Pierced Primers - Excessive Headspace?


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RavenVT100
March 19, 2007, 04:30 PM
I have an SPR-style build that uses a Bushmaster bolt and barrel with a 5.56 chamber.

When I originally purchased the bolt and barrel from Bushmaster, I requested that they headspace it for me, which they claim they did on my invoice.

I am having issues with pierced primers now with this rifle. Yesterday I fired some handloads followed by a string of eight XM193. Four of the handloads, out of 50, were retrieved with sooted, pierced primers. My firing pin is now pitted and needs to be replaced.

Could this be a sign of excess headspace, or is it more likely to be a firing pin protrusion issue combined with insufficient primer cup thickness? I was using Winchester WSR primers. I would like everyone's input before I go buy headspace gauges. I had trusted that Bushmaster would have spaced this for me; I am hoping that they did.

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floridaboy
March 19, 2007, 04:33 PM
I'm no expert on Bushmasters, but my guess is your firing pin protrudes to far. Headspace usually shows up as a ring around the case, or a case separation.

Plink
March 19, 2007, 05:01 PM
It could easily be incorrect firing pin protrusion. I'd have that checked. It's a simple adjustment so it won't cost much.

As for the handloads, you might want to go with CCI primers or primers designed for military loads, as they're a bit tougher. Guns designed to function with harder military primers will occasionally pierce softer ones. I've had that happen with several different models over the years.

RavenVT100
March 19, 2007, 05:41 PM
I've checked for a ring, as well as examining the insides of each case for cracks. No signs of impending case head separation. I am going to pay strict attention to this batch of brass.

A couple extra pins plus the gauge was ordered from BFI today. In addition, I ordered a couple boxes of CCI BR4s, which according to this site (http://www.radomski.us/njhp/cart_tech.htm) have as much cup thickness as the military primers.

I've got a thread going about the WSRs in the reloading forum, but I figured it would be a good idea to analyze the headspace issue here.

It's a simple adjustment so it won't cost much.

What is involved in adjusting firing pin protrusion?

ocabj
March 19, 2007, 06:57 PM
This is why I advise against using Winchester SR primers in the AR. I use CCI 400s and CCI BR4. Others use Remington 7-1/2. For some reason Winchester SR is prone to primer piercing in the AR, even with mild loads. I've had this happen often with Winchester SR with only 24.0gr of Varget behind a 77gr bullet.

Change your firing pin and change primers.

Sunray
March 20, 2007, 02:02 AM
CCI #34 "military" primers are a marketing thing. CCI BR4's are benchrest primers. You don't need either.
Did the 193 ammo have any punctured primers?
"...firing pin is now pitted..." What powder? If you had no trouble before you had the Bushmaster parts put it, I'd be calling them.

RavenVT100
March 20, 2007, 08:01 AM
The XM193 did not, nor has it ever, had any primers pierced with this gun.

The powder in the handloads was Varget, loaded .4 grains above minimum.

Jim K
March 20, 2007, 10:52 PM
"Pierced" primers are not the result of bad headspace or excessive firing pin protrusion. They are the result of a weak mainspring or too light a firing pin that reduces firing pin momentum and allows the primer metal to push back into the firing pin hole, thus punching out a piece of metal. A different primer may help, but the thinner primer metal is not the real reason for the problem.

Jim

Sunray
March 21, 2007, 12:08 AM
"...The XM193 did not, nor has it ever..." Call Bushmaster.

RavenVT100
March 21, 2007, 09:34 AM
"Pierced" primers are not the result of bad headspace or excessive firing pin protrusion. They are the result of a weak mainspring or too light a firing pin that reduces firing pin momentum and allows the primer metal to push back into the firing pin hole, thus punching out a piece of metal. A different primer may help, but the thinner primer metal is not the real reason for the problem.

Weak mainspring? Are you referring to the buffer spring or the hammer spring? This is an AR. I've never heard of any of the springs in an AR be referred to as a mainspring.

If you had no trouble before you had the Bushmaster parts put it, I'd be calling them.

This rifle always had bushmaster parts--The barrel, bolt, carrier group, and lower are all bushmaster. This didn't start until I started using handloads with the WSR primers.

chris allen
March 21, 2007, 10:38 AM
Pierced primers are not an indicator for excessive headspace.

hagar
March 21, 2007, 11:17 AM
The problem lies with the Winchester primers. Change to something else, get a new firing pin first, and it will go away.

rbernie
March 21, 2007, 11:39 AM
ARs have no firing pin spring. I presume that the firing pin is USGI-spec steel and not titanium or other such exotica.

I suspect the issue lays with the combination of commercial primers and the brass used. What bullets were used in the handloads, what OAL were the loads set to, and whose brass was used?

