Magnified introducing parallax?

Do magbfiers introduce parallax? I’d assume no.

I was zeroing and breaking in my new 16” barrel on my AR today. First box of PMC bronze 55gr turned in great results. Bushnell TRS-25 and generic 3x magnifier (yes mounted behind the red dot). My old 16” barrel was consistently 3.5MOA no matter what I feed it. This new barrel turned in 1.5-2MOA groups at 50yds for all 4 5 shot groups.

Next a box of federal LC M193. 5-8MOA at 100yds. 5 rounds of Hornady steel match the same. PPU 55gr .223 a little better at 50yds, but still printing about 4-5MOA.

I swapped BCGs between my upper, scrubbed out the barrel and finished off the box of 55gr PPU. 3-4MOA. Then a box of 69gr PPU HPBT and it was 3x5 shot groups of the same and then the final one turned in a nice clean 1.2MOA and then I had to pack it up for the day.

No fliers in these groups, there were all just spread out.

All were with the magnifier UNTIL the last 5 shot group when I took it off and turned in that best group of the day. A couple of times I noticed it was getting loose on the rail and once in the middle when I noticed it was getting loose it was also touching the red dot at that point, so I moved it back a space on the rail (so the last few groups with the magnifier it was spaced further back).

So that PMC was shot with the magnifier and were really good (IMHO and considering a 3 MOA red dot in use). That last group of the PPU 69gr was also fantastic and had no magnifier used at all.

Any thoughts? Next time I will leave the magnifier at home. Could a bad/loose/in contact with the red dot magnifier screw up my groups?

Could some of those just be barrel break-in? It was only about 60 rounds total shot through the rifle (did some shooting with my 20” also).

Windy as heck today, but not so bad it would screw up my groups this bad at these distances and I was mostly shooting when the breeze died down.

Any chance of seeing a picture of your set up(gun with sight and magnifier on it)?

Rate of twist?

Did you mount this new barrel yourself?

outrider58 said:

Any chance of seeing a picture of your set up(gun with sight and magnifier on it)?

Rate of twist?

Did you mount this new barrel yourself?

Click to expand...

Yup, barrel mounted myself. Used a torque wrench and crows foot wrench, so it should be properly torqued. I'll try to get pictures later this evening of how it was setup.

1:8 twist on the barrel. What is nuts to me is that the PMC was shooting universally well, then nothing shot well at all, and the PPU 69gr wasn't even shooting that great, but suddenly shot great once I took the magnifier off the rifle, but only that final group before I had to pack it up and head home.

I double checked the red dot and it is tight. No loose screws, no give in it.

I may drop some BUIS on to the rifle before I go to the range next time and double check with both the red dot, and irons and NO magnifier. See if there is any chance it is the red dot is having problems. Sadly I don't have any spare rifle scopes to try with one to see what the best possible accuracy is out of this setup. It seems to have promise, but I am just all kinds of confused why the groups fell apart, and then one great group was turned in (and it wasn't like a 2 shot group, 5 shot, so even random chance shouldn't have had 4 holes basically touching and a 5th one half an inch off the main group at 50yds).

I lied. I ran and grabbed pics quickly. Here it is with how I normally run it (just the TRS-25) and here it is with how I had the magnifier mounted at the end. earlier on I had it one slot closer so it was maybe half a millimeter off the red dot. The magnifier came loose once or twice and once I noticed because the red dot was almost as the bottom of the magnifier and I went “that’s not right” and realized the base knob had come loose.

I wish I had had more time to shoot with just the red dot a few groups.

One thing I did find, the LaRue MBT trigger rocks!

I just realized not the best pictures. I can get better ones later if that helps

I'm not saying this will make a big difference, but I recommend you move the red dot forward so it is centered more over the ejection port. That way, you can move the magnifier forward. The ocular bell shouldn't extend rearward beyond the receiver end plate.

3x magnifies generally don't have noticeable parallax. Mainly because of their fixed, low power.

Did you true the upper receiver extension (the area where the barrel extension snugs up to the receiver)?

Did you seat the barrel with Locktite 620?

Those two steps are not mandatory, but they will head off possible problems.

Before you go digging deeper into your gun(other than repositioning your sights), buy some Black Hills 68gr. match ammo and see how that shoots. Your gun should do better than 1.5" @ 50 yards. If you can't find any, come see me. I have plenty.

If you are accuracy testing just buy a lower end scope. I did just for that purpose. All but one of the red dot sights I have used are not precise for my eyes. All the ammo you said you used shows proportionate accuracy in my guns at 50 and 100 yards. With a red dot...my 100 yard groups open up disproportionately. I do better with irons over the red dots at longer ranges.

outrider58 said:

I'm not saying this will make a big difference, but I recommend you move the red dot forward so it is centered more over the ejection port. That way, you can move the magnifier forward. The ocular bell shouldn't extend rearward beyond the receiver end plate.

3x magnifies generally don't have noticeable parallax. Mainly because of their fixed, low power.

Did you true the upper receiver extension (the area where the barrel extension snugs up to the receiver)?

Did you seat the barrel with Locktite 620?

Those two steps are not mandatory, but they will head off possible problems.

Before you go digging deeper into your gun(other than repositioning your sights), buy some Black Hills 68gr. match ammo and see how that shoots. Your gun should do better than 1.5" @ 50 yards. If you can't find any, come see me. I have plenty.

Click to expand...

