die to resize, just take the pin out of your regular die.
Refresh my memory: Is the problem based on measurements alone or actually chambering them?
What does one of these cases measure after having the bolt dropped on it?

Frank

 

[Rocketvapor]

The body only die doesn't touch the neck, can resize shoulders (bump).
It's not small base.

Just a couple thou OVER chamber length can require feeding a second time just to get the bolt to close with an AR. Crushing the case by dropping the bolt might depend on anneal condition and brass/caliber.
Happened in a 60 round comp. (measurement error during reloading)
Playing with loaded rounds isn't recommended but a body only die can correct base to datum cases that are too long.
I now fit check all competition rounds.

 

[jelenko]

Is the problem based on measurements alone or actually chambering them?
What does one of these cases measure after having the bolt dropped on it?

Great question.
The measurements are based on a Whidden case gauge that's calibrated to a Clymer go gauge. The Whidden gauge reads -1 on the go gauge. A sample of the cases measures 0 to + 2 1/2 in the Whidden gauge. I.e., +1 to + 3 1/2 above SAAMI min.

I have tested several cases [again, these are cases only] in the rifle by manually pushing the bolt carrier forward. The bolt will close on cases that are very close to 0 on the Whidden gauge and won't close on cases that are just a smidgen more 0 => indicates the headspace of the chamber is very close to +1 [i.e., 0 on the Whidden gauge.

When a case is chambered by releasing the bolt carrier from the open position, cases come out real close to 0 on the Whidden gauge [i.e., they are real close to the same size as the chamber].

 

[jelenko]

Playing with loaded rounds isn't recommended but a body only die can correct base to datum cases that are too long.
I now fit check all competition rounds.

These cases are all still just cases - but have been primed. Because there's several thousand and because I'm trying to avoid the processing work by having a third party process them, I'm hoping to not have to size them again.

I also check all rapid fire rounds using a firing pin with the tip ground off - so there is no protrusion.

In the past, when cases have come back over SAAMI 0 I have used them in off hand and sitting practice. Probably ~ 1K. Never had any feeding/extracting issues.

For the future, I need to remember to do an incoming QC check when the cases are returned from the processor. They are usually all to spec, but, not always as it turns out.

 

[fkimble@charter.net]

"In the past, when cases have come back over SAAMI 0 I have used them in off hand and sitting practice. Probably ~ 1K. Never had any feeding/extracting issues."

Sounds like a plan!

Frank

 

[searcher]

What would be the impact on the accuracy in an AR15 if the headspace of the cases are 2-3 thousandths more than the chamber? I.e., the cases are being sized down 2-3 thousandths as the bolt slams shut?
Assume the load typically produces 5 shot groups 1/2 to 3/4 MOA at 100 yards.

Thanks

PS. I'm not concerned about potential failures to chamber - just on the impact, if any, on accuracy.

In my experience of running ammo that had shoulders .002"- .003" longer than chamber, the accuracy, using a proven load in all other respects, showed increased accuracy. That closing bolt inertia will smack the shoulder down to zero clearance. I like to be sure my bolt lugs are well lubed, am using a full-power mainspring, use brass that is not overdue for annealing and I don't run hot loads. It is hard to say how much (if any) improvement you will get in a given rifle with a given load, as you are in essence, changing the internal case capacity just a tad when pushing the shoulder out - as well as bearing surface contact of the neck to the bullet a bit less, etc., etc.. The changes are all very minute - but those changes, collectively, can improve or worsen your tune. That said, repeatable headspace is one of the biggest shortfalls of any semi-auto in respect to accuracy. This eliminates the headspace issue, and you will likely see improvement once powder is re-adjusted, if necessary, to fine tune. I have found it helps a LOT to turn the necks (I skim to 80% +/- clean metal) to get the juncture of the neck and shoulder concentric where contact will be made when the round is pushed into the forward position of the chamber. Of course, the added benefit of neck skimming is a more uniform bullet release - another big problem with A/R ammo that must already have the added tension to keep the bullet from slipping when the round slams home into the chamber. I doubt you would not be able to get a round that is .003" long on the shoulder to load if the rifle is clean, properly lubricated, etc. You can make up a few dummy rounds without primer or powder to see for yourself.

