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Old April 15, 2019, 05:44 PM   #1
ks_wayward_son
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AR light primer strikes

Recently have had a chance to take my newly built AR to the range and it has been enjoyable. Except, I have had a few light primer strikes.

I've run XM 193 and 855 through my rig without any problems really, except my barrel is a 1:7 and I figured it could group better than the 55 and 62 grains. Therefore, I ran some Frontier Match 75 grain HPBT through it. Man, did it like those. Except, out of approximately 40 rounds, I had 2 light strikes with no ignition.

I am using a Rise Armament RA 140 trigger, which is sweet. I had only put about 200 or maybe no more than 300 of the XMs through the pipe before trying the Frontiers, so I don't really think I can blame the malfunctions on carbon buildup. My build is a mid-length and I am currently running a standard/carbine buffer.

Would I benefit from perhaps an H1 or H2 buffer for the Frontiers? I didn't seem to have much trouble with the xm's like I said, but I'd really like reliable function with those 75s.
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Old April 15, 2019, 07:07 PM   #2
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Buffer weight isnt going to assist in hard primers or light weight hammer springs. Drop in another fire control group and retest.
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Old April 15, 2019, 08:31 PM   #3
CarJunkieLS1
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Faulty ammo...
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Old April 15, 2019, 10:00 PM   #4
ks_wayward_son
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CarJunkie...have you had problems with Frontier ammo? Do they have a tendency to use hard primers?
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Old April 15, 2019, 10:01 PM   #5
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I've always used relatively heavy hammer springs, or the stock ones. Doing that I've never had a light strike.
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Old April 15, 2019, 10:43 PM   #6
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I have a new .223 bbl that I've put about 200 rounds through (TC Encore) of reloaded ammo and I've had NO failures to fire. I bought a box of Hornady V-Max ammo and thirty percent of them wouldn't go off. I tried them all again and about a fourth went off. I called Hornady about them and they said they have no reports of this. However, it's all over the internet and it's been going on for several years. I don't know what primers they use, but my CCI, Federal, and Winchester all work 100%. It's your ammo.
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Old April 15, 2019, 10:51 PM   #7
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Have a Timney trigger that gives light strikes with NATO ammo. The hammer spring is the issue.
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Old April 16, 2019, 06:19 AM   #8
CarJunkieLS1
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Quote:
Originally Posted by ks_wayward_son View Post
CarJunkie...have you had problems with Frontier ammo? Do they have a tendency to use hard primers?
I don't shoot factory ammo, but a few rounds out of a few hundred and you've shot multiple types of ammo just says it's not a rifle problem.

I'm not familiar with the RA triggers but if they use lighter springs and hammer to reduce pull weight then that could be an issue too. Have you checked to see how much firing pin protrusion you have?
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Old April 16, 2019, 10:45 AM   #9
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Having built several dozen Ar's --IMO chances are extremely high there's something out of tune with your build as the real cause is my net guess--happens to me occasionally and it takes a bit sleuthing to discover the cause. Impossible to definitively nail down a cause based on net guesses IMO--but what I would guess is that if the problem is intermittent ignition of primer (and nothing is wrong with the trigger group) something is preventing a complete in-battery chambering of your cartridge on occasion.
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Old April 16, 2019, 01:50 PM   #10
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My layman's understanding, if you have a lighter trigger its going to feel better but strike lighter and is therefore more likely to fail in this manner.. of course there are other parts involved but what Ive seen most likely its a lack of compatibility between trigger and ammo.

Also you can put springs in backwards and have a really great feeling trigger that light strikes too (I have seen first hand )..

Recently I read a review on a $3000 AR, from one of those high end "trust your life to it" manufactures, which comes with a $400 trigger out of the box. The review included issues with light strikes across various types of ammunition.
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Old April 16, 2019, 06:44 PM   #11
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I'm running Hiperfire EDT triggers and don't have problems with light strikes or fail to fire with hornady, frontier, or any other ammo.
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Old April 17, 2019, 05:50 AM   #12
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Most common cause is hammer spring installed backwards, also check if bolt is fully closed.
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Old April 17, 2019, 07:30 AM   #13
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"something is preventing a complete in-battery chambering of your cartridge on occasion."