I didn’t true it. I sued Aeroshell, not locktite when I torqued down the barrel nut. The issue with the mag icier is that the eye relief is pretty short on it. So if I want full field of view it needs to be that far back, or else I have to climb way down the stock.

I can try moving them both up a spot or two.

I’ll also look at getting some black hills. I do have some Hornady 75gr match as well as Hornady frontier 55gr and 68gr match. The 55gr match also turned in a bad performance. Still trying to figure out what the crazy issues were. I’ve got at least another box or two of PMC bronze. I am thinking when I head back I will take a box of that and a few boxes of some other stuff and give it a shot with irons in tow and skip the magnifier. See what my results are. Try several weights of match ammo.

So interesting thing I found. This.

https://m.youtube.com/watch?v=2jPVvt5-1JM

The TRS-25 definitely has noticeable parallax shift. I haven’t noticed it, but I didn’t really check for it either and I’ve onky used this magnifier twice before (with old barrel I also remember thinking the magnifier didn’t help my accuracy any. It helped see my target better, but my actual group sizes were no better or maybe even a little worse). A magnifier, especially one that isn’t staying tight would probably make that parallax worse if I was repositioning shot to shot to keep my view centered through the tube, even if only shifting a fraction.

Certainly time to retest with just the red dot and BUIS on the rifle on a calm day with several loads in tow.

outrider58 said:

I'm not saying this will make a big difference, but I recommend you move the red dot forward so it is centered more over the ejection port. That way, you can move the magnifier forward. The ocular bell shouldn't extend rearward beyond the receiver end plate.

3x magnifies generally don't have noticeable parallax. Mainly because of their fixed, low power.

Did you true the upper receiver extension (the area where the barrel extension snugs up to the receiver)?

Did you seat the barrel with Locktite 620?

Click to expand...

Sorry for the lack of clarity. The Locktite 620 is applied in a thin, even coat to the barrel extension (the part that inserts into the receiver extension. Wipe off all the excess before applying aero shell and engaging the barrel nut).



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outrider58 said:

Sorry for the lack of clarity. The Locktite 620 is applied in a thin, even coat to the barrel extension (the part that inserts into the receiver extension. Wipe off all the excess before applying aero shell and engaging the barrel nut).



Sent from my SM-G965U using Tapatalk

Click to expand...

Ahhh! I see. Definitely didn’t do that. I guess if this continues to present issues I know what I am doing later... :-)

So the path I am going down is I ordered a Brownell’s barrel lapping tool and lapping compound. I figure in for a penny, in for a pound. I’ll lap the upper receiver and bed the barrel extension with locktite.

Then when I go back to the range I am going to take my spare Bushnell TRS-25, my BUIS AND my 20” so I can swap my scope/mount from my 20” to my 16” and take it for a spin, then remount and rezero on my 20”.

See what the heck it’s actually made of.

I have a spare cantilever mount, one of these days soon I need to get a cheap scope to drop in to it just for testing new builds. But I figure this will do for now.

I still kind of suspect it was/is an optics issue. But I might as well put in the work to try to maximize the accuracy potential and if it is part of what is causing problems, hopefully fix it. I also don’t mind putting the work in to future builds to increase accuracy either (my 20” I plan to replace the barrel soon with a new SS nitrided 5r fluted HBAR barrel, since I am absolutely looking for an accurate build, lapping and bedding that upper isn’t a bad idea).

lazarus said:

So the path I am going down is I ordered a Brownell’s barrel lapping tool and lapping compound. I figure in for a penny, in for a pound. I’ll lap the upper receiver and bed the barrel extension with locktite.

Then when I go back to the range I am going to take my spare Bushnell TRS-25, my BUIS AND my 20” so I can swap my scope/mount from my 20” to my 16” and take it for a spin, then remount and rezero on my 20”.

See what the heck it’s actually made of.

I have a spare cantilever mount, one of these days soon I need to get a cheap scope to drop in to it just for testing new builds. But I figure this will do for now.

I still kind of suspect it was/is an optics issue. But I might as well put in the work to try to maximize the accuracy potential and if it is part of what is causing problems, hopefully fix it. I also don’t mind putting the work in to future builds to increase accuracy either (my 20” I plan to replace the barrel soon with a new SS nitrided 5r fluted HBAR barrel, since I am absolutely looking for an accurate build, lapping and bedding that upper isn’t a bad idea).

Click to expand...

Sounds like a good plan.

I totally agree with Magnumite that the best way to help realize the accuracy of your rifle will be to put a scope on it. Even if your future plan.is to go back to a red dot, you'll have a true realization of what you rifle will be capable of.

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outrider58 said:

Sounds like a good plan.

I totally agree with Magnumite that the best way to help realize the accuracy of your rifle will be to put a scope on it. Even if your future plan.is to go back to a red dot, you'll have a true realization of what you rifle will be capable of.

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Click to expand...

Okay, thanks!

Maybe some day I’ll consider a 2.5 or 3x prism sight. Mostly want to keep this one as light as possible (and as light as MD will allow) and also more of an HD rifle. So the red dot seems more appropriate to me for very close range, high stress use. 10MOA is fine accuracy for corse the house use.

That said, I’d like something that can manage 2MOA with the mounted optic/sighting system and basic platform accuracy.

I have several rifles where I assign both a scope on a quick release and a Red Dot on a quick release.

With the exception of adhering to 3 gun rules, this arraingement has served me better than a magnifier behind a Red Dot

YMMV