Impact on accuracy with headspace too long

[jelenko]

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.

 

[GLShooter]

Extraction will be a real bear. Accuracy will probably suffer as the cases will vary on how they set in the bolt/chamber.

 

[chkunz]

I would say that if the gun blows up, a

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

I would say that if the gun blows up, accuracy will suffer.

 

[Bronsin]

I doubt they would even chamber. I would have to use a hammer to seat cases that long in a bolt action.

 

[fkimble@charter.net]

So you didn't size them enough before loading and now your wondering how they will shoot? Not your Atterbury ammo I hope!

If they chamber and lockup, you probably won't see much difference. The gun will not have a problem extracting them assuming gas system is in working order. Take some of the .003 over one's and see how they shoot. If they work fine then the .002' will be fine also. If you have a safe place at home to drop the bolt on a couple, that should determine if they will chamber. Just take a cleaning rod with you. May, just to be safe, remove the firing pin from the bolt on the first couple.

Frank

 

[jelenko]

I doubt they would even chamber. I would have to use a hammer to seat cases that long in a bolt action.

Yeah. The AR chambers them absolutely no issue.
These were processed by someone else.
A few years ago, some that came back from a different processor were + 5 over the chamber size. Fed and chambered with no issues.

 

[jelenko]

So you didn't size them enough before loading and now your wondering how they will shoot? Not your Atterbury ammo I hope!

If they chamber and lockup, you probably won't see much difference. The gun will not have a problem extracting them assuming gas system is in working order. Take some of the .003 over one's and see how they shoot. If they work fine then the .002' will be fine also. If you have a safe place at home to drop the bolt on a couple, that should determine if they will chamber. Just take a cleaning rod with you. May, just to be safe, remove the firing pin from the bolt on the first couple.

Frank

Thanks.
Yeah. They were processed by a third party.

I didn't notice the headspace issue until I had already primed the cases [couple thousand]. Fortunately, use different cases for matches.
As you mentioned, the empty cases chamber just fine when the bolt is released.

While these cases are used for practice, I like to have the accuracy essentially the same so I get good feedback.

I've got some rounds loaded up to test.

 

[jelenko]

Extraction will be a real bear. Accuracy will probably suffer as the cases will vary on how they set in the bolt/chamber.

Yeah. Pretty sure it won't be good for accuracy. Just wondering how much. Anything less than 1-2 tenths of an MOA increase would be fine.

 

[sneakboxer]

I had some rounds with long headspace a while back and they shot fine. But the one time I had to unload a few live rounds from the chamber they required mortaring. So keep that in mind. I have also heard that running an AR without the firing pin can allow the cam pin to turn and lock up the rifle. I have never seen that myself but don't want to find out the hard way.

 

[DShortt]

Wait. If the brass is 2-3 thousands too long for the chamber then they wouldn't chamber without some mechanical force. If they're 2-3 thousands over your base to ogive measurement then they will probably chamber but then you have a jammed condition which can potentially cause over pressure problems.
So. Is this really a headspace issue or is it a BTO/overall length issue?

 

[jelenko]

Wait. If the brass is 2-3 thousands too long for the chamber then they wouldn't chamber without some mechanical force. If they're 2-3 thousands over your base to ogive measurement then they will probably chamber but then you have a jammed condition which can potentially cause over pressure problems.
So. Is this really a headspace issue or is it a BTO/overall length issue?

In an AR, the bolt closing mashes the cases enough that it resizes them - without a hiccup!

The bullets are seated to 2.235 - so no jamming into the lands. The cases are trimmed to 1.750 so not jamming into the freebore.

 

[jelenko]

I had some rounds with long headspace a while back and they shot fine. But the one time I had to unload a few live rounds from the chamber they required mortaring. So keep that in mind. I have also heard that running an AR without the firing pin can allow the cam pin to turn and lock up the rifle. I have never seen that myself but don't want to find out the hard way.

I can confirm the cycling the bolt carrier without a firing pin does jam the whole thing

Interestingly, opening the bolt with a case only [with no powder/bullet] comes right open.

 

[chkunz]

the cases are being sized down 2-3 thousandths as the bolt slams shut?

I think there is a serious safety potential with trying to chamber ammo that is a tight fit in a military type semi auto with a floating firming pin. This can lead to a slam fire or an out of battery KABOOM. This is not an accuracy issue it is a safety issue. I would urge you in the strongest terms to not do this.

 

[jelenko]

I think there is a serious safety potential with trying to chamber ammo that is a tight fit in a military type semi auto with a floating firming pin. This can lead to a slam fire or an out of battery KABOOM. This is not an accuracy issue it is a safety issue. I would urge you in the strongest terms to not do this.

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

Ewwe.

 

[cem]

As properly noted above in the special case of the AR15 Stoner design a short firing pin - shades of Bob Lee Swagger - can be used when testing cycling. A short firing pin can be a handy pin punch. Using the same firing pin for shooting and pin punching is a bad idea. No firing pin cannot be used.

If no powder charge and no bullet seated I'd definitely bump the shoulder then load. I do have Redding Instant Indicators and a full set of headspace gages by thousands and a case feeder progressive so I'd tend to do the job what I might think as the right way bumping followed by gaging as the case goes around.

In the circumstances as described with loaded ammunition I would worry about slam fires as perhaps the case slows down while the bolt carrier group has a head of steam. I would also worry about over all length and bullet release if the neck gets too far forward as in any case that needs trimming for OAL. Assuming mil spec primers and the neck doesn't get too far into the throat - bottom line in a 5.56 chamber I'd probably shoot them up. In a .223 chamber I would hesitate a long time.

 

[whatsupdoc]

Confusing post, if your measurements are correct then why are you trying to use ammo that will not properly fit the chamber?

If you are experiencing the case shoulder bumping back after chambering
a round by dropping the BC that is normal.

 

[jelenko]

Confusing post, if your measurements are correct then why are you trying to use ammo that will not properly fit the chamber?

If you are experiencing the case shoulder bumping back after chambering
a round by dropping the BC that is normal.

First, it's primed cases, not ammo.

It's several thousand cases processed by a third party. I'd like to avoid having to resize them because I already paid to them processed. If there's a safety issue, then I'd resize them.

 

[Dkk37058]

If the case is long at the Datam line you can get a Redding small base die and resize the loaded case. it doesn’t have a decamping rod and doesn’t touch the case neck it’ll resize the base of the case and bump the shoulder back with the amount of headspace you want after you adjust the die.
I’ve done this before

 

[DShortt]

First, it's primed cases, not ammo.

It's several thousand cases processed by a third party. I'd like to avoid having to resize them because I already paid to them processed. If there's a safety issue, then I'd resize them.

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.

 

[jelenko]

As properly noted above in the special case of the AR15 Stoner design a short firing pin - shades of Bob Lee Swagger - can be used when testing cycling. A short firing pin can be a handy pin punch. Using a firing pin for shooting and pin punching is a bad idea. No firing pin cannot be used.

In the circumstances as described I would worry about slam fires as perhaps the case slows down while the bolt carrier group has a head of steam. I would also worry about over all length and bullet release if the neck gets too far forward as in any case that needs trimming for OAL. Assuming mil spec primers and the neck doesn't get too far into the throat - bottom line in a 5.56 chamber I'd probably shoot them up. In a .223 chamber I would hesitate a long time.

Hmmm. The primers are CCI 450's. It's a Wylde chamber. The cases are all 1.750 or less.