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In a recent thread http://rugerforum.net/optics/82255-lightweight-scope-10-22-a-3.html , there was a discussion about changing the parallax adjustment on a high power rifle scope to make it better suited for a rimfire ... changing from a typical corrected distance of 100 yards to a more practical distance of 50 yards. I decided to try the suggested procedure with one of my own scopes and found it works but ... it raised a couple questions ... especially about loosing the nitrogen in the scope when removing the lock collar on the front lens.

After doing some research and talking to the experts at Burris, I found out some valuable information. First, nitrogen is used to purge the normal air (which contains moisture) out of a scope and replace it with "dry" nitrogen. This procedure is done to prevent moisture from condensing inside the scope (fogging up), and to prevent oxidation of the scopes internal components ... namely when dissimilar metals such as aluminum and brass are in contact with each other, they tend to create galvanic action (corrosion) and over time will literally destroy the integrity of the scope from the inside. Further, nitrogen makes the "O" rings used to seal the scope tube last much longer.

Most scope manufactures purge the ambient air out of a scope during the manufacturing process .... good enough where the scope will at least be fog free when the customer buys it. The better quality scopes are purged with nitrogen then filled with nitrogen and sealed by "O" rings on each turret screw, plus the front and rear lens housings and any other potential leak areas such as a side dial or turret bases.

What makes a non-nitrogen filled scope draw moisture? It's a change in barometric pressure caused by changing climate conditions or a change in altitude. As the pressure outside the scope is increased (higher barametric pressure or lower elevation), the scope will literally suck outside air into the tube. Further, if barametric pressure is low or you are at a high altitude, the pressure inside the scope increases and will allow dry air to leak out. As a scope goes through several barametric pressure cycles, the dry air inside the tube will eventually be displaced by moist air, unless the tube is sealed very well. When temperature drops below the dew point, moisture will condense on the lenses and other parts inside the scope tube.

There are at least two different procedures for "nitrogen filling" ... the cheapest, easiest, and most common with cheaper scopes is to install a port ... much like a tire stem valve where nitrogen is pumped into the scope tube and allowed to vent through a turret screw hole. Once the scope has been purged, the turret screw is installed and sealed by an "O" ring, then the scope is pressurized slightly with more nitrogen. This is a very effective and probably the best way to fill a scope with nitrogen, however after the scope has been filled, the valve has to be sealed so this process is a "one time deal" and can not be used again.

Burris feels so strongly about this nitrogen filling concept that they nitrogen purge each scope 24 times inside a vacuum chamber then fill it with pure nitrogen and seal it. They also use double "O" rings at each potential place where the scope could leak. They claim their process is the best of all scope manufacturers. Of course I had to ask "why the extreme measures?" The answer was ... "if you ever had an expensive scope fog up on a hunt you would understand. Plus ... Burris scopes have a lifetime gurantee so if moisture was allowed to get inside, they will not last as long." I was also told ... Burris' main competitor (Leupold) only uses single "O" rings and doesn't go through near as much effort to purge their scopes.

My primary question to Burris was "What did I do to my Japanese scope by removing the front lens collar?" Answer: "At a minimum, some of the nitrogen leaked out and was displaced by normal air. The amount of moisture inside the scope will depend on how long you left it unsealed, the barometric pressure, and how high the humidity was at the time. It did not instantly ruin the scope but it is now more subject to fogging and its extended life has been shortened. Some scope manufacturers will repurge and fill their own brand of scopes for a fee. Burris will not do this on any brand other than their own."

"What about bagging the scope with Silgel to absorb moisture with the collar removed?" Answer: "Silgel will absorb some moisture but unless you have a way to purge the air out of the scope, it would not be effective enough to matter."

"How about testing the scope in a refridgerator?" Answer: "Yes, this will work but if your scope does fog up, it would be very difficult to remove the water droplets and may make the scope unuseable.

Last, I had to ask about changing the parallax adjustment and got this for a reply ... "Burris does not recommend this procedure for obvious reasons. The lenses in our scopes are designed for an approximate parallax correction at a given distance then precision adjusted for the corrected distance as noted in our advertised specifications. The process for precision adjustment is basically the same as you noted, however there are issues involved with changing the adjustment radically without changing the lenses. Yes, it will work but because parallax is much more critical at closer distances, if you radically change the distance for correction, you lose focus at longer distances. Burris strongly recommends buying a rimfire scope instead of trying to modify parallax correction for a high power rifle scope."

