How to deal with Cold Barrel zero???

[tdot]

I have a Kimber Montana, the rifle has been a sub MOA rifle since new. I've worked a few handloads up that are consistently approaching 1/2MOA.

At the start of this season, I started to use Hammer Hunter 152, through the load development I was approaching 1/4 MOA with a specific handload. As I was proving the load and sighting in the rifle, suddenly all shite hits the fan and suddenly I cant hit within a 3MOA circle. I ask 2 other guys at the range to try the rifle. No one can hit anything... so it's not me, but suddenly it's a bad breakup about to happen.

I check the scope, action screws.... nothing. Finally I pull the action from the stock. There was a tiny leaf under the barrel. A friggin leaf.

I reassemble the rifle. Doesnt shoot as well as before. I decide to bed the action. I'm now out of Hammer 152's. I need to start a new load. Decide I dont want problems again, so bed the scope as well....

Start a load with Hammer Hunter 166's, withing 15 rounds I have a load that clover leafs at 100yards

I zero the rifle and then come back to the range a few days later to check it and confirm everything.

The results are irritating. My cold bore shot is 1.5 MOA to the left and 0.25 MOA high of a 4 shot clover leaf.

I've had this exact pattern 2 days in a row.

Is there something I'm missing? I've never had a cold bore shot so far away from the main group.

Do I zero to where the cold bore shot is? Somewhere in between the cold bore and the main group?

Other ideas? Suggestions?

 

[Smithb9841]

Have you tried going back to your original load that was approaching 1/2” MOA? How many rounds since you last cleaned the barrel?
I think I would try to replicate your original load that shot 1/2” MOA

 

[gbflyer]

A good bedding job is no joke. If you’ve done a few of them before with good result then you probably know what to do. If it’s your first time then you might not have gotten lucky. I’ve made a few of them worse before I got a few under my belt. No offense, Hell maybe you’re a pro that does it all the time.

I’ve never seen one of those pencil barrels that didn’t move around. Full length bedding has help me in the past with that. One of the guys on here swears up and down that the Barrett Fieldcraft, as an example, is perfect though I certainly can’t prove otherwise.

Hope you sort it out. Frustrating.

 

[OXN939]

Do I zero to where the cold bore shot is? Somewhere in between the cold bore and the main group?

Yes. That cloverleaf group is indicative of your rifle's performance under *those* conditions- that is to say, with a bore that is both hot and dirty. To get a real cold bore zero, you want to give it a while between each shot. If you have the time, I mean like ten minutes depending on ambient temperature. Also, if you're sighting in for a clean bore zero, clean it between each round while you're confirming zero.

I'm sure there are lots of other schools of thought out there, but that's what works for me!

 

[VAHunter01]

100% of my cold bore POA/POI issues have been due to bedding or fouling.

I’ve used tip pressure, full length bedding and moly coating in the past to fix it.

 

[Badge171]

Sir .depending how clean your firearm is when your range time is over is a consideration. Is there any copper fouling ? If you clean the barrel are you oiling after your done? We have found a oiling a barrel is great for storage, but for regular shooting a clean DRY barrel gives consistent cold barrel shots. Also Having a Few lighweight Kimbers that first shot or 2, takes a second to get your routine in order. And that can make all the difference.

 

[Cahunter805]

I agree it’s most likely a bedding/pressure issue. Did you free float the barrel? Is the bedding stress free?
Many times on a Kimber these things need to be checked.
Have you checked the front scope screw contacting the barrel threads? Shorten the screw so it doesn’t touch when torqued down.
Magazine box height- A lot of times the mag box is a little tall and needs to be shortened. You can tell by it digging into the stock in the magazine well.
Here is a great write up for tips.

Montana tinkering....

I get several PM's asking questions about what I do to improve accuracy with Kimber Montana's. I've decided to start a thread detailing the steps I take and the things I look for shortly after buying one. First and foremost, I'm not a gunsmith. These "improvements" weren...

www.24hourcampfire.com

 

[Tumbleweed]

To me this has scope failure written all over it. You said you checked the scope, did you replace it with a known good one for testing?


Sent from my iPhone using Tapatalk

 

[Shooter71]

Sounds mechanical, which includes the shooter, bench setup etc.
It’s almost never load related. Try a 10+ shot group, one shot at a time and see if it actually fills in around the first shot.

 

[Bigwindymt]

I had the same problem with my son's 7mm-08. I started load development using a velocity node and had the same story almost exactly. By shot 2-3, everything would settle in. I ended up doing all sorts of things to improve the mechanical accuracy with minimal gain.

The only variable that showed results was chasing the middle of my accuracy node on my handloads. Had to drop velocity more than I expected. Cold zero is still slightly higher in this rifle (< 1moa), but I know this and can adjust.

 

[tdot]

Just got back from a spontaneous 2 day hunt. Got a nice muley! Hit him at 200 yards at a 20 degree incline from a very hasty seated position. One and done. So the zero worked, but I'd still like to improve it.

