Cutting new throat

[halfmoanut]

I have a 6x47 Lapua and I am told that around 650-750 rd count it should have a new throat cut in it. I am curious to know what is actually done and does it save barrel length,and how many more rounds will I see before the accuracy falls off? Also should it be crowned again when this is done?And can it be cut off front and rear and be chambered all over again after re-throating?

 

[Preacher]

That don't seem like a lot of rounds fired to have the throat go bad, maybe in very extreme circumstances but I doubt it unless it was stressed by a lot of heat...
The throat can be extended with a throating reamer and it will make the barrel shorter
internally....
You should be able under normal circumstances to run a few thousand rounds down range before accuracy drops off...
If the crowns in perfect shape there is no need to redo it...
If the barrel is fat enough at the right spots it can be cut front and back to make a new shorter barrel........
Unless your using a separate throater the chamber reamer will cut the new throat while it's cutting the chamber.....

 

[mpryne]

I would be curious to know if that information was given to you by a gunsmith or what? I wasn't clear in your post if that was from someone who already bore scoped it. Or if it was someone saying that it should just be done 'just because'. Something sounds fishy.

 

[JohnPierce]

You should be able to get more out of the barrel than 600 or so hundred rounds, however I have seen improvements after 400 rounds in my PPC by simply touching up the lead with a tool supplied by Dave Kiff. It required about .015 metal removal to have like new lead and no suffer of accuracy. In fact the barrel shot like new again.
For the crown, it will not hurt, but have positive improvement to remove about .250 from the muzzle and give it a new crown cut.

I feel if you are considering cutting the breach and rechambering, that you have gotten enough life from that barrel and its time to move on.

 

[Ackman]

I have a 6x47 Lapua and I am told that around 650-750 rd count it should have a new throat cut in it. I am curious to know what is actually done and does it save barrel length,and how many more rounds will I see before the accuracy falls off? Also should it be crowned again when this is done?And can it be cut off front and rear and be chambered all over again after re-throating?

There's no set number of rounds before a throat needs to be renewed. You go by wear/erosion and ultimately by how much accuracy has been lost. No way to predict that.

Cutting a new throat is done by rechambering. That means shortening the breech end at least enough to run the reamer in and cut however much of the throat is worn. That'll mean at least one neck length. If there's lots of wear, you cut off the threads completely and start over....makes the barrel about 3/4' shorter. It's NOT done by running a throating reamer in there.

No need to touch the crown, that's at the other end. Throat wear has no effect on the crown.

 

[RMiller]

My 6x47L is at 600 rounds as I speak and I just got a look down it with a scope and I must say I was shocked to say the least.
It is pretty bad. The 1st 1/8' of the throat is badly eroded.
Heat cracking is pretty bad for at least 8' into the bore.

The reason I even checked it with a scope so early in its life was because when I was loading up for a match I decided I should check and see if my lands had moved at all. It had been a match or 2 since I last checked it. Well they did.
They moved .045' forward. That a lot in the short time between checks So now I adjusted my seating depth for it but my barrel is not long till Ill cut it and set it back.

I do run mine pretty hot so I cant complain to much but if someone says after 600 rounds you ll need to set your barrel
back you should believe they just may be close.

With that being said, if I had to pay to have mine set back id keep shooting it till it wasn't competitive. I can set it back my self so that changes things.

 

[Rustystud]

Have a couple of questions. Are you shooting Benchrest, Cross the Course, Prone or what? With Benchrest to be competetive you have to have equipment that is capable of shooting in the .2s and teens. With cross the course and long range prone if your gun will shoot .5 moa or better you can shoot clean scores. F-Class rifles need to shoot .25 moa to be consistent winners.

Chambers are cut with reamers. The throat length remains constant with relationship to the rest of the chamber during the reaming process. Reamers are ordered with specific throat lengths and lead angles. This is done to accomodate particular bullet lengths. Some gunsmiths buy reamers with no or very short throats then buy what is called a throating reamer. The throating reamer is used to extend an existing throat. The gunsmith using a throating reamer has to be very careful for a number of reasons. The first is the throat needs to be both co- axially and concentrically aligned with both the chamber and bore. Another factor is the throating reamer is removing very little material and can undercut the throat very easily.

Throat lengths grow with shooting. It is known as throat erosion where the hot expanding gasses melt away the actual throat surface. The more consistent the throat edge the better bullet engagement. This adds to some more accuracy. I can not see recutting the throats in anything other than a BR gun for the life of the barrel. Some folks setback a barrel at about 2/3 to 3/4 of a normal barrel life and usually get another 1/2 life added to the barrel. This is dependent on the cartridge velocity/pressure. With extreme presure cartridges most folks just shoot them out with one chambering and not setting them back due to cost.

Are you talking about opening up the throat or setting back the entire chamber?

Nat Lambeth