March 30mm tube true diameter??

[Willie]

I went to mount a March 3-24x52 FFP scope in a new set of 30mm ARC rings and it would not seat in the rings mounted very loosely on a Stiller 20 moa rail, nor would the rings fit the tube when off the rail.
I then checked the ARC rings on 3 other brands of 30mm scopes and they fit perfectly. WTH?
Not having a 2" mic, I measured the tube with 4 different calipers and after many measurements, came up with 30.1mm. Not a real accurate way to measure, but the tube is somewhat larger than 30mm.
My question is "Has anyone running March scopes had this problem, heard of this or have a 2mm mic to measure their actual tube diameter?"
I talked to Ted @ ARC and his thought was my March was slightly over true 30mm. Does anyone have an idea of March's tolerances?

 

[JRS]

Talk to Shiraz.

 

[nakneker]

I have that scope, no problems with rings or fit at all. JRS gives you good advice though.

 

[Willie]

Talk to Shiraz.

Sent him an email on Friday, waiting for a reply. Just thought I'd ask. I know there's bound to be +/- variances in both tube diameter and and ring bore IDs. I did go thru checking 3 sets of new rings for comparison. The Leopold and TPS rings fit very snugly and would require a lapping, most likely, once on the rail. The 30 mm Seekin rings were a good fit. Monday, I'll take all parts to a machinist friend for accurate measurements and try to get to the bottom of this.

 

[Willie]

There was a slight delay, while they checked with the engineers, but I got the response from March today. They said they set tube diameter at 30.05mm +/- .05. That means I'll have to lap the ARC rings to fit, so I'll either use the March rings they are sending or my Seekin lows. Not the end of the world, but a PITA. March did tell me the tube has to be picked up free of rings to adjust verticals or horizontal placement. Well, just as long as it doesn't move or mar the tube, I'll be happy.

 

[R.Morehouse]

March makes some real high quality rings that look great on my 36-55 EPZ..............

 

[DBLNUT]

There was a slight delay, while they checked with the engineers, but I got the response from March today. They said they set tube diameter at 30.05mm +/- .05. That means I'll have to lap the ARC rings to fit, so I'll either use the March rings they are sending or my Seekin lows. Not the end of the world, but a PITA. March did tell me the tube has to be picked up free of rings to adjust verticals or horizontal placement. Well, just as long as it doesn't move or mar the tube, I'll be happy.

30MM is 1.181inches
30.05 plus or minus .05MM is 1.181 on the low side and 1.185 on the high side.

That's only .004 thousands.

 

[spclark]

This was posted by member <Nightforce-TL> over on the US Rifleteams National Match Forum last August:

There has been serious debate as to what makes a good scope for Service Rifle Competition, so I though as an industry insider and competitor myself, I would offer my perspective:

-With quality optics, you do very much get what you pay for and that investment will typically far outlast that of the less expensive optics.The buy once, cry once adage is very true. There are optics that are "good enough" for less money, but they will typically have their shortcomings. There are reasons the manufacturer justifies the lesser cost. With optics, everything is a trade off.

-Focus on the long term; a scope that tracks good out of the box may not always track the same later. Companies typically have a track record of success in this area.

-Quality precision riflescopes are about tight and consistent tolerances, quality materials and quality control. All things that increase cost. Refer to first bullet point.

-Verify that the optic tracks straight and true in both directions and that the click values are accurate. Do this for the full range that you expect to utilize the scope. Typically this is done at 100 yards for higher magnification scopes, but by reducing the values to half and doing it at 50 yards (angular system of measurement applies) typically is a little easier and more accurate given the lower magnification.

-Make sure the scope repeats itself by performing at least a dozen RTZ (return to zero) tests after dialing different increments, shooting a round and dialing back to your original zero - a ZeroStop is a great function

-Make sure it maintains zero (POI) - fire a round at a known target spot and knock on the scope with a closed fist and fire again. Watch for any shift. There should be NONE.

-Verify that the reticle subtends properly at the calibrated magnification if using it for holds.