I realize some of the information I got from Burris was "company line" but they did make some very valid points ... especially about nitrogen. I don't believe I will modify any more scopes based on this information. YMMV.
 

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Thank you for sharing Burris' perspective.

Something I don't understand, and hope you can help with/explain, is how one can 'purge' a scope with nitrogen without 'filling' it with nitrogen at the same time. Any thoughts?

I quite accidentally rotated the objective lens on a Nikon the other day. It was surprisingly loose, and something felt funny as I was working with the rifle. Investigation showed that the 'funny' feeling was the objective assembly rotating. I snugged it back up, but it easily moved enough to have changed 'best' parallax adjustment distance from 100 to 50 yards.
 

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Thanks for the information...I've not hunted for a number of years but "back in the day"...in the 50's and 60's when we "all" used Weaver K-4 scopes...the deal was....always leave your gun outside over night when it was cold because if you kept it in the tent or cabin with the heater when you hit the cold in the morning it would fill the scope with fog and often it wouldn't clear up all day...probably no nitrogen filled in those days...just makes sense...no moisture and no fogging.
 

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MZ5, Purging simply means to remove and replace so I'm sure they do "fill" it when they purge. Removing the nitrogen is done by placing the scope in a vacuum chamber and literally sucking the air out. The goal is to reduce moisture as close to 0% as possible. Filling it just one time obviously doesn't doesn't get the job done.

I don't know how may turns you made on your Nikon but on my 4x scope, it took about 10 full turns (unscrewing) to change the parallax correction from 100 to 50 yards.

opos, Yes, I do remember the old steel tube Weavers ... I owned several of them. They were not nitrogen filled nor were they sealed .... I took a bunch of them apart, cleaned up the innards and put them back together. Other than fogging up, they were nearly indestructable.
 

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Nice write up. If you do decide that you want to change your set parallax distance and you own a Burris scopes we will change it to whatever distance you desire. Just thought I'd let you guys know.

Another process used by some of the lesser expensive scope manufacturers is to use what they call a "nitrogen environment" when assembling the scope. This basically means they don't purge the air at all but simply have an area (I personally imagine a bucket in my mind) that is filled with nitrogen and "swish" it around before closing it up. With nitrogen being heavier than air you can literally fill an open bucket with the stuff.
 

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I have an old Weaver 4X scope that is dirty on the inside. I thought about taking it apart, cleaning it and then purging it with argon. Argon is easy for me to get as where I work there are multiple welders. I need to look up if argon is heavier or lighter than air so I know which way to hold the scope when I fill it. Argon gas is what most newer house windows are filled with.

Edit: Good to know that the old Weavers are not sealed.
 

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Discussion Starter #8 (Edited)
Burris Optics, Thanks for chiming in .... I was very impressed with the person I talked to at Burris ... maybe it was you??? BTW, I own several Burris scopes and have been very happy with them. The last one I bought (FullField II) had "Made in the Phillipines" on the box. What's up with that? I thought all Burris scopes were made in Colorado.

I'll bet you cringe when you see what customers do to your scopes.

"nitrogen environment"
With some of the cheap Chinese crap on the market, it wouldn't surprise me if some assembler just wispered "nitrogen" on the scope and called it good.

IanS, Argon is lighter than air but I doubt if it will do much good to purge your Weaver with it. The turrets and turret screws are not sealed so it will all leak out.
 

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Since we have the Burris folks on board, I have a question. If a customer does mess with the front lens to change parallax and thereby lose some nitrogen in the process, has the customer then voided the warranty? Would Burris re-purge for free, under the warranty, or charge the customer for the service?
 

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... and to piggy back on NCG's post ... what does Burris charge to change the parralax corrected distance?

Do they really purge Burris scopes 24 times?
 

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Interesting response from Burris, as you point out it does likely contain 'company line' statements.

My own comments are based on my own personal experiences over the last 25 years of messing with scopes.

I have re-parallaxed more scopes than I care to remember and made significant alterations to other scopes - such as swapping low profile turrets for target turrets on Leupolds.

Number of incidents of fogging or other scope failures to date - zero.

The above will not stop me adapting a scope to my requirements.

