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FTF Light Primer Strikes. Origin Action/IMI Mk262

S

saddlerocker

Private
Full Member
Minuteman
Feb 23, 2013
203
119
PA
#1
I thought I had seen a related thread recently, but I cannot find it now.

I took my new "build" out today for the first time to get it sighted in.

Its a Bighorn Origin with a Hawk Hill 223 Wylde Chamber barrel and TT Special.

I Shot
2014ish Federal 55gr .223 (Just to get on paper at 25yds)
2016 5.56 Magtech MK262 Clone
2023 5.56 IMI MK262 Clone in Commercial packaging
2015 5.56 IMI MK262 Brown Box
2023 5.56 Black Hills Redbox 77gr TMK

Everything shot fine except both of the IMI loads. Lots of FTF due to light primer strikes I guess. All had an indentation, but no bang. I tried to re-fire them all and 2 of 5 or so did fire the 2nd try.
I assume they just have harder primers, but is there anything that can be done? Like a stronger firing pin spring?
Adjusting the TriggerTech Special to a heavier pull wouldn't help would it?
 
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#2
I belive the consensus on that previous thread was:

Disassemble inspect and clean the bolt. Sometimes on a new build there can be greese or crud draging on the spring and pin.

If that's not is ask the action maker to send you the next heavier spring.

Adjusting the trigger is unlikely to help.

That's where I would start anyhow.
 
#3
diverdon said:
I belive the consensus on that previous thread was:

Disassemble inspect and clean the bolt. Sometimes on a new build there can be greese or crud draging on the spring and pin.

If that's not is ask the action maker to send you the next heavier spring.

Adjusting the trigger is unlikely to help.

That's where I would start anyhow.
Click to expand...
Thanks.
If there is a heavier spring, that is good to know.

I wasnt sure if its generally accepted that Mil. 5.56 loads are hit or miss in a bolt gun, or if most people have no problem with it.
 
#4
saddlerocker said:
Thanks.
If there is a heavier spring, that is good to know.

I wasnt sure if its generally accepted that Mil. 5.56 loads are hit or miss in a bolt gun, or if most people have no problem with it.
Click to expand...


As I understand it: When you run the bolt it cock the firing pin against the spring. This adds to the force you have to apply to either open or close the bolt. If the force is too high people complain "the bolt feels heavy or rough." So it seems manufactures are biased toward the lightest spring that they think will work.
 
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#7
It could be such a thing that the IMI ammo was "shorter" to the shoulder, allowing it to be further into the chamber there by giving gap at the rear and being slightly out of reach of the firing pin itself. If you had a comparator to measure bump with, you could tell.
 
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#8
BrienM said:
It could be such a thing that the IMI ammo was "shorter" to the shoulder, allowing it to be further into the chamber there by giving gap at the rear and being slightly out of reach of the firing pin itself. If you had a comparator to measure bump with, you could tell.
Click to expand...
Unfortunately I am shooting these factory loads because I dont reload or have fancy tools like that lol.
I have digital calipers :LOL:
 
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#9
If it only did it with IMI, I'd just steer away from it then. May just be an issue with it rather than your bolt or spring tension. Like someone else said earlier, if you increase the spring pressure, it makes the bolt harder to lift and close back down.
 
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#10
I have a salad days stash of MK262. Half is IMI and Half is Magtech.
The Magtech shot best today. Wish I could get more of that for .54cpr
Hopefully AAC gets their sh*t together and that might be my main fodder.
Ill give it some time and see what happens.
Good to know a stronger firing pin spring should be obtainable and remedy the issue if needed.
 
#12
I have some of the 75gr Hornady HPBT, 77gr SMK, and their own 77gr OTM, I didn't try any today though.
They definitely have some issues with dents in the shoulder area and had issues with large SD at times.
Hopefully they smooth it out and are a decent option going forward.
 
#16
I had some light-strike issues recently with my Origin when using harder-to-set-off-AR-style Winchester #41 primers (even though it was still 100% reliable with CCI450s).

I tracked it down to being a worn/weak firing-pin spring (the spring had over 2500rds and maybe half that many dry fire cycles on it), I swapped in a fresh spring and all was well again. From now on I plan to swap in a new spring every barrel or 2500rds.

That said, Ray @ Zermatt sent me an alternate cocking-piece to try if the new spring didn't do the trick. He said it would alter the bolt's cocking feel (probably for the worse instead of better), but I'm happy to have it for just-in-case because I care more about 100% ignition than having the lightest bolt-lift on the line. Hopefully, I'll never need to try/use it.

Zermatt CS is awesome, reach out to them and they'll get you taken care of.
 
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#18
Given all of the information, my opinion is that the root of the issue is the ammunition. The action functions with some but not all mil spec ammunition which is pretty consistent with what we've seen over the years.

