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Angled bases and things that happen

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/18/2006 at 18:52
Mike McDonald View Drop Down
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In another topic , I forget which one, I commented on a cheap and dirty way to test a scope with little time invested.

It occrred to me that illustration might be in order, so you're all stuck with another diatribe from yours truly.

Alot of shooters mount scopes on angles bases to extend the range of elevation adjustment available to them.

Most often it's just a fashion statement and not well thought out.  There are consequences to this and I thought it best to simulate those in order to provide a better understanding. 
What I did was take a multi thousand dollar scope, not a cheap wally world unit, but one of the best on the market, and crank the elevation all the way down to the bottom stop.  It was then backed out 10 moa to simulate being on a 20 minute base.  The scope sat in this condition for 5 days.
At the range, a cold bore target was shot, after having dialed back my correct recorded  100 yard zero setting, you have your zero setting noted in moa from bottom of elevation don't you?
What follows is the picture of what has happened with the scope internals;



You can see that the elevator spring has taken a set, and is now not holding the erector assembly against the adjustment flats with enough tension to prevent bouncing from shot to shot.  A rifle that once shot a 1 hole group now shoots patterns, and not to the point of original zero.

Fast forward 4 hours, in which time the elevation has been run to max height, and we dial back to  our 100 yard zero and shoot another group;



You can see the low shot, shot number 1 followed by four shots in a decent cluster.  Still a full moa low from zero setting.  The spring has taken a set, and will not recover from this compression.  The scope does track properly because it's agood quality, properly wound and tempered and of sufficient length to allow for just this occurance, and once rezeroed performs just like it always has.

Now imagine you're the shooter who owns a $1000.00 plus optic on a fashionable 20moa or better (worse?) angled base.  Ever wondered why your zero shifts and your load shoots better far than near?


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/18/2006 at 19:31
Anthony View Drop Down
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I don't mean to bust your chops here but I have a 20 moa base, mounted on it are 1/2" rings(from base to tube) this is my preference due to the shape of my cheek and jaw. Even with the elevated base it needed to be cranked up +2 moa from the center for 100yds, now I don't even come close to knowing as much as you do about scopes, but I do know that companies that make scopes store them at the very center and it would be quite stupid to shorten the shelf life so much by subjecting the spring to too much tension for long periods of time. And leave a lot of unsatisfied customers that will no longer buy there products. The rifle doesn't produce "bughole" groups like some of yours but it is sub-moa. basically what I am trying to say is that as long as you don't buy something like a 40moa base you will be fine, I have found that on average you have to bring it up a whole 10 minutes, and so if you shim it for 10 moa shouldn't that be fine?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/18/2006 at 20:46
Mike McDonald View Drop Down
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Sounds like the 20moa base on your rifle is just correcting a fault in the receiver machining spec.  It's not common but I've seen it a few times.  Obviously in an instance like this you're really shooting froma a flat base.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/19/2006 at 14:15
Trinidad View Drop Down
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Great post mike, I see this alot on 100yd weekend in a blue moon rifles.

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2006 at 21:24
Mike McDonald View Drop Down
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Just a follow up to show that good scopes can recover from intentional abuse by their owners  



Funny story behind this...well at least if you'd been there.

I'm at my favorite range delivering some items for an upcomming match and.............well who goes to the range unarmed right?

So I get the PacNor out of the trunk and walk right into a 5 day LE only sniper school, full of students eager to learn.
They'e on day 2 of the itteration, which is the first full 8 hour range day of the class and they are still green and somewhat intimidated after having spent  day  1 with a pair of "real world been to several continents and did this already for over 20 years instructors", one of whoom is now running the firing line.

 Instructor friend see's me, goes down range and sets a target right in the middle of all students targets.  I got a feeling I know what he's up to...
Line is called hot and from my shooting point , 45 degrees off center to the target, the only shot I intend to fire that day went..........................well..it went where you see it.
The students at this point are not shooting quite this well just yet and it's a bit unnerving for them to see some nondescript old guy show up in a taurus with a trunk full of go gear and pull this stunt.

We go pull targets and the instructor iis being asked " who is that dude?"  Answer they didn't get of course is that I'm nobody at all.
He never told them and they're still wondering, and the instructor I'm sure is beating them over the head with the experience, just cuz he has a warped sense of humor. 

By the end of the week the Texas LE community will have 8 very highly trained shooters thanks to these two guys.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/20/2006 at 22:04
Anthony View Drop Down
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I recall on one occasion at the pistol range (25yds) an average guy sweating beads, and holding a sig 226 with a massive tremor. I was very proud of my neat 4 inch group with my USP, and I peeked over at his target, no joke there was a 1 inch hole about 1.5 inches below the center of the target.  I said; "how do you do that?". he looks at me with surprise and says; "I thought that was normal?" I pointed to a target that was about 3'x1.5' in another lane that looked like it the shooter had hit the center 3 times and everything else 10 times, and replied: "that is normal", "how long have you been shooting that thing?". He tells me that he was renting it for the day and still doesn't really own a gun yet. I handed him my beretta 96 that no one I met has ever been able to group well, and shoots 1.5" group with it.

 

I went to the range that day with confidence, and left feeling like I was... well not the envy of the range, that is for sure. I guess what I am saying is that there are those that have it and those that don't, and apparently I don't!!

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2006 at 16:30
Rusty View Drop Down
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Mike

 

Regarding your statement: 

"You can see the low shot, shot number 1 followed by four shots in a decent cluster.  Still a full moa low from zero setting.  The spring has taken a set, and will not recover from this compression.  The scope does track properly because it's agood quality, properly wound and tempered and of sufficient length to allow for just this occurance, and once rezeroed performs just like it always has."

 

Can't you crank up the elevation, and reset the zero on the scope, and not put a "set" on the erector spring?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/25/2006 at 18:06
Mike McDonald View Drop Down
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Rusty,

Yes, look at the last pic,  I reset the zero and it holds just fine.
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