Just one other thought to bear in mind - this is the composition of normal air:

Nitrogen -- N2 -- 78.084%

Oxygen -- O2 -- 20.9476%

Argon -- Ar -- 0.934%

Carbon Dioxide -- CO2 -- 0.0314%

Neon -- Ne -- 0.001818%

Methane -- CH4 -- 0.0002%

Pretty much the only problematic issue with normal air is water vapour content. A scope filled with dry air is basically no more likely to fog than if nitrogen 'purged'.

The galvanic corrosion issue I think is a bit of a red herring here, unless the moisture contains a dissolved electrolyte. Pure water is merely a solvent not an electrolyte in its own right.
 

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IanS, Argon is lighter than air but I doubt if it will do much good to purge your Weaver with it. The turrets and turret screws are not sealed so it will all leak out.
Ah, I didnt think about the turrets and turret screws. I was mainly thinking about the caps that hold the lenses in. Im glad I mentioned my idea here, now I dont have to waste my time filling with argon. I can just tear it apart and clean it.
 

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Burris Optics, Thanks for chiming in .... I was very impressed with the person I talked to at Burris ... maybe it was you??? BTW, I own several Burris scopes and have been very happy with them. The last one I bought (FullField II) had "Made in the Phillipines" on the box. What's up with that? I thought all Burris scopes were made in Colorado.

I'll bet you cringe when you see what customers do to your scopes.
I'm sure you talked with one of the CS reps but they are very good at what they do and are very helpful and informative.

We've been manufacturing our FF line in the Philippines for several years now and we've been happy with the end product. As much as we would love to be able to build them here in the US as we had for so many years it was just impossible to do that and keep our pricing where we wanted. We continue to build scopes here in the US but as you can imagine it is reserved for our higher end scopes. Please keep in mind that we have strict control on our scope manufacturing even overseas.

I've seen just about everything happen to our scopes. Nothing surprises me anymore but in the end we usually take care of the problem.
 

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Since we have the Burris folks on board, I have a question. If a customer does mess with the front lens to change parallax and thereby lose some nitrogen in the process, has the customer then voided the warranty? Would Burris re-purge for free, under the warranty, or charge the customer for the service?
Technically you have voided the warranty and we have every right to refuse to do any repairs or even charge you for it. Do we usually do that? No we don't. We try to help our customers whenever we can as long as it's within reason. Re-purging isn't a problem if it needs it but I highly suggest that you just contact CS and send your scope in so we can change you parallax setting for you. We don't charge for you to do that and you'll know it's been done correctly.
 

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... and to piggy back on NCG's post ... what does Burris charge to change the parralax corrected distance?

Do they really purge Burris scopes 24 times?
We won't charge you anything to do that. You will need to pay to ship your scope to us but we ship it back to you on our dime.

Yes we absolutely purge 24 times on every scope we make. No exceptions.
 

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Technically you have voided the warranty and we have every right to refuse to do any repairs or even charge you for it. Do we usually do that? No we don't. We try to help our customers whenever we can as long as it's within reason. Re-purging isn't a problem if it needs it but I highly suggest that you just contact CS and send your scope in so we can change you parallax setting for you. We don't charge for you to do that and you'll know it's been done correctly.
Thank-you. (Just bought a Burris 4x pistol scope, by the way and love it. :))
 

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We've been manufacturing our FF line in the Philippines for several years now and we've been happy with the end product. As much as we would love to be able to build them here in the US as we had for so many years it was just impossible to do that and keep our pricing where we wanted. We continue to build scopes here in the US but as you can imagine it is reserved for our higher end scopes. Please keep in mind that we have strict control on our scope manufacturing even overseas.

I had a Timberline 4.5-14x32 scope for a while, I would have to say it was a damned fine little scope, in fact I personally thought it had better optics than a 3-12x32 US made Burris I owned several years earlier. The Timberline had the mag range I wanted, it focussed down to 10 yds (and less IIRC) and had a perfect eye relief as well, the only thing that let it down and which is why I sold it on, was the reticle in my example was a bit too fine and I was losing it against dark targets.

Let me qualify the last bit, I used it on my .44 Henry lever action to shoot a series of competitions under the name 'Gallery Rifle' here in the UK, some of these comps have quick timed stages where a target makes a 2 second exposure for one shot to be fired and 3 second exposure for two shots. The target have a disruptive pattern, so a very fine reticle can be a disadvantage to acquiring a good sight picture in the face times of the target.