Out of curiosity, what is the barrel length and gas system?

Pierced primers are not an indicator for excessive headspace.As I understand things, pierced primers *can* be a symptom (but it's not likely). The theory is that if the primer is free to back out of its pocket too fast (loose primer pockets, soft primer cup) and the headspace allows the primer to back too far out of its pocket, the primer can be driven hard into the still-extended firing pin, resulting in a pierced cup.

Having said that - I believe the issue is not headspace (since Bushy certainly set that) but rather a combination of gas pressure curves and primers/brass used. Changing any of the above would likely resolve the issue.

RavenVT100
March 21, 2007, 11:53 AM
I suspect the issue lays with the combination of commercial primers and the brass used. What bullets were used in the handloads, what OAL were the loads set to, and whose brass was used?

Out of curiosity, what is the barrel length and gas system?

That is my running theory as well.

Brass: Federal Lake City 01 (Nato Stamp), had crimp (swaged out)
Bullet: Sierra Match King 69gr HPBT
OAL: 2.260"
Powder: Varget
Charge: 23.8gr
Primer: Winchester Small Rifle (WSR)

Barrel Length: 24"
Chamber: 5.56 NATO
Gas System: 20" Rifle Length

rbernie
March 21, 2007, 12:58 PM
The powder charge is pretty high for MilSurp brass; it's thicker and needs you to reduce the powder charge by a bit (rule of thumb says to reduce by 10%). I'm running 24.5gr on Varget with CCI primers in commercial brass, and that's about as hot as I can go in some of my chambers. You may just have had a hot load there.....

I presume that the OAl is really 2.260" and not 2.6" - correct?

RavenVT100
March 21, 2007, 01:35 PM
Correct, that was a typo.

EDIT: The Lyman manual specifies 23.4g as the minimum load for Varget. There were no pressure signs on the primers--they were not flattened, just pierced.

rbernie
March 21, 2007, 02:11 PM
Does the Lyman manual's loads use milspec or commercial brass?

RavenVT100
March 21, 2007, 03:11 PM
I don't have it with me at the moment but I would have to say with almost 100% certainty that it uses commercial brass.

I do not doubt what you say and will take it under serious advisement when I restart developing the load with new primers. I had been under the impression that the military-is-thicker thing applied mainly to .308/7.62x51 and not 5.56.

rbernie
March 21, 2007, 04:53 PM
Avoid Federal brass; the primer pockets tend to be very loose. I use either Rem or Winchester with good success. I'm also partial to CCI 200s (LR) and 400 (SM) - they are consistent and tend to give me lower pressures for a given velocity than other primers...

Physical Specs
Cup Thickness Diameter Height
CCI 200 .027" .2112" .118"
CCI 250 .027" .2113" .118"
Federal 210 .027" .2120" .117"
Remington 9 1/2 .027" .2100" .119"
Winchester LR .027" .2114" .121"

Brissance:
Brand/Type Power Average Range Std. Dev
1 Fed Match GM215M 6.12 5.23-6.8 .351
2 Federal 215 LRM 5.69 5.2-6.5 .4437
3 CCI 250 LRM 5.66 4.5-7.4 .4832
4 Winchester WLRM 5.45 5.1-6.0 .2046
5 Remington 9 1/2 LRM 5.09 3.5-6.75 .6641
6 Winchester WLR 4.8 4.1-6.0 .4300
7 Remington 9 1/2 LR 4.75 3.7-6.25 .5679
8 Fed Match GM210M 4.64 4.0-5.6 .3296
9 Federal 210 LR 4.62 3.7-5.5 .3997
10 CCI BR2 4.37 4.0-5.0 .2460
11 CCI 200 LR 4.28 3.8-4.8. .3218

Jim K
March 22, 2007, 01:20 PM
Hi, RavenVt100,

In firearms terminology, the mainspring is the spring that causes the gun to fire, in other words the spring that drives the hammer or firing pin. In the AR-15 system, it drives the hammer; in a rifle like the M1903, it drives the firing pin.

When a rifle fires, the force driving the firing pin must be enough so the firing pin remains in the forward position long enough to resist the pressure coming from within the primer. If it does not do so, the primer material forces it back and then can extrude into the firing pin hole. This causes either a "flattened" or "pierced" primer, depending on the design of the firing pin and how much support it has.

Jim

RavenVT100
March 22, 2007, 04:29 PM
Thanks Jim, that does clear it up quite a bit.

The trigger is a RRA 2-stage match. Not sure what to do as far as the spring is concerned; I do not yet know enough about what is causing this to consider that a major factor.

