Light rifles, big cartridges, and scope mounts - learned my lesson, now it's time to pass it on.

codyadams

Well-Known Member
Joined
Jan 7, 2015
Messages
3,629
Location
Southwest Wyoming
I'll start this thread by saying that I am in no way bashing on the manufactured of the scope mount I used, it is in no way the mounts fault, but instead my fault for not choosing the appropriate mounting solution for the extreme situation I put it in. The mount I used is a quality piece of kit, and I have used it on other rifles with good results.

I just discovered this yesterday, and I am frustrated it took me this long, and I should have known better, but now I do.

I have a relatively light .338 Norma Magnum, all in with 3 rounds ready to hunt, it weighs 9.6 lbs. It has a MBM titanium 5 port Beast brake, which does a fantastic job of managing the rifle, I spotted every impact last year during hunting, from 180 yards to 883. I would put the felt recoil to about that of a heavy .308 winchester, shooting side by side with my fathers 10.5 lb AR-10 in .308, it is very similar. However, when building this rifle, I knew that the entire amount of recoil would be felt by my optic mounting solution, as that is initiated prior to the muzzle brake doing it's thing and slowing down the recoil. That recoil comes out to just shy of 50 ft-lbs and about 18 fps with my loads, so pretty significant.

Because of that, I upgraded my base screws from 6-48 to 8-40. When choosing a mount, I wanted to keep weight down, but also keep a solid mount. This is where I messed up. I chose to go with a DNZ 1 piece base/4 screw ring combo, as seen in the photos. I bedded the mount to the receiver with devcon for added strength and to keep everything perfectly strait. Next, I bedded the March 2.5-25x52 into the rings, again with devcon. I polished kiwi shoe polish into the scope tube until it was a high polish, an extremely thin layer to ensure the best bedding possible. The bed job came out great, I could push the scope down into the lower rings and nearly lift the rifle up with only the fit, not even having the ring caps on, so I was very confident that after proper torqueing of the bedded ring caps, the scope wasn't going anywhere. In checking the March scope manual, it only stated that usual torque for ring caps is 15-20 in-lbs, but will vary based on manufacturer. The DNZ rings stated a max of 25 in-lbs, so I torqued to 20 in-lbs as that was the top end listed in the scope manual.

During load development, the rifle would shoot very good, but have an occasional flyer, never bad, usually within .75 MOA of my group, but nevertheless, it would happen. I chalked it up to my shooting, groups were still always under 1 MOA, most of them falling well under half MOA. During my hunting season last year, all was going well, the rifle was used for several pronghorn out to just under 700 yards with stellar performance, that is until my mule deer.

I hiked in to one of my honey holes at first light, and like they were on que, I spotted a group of bucks out in a field about 570 yards off. There was one nice buck in the group that was a 160 class buck, so I decided to take him. It was first light, sun wasn't up and there was nearly no wind, so since I was shooting across a canyon, I doped for a 2 mph L to R wind, going up the canyon. I settled in behind the rifle, lined up on the buck, and took a perfect shot. As I was waiting for impact, I knew that was a dead buck for sure, until I saw the impact high right, over his back and back by his flank. I knew this wasn't right, so I adjusted to my impact quickly. The buck ran about 60 yards and stopped, pretty close to the same range. I lined up again, took another shot and placed a perfect quartering to shoulder hit, and dumped him in his tracks. However, I had to adjust 2 MOA to the left and down almost the same for the hit. This was a verified load, and I was confused. After I got the buck off the mountain, I went to the range and shot it. Sure enough, I was hitting around 1.5 MOA high, and 2 MOA right. I re-zeroed, shot a confirmation group, and shot some steel at range, and everything seemed good. I was confused why it happened in the first place, but everything seemed good again.

Then, I went on my elk hunt. We got on to a large herd, and I picked out a 320ish bull. Range was 883, so I knew I needed to take my time, but thankfully I had plenty. There was a pretty stout ground wind, but the wind out in the canyon was consistent, around 5 mph left to right, and between mirage and debris floating in the air, it was relatively easy to read the wind. I lined up my shot, and fired. Again, I saw the impact high right, almost the same place, over his back and back near the flank. I dialed to my impact, he moved a short distance laterally and stopped. I lined up a second shot, and on impact dumped him, the bullet hit right at the neck shoulder junction. Then, my season was over.

In the off season I began doing load development on a different bullet. The other day, I took a picture of my rifle in a new tripod I got. I was looking at the photo, adoring my beautiful rifle, when I noticed something off. The proportions of the scope/mount didn't look right, and there seemed to be more room between the barrel and scope bell than there previously was. I dug up a photo of my rifle from right before my 2020 season, and saw the difference in the photos below.