As Timberline's are quite difficult to find in the UK, I had to go with the reticle on the example I found IIRC it was a ballistic plex. By choice a nice bold duplex type reticle would be my preference. When winning scores in the top class (where I currently sit) are on the maximum of 300 points and it is a countback on x-ring hits it is critical that the equipment is spot on for the needs.
 

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Another process used by some of the lesser expensive scope manufacturers is to use what they call a "nitrogen environment" when assembling the scope. This basically means they don't purge the air at all but simply have an area (I personally imagine a bucket in my mind) that is filled with nitrogen and "swish" it around before closing it up. With nitrogen being heavier than air you can literally fill an open bucket with the stuff.
That is technically incorrect.
Nitrogen gas is less dense than air.
That would work with Argon, which is quite a bit denser than air.
In my industry where work is done with water reactive metals, pyrophoric, oxygen sensitive, and explosive materials, the standard is to evacuate a vessel with vacuum, repressurize with nitrogen, then repeat 2x, for a total of 3 cycles. Argon is used in applications where a solid might have to be added to a reactor but an inert and dry atmosphere is to be maintained (absent of drafts or air currents, Ar will more or less stay put for short periods of time).
Purging 24X would certainly be overkill, but I can't fault an extra step to ensure quality.
 

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rockdrill, Obviously our needs are much different. For me, it only makes sense to either have the scope company do the parallax correction and do the nitrogen trick if necessary or to just buy the right scope to begin with, just as the customer rep from Burris suggested.

The composition of air is really immaterial ... it's the humidity compounded by extreme weather conditions that we fight here on a daily basis. Here's some examples ... two years ago the Missouri River flooded and got within 30 meters of my house. Last year we had a bad drought ... virtually no rain for 6 months. This past May was really extreme ... on May 2, we had 6" of snow and a mere 10 days later we had a record 101 deg F. In mid-May we had a hail storm that demolished the siding and roof on our house. It only lasted about 10 minutes but we had hail stones as large a base balls. Our normal yearly temperature extreme from hottest to coldest is over 120 deg F. Right now it is raining and the barometer has dropped very low. I can almost bet when the front passes, we will see the barometer jump up very quickly. Further, (no offence) but the "mountains" you have in the UK are nothing more than hills here. Where I live is about 1200 ft (365 meters) elevation but at least once or twice a year I drive to Estes Park, Co to visit my friend and do some shooting. Where he lives is about 7500 ft ev (2300 meters) but where we shoot just a half hour away is 11,000 ft ev (3350 meters). I used to hunt deer and elk in this same area. These are the very reasons why a scope will suck in moisture and I suspect it is also the reason why Burris goes to such extremes purging, nitrogen filling, and sealing their scopes.

As for galvanic action .... the old Weaver K series were notorious for internal corrosion due to galvanic action. Steel outer tube, aluminum inner tube, and brass parts ... a bad combination. It is not unusual to see the inside of the outer tube rusted and pitted with green slime on the brass parts and severe corrosion on the inner tube. If humidity was indeed pure water, it would not form an electrolyte but no doubt, some other foreign stuff in the air changes that.

Most of the scopes I own were bought for a specific gun and application. I have also accumulated several scopes (mostly cheaper ones) from various gun trades. It wouldn't bother me a bit to alter the parallax adjustments on cheap scopes ... if they go bad, I'm not out much and I doubt if they were even sealed or nitrogen filled to start with. That said, most of my other scopes are quite expensive so I don't want to risk potential damage. I have several Burris scopes as well as Nikons, and Leupolds ... but my pride and joy is a Shephard 6~18x40 Varminter that I purchased directly from the Shephard factory, just a 20 minute drive in Wahoo, NE. If you never heard of a Shephard, it's worth the time to check out their web site: THE ONLY RANGE FINDING SCOPE THAT DOES NOT REQUIRE 3 HANDS TO OPERATE

Please don't take my point of view as an attack or even an argument about your dealings with scopes. As I said before ... our needs are much different so if your modifications have worked out for you, I'm happy ... any yes, maybe a bit jealous too.
 

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Nitrogen purging is a standard industry practice to obtain a 'gas free' and moisture free environment. Typcally this takes at least 3 complete volume exchanges in large areas, like ships. The fact that Burris is doing this 24 times is overkill and in my mind means it is an absolute that there is no moisture inside.

FWIW I have done this to a couple of lower end scopes - I don't even remember what brand now - but I have not had any problems with them since. Both on are hunting 10/22s.
 
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