You can adjust the action to accommodate the ammunition, but it's going to come at the cost of feel in the bolt manipulation. What we'd do to accommodate the harder primer cups is add firing pin travel by introducing cock on close. The Origin is setup to time within ~0.010" with TriggerTech triggers so we'd start by adding ~0.015" of travel with a different cocking piece and see where you end up.

You could also try taking 0.010" - 0.015" of material off of the bottom of the cocking piece to create more clearance between the cocking piece and the trigger sear when the firing pin is dropping. We've seen some changes in the height of the sear from TT over the last year or so and that's introduced issues with other systems, but generally not the Origin.

Overall, my advice would be to kick the mil spec ammo and any primers similar down the road and run the better quality of the ammunition you've got access to. You'll have better success overall in the bolt gun with that anyways. But, if the ammo is something you've got your heart set on running, we can introduce cock on close to the system and get better ignition on that specific ammo.

Thanks - Ray
 
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#19
@Zermatt Arms
Thank you for the reply.

Since it is brand new, I will give it some more time to break-in.
It is good to know a different cocking piece (or some filing/sanding) should remedy the issue if I decide to go that route. (At some expense to bolt manipulation).

If it proves to be flawless with all other 5.56, I may just save the IMI for the ARs.
Unfortunately, the reason for building this rifle was to shoot the inexpensive Matchking loaded Mil ammo I have on hand as I don't reload.
 
#20
Zermatt Arms said:
Given all of the information, my opinion is that the root of the issue is the ammunition. The action functions with some but not all mil spec ammunition which is pretty consistent with what we've seen over the years.

You can adjust the action to accommodate the ammunition, but it's going to come at the cost of feel in the bolt manipulation. What we'd do to accommodate the harder primer cups is add firing pin travel by introducing cock on close. The Origin is setup to time within ~0.010" with TriggerTech triggers so we'd start by adding ~0.015" of travel with a different cocking piece and see where you end up.

You could also try taking 0.010" - 0.015" of material off of the bottom of the cocking piece to create more clearance between the cocking piece and the trigger sear when the firing pin is dropping. We've seen some changes in the height of the sear from TT over the last year or so and that's introduced issues with other systems, but generally not the Origin.

Overall, my advice would be to kick the mil spec ammo and any primers similar down the road and run the better quality of the ammunition you've got access to. You'll have better success overall in the bolt gun with that anyways. But, if the ammo is something you've got your heart set on running, we can introduce cock on close to the system and get better ignition on that specific ammo.

Thanks - Ray
Click to expand...
You guys rock

More and more why I’m gonna get another Origin down the road
 
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#21
Got out again today, but didnt try the IMI again.
Everything functioned well.
If I can get these results with AAC Im not going to worry about the IMI issues.
The gun can certainly do better. I am a novice regarding precision shooting, lacking any real fundamentals.
5rd groups and 10rds of Magtech in the center (Magtech did well yesterday, not today)

1000003297.jpg
 
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#22
I think the general view on that earlier thread was that changing the trigger wouldn't likely be helpful. I occasionally have problems with huge SD and there are undoubtedly some dents in the shoulder area of the 75gr Hornady HPBT that I have.
 
#23
powdahound76 said:
I saw someone, @clcustom1911 I think, saying his current batch of AAC 77 gr was shooting really well.
Click to expand...
Yup. @GumbyActual , @TheGerman and I all shot the AAC 77gr SMK and AAC 77gr house bullet ammo out of our Mk12's. Roughly 2750fps, SD 15, 1-1.5moa. Definitely a worthy offering in place of IMI 77gr or, dare I say.... Black Hills MK262. I'm definitely buying more.
 
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#25
PXL_20240407_153955146.jpg

My new origin has this same issue. 15/20 rounds had light primer strikes it seems. The ones it did fire didn't seem to have any visible issues. I also checked the headspace using go/ no go and things are correct. Not sure if maybe somethings up with the bolt
 
#26
SuperToaster said:
View attachment 8390874
My new origin has this same issue. 15/20 rounds had light primer strikes it seems. The ones it did fire didn't seem to have any visible issues. I also checked the headspace using go/ no go and things are correct. Not sure if maybe somethings up with the bolt
Click to expand...

Factory ammo?
I'm not real familiar with 6.5 creed, but is it common to use a harder "Mil" primer?
I'm guessing yes, since a lot of people have 6.5 creed semi autos with a floating firing pin.

As Origin stated above, it can be fixed at the expense of bolt lift/ lock.
I am tempted to see how much heavier it would make it. Lift and lock is real light on mine currently.
 
#27
BrienM said:
It could be such a thing that the IMI ammo was "shorter" to the shoulder, allowing it to be further into the chamber there by giving gap at the rear and being slightly out of reach of the firing pin itself. If you had a comparator to measure bump with, you could tell.
Click to expand...
Your a got damn genius Gump. Your fucking IQ must be 160.

Joking aside, headspace is shorter for these rounds and causing lps. Your assumption was spot on.
 
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