Before season, 2020 -
Screenshot_20210602-234415_Gallery.jpg


Just a few days ago -
Screenshot_20210602-234902_Gallery.jpg


Notice the difference where the scope level is in relation to the turret body, as well as where the rear ring is in relation to the eye piece. The scope had scooted forward nearly a quarter of an inch in around 100 rounds. While I can't say 100% that is what caused my issues during hunting season this year, I wouldn't be surprised if that was the cause. So, to remedy this, here are my plans -

I ordered a 20MOA rail. I am going to bed and pin it to the receiver. While the pinning may not be necessary, it will be added insurance on that aspect of the mount system. The rail has an integrated level, making room so that the entire scope tube can be used for....

2 sets (4 rings) of Seekins precision rings. I will put 2 of the rings pushing forward, 2 of them pushing rearward, to counteract the thrust created by the muzzle brake. I believe this is what Kirby Allen does on his rifles. I will bed the scope into the rings again, but this time I will not use release. The scope will still come out if needed, at most some heat can be used to help them release.

This is the strongest most secure method I can think of to keep the scope in place. I also plan on marking the scope tube with a marker in an inconspicuous location, so that I can monitor for any movement of the tube in these rings, though if it does, I'm not really sure what more I can do to prevent it, but at least I will know.

I will update this thread as time progresses, but I figured that since I had to learn the hard way, I would admit my faults and hopefully help the next fella to prevent this issue. Just go overkill from the start with big boomers like this, just like the professionals do (there is a reason they do it) and you will not have the problems.

Thanks all, and good shooting.
 
Last edited:

HARPERC

Well-Known Member
Joined
Jan 28, 2011
Messages
6,793
Location
Spokane, WA
Very well done Cody.

I've learned those lessons in a similar fashion, misery loves company and hearing, OK! it's not just me has benefits.

I learned from JE customs videos muzzle brakes don't stop those forces, but redirect them. The better the brake works for the shooter, the harder it may be on rifle and scope. Lots of forces involved for sure.

I have a new build started, and when picking the action an integral rail is a must. It's good more factory rifles are coming that way, again I tend to purchase with this as a big factor

Even just travel can be hard on rifles and scopes, the more solid I can get the better I like it. Once you've busted a few things over engineered becomes a part of the process.

Really very nicely done.
 

codyadams

Well-Known Member
Joined
Jan 7, 2015
Messages
3,629
Location
Southwest Wyoming
Very well done Cody.

I've learned those lessons in a similar fashion, misery loves company and hearing, OK! it's not just me has benefits.

I learned from JE customs videos muzzle brakes don't stop those forces, but redirect them. The better the brake works for the shooter, the harder it may be on rifle and scope. Lots of forces involved for sure.

I have a new build started, and when picking the action an integral rail is a must. It's good more factory rifles are coming that way, again I tend to purchase with this as a big factor

Even just travel can be hard on rifles and scopes, the more solid I can get the better I like it. Once you've busted a few things over engineered becomes a part of the process.

Really very nicely done.
Thank you sir, I appreciate it. I was pretty surprised, after bedding the optic, it was an incredibly perfect fit, with less than finger tightness on the screws, I could not get the scope to move when fine tuning for level and eye relief, after being torqued down to 20 in/lbs on all 8 screws on the two top caps, the fact that it moved is incredible. Then add in the fact that it butted up against the scope level, that is lapped and torqued down at 18 in/lbs, and moved that as well, is insane. The amount of force to do that is incredible, and it isn't like it's a terribly heavy optic, it's only 25 ounces. I know from now on, over built is going to be the standard for me.
 

hugheserj

Well-Known Member
Joined
Nov 14, 2018
Messages
56
Location
New Zealand
The Zeiss V8 I have with 36mm tube which I've had on a 300WM and 30 Nosler is much the same and there are limited options for 36mm rings. I've noticed it moving and had to torque it above the manufacturers specs to stop the scope creeping backwards. Your observations and ways to correct make sense.
My scope has stopped moving now but if it hadn't, my next plan was to put some silicon or rosin in the rings.
 

Varmint Hunter

Well-Known Member
Joined
Dec 26, 2001
Messages
4,204
Location
Long Island, New York
I'm a no-frills scope mounter and have gotten to appreciate the Burris Signature rings on most of my big game rifles. Loaded with maximum charges and heavy bullets, I have not had a scope move on my 300RUM or 338RUM. Both are standard weight rifles with Kirby's PK side discharge brake. Even my 500 S&W shorty rifle wears Signature rings w/o issue.

