POI shift with different barrel

A

afrench

Member
i bought a used 6ppc benchgun that came with several barrels. i've tried a few of them and all of them have the same poi within an inch or so of the others except for one. this one barrel hits 5-6 inches away at 3:00 at 100 yards. it seems to be grouping well so far, but i need to spend more time with it developing loads.

is the difference in poi a potential problem? just curious if the threads/shoulder/chamber may be off center.

thanks for any input.

aaron
 
Probably smithed by a different person using a different method of bore alignment. Notice to see if you can determine any different tracking quality in that one from the others.
 
POI shift

Not all barrels are drilled perfectly straight. If the barrel has a little belly in it, it will print in a different place. Just make a note of where it prints and attach to the barrel. When you put the barrel on, make the adjustment and your set.
 
I think Dave hit the nail on the head. I've seen that as well quite frequently where a muzzle can be indicated in to .0002 and chamber end as well, what happens between the two points is going to determine where the bullet hits on paper. I imagine it would be a lot worse than that if the barrel was chambered where the muzzle end is moved around to get two points at the chamber end running concentric.
 
Butch, I probably need to explain that a little more than the simple statement I made and I don't mean anything negative by those that chamber that way. Their method seems to work for them and that's all that matters anyway.

However, if a barrel is set up in the lathe by moving the muzzle end of the barrel around to get two points in alignment at the chamber end, for instance, where the reamer starts into the barrel and the projected throat of the chamber, the muzzle could be .015, .020 or more thousandths out of center line of the lathe axis when the barrel is chambered. They normally take this amount that the muzzle is out of centerline of the lathe axis and point the barrel to where it's pointing up, letting gravity take care of the bullet as it goes on it's path. If you change from one barrel that is pointing .015" up and the next one that is pointing .005" up, more than likely at 100 yards or so they won't be hitting very close at all to where the other barrel was. It's unlikely enough that you'll be hitting very close to the same point of impact from one barrel to the next even with the barrel centered in the lathe axis when centering at the muzzle and at the projected throat. If you can change barrels from one barrel to the next and not have to change your scope much, then you are pretty fortunate and have a couple of pretty straight barrels. How straight the bore is in a barrel doesn't seem to have much effect on how a barrel shoots, but it does make it easier to get a good chamber to have a straight barrel.
 
Knowing that we all want straight barrels, but few really are perfectly straight. What would be the better of two scenarios?

Having a (not straight) barrel chambered and threaded where the chamber and tenon are concentric to the center of bore in the protion of the (not straight) barrel where the chamber and thread tenon is to be?

Or Having a (not straight) barrel chambered and threaded where the chamber and threads are concentric to an imaginary straight line between center of bore at the breach end of a (not straight) barrel and the center of bore at muzzle end of same (not straight) barrel?

A third Scenario might be?

lets say one day we get a perfectly straight barrel...

The two scenarios would be the same right? So which would be the better way to have that barrel chambered and threaded, or in this case would it matter?

Paul
 
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Paul, with a perfectly straight barrel, either method should theoretically get the same results as it would make no difference where you were able to indicate in the barrel whether at the muzzle, breech or the middle of the bore if you could get there. It would be running dead true no matter where you indicated. As long as the chamber is cut concentric to the bore, it shouldn't make any difference how it's done. I don't know whether you remember or have read a statement that was in Warren Page's "The Accurate Rifle" that is if I remember correctly. There were two barrels, one was crooked as a snake, the other was pretty straight. The crooked barrel shot lights out, the straight one was just so so. Of course, that was a long time ago and aggs have gotten better and better. A barrel will either shoot or it won't. But, the job of anyone chambering barrels is to have a method that takes the gunsmith out of the equation as to whether a barrel will shoot or not.

I want the throat of my barrels centered with the chamber. That's where the bullet starts, that's where I want to start the centering of the barrel in the lathe. Most barrels aren't crooked enough to make much difference. Every once in a great while you'll run across a barrel that isn't the straightest. Thankfully, they are few and far between.

Mike
 
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Dave B said:
Not all barrels are drilled perfectly straight. If the barrel has a little belly in it, it will print in a different place. Just make a note of where it prints and attach to the barrel. When you put the barrel on, make the adjustment and your set.
Click to expand...

I have chambered several barrels in the last few years that have had considerable curve in them. If the chamber neck, chamber body, tenon shoulder and muzzle exit point are all in alignment, the barrel will shoot straight ahead as will the others that were chambered with this method and have different amounts of curvature.

As stated above, the amount of curve between the muzzle and chamber doesn't seem to have any negative accuracy effect.
 
Pat McMillian

started me out in the game a long time ago. He always told me that a barrel with a bit of a curve in it shot better. Now its very possible that he told me that bPatecause of how crooked some of his barrels were.
Once a very well known barrel make went elk hunting with me in Arizona. After he got home he sent me a 15 twist 6mm barrel to try as Skip Otto was setting us all on fire with one he had. The guy I gave it to to chamber called me a few days later and said we ought to sent it back as it was the crookedest barrel he had ever see. I told him that as the barrel was free I wouldn't consider sending it back with a complaint and to chamber it anyway.
As it turned, out this barrel tricked me in the same way Skip's barrel tricked him.
It shot so good, I thought it was me!
 
Dave B said:
we ought to sent it back as it was the crookedest barrel he had ever see. I told him that as the barrel was free I wouldn't consider sending it back with a complaint and to chamber it anyway.
As it turned, out this barrel tricked me in the same way Skip's barrel tricked him.
It shot so good, I thought it was me!
Click to expand...

Think about it Dave, in a crooked barrel the bullet has to travel further, and burns more of the powder, and gains more velocity, and spends less time in the wind!!
 
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