New Rifle mulfanction

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CZ-75BD

CZ-75BD

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Mar 28, 2011
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Today took to range for the first time my first selfasambled rifle.
I had two magazines loaded with PPU M193 5.56x45mm rounds.
Out of 60 rounds I had 7 misfired. Upper PSA 5.56x45 1/7 twist, Lover Omni-Hybrid.
Magazines Amend2.
No problem ejecting or feeding, just looks like it was not enough of impact on primer. made small hole on primer, but did not fire.
Any suggestion?
 
check to make sure you have the correct orientation on the hammer spring. It is possible to install it backwards by accident.

At least, that's what I would look at first given the symptoms. But then again, I am a newbie around these parts :)
 
Check the hammer spring for proper orientation. The spring tails on both sides should lay on top of the trigger pin that holds the trigger in the lower. Additionally the spring needs to be oriented on the hammer for maximum spring tension when installed on the hammer.

Good luck!
 
Yep, the hammer spring is probably in backwards. It isn't that hard to correct. I messed that up when I put my lower together.
 
Also make sure bolt is fully closed by pressing forward assist. I had that happened, when hammer falls, it will close the bolt but rub energy off and light primer hit. It happens more when rifle is new and will wear in eventually. Make sure the bolt/carrier/gas rings are well lubed.
 
I got upper assembled from PSA, beleve they should check spring orientation, but will check to make sure.
Regarding forward assistant that might be the case. I had before AR in 9mm and it not required. Will check next time
Thank you for advices.
 
agtman said:
Most of the problem right there.
Click to expand...
It can be, but doesn't need to be that way.
If you do your research, and are careful and methodical while building it, you can achieve good results on your first try.
 
"It could also be a weak hammer spring"

All parts in the lower also brand new from PSA.
If spring is weak would it be problem firing all the time?
 
CZ-75BD said:
"It could also be a weak hammer spring"

All parts in the lower also brand new from PSA.
If spring is weak would it be problem firing all the time?
Click to expand...
No. A spring could be just weak enough to cause intermittent problems.

It is possible to get a bad spring from the factory. I don't know for certain you have a bad spring. Just putting it out there as something to check for, considering the circumstances
 
ar-newbie said:
have you actually checked the hammer spring orientation?
image004.jpg
Click to expand...
Yes, I have had check, what I missed is that I used Federal rounds, not PPU, I took wrong magazines, loaded with Federal. I heard that Federal have much harder primer.
Will check all members' advises and next time try different rounds.
 
Last edited:
ar-newbie,

Thanks for posting that image.
It certainly is a lot more "high road" than semi slamming some one and does a great job of showing how that spring should be on the hammer.

This was a major item with the M-16A1. The TC and FM both at the time said that troopers were not to take apart their lower in any way shape or form.....yet everyone did just so they could clean the rifles well enough that the armorer would take it back. Troopers used their firing pin as a punch and generally just punched out the two pins that held the hammer and trigger. Occasionally someone got ambitious enough to punch out the auto sear some thing most of us "civilians" don't have to be concerned with, though their are more than a few around THR with pretty stamps on expensive paper. Any how the spring would get put on backwards and sometimes the armorer or his assistant would miss it and so next range or field trip just the sort of problems the OP has reported would happen. If the full auto part's spring unwound itself just one turn then the rifle became a single shot straight pull when ever it was set on "AUTO"

My old "Battle Buddy" used to tell new guys "If the hammer is not a PITA to re install, you have the spring on backwards!"

If the armorer looked into the lower and saw only a single turn of wire with the hammer cocked, he handed the rifle back to you and said awful things about your family. If he saw two wires on either side of the hammer all was good.

-kBob
 
So it turns out that there were 7 rounds misfired FEDERAL 5.56. That would go to the lower being built with a lighter than normal spring tension. The hammer spring, by Stoners deliberate design, determines the trigger pull weight. Go too light and it causes misfires with hard military primers.

PSA lpk but not determined if milspec, lower is Omni but that shouldn't be an issue.

Remains to be seen about the hammer spring tension. On a minor scale the firing pin may be simply a few thousandths too short. Faulty QC does happen and it's a known but rare issue.

Try it with a known military spec firing pin and see it that changes. Secondly, a different lot of Federal as that primed case may be the reason for it being on the market - hard primers that don't meet spec. They are deliberately harder than civilian primers because the firing pin isn't restrained and it cuts down on the extremely rare and undocumented slam fire when locking the chamber.

PS double check and clean the firing pin hole in the bolt just to make sure there is no heavy grease or other debris.
 
I ordered Wolf Extra power hammer spring and new titanium firing pin, should be next week.
Will replace and see how it works.
Thank you all for the input.
 
Wiith proper spec parts and springs installed correctly you should not need the Wolf spring and titanium firing pin, I would replace the springs and pin from my parts drawer and test fire. Absent having spare parts ( you should always keep spare springs, pins, detents, extra complete bolt, and a firing pin or two on hand at all times, cheap but often necessary) you are on a path that should produce results. I actually had the tip of a firing pin break off after just a few rounds, first time i even heard of a pin breaking so stuff happens.
 
Ibmikey said:
Wiith proper spec parts and springs installed correctly you should not need the Wolf spring and titanium firing pin, I would replace the springs and pin from my parts drawer and test fire. Absent having spare parts ( you should always keep spare springs, pins, detents, extra complete bolt, and a firing pin or two on hand at all times, cheap but often necessary) you are on a path that should produce results. I actually had the tip of a firing pin break off after just a few rounds, first time i even heard of a pin breaking so stuff happens.
Click to expand...

Noted, I'm new to rifle building.. I have another AR in 7.62 x 39 and have had AR in 9 mm, never had problems before.This one first actually in standard caliber :rofl:.
 
Never, ever, have I had a light strike on any ammo with a stock trigger and correctly installed hammer spring. New parts are probably not your answer.

Even if the spring is not backwards, if the legs of the spring are sitting in the bottom of the lower instead of on top of the trigger axis pin, there will be less tension on the hammer spring and light strikes can result.

I would double/triple check the installation of the hammer spring. Post pictures of the inside of the lower.
 
ny32182 said:
Never, ever, have I had a light strike on any ammo with a stock trigger and correctly installed hammer spring. New parts are probably not your answer.

Even if the spring is not backwards, if the legs of the spring are sitting in the bottom of the lower instead of on top of the trigger axis pin, there will be less tension on the hammer spring and light strikes can result.

I would double/triple check the installation of the hammer spring. Post pictures of the inside of the lower.
Click to expand...
 

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