An unusual experience

C

cdoc42

New member
On a previous thread I posted about difficulty achieving a satisfactory group with a Kimber 84 Hunter in 6.5 Creedmore after using different combinations of 3 powders and bullets from Berger, Hornady and Sierra. I mentioned that I wrote to Kimber for suggestions or advice and one poster requested that I report their response. After two different letters I still have not had ANY reply from Kimber.

But I want to relate an experience that has not happened before in my 39 years of handloading and shooting. The Kimber 84 is free-floated, but I read in the past that providing contact with the stock and barrel just near the end of the forearm may improve accuracy. So I wedged 0.25 inch pieces of stock from a 3x5 index card on both sides of the barrel about 1 inch from the end of the forearm. My first shot went 6 inches high; I adjusted the scope setting and the next shot was to the left of the bull at 10 o'clock. The next two shots did not hit the paper. I covered the 4x4 feet target with white table paper, centered my target therein, and fired again. No bullet hole. I looked at the rifle to find the scope had been ripped from the back base and driven forward through the front ring, leaving obvious friction marks on the scope. The small wings that are held tight by the locking windage nuts on the rear mount looked like they were filed off!

The load I used was not new; it previously was the best I could get with a Sierra bullet and Superformance powder. The outdoor temperature was 40 degrees. My thought is, immobilizing the barrel and stock at the forearm created a tremendous transfer of recoil energy to the rear base.

Any thoughts?
 
Well, some force got there that wasn't planned for in the scope mounting designs.

The Kimber 84 action isn't the stiffest out there, but it's much stiffer than an Enfield or Mauser 98. It isn't impossible that the barrel shim caused some harmonic wave functions to all congregate at that point at the same time and shear the metal.

Pics would help.

Jimro
 
Pieces of a 3x5 index card don't do much when just stuffed on the sides of the barrel. The pressure point needs to be under the barrel.
"...the scope had been ripped from the back base..." Wasn't caused by putting bits of light card board in. That suggests the scope rings weren't tight enough.
The pressure point doesn't/should not immobilize the barrel and stock either. Bits of cardboard won't do it anyway. The barrel vibrates when fired. The pressure point is just there to help control those vibrations.
Take off the stock and look at the recoil lug.
 
I wouldn't think the shims would induce such a change in recoil to move the scope. I've done the same experiment on heavier recoiling rifles with out a problem. I wonder if your groups all along could be traced to the mounts that weren't as tight as needed. That is what I've experanced on a 300 Weatherby. The rifle had been used with OK groups but during a hunt managed to become loose and ruin the fellows hunt. After returning home I inspected it for him and found the rings and bases were loose and after tightening the rifle shoots great. Since you will be needing new rings and mounts you could soon know if that could be the hidden cause all along.
I see I didn't type as fast enough.:)
 
You fired and no bullet hole in target then look at rifle and scope is ripped from rear base moved forward to front rings.

I'm trying to figure out how you shot thru that scope and not seen it move It sure didn't move after but could of moved some after first miss.

I think I could understand why Kimber didn't replied.

The next two shots did not hit the paper. I covered the 4x4 feet target with white table paper, centered my target therein, and fired again. No bullet hole. I looked at the rifle to find the scope had been ripped from the back base and driven forward through the front ring, leaving obvious friction marks on the scope. The small wings that are held tight by the locking windage nuts on the rear mount looked like they were filed off!
 
I agree the inaccuracy could be traced to the rear ring being loose, although I do remember checking them at one time when I wasn't getting good groups. I have a suspicion it just started to happen at this shooting session because previously, although I could not consistently get a good group, I didn't have any sessions where there were flyers all over the place with the multiple loads I developed.

The base mounts were tight when I replaced the rings today, so they were not an issue. I sure can't figure any other reason. There was no fired case extraction difficulty

Roper mentioned that as a reason Kimber didn't answer, but this was not an issue when I wrote to them. My communication was just about the poor accuracy, in relation to their 1-MOA claim. As a matter of fact, I did mention to them that the scope was not loose (at that time).
 
Pieces of a 3x5 index card don't do much when just stuffed on the sides of the barrel. The pressure point needs to be under the barrel.
Click to expand...
Shimming in two places 45 degrees from bottom center is better than one spot directly under the barrel.

I don't think the shims had anything to do with the mount failure though since they wouldn't increase recoil.
 
If the shim tied the stock to the gun better, that would actually reduce the recoil impulse by adding the mass of the stock into what the recoil has to move. However, there is a remote possibility that a the shims forced a flexure node that strained the action if it were loose in the stock. It would have to be remote, though, as Remington has made stocks with "Remington bumps" this way on purpose for years, and I've never heard of anything like it happening to one of them. Other problems, yes, but not that one.

So I think this is a coincidence. If the screws sheared off cleanly, it sounds like they were over-stressed by too much torque, in which case they could fatigue and shear off. "Too much torque" in this instance means too much for the individual screws used, which, if they somehow failed to get proper heat treatment, could be a lot less than the published torque spec. So you may have had defective screws. I would replace and remount and use a torque driver.

Another path would be to get some of the Burris Signature rings with Pos-Align inserts. In the unlikely event you had some kind of flexure in the action, these should stress the scope less by allowing a little off-axis movement. Their catalog lists which ones for which rifle. They also make a tac scope ring with that Pos-Align insert that has like three hardened socket head screws on each side of each ring, so getting loose would be improbable.

