DSA upper shooting Low

[Kansasbobcat]

Just tested metric kit today with recent sale DSA upper that elevation will only zero with Israeli rear sight. ( I always check barrels for run-out so do not think bent barrel is the problem) Just wondering about others experience with recent sale uppers

 

[Qwkctrss]

Just built an imbel kit with no issues on new cast upper

 

[Flypaper]

Get a shorter front sight??

 

[hkshooter]

It's a documented problem but specifically with Israeli cast uppers. Mark Gumplumber ARS has found a good number of these, enough so that it constitutes a pattern. He talks about it on this sight.
Fortunately, my own Israeli cast upper, one I bought before enough had been sold to find a problem, is fine and zeros well with standard sights. The same kit being built on both an IMBEL and then once they were released, an early cast upper verifies that my kit is happy on both receivers.
As mentioned, you can try a shorter front sight and be sure it's screwed in as far as it will go.

Interestingly, I recently had a DSA forged StG58 receiver that also shot low. So low that a no dot sight screwed all the way in finally brought the impact up to an acceptable place, I didn't worry about it since it was able to be corrected.

 

[Kansasbobcat]

I have tried no dot and actually milled about 0.040 off the top of the base where the sight screws in to get a better sight picture. I am going to try checking bore of rifle with level to see if is level with bottom of receiver using 123 block. Would be nice to be able to predict which receivers are really off on elevation issue without complete assembly and test firing.

 

[Kansasbobcat]

I realize that the leveling idea is probably a waste of time if the hinge pin hole is mislocated and tipping the entire assembly downward when assembled to lower.

 

[hkshooter]

I realize that the leveling idea is probably a waste of time if the hinge pin hole is mislocated and tipping the entire assembly downward when assembled to lower.

Exactly. Mark is one of the more thorough people I know when it comes to inspection but he got to the point where he's not exactly sure what the issue is. If I remember correctly he also believes it has something to do with the location of the pivot hole. That's a very difficult location to measure without special equipment. IIRC, the locking shoulder is the datum.

 

[CTW]

So I just put together two RiFALs on the sale uppers and one is fine and the other has to put the rear sight on the 500 setting to zero out at 100 yards with a 2 dot front sight post screwed all the way down.

 

[OLDMANPBK]

Consistency has never been one of DSA's strong points.

 

[CTW]

You know they both function very well just one shoots low Had the same issue with my Izzy build. Finally got the low post and got it working.

 

[W.E.G.]

Say no to the nubbin.

Move rear sight to wherever it needs to be to zero for 200 yards.

At any distance farther than 300 yards, you aren’t shooting at anything smaller than a Buick with a FAL and iron sights.

 

[CTW]

That is good advice thanks

 

[meltblown]

Still sucks that the damn things are off. I will never buy one. I'd return it and tell them to send another.

 

[CTW]

Still sucks that the damn things are off. I will never buy one. I'd return it and tell them to send another.

It pisses me off too

 

[CTW]

You know when I had the problem with my Israeli upper I contacted them. They wanted me to pay $59 for the site post that they said would make it work. My rifle wasn’t a factory rifle or they would send it out for free. I didn’t even respond back. I called Brad a Gunthings and he sold me one for $20 that made it work.

 

[gunplumber]

DSA current ( 2019 to present) receviers are defective in several ways. This is for both the forged and the cast, with milled being statistically worse.

The front and bottom aspects of the receiver lug binds on the lower
The dust plate binds on the hinge area

This tells me

Hinge hole is too high
Lug is too low
Lug is too far forward (or)
Hinge hole too far forward.

I suspect the former or the wings would bind.
And on the forged, for some bizarre reason, DSA deleted a line of code on some, such that the corner clearances on the underside are left off, preventing lockup They didn't used to be. They are cast into the cast receiver.

While these discrepancies are "slight" inasmuch as I have to machine "only" .005-.010" off the surfaces top work around the problem, ALL DSA current production receivers manifest with shooting way low. This requires custom rear sights or custom stubby front sight or both.

I can only conclude that these known issues are what causes them to shoot low. It is possible there is an issue with the relationship of the receiver threads to centerline on the receiver, and the above noted problems are separate from shooting low. But I think it is logical to assume the defects cause the shooting low, at least until there is evidence to support defect in thread position.

DSA has known this for 3-4 years but simply doesn't give a shit. As they are the only game in town, the consumer has to bend over and take "The Chicago Way" up the ass, or get no receiver at all.

 

[hkshooter]

Sums it up, Methinks.

 

[mountainman]

Looking at 2 AR flip apertures for low shooting paras sitting by my keyboard. Gonna have to get a base for these though. Interested anyone? one like this and one like

 

[STG_58_guy]

DSA current ( 2019 to present) receviers are defective in several ways. This is for both the forged and the cast, with milled being statistically worse.

The front and bottom aspects of the receiver lug binds on the lower
The dust plate binds on the hinge area

This tells me

Hinge hole is too high
Lug is too low
Lug is too far forward (or)
Hinge hole too far forward.

I suspect the former or the wings would bind.
And on the forged, for some bizarre reason, DSA deleted a line of code on some, such that the corner clearances on the underside are left off, preventing lockup They didn't used to be. They are cast into the cast receiver.

While these discrepancies are "slight" inasmuch as I have to machine "only" .005-.010" off the surfaces top work around the problem, ALL DSA current production receivers manifest with shooting way low. This requires custom rear sights or custom stubby front sight or both.

