How to counterbore a barrel?

[HankC1]

Bought an old mauser, the bore is dark but still have some shine and rifling is distinct. Noticed the rifling near muzzle is almost gone, drop a bullet with rear end first and it will go in almost 3/4" and stop. I have not shot it yet, but think I may need to counterbored it. How to do it without a lathe? Can I use a handdrill and a regular drill bit? How much oversize and how to remove burrs after counterbore? Thanks.

[kraigwy]

Ain't gonna happen with a drill. Drill bits walk too much.

To do it propertly you need a lathe. The bore has to be lined up perfectly, not the barrel, the bore. Often they're not the same.

If I was going to do it, I'd remove the barrel from the action, using a 4 jaw chuck line up the bore, then counter bore the muzzle.

Before you do anything, shoot it to see if it really needs counter bored. You might find out it shoots fine just like it is.

[Creeper]

How to do it without a lathe?

I'm not sure who rents a piloted drill and reamer for that application... that's what you need. There are several gunsmithing tool renters on line... but most list re-crowning tools, not muzzle counterbores.

Check with the following and see what they might have.

http://guntoolrentals.com/

http://www.4-dproducts.com/

http://www.reamerrentals.com/

[Bart B.]

Cut an inch off the muzzle then recrown it.

[hoghunting]

Cut an inch off the muzzle then recrown it.

My suggestion also as it's much easier and less expensive.

[HankC1]

I would have cut the barrel and recrown if it is a sporter but it is in military configuration and front sight is there. Checked into the tool rental places, they don't have any tool to counterbore muzzle. Did my search on the web, not much info found but did came across a posting that he uses a handdrill and drill bit to do it and was fine. No detail mentioned. My thought is the drill bit should follow the bore if I start with a drill bit just a tad larger and progressively increase the size. How much oversize needed? Not sure how to clean up the burrs afterwards but think I can make a rod to go into the bore to recrown. I will shoot it first before I do anything stupid. It is an Izzy 308 Mauser and I like to keep it in military configuration.

[F. Guffey]

I have tools, lots of tools, I have counter sinks, drill a hole for a guide, then take a tool that has a pilot, use the drilled hole as a guide for the pilot etc... I have tools that are designed to be used in a mill, same thing, but different, I can use gun friendly pilots or I can prevent the pilot from turning. Then there are core hole drills.

Same thing but different, it is not necessary to drill a hole for the pilot when in threr is a hole in the barrel. .

Then there is that part where the muzzle is tapered as in it is a bore with varying diameters, on one end the taper is called throat erosion, back to the muzzle, the taper at the muzzle, it is caused by a bad habit?

Cutting the barrel? As the man said, cutting the barrel will create another problem if the front sight is to be used.

F. Guffey

[tobnpr]

Not going to shoot well if the rifling is screwed up and it hasn't been counterbored.

Wonder if you could cut/crown, then cut a new dovetail with the Wheeler dovetail cutting fixture and install a new Williams front sight that would work...

Or, get a short-chambered replacement barrel from someplace like Numrich:
http://www.gunpartscorp.com/Manufact...rels-34391.htm

[Hylander]

You don't say what model Mauser.
If K98, 24/47 or M48 you can remove the front sight by unsoldering then cut and crown and solder the front sight back on.
Or on the cheap if the cheap, you counter bore using a slightly larger than bore drill bit and a drill press, it is farly easy and works good, I have done several and each time accuracy has improved.
Of course a lathe is better but if the bore is not that great paying a smith is a waste of money.

[HankC1]

It is an Israel K98 Mauser in 7.62NATO. Shoot the Mauser today. It sucks! Almost 12" spread at 50 yds. Going to try counterbore with a drill bit to see how it goes. If still not working I have couple 1912 Chilian 7.62NATO Mauser barrels that I can put on, but it won't be an Israel Mauser anymore. When I bought the rifle, I asked the seller about bore condition and was told it is good!