If you go ahead with the shimming after the scope is straightened out, not that the position of the shim along the barrel should be tuned to the best accuracy with your go-to load. Other loads may have other barrel timing and may need retuning after adding the shims. The Smart Stock product is a Nylon shim in a small channel with an adjustment screw to allow you to tweak the shim position. However, Remington stock bumps are in just one position and seem to work at least OK with a variety of loads. I home version of what Harold Vaughn termed "O'Connor bedding" (because the first version he heard described was in a Jack O'Connor article) is described below.

OConner%20Bedding%20B_zpsk4sgtzys.gif
 
This is one thing I go on and on about, no one listens and most try to shout me down...

There is no substitute for 'Heavy Metal' when it comes to mounts/rings.
You only have to freeze your aluminum rail, measure it, then let it come up to about 80* or 90*F and measure it again to see how much thermal expansion happens...

Aluminum expands/contracts no where the rate the steel (reciever) does, thus warping the reciever and/or bending the optics tube...

When your mount rail is steel, and securely attached, it supports the reciever.

Then there are rings...
I can't stress enough that cheap rings are the best way to hit nothing consistently.

This is the part where guys go on & on about what 'THEY' have, saying they hit this or that...
But never in all weather conditions when you get to the truth, it's ALWAYS fair weather shooters.

There is a reason Ken Ferrel & others make highly accurate rings/mounts that cost in the hundreds of dollars, because they work in all weather/circumstances.

Cheap rings don't fit the optics tubes. Period.
When they are so out of round & off size specification they have to add cloth or rubberized tape to hold the tube, something is WAY WRONG!

I spend as much time fitting optics mounts as I do squaring receivers/barrels and cutting chambers.
If the rings aren't lapped SQUARE & ROUND the tube is going to wind up some goofy shape, oval, egg shaped, bent in the middle, etc.

If the rings/tube aren't aligned with the bore, the rifle is NEVER going to shoot anywhere near ballistics tables.
Ballistics tables were developed on shooting fixtures with propley aligned optics/mounts...
Line of
Sight even SLIGHTLY skewed to bore centerline will multiply with distance...
It's a physics thing and you can't rewrite the laws of physics with wishful thinking...

Screw an aluminum optic mount/rings on a rifle in a 75*F room,
Take it outside in 40*F weather and I guarintee the torque reading on the screws will change since you hit the 'Sweet Spot' for thermal expansion/contraction of aluminum...

I was at a shooting match in the very early 80s,
NATO troops from all over competing.
In civilian cloths, with my civilian rifle (Mauser 98 action) some of the British troops asked if I was Canadian or American.
I asked why they ask,
They said 'Americans' would put $100 optic on a $1,000 rifle,
While the rest of the world puts $1,000 optic on $100 rifle and runs right with the Americans... (and they are correct).

Even when people buy a 'Good' optic, they drop the ball on rings/mounts.
Aluminum is fine @100 yds for fair weather shooting,
No way I use aluminum from ANYONE when all weather shooting or trying to reach long distance on cold bore shots...
I had to learn the hard way, take it for what you paid for it and learn the same lessons yourself.
 
I have had this egg on my face.

I was fixing up the mounts on my 7mm08 sportized Mauser 98 and had the ENTIRE scope fly off at the range while my buddy shot my rifle. Very embarrassing.

I assume we are talking about the Leopold/Redfield style bases with the windage screws on the rear mount? I have never understood why they sell so many of these. I have literally never needed something like that and always assumed it was a holdout from ages ago when scopes had to be physically moved to adjust them to zero.

So if that is correct, and since you need a new base anyways, may I suggest you get a dovetail rear to go with the dovetail front and then make sure the bases are correctly torqued as well.

You will need a new rear ring with this new base as well. I have the dual dovetail rings and bases on my model 70 300 WSM and my buddy has them on his 06 xbolt and they are rock solid on both.

I think you will find the base was working loose and that is the cause of your accuracy issues even from the start when you thought they were tight.

Good shooting!
 
I thank everyone for their participation. The shim procedure I tried WAS similar to what Unclenick posted, and I believe it was due to an identical post of his in the past.

That said, I think disseminator described the problem (suspected by others), and the lesson I learned told me one can't live long enough to experience everything. Counting my first scoped .22 rifle, I've been shooting 61 years and I have never had this experience until now.

I replaced the rings, but left the base mounts intact. It became apparent to me that the rear mount HAD to have been undetectably loose (they seemed to be tight when I checked along the way) but finally broke loose, as evidenced by these results on the range, 100 yards, yesterday:

Hornady 140gr SST, H4350 40.0gr, seat 0.08" from leade: 5-1/2" linear group

Berger 130gr VLD, SuperFormance 44.0gr, seat 0.98" to leade: 3 shots, 0.861 inches

Sierra 140gr, Superformance 43.0gr, seat 0.02" from the leade: 3 shots, 0.486"

Berger 140gr VLD, H4350 40.0gr, seat 0.065" from leade: 3 shots - perfect cloverleaf measuring 0.236 inches!!

All bullets were seated to fit the magazine. I recognize more than 3 shots is recommended to properly assess accuracy, but that may be for competitive shooting reasons. For hunting purposes, IF one needs more than one shot, there's a degree of comfort knowing the next 2, at least, will follow the first, so the miss was the shooter, not the rifle/bullet combination.

Once again, this forum and all of you contributors, provides evidence that there still exists in America a fraternal interest group having a bond that allows sharing of information without selfish interference.
 
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