Home Forums Hunting & Shooting Hunting Rifles Kimber Montana inexplicable accuracy change

I've got a small delimma I am trying to sort out. I bought a new-to-me Kimber Montana in 25-06. Did the Kimber "pre-flight" procedure, except glass bedding the rifle. When re-installing the action back into the stock, I torqued the action screws to the Kimber recommended values of 45in-lb front and 35 in-lb rear. I mounted a Kahles 3-9x42 CL scope on it in Talley Lightweight mounts. Scope mounting included lapping the rings, marking the top rings so they could mount to the same base in the same orientation, torquing the screws to recommended torque values with a torque wrench, and Loc-Tighting the threads. The gun shot well at the range, including a 1/2" group with Barnes 100gr TTSX factory ammo. I was happy. Original thread is below:

https://www.24hourcampfire.com/ubbt...25-06-a-good-little-shooter#Post13057587

Of course, never being satisfied and wanting better groups, I decided to adjust the trigger from its 4.25lb pull weight to 2.5lbs. I had to remove the stock to do so. I torqued the screws back to the recommended values after re-installing.

I also swapped from the Kahles scope to a Zeiss Conquest HD5 3-15x42. When I did the scope swap, I rotated the front scope mount 180 degrees to better support the longer Zeiss scope. This included re-lapping the scope rings, and torquing the screws to the same values as before, plus Loc-Tight. The new configuration:



Went to the range on Friday, and was shocked and disappointed to now get 1.25" groups with the exact same load that was shooting 1/2" groups. Arhg & WTF!

Obviously something changed, but what? I checked all the screws I could access without taking things apart, and they are all good.

Yah, it is a different scope, but a new Zeiss Conquest is hardly a scope to be suspect of. And, swapping back to the Kahles will require rotating the front mount and re-lapping the rings again - not a simple procedure. I've ordered Warne Two-Piece Mounts and Burris Signature Zee Rings to temporarily substitute for the Talleys to make swapping scopes easier without lapping, but that stuff won't arrive for a week.

I had pulled the action from the stock when I did the pre-flight, and I didn't do anything different in this regard the second time around.

I tried to slip a dollar bill through the barrel channel, and it won't fit, meaning the barrel is not free floated. But I didn't do this test before I made all the changes so I don't know if this is different than before. But, I thought all Montana's were free-floated, so not sure what's going on there?

So, the question is, where to start troubleshooting? Do I just wait for the new scope mounts to arrive, and go back to the tried-and-true Kahles, and troubleshoot from there. Or, are there some easy things to check for problems in the mean time? The non-free-floating barrel is suspicious to me, but the gun was shooting 1/2" groups with the factory bedding, so, while glass bedding the action won't hurt, lack of glass bedding isn't the problem.

Anyone got any thoughts? Any suggestions?

That's why I hate changing multiple things at once, especially on a rifle that shoots well. Go through the pre-flight again, and pull the stock off and reset it in the bedding. If that doesn't work, then wait until your new rings and bases come in and try the old scope. If none of that works then I'd start considering bedding the rifle.

I know you just changed the scope/rings...... it's always where I start...so I'd look again.

Check the mag box and make sure it's not binding.

I want something either free floated (+/- shank bedding), full length bedded, or bedded with a pressure point exactly where I desire it. Touching here or there is not a good thing.

When the mechanical is good check the scope.

So you flipped your talleys and lapped them a second time. Why not just leave well enough alone? I believe they say not to lap talley lightweights as well... I wonder why? It sounds like the rifle was good before you fu cked with it...

With how many groups of how many shots each did you determine the gun's accuracy before and after swapping the scopes?

I ask because one 3shot 1/2" group is not statistically relevant -a fluke, in other words- and perfectly compatible with a following 3 shot group measuring 1,25"

Holy smokes all kinds of [bleep] going on all at once.. I have never lapped Talley rings and that's all I run. One of the first things I would done was bed the rifle and float the barrel. Not play musical chairs with scopes...So with all that bed the rifle and float the barrel.. then get back to us, also check run out on your ammo...

I was thinking exactly the same as this. That 3 shot group could just be a fluke. It’s happened to me countless times which is why I always shoot 5 shot groups to ascertain the characteristics of any given load during development or certainly when I’m trying to validate my data. For example if I shot your 3 shot group (in the .5’s) I would then validate that with a 5 shot group with the same load. In my mind your rifle doesn’t shoot that ammo as well as your first 3 shot group would make you think it would. Shoot another 5 shot group with that ammo and another one, then add all together and divide by the number of shot groups in order to get an average is what my suggestion would be. It’s as simple as that in my mind. Nothing wrong with the rifle, scope or anything else - just typical centrefire performance using a factory rifle, shooting factory ammo.

I'd be checking fasteners to see if anything is dead heading on the bolt, the put it back to the original configuration and see if the group was a fluke. Don't be fooled by randomness.

Have you cleaned the barrel? You can shoot some rifles 100 times before they needs cleaning, some want to be cleaned after 30. Maybe the groups are opening due to fouling.

Oh Hell no. I have this AR10. It is a .1xx rifle. I shot this 3 shot group once to prove it... Some guys have their foot shoved so far up their azz, all they see is their shinbone..

So let me get this straight... Maybe you should have tried a scope with a 30mm tube, after lapping the rings twice. And the marks you put on the talleys: Pure genius.

"Some guys have their foot shoved so far up their azz, all they see is their shinbone."

lol!!

Apologies in advance and I hope you don't mind, but that is so good I am appropriating it for my own use.

You did the Kimber pre-flight checklist the first time?

So you shortened the forward most screw for your front Talley so it's not making contact with the barrel threads?

When you swapped the front base did you make certain the short screw went into the correct hole?

David

Canazes9, thanks for the good questions.

"So you shortened the forward most screw for your front Talley so it's not making contact with the barrel threads?" -- yes

"When you swapped the front base did you make certain the short screw went into the correct hole?" -- yes

Try a new set of rings. I do lap Talley's but very very little. I would never do a set twice.

How many .5" groups did you shoot the first time? If only one, it may have just been a fluke and you are chasing an accuracy standard that doesn't exist.

I know others had mentioned that, and it is a fair point. I did shoot just one 1/2" group (actually, it measured 0.542") with that particular load (Barnes Vortex 100gr TTSX). After the Barnes Vortex, I shot a 0.639" group with Federal Premium Vital Shok pushing 115 gr Nosler Partitions. Two other factory loads shot under 1" during that range session, as well. I did shoot just one 3-shot with each of the 8 loadings I tried that day.

^ My thoughts too

Excellent post. Here's a great read from another site:

The trouble with 3 shot groups

Good question. Barrel was cleaned with "Wipe-Out" until no blue color showed on the patch. The bore was then swabbed with RemOil. Then a dry patch was run through the bore. This was done after every 9 shots.

The 1.25" group came after the barrel was cleaned, and one fouling shot had been fired.