Is there any elevation built into the top scope rails of a Barrett 98B??

[TonyR]

We were shooting a Barrett 98B 3338 Lapua with a NF NSX yesterday and were 2 MOA short of elevation to come up for 1000 yards. Does anyone know if there is any elevation built into the top accessary rail??
Thanks

 

[spclark]

There's no mention of such on the 98B specs page at http://www.barrett.net/firearms/model98b so my SWAG on this is no, there isn't.

Unless some other 98B user answers your question with a more positive spin, you'll need to contact the folks at Barrett for a definitive answer.

2 MOA error at 1K can be the result of many calculation errors though, depending on the numbers you're plugging into the mix.

Or it may be the scope itself; have you checked out how accurate the elevation adjustment is at a shorter distance so as to work up a correction factor?

 

[TonyR]

No calculations were involved. We were dialing the scope from point of aim to point of impact and ran out of elevation adjustment. I was surprised because the rifle is designed for 1000 shooting. We were shooting Sierra 250 Match Kings at about 2750. Maybe the 300gr Scenar will do better.

 

[spclark]

Hmmm. Using JBM (65°, 65% humidity, 800 feet elev., sight 1.5" above bore) & a G1 number for the 250 Sierra I get 30" MOA drop @ 1K.

Two turns of the knob should be enough if you're zeroed at 100 yards. (I don't have a Nightforce but my Leupold Vari-X III is 15 minutes to the full rotation)

Using Litz's G7 number it's only .7 MOA flatter.

What do you base your velocity numbers on? A chrono? Previous results with the same load in a different rifle? What kind of scope rings are you using?

 

[js223]

I also come up with 30.1MOA from a 100 yd zero for the 250SMK@2750, standard conditions and 1.5" scope height.
While I do not have one of these, I think the answer is no slope. What does the NSX have for elevation range? I'm thinking that he had to use some elevation just to get a 100yd zero. Suggest getting either a sloped rail, or Burris Signature Zee rings that have inserts. The 30mm rings come with size 10 inserts, so he could set it +10 in back and -10 in front.

As far as bullet choice, the 300SMK if it's going 2700 (Sierra's listed max load) would drop about 27.5MOA in the same conditions.

 

[TonyR]

I have a very good infrared chronograph so I feel pretty good about the velocity. QuickLoad's ballistics program gave 26.5 MOA up from a 300 Yard zero which we had just obtained earlier in the session. Sounds very consistent with the numbers you have been getting based on a 100 yard zero. I'll have to take a closer look at his scope to see what the adjustments are. He has the R2 reticule with the hash marks so it is not hard to hold up 2 MOA if necessary. I told him about the Z Rings. I use them on my 22RF to shoot 200 yards.
Thanks very much for all the replies.

 

[Lapuatom]

I really don't think you should of had any problem dialing for that distance even with an even rail as the NXS has 100 min, of vertical adjustment.Even if your adjustment is half way through it's travel when sighted in @ 100 yards,there should have been plenty of adjustment to make the hit. My rifle is fitted with a 20moa rail,I shoot 300 gr. SMK's @ 2740 with my 338LM and it only calls for 27.2 moa @ 1000yds. Maybe some other kind of alignment problem.

 

[TonyR]

Thanks to everyone who replied. It turns out that the 98B does have a flat top rail. His model NSX does not have as much elevation range as some but Barrett sells special rings with some sort of pin that can be set to give either 15 or 40 extra MOA (for about $285.00). He was able to exchange his Nightforce rings at his dealer and the Barrett rings should arrive next week.
Thanks again