-If you have to rap on your adjustments to get them to move after making an adjustment - this is not acceptable.

-Check for diopter shift. Diopter is there to focus your reticle to your eye. Diopter does add and remove a small amount of magnification so it is possible to make your true 1x optic, 1.1x or even less than 1x. Set diopter on the highest mag and make sure it maintains reticle focus as you dial the magnification back. This can cause great eye fatigue.

-Use a torque wrench on your rings and bases.

-Use rings designed by the scope manufacturer when possible - they know their tolerances best and design for an optimal system.

There is not a generic scope tube size, they all differ and vary by 3 to 4 decimal points (it does matter). This especially matters when torque wrenches are not used as there can quickly be stress transfer to internal parts. When in doubt, ask your ring/mount manufacturer if they have tested with "X" scope or consulted with the engineers of "X". Geissele is good to go.

-Warranties that read like an insurance policy are great until your scope craps the bed in the middle of a championship match. Often, the best warranty is the one that you will never need and knowing the scope company will cover a failure if you do have one.

I am one that questions everything. Trust but verify. This is a game where equipment matters as much as the shooter; more evident at the higher levels.

When I give a presentation on optics, the first slide states the scopes purpose. It is there to replace your iron sights and needs to be every bit as robust - that could not be more true than for you guys being as that you have always been iron sight dependent.

The above is very much what justifies the overall cost of a Nightforce riflescope or others similar. Over the years, I have used just about every low power variable there is in the sport of 3 Gun. I quickly came to find out what worked and what did not. I purchased a many of $5-$800 optics only to have them fail when it mattered most. I came to appreciate quality optics and quality gear as they impacted my performance and it made the investment easier to swallow and more justifiable. That $3000 riflescope quickly looked cheap when I looked at all the money wasted (scopes, match fees, ammo, travel, lodging, etc.) trying to obtain performance at a lesser cost. That lesser cost is plenty acceptable if your are willing to accept the failures when they occur.

In my opinion, the most important factors to success in any competition is CONFIDENCE! Confidence in my ability to perform on demand and confidence that my equipment will perform reliably when I expect it to. When I can go into any match and feel CONFIDENT, I typically never lost.

I've colored the quoted text that addresses whether tight rings on a tube that's larger than their ID can affect performance.

I suspect much - if not all - of the above is equally applicable to optics not used for service rifle competition too.

 

[JRS]

Perfect, along with zero tolerance and a lifetime warranty is achievable. How much are you willing to pay for it?

 

[johara1]

You may want to check the rings for true size, they maybe under sized and when mounted they maybe out of alignment. That is why you bed the mount and Lapp the rings. be sure to file the sharp edges off the inside edges where they mate together or you will have ring marks...... Jim

 

[Willie]

UPDATE: The March rings arrived arrived and appeared to be high quality. One thing that surprised me was no instructions or their recommendations for torque values. Had to call to get the torque specs. Upon removing the cap screws and ring tops, I found them to have anti-seize lube, which I cleaned off with acetone and a fine brush. I prefer the blue loktite approach.

I already had my rail spacing, so I mounted the bases and tightened to 60 in.#. I then tightened my Kokopelli alignment bars in place with ring tops for a trial fitting. They lined up perfectly on on planes, so I removed them and set the March in the lowers. It was a perfect fit, very slight resistance when I set eye relief and vertical. I did do a very light lap, with a fine compound, and mounted it up, triple checked everything, and tightened it to 25in.#. March tech said 23-28 in# min/max. Seemed like a high number to me.

I had a few left over rounds, so I ran to range and it zeroed @ 200 yards with 1&3/4 moa from horizontal center. Not my final load, but I was impressed. One thing I liked was the flats on cap rings, with the rifle and scope leveled, I was able to put a level on the cap rings. Sure made it easy to keep gaps equal when torquing. Also, the zero stop is the simplest to set, I've ever dealt with.

Thanks for the input, Guys. Time will tell, but for now, I'm a happy camper.