Barrel slugging

[Hannibal]

I was speaking with a gunsmith that I very much respect today and asked him if he slugs barrels before he chambers them. His reply was that he found it unnecessary for centerfire rifles which surprised me. I adopted the practice several years ago because I was having accuracy issues with a couple of rifles and found that when I slugged them the muzzle end was .0015" larger on one and .002" larger on the other than at the chamber. This was before bore scopes were readily available but I could not detect any other defects in these barrels.

So I am curious now. I know several here have more experience with this than I do so I just wondered. Is this a normal practice for you or am I wasting my time?

Thanks for looking.

[john.k]

It was usually specified in military rifle contracts that a lead slug pushed through the finished bore should have a regular resistance,with no loose or tight spots ........Its well documented that a slight loose bore at the muzzle will ruin accuracy............I recall a new CZ 222 that was returned twice by buyers for poor grouping ......when checked out ,there was a approx 1" loose spot at the muzzle ......with the barrel shortened and recrowned ,the rifle shot sub 1" groups,

[john.k]

Barrels from any recognized maker today are gauged to sub tenths before being button rifled ,and after buttoning are electronically checked ....so any one using the barrel can be sure that the dimensions specified are exact ,and any chamber reamer made by a quality maker will work without further checking.

[ascast]

Maybe true if buying top shelf barrels, buy in my limited experience ( bottom shelf or off the floor barrels) loose muzzles or crowns will ruin a rifle. I might look for another smith.

[Hannibal]

My thinking has been trust, but verify. I won't drag anyone's name through the mud but I've been astonished at some of the things I have found from big names.

Mostly just curious if anyone else ever bothers to check.

[Outpost75]

READ THE STICKY!!!!

Do pound cast of chamber neck and origin of rifling. IGNORE groove diameter of barrel.

INSTEAD determine safe release clearance for chamber neck and order mold from Accurate to fit rifle throat or revolver ball seat and dimension nose contour to lightly contact origin of rifling.

[Hannibal]

READ THE STICKY!!!!

Do pound cast of chamber neck and origin of rifling. IGNORE groove diameter of barrel.

INSTEAD determine safe release clearance for chamber neck and order mold from Accurate to fit rifle throat or revolver ball seat and dimension nose contour to lightly contact origin of rifling.

Sir I'm speaking about barrel blanks, not selecting a diameter for proper fit of a barrel that is already chambered. I apologize for not making that clear.
Your advice is correct for bullet fitment. Thank you.

[Outpost75]

Depending upon extent of cold working, button driving force and stress relief it is normal for bore and groove dimensions to enlarge a bit where machining is heaviest. Hammer forged barrels generally get tighter towards the muzzle when tapered. Buttoned barrels the opposite if not properly stress relieved. Cut rifled suffer least from this affliction.

[john.k]

The best way to measure/check barrel blanks is with a set of pin gauges .........the important fit is the reamer pilot ...if too tight they squawk,or worse seize and break off.

[JSnover]

Maybe true if buying top shelf barrels, buy in my limited experience ( bottom shelf or off the floor barrels) loose muzzles or crowns will ruin a rifle. I might look for another smith.
I'm no gunsmith but every project I've ever started with junk, it took a lot more work to make it 'nice.' Save yourself and the 'smith some headaches and buy a quality barrel.

[Hannibal]

I'm no gunsmith but every project I've ever started with junk, it took a lot more work to make it 'nice.' Save yourself and the 'smith some headaches and buy a quality barrel.

My experience has been that a big name does NOT automatically mean a quality product. Which is why I'm asking if anyone else even checks.

[john.k]

Any new barrel will have a 'direction' and also an instruction to cut off the last inch or so .

[M-Tecs]

I was speaking with a gunsmith that I very much respect today and asked him if he slugs barrels before he chambers them. His reply was that he found it unnecessary for centerfire rifles which surprised me. I adopted the practice several years ago because I was having accuracy issues with a couple of rifles and found that when I slugged them the muzzle end was .0015" larger on one and .002" larger on the other than at the chamber. This was before bore scopes were readily available but I could not detect any other defects in these barrels.

So I am curious now. I know several here have more experience with this than I do so I just wondered. Is this a normal practice for you or am I wasting my time?

Thanks for looking.

Accuracy smith are mostly interested in the reamers floating bushing to the bore diameter fit. For any of the competition chamberings I do I have bushing sets in no larger than .0002" steps. In some like 6mm I have .0001" step sets. I mostly use hand lapped cut rifled barrels so slugging provides me with very little, if any, useable information. One lower end barrels slugging will indicate loose spots or reverse tapers.

Bore scopes provide zero information about size.


Depending upon extent of cold working, button driving force and stress relief it is normal for bore and groove dimensions to enlarge a bit where machining is heaviest. Hammer forged barrels generally get tighter towards the muzzle when tapered. Buttoned barrels the opposite if not properly stress relieved. Cut rifled suffer least from this affliction.

That is 100% correct.

I no longer have access to air gauges but when I did I checked a lot of M14 and M1A barrels. Most had a reverse taper of .0005" yet they would hold X ring at a 1,000 yards.

I've chambered maybe 250 barrels. Three have not shot to expectations. If, and heavy on the if, I could slug and measure each blank in 15 minutes each that's 62.5 hours slugging. It took me much less than that to have the manufactures replace the barrels and install it.