 

[jelenko]

In my experience of running ammo that had shoulders .002"- .003" longer than chamber, the accuracy, using a proven load in all other respects, showed increased accuracy. That closing bolt inertia will smack the shoulder down to zero clearance. I like to be sure my bolt lugs are well lubed, am using a full-power mainspring, use brass that is not overdue for annealing and I don't run hot loads. It is hard to say how much (if any) improvement you will get in a given rifle with a given load, as you are in essence, changing the internal case capacity just a tad when pushing the shoulder out - as well as bearing surface contact of the neck to the bullet a bit less, etc., etc.. The changes are all very minute - but those changes, collectively, can improve or worsen your tune. That said, repeatable headspace is one of the biggest shortfalls of any semi-auto in respect to accuracy. This eliminates the headspace issue, and you will likely see improvement once powder is re-adjusted, if necessary, to fine tune. I have found it helps a LOT to turn the necks (I skim to 80% +/- clean metal) to get the juncture of the neck and shoulder concentric where contact will be made when the round is pushed into the forward position of the chamber. Of course, the added benefit of neck skimming is a more uniform bullet release - another big problem with A/R ammo that must already have the added tension to keep the bullet from slipping when the round slams home into the chamber. I doubt you would not be able to get a round that is .003" long on the shoulder to load if the rifle is clean, properly lubricated, etc. You can make up a few dummy rounds without primer or powder to see for yourself.

Thanks!

 

[searcher]

Oh, yeah. The case head/primer are going to be sticking out as the bolt and firing pin slam home.

Ewwe.

Thanks!

Sure. There are concerns about slam fires, though one needs to look at the loading process. Brass is sized in normal manner other than being a few .000 long on the shoulder. When a round is stripped off the magazine and pushed by the bolt into the chamber, there is no unnatural resistance until the shoulder makes contact with the end of the chamber. That .003" is moved before the bolt even hiccups to a halt. If one loads a dummy round into the chamber and you pull the charging handle back only 1/4 of the way and release it on the round, you will see that the .003" was pushed back with ease, and at a force level that would not have put a dent in a primer, let alone ignite one. That does not mean that a slam-fire cannot occur. Anytime you take up clearance between the firing pin and the primer, chances increase. My belief, right or wrong, is that the .003" is pushed down before the firing pin begins enough forward inertia to do anything. Personally, I'd want to make a few dummy rounds (with live primers and no powder or bullet), drop them, one at a time, into the chamber and let the bolt slam home from the full rear position. I'd then look at the primer and see how much of an indentation is on the primer as compared to a loaded and ejected live round. I'd also only use thick-cupped primers like CCI-450's, Military primers, Federal A/R primers, Remington 7 1/2, Tula or Wolff magnum primers, etc. If the dent (if present) is acceptable, it will not be worse when loading off the magazine - it will be not as bad. Just my 2c

 

[jelenko]

Interesting.

The dents in the primer appear indistinguishable under 5X mag for cases sized less than the chamber and those longer than the chamber.
They appear the same with stripping the case from a mag.

 

[bobcat93]

What would be the impact on the accuracy in an AR15 if the headspace of the cases are 2-3 thousandths more than the chamber? I.e., the cases are being sized down 2-3 thousandths as the bolt slams shut?
Assume the load typically produces 5 shot groups 1/2 to 3/4 MOA at 100 yards.

Thanks

PS. I'm not concerned about potential failures to chamber - just on the impact, if any, on accuracy.

Hey man..quick question..did you receive or send them a bolt when you purchased the barrel?..
You can pick up a few bolts and maybe find a set of used heads space gauges on line
I'm not sure who specs may be different..but if have heard of this issue, and that's how it was cheaply corrected...
Some bolt specs are different for this reason..
Hope it helps..(it can be corrected)

 

[jelenko]

Hmm. I do have several bolts lying around - I'll see if any make a difference.

At the same time, if the accuracy is not degraded, I'm good to go. These cases will all be used for practice.

