Zero Shift When Swapping Glock Uppers

[Sensei]

I recently purchased on of the Talo G45.5 with factory cut Aimpoint ACRO P2 optics. Naturally, the thought crossed my mind to swap the upper with one of my G19.5 lowers. Of course, this begs the question of what degree of zero shift (if any) should one expect when swapping lowers. I’ve dabbled with this question before getting into carry optics. However, the width of Amiglo HD front sights is such that precise groups beyond 15-20 yards is more a limitation of the sights rather than zero shift. The 3 MOA dot allows more precise estimates.

Here is a 5-round group of 124 grain SB from the G45.5 fired at 25 yards from a sandbag:



Here is another 5 rounds fired from the same upper on a G19 lower:



The far left round is probably more me than the gun. As you can see, minimal to any zero shift. Overall group size is roughly similar.

[GJM]

I have never detected a zero shift when switching Glock uppers.

[G19Fan]

Never had a zero shift swapping complete uppers to another lower

Of course if barrel is different that would cause zero shift

[1Rangemaster]

…when I’ve moved dots back and forth on MOS slides-and one direct milled for ACRO- no shift when torqued the same. It makes sense to me as the tolerances seem pretty tight. I always confirm@25 yards to “feel” better.
To the OP: the groups seem gtg to me, sir-I wish I was that consistent. If I can stay “ in the black” to 25 yards, I’m a happy guy. I may get flamed here @PF, but IMHO if one can stay inside of 6-8” @25 yards, it’s good enough for “guvment work”.
There’s a plate rack on a club range I frequent, and if I can pull off a few 3-4second draws to a hit @25y, I’m content in the context of a “defensive “shot. OMMV.
I like the TLG “Three-Fifty-7” drill when I can arrange it. That’s a shot from ready to a 50 yard steel silhouette in 3seconds or less. Done 7 times to pass. May try that next week when I’m at the big city range…

[G19Fan]

…when I’ve moved dots back and forth on MOS slides-and one direct milled for ACRO- no shift when torqued the same. It makes sense to me as the tolerances seem pretty tight. I always confirm@25 yards to “feel” better.
To the OP: the groups seem gtg to me, sir-I wish I was that consistent. If I can stay “ in the black” to 25 yards, I’m a happy guy. I may get flamed here @PF, but IMHO if one can stay inside of 6-8” @25 yards, it’s good enough for “guvment work”.
There’s a plate rack on a club range I frequent, and if I can pull off a few 3-4second draws to a hit @25y, I’m content in the context of a “defensive “shot. OMMV.
I like the TLG “Three-Fifty-7” drill when I can arrange it. That’s a shot from ready to a 50 yard steel silhouette in 3seconds or less. Done 7 times to pass. May try that next week when I’m at the big city range…

I zero standing at 25 yards.

As long as all 10 shots are I the back of a b8 witj at least 5 in the 10 or better I call it good

[42Willys]

Good idea for an experiment and good shooting

[LittleLebowski]

It’s all about barrel to slide lockup, I don’t think the lower frame adds anything insofar as mechanical accuracy.

[Sensei]

I tend to agree that barrel/slide lookup is the driving factor. I have some factory threaded barrels and plan to update this thread in a week or two with the shift from a factory barrel swap.

As an aside, I don’t do much pistol shooting beyond 20 yards and almost never at a B8. It was eye opening to see the shift between loads at this distance. I’m talking 3-4 inches in any direction between quality loads at 25 yards. This really speaks to the need to drift your irons depending on the groups at 25 yards if you hope to make consistent 50+ yard hits.

[G19Fan]

I tend to agree that barrel/slide lookup is the driving factor. I have some factory threaded barrels and plan to update this thread in a week or two with the shift from a factory barrel swap.

As an aside, I don’t do much pistol shooting beyond 20 yards and almost never at a B8. It was eye opening to see the shift between loads at this distance. I’m talking 3-4 inches in any direction between quality loads at 25 yards. This really speaks to the need to drift your irons depending on the groups at 25 yards if you hope to make consistent 50+ yard hits.

For same grain I rarely have seen that much variance. Even 115 to 124 is relatively close depending on brand. 147 can be off a good amount in my exp

[Sensei]

Here are 2 targets fired resting on a Caldwell Tackdriver bag using a G34.5 equipped with Trijicon SRO and GPT (gen2) at 25 yards. All ammo was S&B 124 grain FMJ but the gun is zeroed for 147 grain HST at 25 yards. The first picture is the absolute best the gun has ever shot with a Glock factory barrel that came with the pistol:


Notice the 1” leftward zero shift with the 124 grain ammo, but this is still the tightest group by about an inch that I’ve ever seen with the gun using any ammo.

The second picture was fired using a factory threaded barrel without the thread protector:


Notice not only the zero shift by about 4” as well as the flyer on the other side of the paper. That flier was not me as the barrel will typically put 4 rounds in about 2-2.5” with a 5th round in orbit. There is no rhyme or reason to when the fliers come in the 5-round string. Shooting the gun with a thread protector results in rounds all over (and off) the paper. For perspective, here is 5 rounds from my G26.5 MOS with stock trigger and Holosun SCS MOS at 20 yards using the same rest and 147 grain HST.