^^^^THIS^^^^
Lube the bolt, clean the locking lugs, make sure the gas tube isn't snagging the gas key.
Give the bore and chamber a good cleaning.
Something is marginally too snug or dragging and is preventing the bolt from going fully into battery 99% of the time when this symptom occurs.
I had a similar issue with a factory built 5.45 upper and tried to solve it by going to progressively stronger hammer and/or action springs to no avail. Finally determined that crud built up in the barrel extension was preventing the bolt's full lock-up about 25% of the time.
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Old April 19, 2019, 06:54 AM   #14
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You are going to have to diagnose your particular problem. Is the bolt fully seated when it happens? It there a problem with the hammer/Spring?

First thing I would do is a good cleaning and install a Wolff extra power hammer spring.

EDIT: Oh, never mind its a drop in trigger. I run MILSPEC triggers in my AR's with a heavy hammer spring. They do not have 3 lb triggers but they go bang everytime.
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Old April 19, 2019, 10:24 AM   #15
ks_wayward_son
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I will definitely give everything a good scrubbing and retest. I am pretty sure there is no binding between the gas key and tube; good alignment. If the cleaning does not work, I may have to do a trigger swap. I have read that the Larue MBTs are great, and maybe a Hyperfire or CMC. It would be beneficial to have the ability to swap out stronger springs if need be. Oh well, my first build so I am getting educated!

Another thought though, I read that the Frontier ammo has bullets which are from Hornady, but are loaded by Lake City. Having fired the 855s and 193s without trouble, wouldn't it be likely the Frontiers would fire just as well, or are the brass, primers, etc. different stock?
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Old April 19, 2019, 04:08 PM   #16
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I have one charging handle that deflects the gas tube a bit down and to the right, that sometimes gave me light strikes. Check the gas tube position when the handle is in the forward position, unlikely but it's worth a look.
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Old April 22, 2019, 02:01 PM   #17
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I agree with Stag and Mobuck as far as not being the trigger . If it's igniting XM-193 and 855 which have the hard primer cups . Then you are likely getting adequate primer strikes or at least have enough power in the hammer to strike the primers hard enough . Something else is holding up or slowing down the hammer as it comes forward . As Stag pointed out , that's going to take some investigating to figure out .

When you say light primer strikes , do you mean you can visibly see the rounds that did not fire have noticeably lighter strikes , meaning not as deep as others that fired ?
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Old April 24, 2019, 12:27 PM   #18
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I'm sure does. The problem is that a portion of the primer strike indentation is from the cartridge backing up over the firing pin, which doesn't happen without firing, so you end up having to drill out the flash hole of a resized case to 1/8" and firing a primer in the empty case to get something to compare to.

You can also try firing some Federal GM205MAR primers, which get their mil sensitivity range by thickening the cup (CCI #41 does it by altering the anvil rather than the cup, so only the Federals will give you indent information directly).

The military has firing pin energy gauges. These consist of something that looks like a headspace gauge but has a flat bottom primer pocket that accepts a calibrated copper slug. How deeply the slug is indented by the firing pin tells them if its energy is in spec. It's a kind of copper crusher for firing pins.

However, it does sound more like failure of the bolt to turn that last little bit. You might need something like Slip 2000 Carbon Killer in the bolt lug recess of the barrel extension. A borescope would help you look.
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Old April 24, 2019, 12:56 PM   #19
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The H1 Buffer is fine, no need to change that. Frontier Ammo (if it's the same one I'm thinking of) is Hornady's plinking ammo. It's cheap and designed for playing around but it is also is said to meet military standards using Berdan vs. Boxer primers according to their latest advertisement.

That said, I agree that it could be your trigger but I would not change it if you like it. I would just avoid Berdan primers because they sit below the head of the case rather then flush like the Boxers.

It sounds to me like you built your rifle with precision in mind so precision ammo is probably more appropriate.
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Old April 24, 2019, 02:15 PM   #20
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Even boxer primers sit about -0.004" from flush, normally, and if they are properly reconsolidated to set the bridge (the anvil compressed into the priming mix by 0.003"). This is especially important in self-loaders with floating firing pins to mitigate the possibility of slamfires. At the same time, because the AR firing pin floats, there is no spring fighting to return it to the bolt, so as long as his firing pin extension is adequate, there should be no problem there.


KWS,

Have you tried firing another set of rounds, but hitting the forward assist after each round chambers and before firing it?
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Old April 24, 2019, 06:59 PM   #21
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Quote:
CCI #41 does it by altering the anvil rather than the cup,
I'd say as well as having the harder cups . Didn't cci change there cups in the 90" to be harder . If not as a whole then the rest of there line to what there military primers cups already where ?
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Old May 7, 2019, 08:41 AM   #22
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Did you try resetting the trigger and striking it again?
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