 

[bobcat93]

I know this is ghetto..but you can take a case that has been fired, put 2 layers of scotch tape on the bottom of the case..set it on a disassemble bolt and see how it all fits in the chamber

 

[bobcat93]

Also..if your not a member check out AR-15.com forum...there is enough information over there and every problem discussed..amazing amount of knowledge and folks willing to help out..they can fix any AR problem..hahaha
Good luck

 

[Rocketvapor]

IF you have an AR-15 bolt that headspaces wrong you must have really bought at the poor end
Maybe it's luck but I've NEVER found a bolt with more that a half thou difference in headspace.
2500 rounds on a 5.56 bolt in a 22 Nolser also hasn't worn the lugs more than a tenth.



0.154" bolt. Never seen a 0.153" or 0.155" bolt for a 5.56 or 6.8SPC.

 

[jelenko]

Guys, the bolt is fine. The cases were resized by a third party. They are between +2 and +3 over a go gauge.

ETA. Changing the bolt did add 1/1000 of headspace.

 

[jelenko]

I know this is ghetto..but you can take a case that has been fired, put 2 layers of scotch tape on the bottom of the case..set it on a disassemble bolt and see how it all fits in the chamber

There aren't any cases fired in the upper in question. The fired cases I have were fired in a different barrel.

Because the brass is processed by a third party, the spec is to size so all brass is just at a go gauge or smaller. I can do this because all my barrels come from the same gunsmith and they are between +1 and +2 to a go gauge. I.e., the cases are not resized relative to the specific barrel and bolt.

 

[bobcat93]

There aren't any cases fired in the upper in question. The fired cases I have were fired in a different barrel.

Because the brass is processed by a third party, the spec is to size so all brass is just at a go gauge or smaller. I can do this because all my barrels come from the same gunsmith and they are between +1 and +2 to a go gauge. I.e., the cases are not resized relative to the specific barrel and bolt.

Ooooooooh!..I got ya...its not the rifle..your trying to cram 10lbs of sh=÷ in a 5lbs bag..hahaha...

So your shooting reloads..some else probably just necked sized and the won't function through your rifle......
EVERY Varmatch barrel ive ever received from krieger has such a tight chamber I can't use factory ammo, or anything with a crimp..not that it needs it
But they jamb up every time..and im left banging my stock on the ground while I pull on the charging handle...
My budy thought he was getting a deal when he purchased 2 ammo cans of surplus 5.56 and none of it will function in his gun...because of the crimp bulge
Simple..
Get an RCBS press mount bullet puller..and separate the components..back out the depriving rod on your die (put of safty glasses)..resize all your brass..no need to deprime..just don't disturb the primers..put the cartridge back together
Try a test run of 20 cases...see how it works..
I would measure the charge of about 5 cases so you know how much powder to dump back in the cases...
Its a perfect winter time project to pass the hrs hahahaha

 

[bobcat93]

Out of safty precautions..
There is a bit more to it then that..brass may need trimmed after sizing..bla,bla,bla..I assume you know the drill..its a labor of love..

 

[jelenko]

Ooooooooh!..I got ya...its not the rifle..your trying to cram 10lbs of sh=÷ in a 5lbs bag..hahaha...

So your shooting reloads..some else probably just necked sized and the won't function through your rifle......
EVERY Varmatch barrel ive ever received from krieger has such a tight chamber I can't use factory ammo, or anything with a crimp..not that it needs it
But they jamb up every time..and im left banging my stock on the ground while I pull on the charging handle...
My budy thought he was getting a deal when he purchased 2 ammo cans of surplus 5.56 and none of it will function in his gun...because of the crimp bulge
Simple..
Get an RCBS press mount bullet puller..and separate the components..back out the depriving rod on your die (put of safty glasses)..resize all your brass..no need to deprime..just don't disturb the primers..put the cartridge back together
Try a test run of 20 cases...see how it works..
I would measure the charge of about 5 cases so you know how much powder to dump back in the cases...
Its a perfect winter time project to pass the hrs hahahaha

bobcat - The third party only processed the brass - clean, deprime, size, trim, deburr, champher.
I load my own rounds.