I know you guys that shoot bench are up on this stuff.

I've a friend w/ a Kimber 84 .260. He's not very happy w/ how it shoots vs. what he paid for it. I noticed that the bedding around the recoil lug isterrible (which is to say non-existant), rolling from side to side when the screws aren't in.

However, the firing pin strikes on the primer are noticably off center. How much is this going to mess with consistent ignition? How much of a difference would it make on a hunting type rifle like this?

Thanks.

Tough question to answer without having the rifle in hand. My first inclination would be to assume that the chamber is not concentric with the bolt. Many factory rifles have "slightly off center" chambers. Accuracy comes with "square and concentric". Any deviation from true, and accuracy suffers.

I have a Kimber Longmaster in .308. My original problems were an occasional failure to fire and accuracy. The only way I could get good accuracy was to put the bullet ogive .010 off the lands. This made the cartridge to long to fit in the magazine.
I took the rifle to one of the better gunsmiths in the area for examination (I didn’t want to mess with sending the rifle back to Kimber), what was found was a firing pin bore in the bolt was very rough and poor action bedding.
I still have the occasional misfire and the accuracy remained the same. After I read this post, I see that the firing pin strikes are off center as well. Could this be the cause of the misfires and accuracy issues?
It looks like I will be sending this rifle back to Kimber. All in all a disappointing experience for the money.

Dave Hyde

I've had a few rifles whose firing pin would strike primers near .040-inch off center and easily seen to be that way. Never seemed to hurt accuracy. Primer compound detonation must have been uniform for all the shots else accuracy would certainly suffer, especially at the longer ranges.

After asking one of the top riflesmiths years ago who catered to competitive shooters (and he built several record-setting and match winning rifles) about this, he said as long as the dimple was no more than half the firing pin's diameter off center on the primer, there typically isn't a problem. When everything's the same for each shot, accuracy happens. Even a sloppy bolt fit in the receiver doesn't matter as long as it's closed and preloaded in place the same way for each shot, 1/4th moa groups at 100 yards to 1/2 moa groups at 600 yards.

Greg Tannel (GTR Rifles and Tooling at 970-353-6176, Kersey, Colorado) is a whiz at bushing firing pins. He centers the bolt on a lathe, drills out the old hole, installs a bushing and then turns down the diameter of the firing pin slightly. The main benefit is elimination of firing pin cratering.

Greg is swamped, but turn around time on a firing pin bush is fast and price is around $60.00, as I recall.


Jordan

I disagree with you on the loose bolt. It will allow the cocking piece to push the back of the bolt up and the upper lug on the bolt will not be touching the lug abutment. I can't see this as helping accuracy.
Butch

Gentlemen,
What I have found on this .308 Kimber Longmaster is that the firing pin is directly in the center of the bolt. This leads me to believe that the chamber may be bored off center. That could affect the accuracy? I still don't understand the failure to fire, though. I had a event this Sunday at the range, out of 50 rounds, I had 2 that misfired.
I have tried every primer I can think of and that does not seem to matter. Any advise?

Thanks

Dave

quote:

Originally posted by Dave Hyde:
Gentlemen,
What I have found on this .308 Kimber Longmaster is that the firing pin is directly in the center of the bolt. This leads me to believe that the chamber may be bored off center. That could affect the accuracy?

I doubt the chamber's off center in the barrel. But sometimes the barrel tenon threads in the receiver will be off center relative to the bolt axis. Which makes a chambered round's primer off center to the firing pin tip. A little off center shouldn't hurt accuracy, a lot may well do so.

This can be fixed by rethreading the receiver for a larger diameter barrel tenon thread, but it will require an oversize barrel tenon (threaded shank) to fit it.

Any 'smith worth his business name can easily check the barreled action for an off-center barrel tenon thread axis. You can too by first stripping the bolt, then putting it in the rifle and closing it, finally looking through the muzzle with the breech end towards a bright light; see if the firing pin hole's well centered in the bore by the light reflections on the lands and grooves. If it's really off center, contact the maker and ask for another barreled action with properly aligned receiver and bore.

If the chamber and threads are cut without removing the barrel from the lathe [which it should be] there is not too much chance of the two having different centers. If the threads are off center it should automaticlly put the chamber out also. If someone cannot indicate a barrel within a couple of tenths, he should not be chambering barrels.

Bart, if that is the way you check a barrel for correctly indicated and cut threads and chamber, I don't think you will be doing too meny barrels for anyone but yourself.