I can only conclude that these known issues are what causes them to shoot low. It is possible there is an issue with the relationship of the receiver threads to centerline on the receiver, and the above noted problems are separate from shooting low. But I think it is logical to assume the defects cause the shooting low, at least until there is evidence to support defect in thread position.

DSA has known this for 3-4 years but simply doesn't give a shit. As they are the only game in town, the consumer has to bend over and take "The Chicago Way" up the ass, or get no receiver at all.

I wish I had diagrams to go with your excellent analysis. I have no idea what the 'dust plate' is. Not sure what the 'receiver lug' is either.

If I had a CAD model of this I could figure it out in 5 minutes. This is Jr. Mechanical Engineer 101. DSA should have solved this easily. Having to use a short front pin or wrong rear sight setting is bullshit. The short front pin screws up your sight picture terribly. No can do.

Mark, if I have this wrong please let me know.

The FAL has a design weakness in that the rear sight is on one half of the gun and the front sight is on the other. If the two halves are prevented from closing all the way, even by only a few thousandths of an inch, the rifle will shoot low. In fact, if the rifle shoots 12 inches low at 100 yards (~12 MOA or 0.2 degrees), you could solve this by rotating the upper an additional 12 MOA 'closed' relative to the lower and then lowering the front sight by 0.056 inches. Without additional rotation, you would need to lower the front sight by 0.074 inches. You get some relief with the additional rotation. Over the years, many builds have had this problem.

Mark, would you agree that the root cause is that the rifle 'doesn't close all the way'??

I'm going to go check my numbers with a sketch. I did this in my head and might have made a mistake. BRB.

Edit: it is more complicated than I originally thought but what I have above should be correct.

 

[Deltaten]

Had this problem with one of my builds....don't recall if it was IMBEL clone or one of Shoty's iterations.
IIRC, installed an Indian rear , as they are a bit taller in the peep location. Fixed it fine. YMMV

 

[MobileHiker]

DSA current ( 2019 to present) receviers are defective in several ways. This is for both the forged and the cast, with milled being statistically worse.

The front and bottom aspects of the receiver lug binds on the lower
The dust plate binds on the hinge area

This tells me

Hinge hole is too high
Lug is too low
Lug is too far forward (or)
Hinge hole too far forward.

I suspect the former or the wings would bind.
And on the forged, for some bizarre reason, DSA deleted a line of code on some, such that the corner clearances on the underside are left off, preventing lockup They didn't used to be. They are cast into the cast receiver.

While these discrepancies are "slight" inasmuch as I have to machine "only" .005-.010" off the surfaces top work around the problem, ALL DSA current production receivers manifest with shooting way low. This requires custom rear sights or custom stubby front sight or both.

I can only conclude that these known issues are what causes them to shoot low. It is possible there is an issue with the relationship of the receiver threads to centerline on the receiver, and the above noted problems are separate from shooting low. But I think it is logical to assume the defects cause the shooting low, at least until there is evidence to support defect in thread position.

DSA has known this for 3-4 years but simply doesn't give a shit. As they are the only game in town, the consumer has to bend over and take "The Chicago Way" up the ass, or get no receiver at all.

This is DSA's explanation when I asked them about fitment issues and low-shooting rifles via email. Was surprised they even responded:

"The sights have nothing to do with the receiver that we offer. The sights are part of the original surplus gas block and the lower trigger frame. If what you have is a light barrel kit then something is off with some of the gas blocks; we built a couple thousand of those rifles a few years ago and about a third of them required a shorter front sight post. We also noted that about a third of the rear sights were driven up to the 600 meter position, indicating that they were using the rear sight to make up for not having a shorter front sight available to them. The kits were imported from a western hemisphere, third world country where they would absolutely do something like this to “make do”. The rest were just fine with a “normal” size sight post. Additionally we know something was wrong with the Israeli design/ manufacture when it came to sights; why else would you make so many different height sight posts when you already had a metered rear sight to adjust for elevation/ distance."

I wont pretend to know if theres any shred of value to their explanation, but found it interesting nonetheless

 

[gunplumber]

It's just another lie from DSA. The receivers are defective, they know they are defective, and they just don't give a shit. They just sell them anyway.

Yes, there are different height front sights - at least 11 sizes from -3 to 0 to +7 (I think I saw a +8 once). If one has a front sight that is too tall , it will shoot low. If you don't have a shorter front sight to exchange, you need to adjust the rear sight elevation. But if I have the shortest factory front sight, a -3, and it shoots low, then it's the receiver.

This is further evidenced by no problems with shooting low when I build an Izzy kit on an IMBEL, or an LMT DSA. Heck, I rebuilt the same kit from an IMBEL to a DSA Izzy, because the customer wanted the Izzy engraving, and I had to switch from a "normal" +2 or +3 front sight to one of my custom front sights that even shorter than a factory -3.

They are defective in lockup as evidenced by the dust plate binding on the hinge area and receiver lock unable to correctly engage the receiver lug. When the relationship between the hinge hole and the lug is fucked up, of course it will affect vertical point of impact.

 

[nvcdl]

I think almost every DSA receiver I've built up except for one needed a taller rear sight - Indian rear sight or Izzy.

 

[easttex]

DSA seems to be battling Century for quality and consistency these days.

 

[raubvogel]

This thread reminded me of these rear sights