Thanks to everyone whose replied. To answer a few of the questions.

Bedding- it was my first bedding job, but lots of experience working with epoxies, fiberglass, etc. So reasonably compotent. The action sits in the stock and doesnt appear to move when I tighten the action bolts down. I've tightened front bolt first and also back bolt first, just to test and the action doesnt appear to move during the tightening process. Any other way to check for stress in a bedding job?

Kimber - I've checked all the usual suspects; shortened screws, magazine, etc.

Cleaning - cleaned it to bare steel about 60 rounds ago. Fired a mix of solid copper an lead thru since then. Kept it dirty as I've never had a loss of accuracy with this barrel dirty until about 175-200 rounds down the pipe.... maybe I should look at that again.

Scope - dont have another 1" tube scope, and dont have rings for this rifle to test eith a 30mm scope. Will have to consider this though.

Barrel - it passes the $5 bill test. But might be a touch tight, considering I can move the stock with too much forearm pressure.

How do I know if I should partially bed the barrel?

I try to only shoot lighterweight rifles, so while the kimber is my lightest, my heaviest is only 2 pounds heavier, trying to stay with similar equipment so that I dont have issues switching between guns.

While working wirh my Kimber, I typically only shoot 1 round every 5 minutes, so the barrel is only warm by shot 5.

 

[zankuleg]

Now that you have a baseline for comparison, try your cold bore shots with a slightly fould bore. Clean it completely, then fire about 5-10 rounds and leave it fouled. Walk away for about 20 minutes to let the barrel cool down to ambient temp and then shoot 1 round. Let it cool completely and fire a second etc. and see which gives you the best group (clean vs fouled cold bore shots). I found that my Remmy 5R prefers a clean cold bore whereas my PSS likes to have about 8-12 foulers through the tube. It'll shoot basically the same POI every time afterwards for about the next 60 rounds. Then it starts to drift a little and it's time to clean again.

 

[FURMAN]

Some people will deny it until they die but some barrels will NOT shoot the cold bore into the group no matter what. I have had a couple. The last one was a Savage 6.5x284. The cold bore was high and right every single time. Then it would group right around .25" and 100 yards. The cold bore was very repeatable but I will not own a barrel that I can't trust the followup shot.

 

[gbflyer]

Just got back from a spontaneous 2 day hunt. Got a nice muley! Hit him at 200 yards at a 20 degree incline from a very hasty seated position. One and done. So the zero worked, but I'd still like to improve it.

Thanks to everyone whose replied. To answer a few of the questions.

Bedding- it was my first bedding job, but lots of experience working with epoxies, fiberglass, etc. So reasonably compotent. The action sits in the stock and doesnt appear to move when I tighten the action bolts down. I've tightened front bolt first and also back bolt first, just to test and the action doesnt appear to move during the tightening process. Any other way to check for stress in a bedding job?

Kimber - I've checked all the usual suspects; shortened screws, magazine, etc.

Cleaning - cleaned it to bare steel about 60 rounds ago. Fired a mix of solid copper an lead thru since then. Kept it dirty as I've never had a loss of accuracy with this barrel dirty until about 175-200 rounds down the pipe.... maybe I should look at that again.

Scope - dont have another 1" tube scope, and dont have rings for this rifle to test eith a 30mm scope. Will have to consider this though.

Barrel - it passes the $5 bill test. But might be a touch tight, considering I can move the stock with too much forearm pressure.

How do I know if I should partially bed the barrel?

I try to only shoot lighterweight rifles, so while the kimber is my lightest, my heaviest is only 2 pounds heavier, trying to stay with similar equipment so that I dont have issues switching between guns.

While working wirh my Kimber, I typically only shoot 1 round every 5 minutes, so the barrel is only warm by shot 5.

Not sure how closely the Kimber resembles the Springfield or Model 70 footprint as I am unfamiliar with Kimber other than seeing one at Sportsman’s Warehouse. With those two, it’s important that the only vertical surface that is effected by the thrust of recoil is the recoil lug. There should be clearance everywhere else. Interference, say behind the trigger and forward of the rear tang screw will drive you nuts.

 

[RosinBag]

Here is what I have found with the Hammer’s and other copper bullets; fouling is quick and the Achilles heel on accuracy. Then if you shoot lead before after or during it gets even worse. I think you have about 15-20 rounds with copper before you need to clean it out completely.

 

[ebubedike]

Now that you have a baseline for comparison, try your cold bore shots with a slightly fould bore. Clean it completely, then fire about 5-10 rounds and leave it fouled. Walk away for about 20 minutes to let the barrel cool down to ambient temp and then shoot 1 round. Let it cool completely and fire a second etc. and see which gives you the best group (clean vs fouled cold bore shots). I found that my Remmy 5R prefers a clean cold bore whereas my PSS likes to have about 8-12 foulers through the tube. It'll shoot basically the same POI every time afterwards for about the next 60 rounds. Then it starts to drift a little and it's time to clean again.