setting back a barrel

F

f21sh

Guest
Hello All
I purchased a borescope recently and was looking at a throat on a 7mm rem mag. The throat is not centered with the bore perfectly. It is not out by much and the barrel has not fired that many rounds. How does one determine if the barrel can be set back and the chambered reamed to correct the alignment with the bore? Barrel contour is a # 6, finished at 27" long. I have seen stock Rem. SPS barrels set back and reamed to improve accuracy however they were all chambered in 308.
Thanks
f21sh
 
time wise a barrel set back is nearly as valuable as chambering a new blank.That said most of us that do it,do our own barrel work....... having machinery at hand. So.... depending on the quality of the barrel....not including factory barrels.Set backs really do help accuracy.
A crooked chamber/unconcentric chamber raises more of a challenge.... if you do your own work I`d try it,by removeing existing threads (approx.1") and starting over using a good piloted reamer.
OMHO
bill larson
 
It's actually more work to fix than chambering a new blank IMO. So, "worth it?" is all in the eye of the beholder. If you're a serious factory class competitor then setting back a 308 is a legal leg-up and worth real money, setting back a factory 7Mag??? Not so much. By the time you rebore it to center you'll have paid for a new blank PLUS the work...


Unless you've got this friend with a lathe.


AND he's good yet will work for free.

AND you're OK wi'dat.....

al
 
Thanks Bill & Al
I do have my own equipment South Bend 13 X 40 lathe with tooling I just have never set back a barrel. I was not sure if there were any rules of thumb or measurements one had to conform too prior to setting back a barrel. The barrel is a kreiger that is why I thinking of making the effort.
Thanks
f21sh
 
I would shoot it first... then if you decide to set it back you will have an accuracy reference to relate to. If it is out only 1 or 2 ten thou you may not see much difference in a 7mm Mag.
 
Here is a major problem. Regardless of your efforts, the reamer will still follow the existing chamber. If that chamber is not perfectly straight with the part of the barrels ID that you want it to be straight with, then your efforts might be wasted.

I set my Competition Barrels back on a regular basis, but I do all of my initial chambering with this in mind. The way I chamber allows me to set a barrel back up exactly the way it came out the first time........jackie
 
f21sh said:
Hello All
I purchased a borescope recently and was looking at a throat on a 7mm rem mag. The throat is not centered with the bore perfectly. It is not out by much and the barrel has not fired that many rounds. How does one determine if the barrel can be set back and the chambered reamed to correct the alignment with the bore? Barrel contour is a # 6, finished at 27" long. I have seen stock Rem. SPS barrels set back and reamed to improve accuracy however they were all chambered in 308.
Thanks
f21sh
Click to expand...
Is this a stainless barrel or chrome-moly? Boots Obermeyer points out on his article about barrel steel that chrome-moly will work harden on firing and can ruin a reamer so be warned.
 
Here is the deal concerning barrel set backs in our shop. First after enough barrel shank is removed to insure that a proper chambering job can be done there has to be enough straight section left to get a hold of. In your case depending on how crooked the chamber is will effect how much you will have to cut off and where the blank was cut the first time. Second after set back the barrel has to be long enough for the chambering to work. In your case with a 7mm Remington Magnum that length would be around 26 inches. Third the barrel needs to worth the effort. In your case a Krieger barrel qualifies if it not heat checked from shooting too fast. A factory barrel isn’t worth the effort in my opinion. You will need one of those long indicating rods like Gordy uses; you can get it from Dave. With the barrel through the headstock you will want to indicate in the bore from the muzzle end of the old throat towards the muzzle about three inches. What you are looking for here is unadulterated bore to indicate and get true to base your new chamber on. Blow off the chamber indications because we already know it sucks. Once you get that much barrel running straight you should be in pretty good shape. You will need to go in and straighten up what is left of the old chamber with a boring bar leaving about .010 in the diameter for the reamer to cut. This needs to be done or the reamer will follow what is already there and we know that sucks. Then all that is left is to thread and chamber using your regular methods. By the way don’t let anyone tell you that a 7 Rem. Mag. won’t shoot because that is a pile of bull feathers. Here is a tip you won’t get there with a .220 go gauge. Didn’t the Brit’s kick our ass in the Worlds with the 7 Rem. Mag. a few years back?

Got My SEMA approved fire suit on.
Nic.
 
I agree with Jackie and proved it for myself. Unless you clean up the existing crooked chamber that reamer will continue to follow the same course.
Since everyone is using some sort of floating reamer design it's a guarantee that reamer will follow the old chamber.
 
