Home Forums Hunting & Shooting Hunting Optics 'P.O.I.T.' syndrome

It's called a half bed...

Its referred to as a half azz bed job.

Rex, it depends on how the tops fit. After the bottoms are bedded and the parting lines relieved (tops and bottoms), a bit of Prussian Blue on the tops and snugging the scope down will show how much contact you have. If it's less than 75 percent, then the tops get lapped and bedded. In the the before and after pics below, you'll get an idea of that.

The top pic is a new BR rifle I just finished late this Summer. The tops/bottoms are bedded as a matter of course as nothing can be left to chance. But I do hunting and live varmint rifles the same way. The guns couldn't be further apart in application but the goal remains the same...as much contact as possible for repeatability and no stress on anything. Instrumented testing has shown that scopes experience an average of 9 G's 'break away' loading in the instant between when the the gun fires and it starts it's rearward movement in recoil. In that instant, the scope will 'weigh' 9 times more than it's actual weight.

And In extreme cases like the one this topic was started about, you can see a shift in POI as the mounting system shakes around after each shot and comes to rest in a different spot each time....even though everything feels and looks 'tight'.

Looking forward to your range results.

Good shootin' -Al

I can see a shift all right.....

You're full of shift.

Regarding 9 G's- I'm actually pretty familiar with what that's like.

Regarding range results, I had a dramatic improvement. I have been struggling to get this .270 WSM down to just sub-MOA performance, and it has refused, with best groups just over an inch.
It's an 8" twist barrel with a long throat and a mag box that allows 3.02 max OAL. Today I took a load with the Sierra 175gr TGK that previously wouldn't break an inch. First three shots of the day from a cold, clean barrel went 0.48". Tried the 145 ELD-X, which had been in the 2" range before. Three in 0.44". See the attached.
I'm a happy camper! I plan to bed the bases & rings now on several more of my rifles.

Thanks again Al!

Rex

Well done, Rex.

My hope is that results like yours encourages others to delve into this area. There's improved accuracy and better optics performance just free for the taking.

Good shootin' -Al

Al has given good advice in this post and something for me to think about. I have bedded bases for sometime now, but not the scope.

Outstanding post, Al. I learned a lot & will certainly be going the extra mile.

While I can see the possibility of an improvement by bedding the rings my question is - would this be an improvement over the Burris Signature system which uses a synthetic insert with the pillow block arrangement?

I am not trying to start a pi$$ing contest, rather I am curious why the Burris system would not be equally good.

drover

As I mentioned earlier, the Burris Signature rings are a nice alternative for those that don't want to bed the rings.

Of course, that still leaves the bases to deal with. -Al

Al:

Thanks for sharing what you've learned and your process. Thanks, too, for always being a gentleman in these discussions.

Mostly for curiosity sake, do you regularly measure the scope tube diameters? If so, how much variation are you seeing these days?

Back in the day I used to measure scopes before I mounted them, and I did find a fair amount of deviation. If they were bigger than 1", I'd use a piece of sand paper as a shim around my lapping bar and get the diameter bigger before giving them a similar bedding treatment to what you do.

Since I've been using mostly 30mm scopes these days, I haven't found near the deviation I used to, so I've pretty well stopped measuring and just pre fit the rings to make sure there isn't an inconsistency before mounting them to the bases.

I missed that post - sorry. I have used the Burris for years and just wanted to be sure I wasn't missing something by doing so.

drover

I dont know how anyone hit anything before scope lapping and scope bedding.

Devine providence?

On newer scopes, there's certainly less variation than earlier stuff. The use of CNC centers for machining the tubes (on even lower end scopes) has certainly been a plus for consistent tube dimensions. The near universal application of matte finishes also helps as the gloss finishes of many earlier scopes varied quite a bit in thickness. No need to mention brand(s) but a couple of near-and-dear brands had tube diameters that routinely ran around .995 with extremely thin tube thicknesses on top of that. Couple those two things with less than straight and misaligned bases and there will be problems. But I always measure the tubes because I don't like surprises. For example, there are three identical, new in the box, 2-8 1" tube scopes here. Two already have homes...one on a 6.5 lb. 308W and the other on a 6.5 lb. 20 Practical fox/coyote calling rifle. All three tube dimensions are identical....at 1.010!

The hard facts are that the great majority of shooters and rifles simply aren't up to the task....so the mounting issues get lost in the noise of the overall inaccuracy of the gun mixed with the shooters limited ability. That won't win me any friends but those are the facts.

For those that want the extra accuracy and performance, it's a process that anyone with a bit of mechanical ability can both grasp the concept of and apply to their rifle. The costs are minimal and a bit of time is all that's required.

And for those that don't...hey, that's cool, too. Go shoot, hunt and enjoy.

After my wife passed away, I decided to retire early from my career in the medical field. This is a hobby for me...I don't do this for a living or a sideline and generally don't do it for hire. For me, it's about solving problems and making things as good as they can be.

Good shootin'. -Al

Al,
I have another question. You said you will bed the scope into the bottom half of the rings, but leave the top half unbedded if there is decent contact area on the scope. So when you lap the bottom of the rings to make enough room for the bedding compound, do you do it with the top half of the rings removed? Thanks again.

Thanks Al, and good shooting to you.

Correct...no tops on when the bottoms are lapped. -Al

Purely for the sake of info, here's an example of one of my 30BR chambered Benchrest guns that I worked with in 2009-2011 to absolutely hold P.O.I. and ensure tracking.

The w/e adjustments were removed and the erector tube was centered in the scope body with two aluminum sleeves. The sleeves were epoxied to the scope tube I.D. and the erector tube was epoxied to the I.D. of the sleeves. The mount was made by Gene Bukys and was a friction style adjuster with a pre-stressed beam that allowed the scope to travel.

It never so much as twitched POI or tracking!

Good shootin'. -Al