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Pierced Primers - Excessive Headspace?

Discussion in 'Gunsmithing and Repairs' started by RavenVT100, Mar 19, 2007.

  1. RavenVT100

    RavenVT100 Well-Known Member

    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.
  2. floridaboy

    floridaboy Well-Known Member

    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.
  3. Plink

    Plink Well-Known Member

    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.
  4. RavenVT100

    RavenVT100 Well-Known Member

    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 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.
    What is involved in adjusting firing pin protrusion?
  5. ocabj

    ocabj Well-Known Member

    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.
  6. Sunray

    Sunray Well-Known Member

    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.
  7. RavenVT100

    RavenVT100 Well-Known Member

    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.
  8. Jim K

    Jim K Well-Known Member

    "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.

  9. Sunray

    Sunray Well-Known Member

    "...The XM193 did not, nor has it ever..." Call Bushmaster.
  10. RavenVT100

    RavenVT100 Well-Known Member

    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.
    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.
  11. chris allen

    chris allen Well-Known Member


    Pierced primers are not an indicator for excessive headspace.
  12. hagar

    hagar member

    The problem lies with the Winchester primers. Change to something else, get a new firing pin first, and it will go away.
  13. rbernie

    rbernie Well-Known Member

    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?

    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.
  14. RavenVT100

    RavenVT100 Well-Known Member

    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
    Last edited: Mar 21, 2007
  15. rbernie

    rbernie Well-Known Member

    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?
  16. RavenVT100

    RavenVT100 Well-Known Member

    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.
    Last edited: Mar 21, 2007
  17. rbernie

    rbernie Well-Known Member

    Does the Lyman manual's loads use milspec or commercial brass?
  18. RavenVT100

    RavenVT100 Well-Known Member

    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.
  19. rbernie

    rbernie Well-Known Member

    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" 
    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
  20. Jim K

    Jim K Well-Known Member

    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.


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