Interesting observation on BPCR long range scope mounting

[texasmac]

Guys,

Some time ago I authored an article on BPCR scope mounting and fully understand how to calculate the adjustment range based on mount spacing and realize that a shorter scope and shorter mount spacing will result in an expanded adjustment range. Recently a guy contacted me asking for advice on mounting a scope to cover an adjustment range for 100 yds to 1000 yds. Not hesitating, I suggested going with a short 18” scope with a 7.2” mount spacing to maximize the adjustment range. His response was, “If the scope was set for 100 yds and you raised the back of the scope sufficiently for a 1000 yd shot, wouldn't the scope wind up looking at the end of the barrel”? His question/concern surprised me as I’ve never mounted a short BPCR scope to cover such a wide range and therefore never considered that possibility of the muzzle blocking the scope view at long range. So I ran through a couple of calculations to find out.

1) Not having a good handle on typical BPCR bullet drop over the extended range, I plugged some values (500gr, 1250fps, .350BC) into an online ballistic calculator and came up with 165 MOA.

2) Using a mount spacing of 7.2” and a rear mount adjustment range of .450” (for a D.Z. Arms Unertl-style mount) results in a total of 225 MOA adjustment range, which is certainly sufficient, but for the following. For 165 MOA the rear mount would have to be adjusted a minimum of 0.33”. Therefore, due to the scope tilt the view would indeed be obstructive by the muzzle.

Overall an interesting exercise and something I had not considered before. I now appreciate the warning on MVA’s site that their long range Creedmoor mount is not recommended for use with their 23” scope on a rifle with a 30” or longer barrel.

Wayne

[kennisondan]

i READ WITH GREAT INTEREST YOUR POSTINGS FROM THE PAST AND IT CREATED NEW KNOWLEGE AND A LOT OF QUESTIONS TO PURSUE.
ON THE TOPIC TODAY WOULD THE ANSWER LIE IN A TALLER MOUNT HEIGHT ? PERHAPS ?
WHAT DID YOU COME UP WITH AS THE PERFECT OR BEST OF THE CHOICES FOR A SCOPE SET UP ?
MY TAKE ON THE INFO WAS THAT THE LEATHERWOOD WAS THE CLEAREST SCOPE OF THE ONES MENTIONED.. THE OTHER TWO OR THREE MFRS HAD MUCH BETTER MOUNTS.. AND THEN THERE IS THE QUESTION OF OTHER MOUNTS THAN THE RHO ETC .. DID i MISS MORE OF THE CONVERSATION THAT OCCURRED.. ? iF THE TANG SIGHTS DO NOT WORK OUT FOR ME i AM PREPARED TO SLASH THAT IDEA AND SPEND ABOUT A THOUSAND TO A BIT MORE BUT i WOULD WANT A GOOD ACCURATE SCOPE ALBEIT SOME LIMITS DUE TO SIZE AND DIFFICULTY OF MOVEMENTS TRYING TO CLICK INSTEAD OF ADJUST MIGHT BE A PROBLEM .. i WANT THEM PRETTY STABLE.
WHAT IS THE BEST OUT THERE BEST COMBINATION OF ALL THE POSSIBLE SCOPE CONFIGURATIONS THAT APPEAR PERIOD CORRECT AND WOULD ALLOW nra SANCTIONING OF THE SHOOT ? OR JUST THE BEST ?
DK

[Kenny Wasserburger]

I have the MVA 23' scope with the Tall Creedmoor Mounts, it will blur out on the barrel at about 1130 yards. I get a slight blur at the bottom of the lens at 1000 of the top of the front sight. If you remove the front sight you get quite a bit more elevation before barrel. This is the rig up I used in 2006 Nationals.

With proper rear and front blocks this will work at a Mile even MVA will make about anything in the way of elevator blocks.

My Main Gripe against the Leatherwood is lack of Paralex adjustment, it is critical at Long Range. Hence in my opinion the Leatherwood is usless for that.

KW
The Lunger

KW
The Lunger

[texasmac]

Kenny,

Good information.

I used an 18" scope on a rifle with a 33" barrel to confirm the potential short scope problem when shooting at long distances. The blurred image of the muzzle appeared in the bottom of the sight image when the rear mount was raised 0.22”. At 0.31” the blurred image touched the cross hairs and obscured the lower half of the sight image. At approximately 0.41” the sight image was completely obscured by the blurred image of the barrel. There was no front sight mounted.

With this setup I've calculated I'd have to raise the rear mount a minimum of 0.33" to adjust for the bullet drop at 1000 yds. Add a little for a margin and scope blocks around 0.4" higher than I'm using now would be required.

Wayne

[craveman85]

what about a side mount like is on winchester lever guns? not the best thing for long range but different and it would work.

[texasmac]

After giving further thought to the setup and experimenting with my rifle, I take back my earlier comment about .4" additional front and back scope blocks fixing the problem with my rifle. As noted earlier, the rifle I experimented with is sighed in at 70 yds. It has 0.18" scope blocks front and back. To provide the correct tilt for shooting out to 1000 yds requires an additional .35" under the rear mount. While maintaining the correct tilt, the scope (front and back) must then be moved up sufficiently to eliminate the barrel image obstruction, requiring an additional .42". Therefore, blocks totaling 0.95” under the rear mount and 0.6” under the front mount would be required. Of course this creates another potential problem, due to the tilt and additional height of the scope, the eyepiece has now been raised an additional 1.15”.

If I seriously considered setting up a scoped rifle for 200 meters to 1000 yd shooting with a 18” scope, I would probably go with the D.Z. Arms mounts since I prefer the Unertl-style mounts over the MVA Malcolm-style mounts. Approximately 152 MOA of adjustment would be required and the D.Z. Arms mount offers 225 MOA adjustment with 7.2” mount spacing. With a 23” scope and 10.34” mount spacing, the D.Z. Arms mounts would be at its limits (156 MOA) and MVA’s Creedmoor mount is the only solution I’m aware of. And there's no question that MVA's mount would be required with a 30" scope

DK,
If money is not an issue MVA is the way to go for most shooters for two reasons. The quality of the their mounts and scopes, and their customer service for those that need some help in figuring out what they need and help with actual mounting. You can possibly save a few bucks by going with D.Z. Arms mounts and even more with a Leatherwood scope, but then other considerations are necessary such as the distances you plan on using the scope for, parallax & fixed or sliding mount, etc. Kenny has much more experience with using a scope than I do and has chosen to go with MVA, which says a lot.

Wayne