Hello gentleman the barrel is stainless steel that has been fired so there will be some case hardening of the steel; maybe fighting some chatter? So if I indicate bore using the long range rod then bore the chamber straight? Would I not have to bore the throat area straight also to get the reamer to run straight down the bore also or would the reamer straighten the throat area out? So at a minimum I would have to at least remove neck and free bore length from the barrel to clean up the chamber? Also there was a thread relief cut in the initial threading not very large though about thread width at best how will that affect the thread seating?
Thanks
f21sh
 
Last edited by a moderator:
Now you're seeing it....

I would straighten the setup using a Grizzly or Gordy Gritters rod (PTG calls it the Grizzly rod) drill out and bore to remove the entire neck/throat, cut off enough to re-thread and not worry about the relief cut if it's in the threads.

IMO the reamer can't straighten anything and forcing the front of the reamer into the crookedy leftover neck/throat is just a guarantee of wallowing the whole mess out.

al
 
This barrel shoots 140 gr. factory ammo 3100 fps through the chronograph 1 moa at 600yds. this was to fire form cases. I have yet to develop hand loads for it. I was just looking at the chamber with the borescope and low and behold off just slightly judging by the scalping at the lands. Now my concern is the fire formed case returning to the chamber will be just off slightly depending on how it is orientated. I guess if I bump the shoulder back slightly more when reloading I maybe able to correct for some of this misalignment. Its the thought of it that counts if you get my drift.
Thanks
f21sh
 
What you see has no bearing on the straightness of the cases. Your chamber is round. There is no misalignment in the chamber, bumping the shoulder back will only create more problems not solve anything.

al
 
Ok I'm learning so am I correct when I look at the scalloping in the junction of the lands (slightly uneven) and that represents misalignment with the bore?

f21sh
 
Niccolo said:
Here is the deal concerning barrel set backs in our shop. First after enough barrel shank is removed to insure that a proper chambering job can be done there has to be enough straight section left to get a hold of. In your case depending on how crooked the chamber is will effect how much you will have to cut off and where the blank was cut the first time. Second after set back the barrel has to be long enough for the chambering to work. In your case with a 7mm Remington Magnum that length would be around 26 inches. Third the barrel needs to worth the effort. In your case a Krieger barrel qualifies if it not heat checked from shooting too fast. A factory barrel isn’t worth the effort in my opinion. You will need one of those long indicating rods like Gordy uses; you can get it from Dave. With the barrel through the headstock you will want to indicate in the bore from the muzzle end of the old throat towards the muzzle about three inches. What you are looking for here is unadulterated bore to indicate and get true to base your new chamber on. Blow off the chamber indications because we already know it sucks. Once you get that much barrel running straight you should be in pretty good shape. You will need to go in and straighten up what is left of the old chamber with a boring bar leaving about .010 in the diameter for the reamer to cut. This needs to be done or the reamer will follow what is already there and we know that sucks. Then all that is left is to thread and chamber using your regular methods. By the way don’t let anyone tell you that a 7 Rem. Mag. won’t shoot because that is a pile of bull feathers. Here is a tip you won’t get there with a .220 go gauge. Didn’t the Brit’s kick our ass in the Worlds with the 7 Rem. Mag. a few years back?

Got My SEMA approved fire suit on.
Nic.
Click to expand...

Love your .220 comment. Lots of gun tinkers don't realize this. The below tool tells all.

Read the indicator, it says 0.212"


measurebelt.jpg
 
f21sh said:
This barrel shoots 140 gr. factory ammo 3100 fps through the chronograph 1 moa at 600yds. this was to fire form cases. I have yet to develop hand loads for it. I was just looking at the chamber with the borescope and low and behold off just slightly judging by the scalping at the lands.
f21sh
Click to expand...

If it shoots factory ammo that well I would certainly work a load for it before doing any work on the barrel. It would not surprise me if it shoots considerably better.

It is going to take a considerably amount of work and possibly more than one attempt to correct and make that chamber 'perfect'.
 
I originally was looking at using the rifle for Varmint & getting started in some F class or Tactical shooting. Looking at building a 7 MM WSM .319 neck to compete also. However I'm also interested in the 6.8 mm WSM configuration. SO I will begin to develop a load for the 7mm REM Mag. maybe it will only be used for Varmint or long range hunter now. Thanks for everyone's help I have learned much from this discussion.
f21sh
 
Sorry Woodhunter neither can I read the wind that well; 6 o'clock in the evening real lucky no wind what so ever @ the range it gets that way once in a blue moon, also "the disproof of luck is consistency". Hopefully I can repeat the grouping with hand loads; oh and still waiting for the blue moon to show up again.

f21sh
 
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