[Hylander]

I would couterbore with a drill bit.
Or better yet start the counter bore with a drill bit and finish with a bottom cut end mill bit, this will give you a clean flat muzzle, you should only need to
go 1/2" to 3/4" deep.
Remove barreled action from stock, remove bolt.
Clamp the barrel in a bench top drill press hanging over floor or in a full size drill press. Place about a 10" peice of dowel in the chuck down the barrel to get the barrel lined up straight and clamp barrel tight. Now release the dowel from the chuck and lat it fall through the bore. Now place your drill bit in the chuck and drill slow, use plenty of oil. When about 1/4" or so remove drill bit and replace with end mill bit and go 1/2" - 3/4"
To finish off take a short peice of dowel and wrap it with some 0000 steel wool soaked in oil and run it on top of the new muzzle in your couterbore, just a little and very light pressure. Your done.
Done forget to push the reg out the bore from the chamber end and clean.

If accuracy is still not acceptable, rebarrel with a NOS .308 Norwegian barrel and call it a day. Only you will know the barrel is not Israeli

[HankC1]

Hylander, thank you for your suggestions. All make sense.
How much oversize I should go? Or I may ask what would be the bore size of a 7.62 silencer? I figure if I go larger than the silencer bore size I should be fine.

[Hylander]

I would use 3/8 bits
No idea of the silencer stuff

[kraigwy]

Or I may ask what would be the bore size of a 7.62 silencer?

Normally suppressors and muzzle brakes are bored .020 over, or a 7.62 (.308) would be .328.

I tad bit bigger wouldn't hurt. I'd still bore it instead of drilling it if it was me, but .375 (3/8) would work.

Instead of drilling, and if you don't want to bore it, ever thought of using a reamer, they make cleaner, more precision holes.

[guncrank]

Double post see below

[guncrank]

Drill out
Then use a standard counterbore.

Figure out the smallest one

As for drill bit not working , well if the crown is square and concerntric to the bore, does not matter how it was formed.

[kraigwy]

Note to self:

Don't let these guys work on your gun

[guncrank]

*

Note to self:

Don't let these guys work on your gun
__________________
I assume you where referring to me

I said as long as the muzzle was square and concerntric

Square and concentric

A lathe is best
Piloted tooling is secondary

A drill would work to crown a muzzle as long as it was square and
Especially for a counterbore.

And my answer was to the OP

[tobnpr]

No collector value to that stick.
Cut and crown it.
D&T a scope mount, slap an optic on it and go shoot it.

Assuming...the rest of the bore is in excellent shape.

[Hylander]

Note to self:

Don't let these guys work on your gun

Remember: Working on an old Mauser with no collector value and bad barrel to begin with, Not worth paying a smith to work on.

[kraigwy]

If its worth doing, it's worth doing right.

[F. Guffey]

“If its worth doing, it's worth doing right”

Kraigwy, I agree, again, what model of Mauser? There are barrels for replacement, I have little interest in restoring to military configuration, I was at the Dallas Market Hall Gun Show this last week end, a dealer came by and was complaining about the rifle he had found, a magnificent Mauser that was drilled and tapped with a mount, rings and scope, a nice shiny barrel with a a very expensive looking stock, his opening statement went something like “Look what someone did to a very rare Mauser”, I reminded him the rifle belong to to the builder, it was his option to do as he pleased, If I need a M1917 action the ears are coming off, those that inflate the value do not will not pay the price.


Bore to? When counter boring the diameter should be adequate, the bullet is leaving the barrel, what the bullet does not need is gas escaping when the bullet leaves the bore, escaping gas can kick the rear of the bullet, the largest diameter counter bore possible is best, in my opinion, I have two that exceed .400”. the two counter bored rifles I have were counter bored because something ran into the muzzle, not because of a tapered bore at the muzzle. If the counter bore bothered me I would replace the barrel, again, there is risk, the rifle may not go back together looking like it did before I started.

F. Guffey

[HankC1]

Would a counterbore hurt the value or I better of just sell the rifle the way it is? (Not going to lie on the bore!) I have a couple good shooter mausers already. It is an Israeli 98K Mauser converted in 7.62NATO and previous owner has put a new military stock on, so it is not really a "collector item".

[Dustin0]

Just sell me the rifle cheap. I will take to guncrank and he can build me another custom Mauser.