Rifle Scopes Bushnell ET35215GZA ERS click value

[flatland1]

Bought a new Bushnell 3.5-21x50GZA in FDE for my 260 Imp 30* late last fall, and finally got around to shooting a box with it last evening. I put a couple of rounds into the X-ring on the reduced SR-21C to confirm my 100yd zero, then moved 1 mil right, 1 mil up, (would've gone 2 mils up, but that'd have taken me off the repair center), 2 mils back left, 1 mil down, and finally 1 mil right, back to original 100yd zero, firing one shot after each adjustment. Scope returned to original zero pretty well, no issue there. But, the two shots fired at 1 mil above the 100yd zero both measured 4-1/8" high, instead of the expected 3.4".

These results go a long way towards explaining why I consistently get groups 4.5"-5" above the aiming point at 600 when I use the 3.5 mil come-up both Shooter & Applied Ballistics calls for with 123s. I've been over this issue at least twice, starting out by confirming my 100yd zero while shooting over the chrono, then using this fresh/real-time velocity data when inputting data for the 600yd come-up. I've got a Kestrel 4500NV, and typically use it so my wind inputs are more than just a SWAG. And we checked my CED M2 chrono against a friend's MagnetoSpeed last August, getting velocity readings out of the M2 that were consistently 4-6fps lower than the MS's output.

We've got a practical steel match coming up in a week, so there's not enough time to get in touch with Bushnell's service dept, get the scope sent in & get it back. If I could get out on a day with decent conditions to double check these results, as well as check it out at 1000yds, I could do the math and come up with a conversion factor. But one of the main reasons I went with the FFP G2DMR reticle in a mil/mil scope was to minimize the amount of mental math while on the line. Has anyone else had this sort of problem with their HDMR or GZA scopes? If so, was Bushnell able to fix it, or replace your scope?

 

[0311@LAR]

I wouldn't put a whole lot of stock in the 2 shots you fired. I would do a whole lot more tracking tests before you get it in your head that the scope isn't working right.

 

[redx]

Did you calibrate your speed in your ballistic program to your actual confirmed dope? I have the same scope and once I calibrated my actual confirmed dope to my apps the scope is dead on out to 1200 on my 6.5 creedmoor

 

[redneckbmxer24]

It definitely shouldn't be tracking like that. If it's consistent though just log actual adjustment in that scope as your dope to get you through the match. If it's returning to zero it's tracking consistently at least.

 

[flatland1]

Need to shoot some more to confirm that the click values are off before calling Bushnell. Three shot group at 100yd zero followed by another 3 at 1 & 2 mils should tell the tale.

Other than this, I've been pretty pleased with the GZA ERS - good optical quality, nice reticle, good return to zero, and the locking turrets & zero stop. Hard to beat it for the price level, but a problem like this makes me all that more curious about some of the new scopes that were announced at SHOT.

 

[flatland1]

Took time today to do the math to come up with correction factors for both elevation & windage click values, based on the results of the box test I shot several days ago. Came up with a factor of .915 for both E & W, then edited the rifle's profile in Shooter to apply those factors. Wind finally died down enough late this afternoon to allow some shooting, so I loaded the truck up with bench, rifles, ammo, etc. and headed down to set up on the 1000yd firing line. Didn't have enough daylight left to confirm how close the correction factors were going to work at both 600 & 1000; felt that shooting at 1000 would be the acid test anyway.

Shooter called for 7.7 mils up & .2 mil left, so I put that on the scope and set down to shoot. Got five out of five hits on the full-size IPSC AR500 target, though I had no idea where the hits were. Turns out four of five went into a 4-3/4" group 4" above & 4" left of the black aiming point on the IPSC target, with one shot (first out of a cold/clean bore?) 13" straight down from the group. My 1000yd firing line is almost 100' above the backstop, which could be a contributing factor to the slightly high impact, but overall, I'm satisfied that I've got a handle on the issue of the clicks being worth a bit more than a tenth of a mil. Time will tell, as we've got a practical steel match coming up next Saturday, and this is the rifle/scope I'll be shooting. Will probably still give the guys at Bushnell a call to discuss this with them, but today's experience inspired confidence in the Bushnell.

 

[LawnMM]

Even minor errors in the fundamentals can produce pretty large changes in point of impact at 1000 yards. Confirm your zero and dial like 10 mils of elevation above it and fire again, say a three shot group at zero and a three shot group at 10 mils. Then measure the actual travel for what you dialed and apply a correction factor. Its pretty rare for a scope to track 100%

 

[flatland1]

LawnMM,
That's what I intend to do - if we ever get a day or two when the wind's not howling - it's already up well over 20mph this morning. Since I had to dink around with the correction factor to get the results I was looking for, it's a sure bet that the data I used (mentioned in my 1st post) weren't truly representative of what the scope's click values really are. Using the value obtained by going out 10 mils as you suggest would give much more meaningful results, and increase the likelihood of getting a correction factor closer to dead nutz on.

I spoke with a tech at Bushnell on the phone this morning, and explained the situation using the same language I posted here. He asked me to write down what had happened, just as I explained it to him, and is sending a call tag out for the scope. I told him I was confident that the correction factor would allow me to shoot with the scope in the match this coming weekend, and would send it back ASAP after that. He knows the folks who host these matches; I took it from our conversation that he'd actually been out to see their range. Great to deal with someone who understands what we're doing, and who wants to do all that he can to make sure we're satisfied with the product he represents. As I mentioned before, I'm happy with the optical quality & features of the ET35245GZA - getting it tuned-up so that the adjustment values are closer to spec will just make a good scope better.

 

[Ming_the_Merciless]

Scope returned to original zero pretty well, no issue there. But, the two shots fired at 1 mil above the 100yd zero both measured 4-1/8" high, instead of the expected 3.4".

A MRAD scope w/ a click value of 0.1 mils, should actually be moving the impact 3.6" not 3.4" at 1 mil. A tenth of mil is equal to 0.36" at 100 yards, so one mil is equal to 3.6". It's a common mistake, getting the numbers switched with MOA, as 1 mil = 3.4 MOA, but 1 MOA does not equal 1", but rather 1.047" (3.4 MOA * 1.047 in/MOA = 3.6"). So it's a typo on Bushnell's website listing a click value of 0.34" at 100 yards. But, you still have about a half an inch of difference to account for at 100 yards, from 4.125" - 3.6", gives a difference of 0.525", which is within your margin of error, assuming a sub-half MOA gun.

As for your discrepancy in elevation holds at 600 yards (3.5 mils - 75.6"), resulting in impacts 4.5-5.0" high (70.6" of drop - 3.3 mils), try holding over instead of dialing to compare the results. If the impacts remain the same at the 3.3 mil line, after using hold overs, then you've ruled out a bad tracking scope and have to true either the BC or muzzle velocity in the ballistic calculator to match actual POIs. If they are different, holding over v. dialing, as you suspect, then your looking at about 0.2 mil difference, so compensate with two clicks on your elevation holds if dialing.