There are unquestionably stronger mounting set-ups available but I haven't had the need for one yet.
 

codyadams

Well-Known Member
Joined
Jan 7, 2015
Messages
3,629
Location
Southwest Wyoming
I know the photos are not quite on the same plane, but it also looks like the gap between ring caps and 1pc mount lower halves has opened up. That could be some of the culprit as well.
You always have a great eye for detail Lance! The first photo was just prior to bedding the rings. I set it up to get a weight, proper eye relief and level, then marked the position of the scope, bedded the scope in that specific location so it would perfectly match the optics contour, then after they cured, torqed the caps down with the optic in the same spot. The extra space you see is from the bedding compound in the rings. Also, prior to removing the screws yesterday morning, I double checked torque of the screws just in case they had worked loose, giving me an easier fix, and they were all still good, none had loosened up. I had used blue lok-tite on them on install, and these DNZ mounts have around half an inch of the ring cap screws engage in the ring bases, so lots of thread contact for the lok-tite to do it's job. I was hoping it was that simple of a fix, but no dice....
 
Last edited:

CO_Guy

Well-Known Member
Joined
Nov 16, 2018
Messages
1,382
Location
CO, USA
Great post. The only scope that slipped on me was the one the gunshop owner installed on my first new rifle, a Win 70 in 270. Since then, I install all of my bases and rings and had zero slippage including on all of my Tikka T3s (including 338wm, 270wsm, 300wsm) that come in at 6.38lb stock. The integral scope mounts that come on the Tikkas and my wife's Ruger 77MKII have worked out really well. The torque spec on the Warne 2 piece base I recently installed, is also 25 inlb and I torque to that level.
 

codyadams

Well-Known Member
Joined
Jan 7, 2015
Messages
3,629
Location
Southwest Wyoming
I'm a no-frills scope mounter and have gotten to appreciate the Burris Signature rings on most of my big game rifles. Loaded with maximum charges and heavy bullets, I have not had a scope move on my 300RUM or 338RUM. Both are standard weight rifles with Kirby's PK side discharge brake. Even my 500 S&W shorty rifle wears Signature rings w/o issue.

There are unquestionably stronger mounting set-ups available but I haven't had the need for one yet.
I use the Burris sig rings on alot of different guns I set up, love them, and never had any issues. I just figured on this rifle, I would go as robust as possible. The heaviest recoiling rifle I have personally used the signature rings on is a 7mm rem mag
 

rammac

Well-Known Member
Joined
Oct 28, 2010
Messages
272
Location
SW Montana
I suspect that your problem was the frictionless fit between the scope and rings. Bedding the rings and polishing the scope tube reduced the friction between the two.

Most rifle chambers are finished to 16 line per inch smoothness so that cartridge case will stick to the chamber, any smoother and the bolt lugs will take a beating because the case will slip and put up to twice the amount of pressure on the lugs.

Before you make all of those changes try roughing the bedding a little and test a few rounds after reinstalling the scope. You won't need much roughness, make a slightly crosshatch pattern using a 600 grit wet dry Emory cloth.
 

Wedgy

Well-Known Member
Joined
Feb 9, 2013
Messages
2,414
Having seen 3 sets of #6 screws sheared off scope bases(not mine) for whatever reason I use only #8 screws and pinned bases or integral bases. Whether it was from recoil or or leverage on the scope I want more than two tiny screws four inches apart holding my rig together if I fall, lean on a tree, or toss my pack in the back of a truck. Devcon without release agent only takes a little bit of heat to get it to release, not a torch. Shep wrote a great piece on pinning a rail that anyone can do.
Cody and I discussed the odd shots and "fliers" and it retrospect all the signs were there from the beginning but not bad enough to warrant a tear down I guess. For those who have chased their tail on this overkill is the way to go. I set my Edges up like Kirby does because he knows better than me what works and I've never had a problem.
From Shep;
I use a #31 drill bit in a drill press. Drill right through the base into the receiver. Don't go all the way through the receiver. I usually put them right between the mounting screw holes. After drilling this .120 diameter hole take an 1/8 drill bit and cut a few pins from it with a cutoff wheel. This is .005 bigger than the hole you drilled. One drop of red locktite and tap the pins in. A small chamfer on the bottom of the pin helps it start in. Practically anyone can do this. These pins are much stronger than screws. I do all my actions like this. Go to 8-40 screws and pins. All on a bedded base. No more problems.
Shep
Photo is one of Kirby's guns
kirby.jpg

 
Top