One thing I did notice is that the pin protrudes distinctly more than the one on my HBAR. I have the protrusion gauge now and will measure it tonight. I also have an extra pin and new primers. This weekend, I'll test it with the new primers and we'll see what happens.

crux
March 22, 2007, 05:21 PM
I would put my money on the primers. I ruined one firing pin with WSRs. I have not had any problem with smoking primers with any other brand. Now I've got some WSRs lying around gathering dust.

W.E.G.
December 26, 2010, 03:13 PM
Yes, I am aware that I am "resurrecting" an old thread.

I discovered that switching from standard SMALL rifle primers to magnum SMALL rifle primers solved all
my primer-piercing and primer-extrusion problems.

Small rifle primers by most manufacturers are much THINNER than their magnum counterpart.
Large rifle primers are the SAME thickness, whether standard or magnum.
http://i227.photobucket.com/albums/dd7/rkba2da/reloading/primerthicknesschart.jpg

Here is an example of the problems that were COMPLETELY SOLVED when I switched from standard
small rifle primers (CCI and others) to magnum small rifle primers.

http://i227.photobucket.com/albums/dd7/rkba2da/reloading/piercedprimer-firingpin-3.jpg

http://i227.photobucket.com/albums/dd7/rkba2da/reloading/piercedprimer-CCI400-52.jpg

http://i227.photobucket.com/albums/dd7/rkba2da/reloading/piercedprimer-CCI400-6.jpg

http://i227.photobucket.com/albums/dd7/rkba2da/reloading/piercedprimer-CCI400-4.jpg

W.E.G.
December 26, 2010, 03:19 PM
Rifle involved in this thin-primer matter was a Colt AR-15, with Krieger match-grade service rifle barrel.

Headspace was correct at 1.473.

Load was pretty warm:
23.5 grains Vihta Vuouri N-135
Remington commercial case (new case)
Sierra 80-grain Match King (moly-koted)
CCI 400 (standard small rifle) primer

Ambient temperature at time of firing was in the 80's.

As noted in the previous post, the piercing and extrusion problems stopped completely when I switched to magnum small rifle primers.

NCsmitty
December 26, 2010, 03:59 PM
As you probably know already, the milspec CCI #41 affords the same cup thickness and brissance as their magnum SR primer.



NCsmitty

W.E.G.
December 26, 2010, 04:08 PM
That is my understanding too.

I have always puzzled about WHY do they bother to offer the CCI #41 if it is, in all respects, IDENTICAL to the CCI 450.

Jim K
December 27, 2010, 12:05 AM
I repeat what I said before. Either the hammer spring is weak or the firing pin is too light. But I will say that thin primers can make the problem worse.

Note that the "standard" primers show extrusion back into the firing pin hole. If you disassemble the bolt after getting those "pierced" primers, you will find small pieces of brass in the firing pin channel from the primers that were "pierced". Switching to the harder/thicker primers solved the problem because they will better resist the internal pressure. But note that ring around the firing pin dent; the primer is still trying to get around the firing pin, indicating either high pressure or a weak firing pin blow or both.

The firing pin is not "punching holes" in the primer, the internal pressure is doing that.

Jim

W.E.G.
December 27, 2010, 04:03 PM
The ring was in part a function of the fact that the boltface around the firing pin orifice was greatly eroded from the hot gases. I don't still have that bolt. Threw it away years ago. The brass in my pic is brass I fired in 1997. Been sitting in a bucket until yesterday. Figured I'd snap a few pics before all the evidence was destroyed.

I went through several hundred pierced primers, several ruined bolts, and several ruined firing pins, in that gun before switching primers.

Yes, there was a lot of primer metal discovered in the mechanism after a day at the range.

I suppose we can debate until we are blue-in-the-face over whether the hammer spring is too weak.

In my opinion, the load was quite hot (run my numbers through Quickload - you will see), and the thin primer metal was the weak link. I could have had the hammer spring of THOR, and I'm quite certain the result would have been the same. Many other of my teammates at the time were using the same, or similar loads, in rifles with different triggers.

In each instance - same result - until we all figured out that we needed to use magnum primers to end the problems we were causing.

Remember too, 1997 was right about the time the mouseguns were overtaking the M14 in service rifle honors. We all thought we had to hot-load (overload?) .223 ammo to be competitive. I have since learned that ragged-edge loads are not generally necessary to achieve success in high power rifle competition.

Jim K
December 27, 2010, 09:41 PM
Well, if the firing pin hole is oversize, primer metal can extrude back around the firing pin regardless of the firing pin momentum. And that also can hang up the gun as at some point, those bits of brass build up and stop the firing pin. Of course, the firing pin hole is probably oversize due to pierced primers resulting from a weak hammer spring or a light hammer, so the thing is circular.

Jim

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