Slugging a barrel for improfections

[6mmdasher]

What is the correct way to slug a barrel to check for tight and lose areas? Also what to expect from a high and low quality barrel?

 

[Rustystud]

I would suggest you inspect your barrel with a bore scope vs slugging your barrel. I think you will gather more useful information. You might even video the inspection. Most quality gunsmiths will do this service for you for a fee. They should provide you with barrel documentation, a narrative report and a tape, CD, or DVD. The cost of the equipment to do this service to this level is over $1000.00 and it takes about an hour to video and put together the report. Expect to pay a $100.00 or more. You can of course ask for just a cliff notes version report for less.
Rustystud

 

[Eddie Harren]

You should read Calfee's articles in PS magazine concerning slugging bores. It is quite informative. I fail to see how a borescope can detect minor variations in the diameter of a bore.
I'm hoping to find someone who can borescope a barrel and say, with certainty, that it will be a "Hummer". That man, and I, are going to be rich.

 

[Rustystud]

Doced:

Pushing a lead slug down a bore gives a cumlitive effect on the lead plug. The maximum land width and height are recorded on the slug. A bore scope view gives the observer a view of the external dementions of the lands and grooves. It allows the viewer to see tool marks, distrotions, copper, carbon, corrosion, throat errosion and looking at the muzzle and crown from inside out. No one can look at a barrel and determine if it is going to be a hummer. Most with experience can look at a barrel and tell you it is not going to be a hummer. I will clarify this and say I have seen some real crappy barrels that shot well, there are exceptions to every rule.
Rustystud

 

[Bob3700]

What is the correct way to slug a barrel to check for tight and lose areas? Also what to expect from a high and low quality barrel?

Rusty certainly has a point on visual inspection of a bbl. You can actually see the condition of the bbl, throat, crown, etc. with a Hawkeye borescope. It is an education in itself. Like Rusty pointed out, you can certainly identify a bad bbl but you sure can't predict a hummer.

That said, I would still slug the bbl. Read Bill Caffe's articles in PS and he will guide you thru the process.

As stated, you cannot "Feel" the bore dimensions with a borescope but you sure can with a lead slug.

I created a slug useing cerrosafe to cast a slug of the bore.
Then I used a brass rod to drive the slug thru the bbl. You can detect the tight and loose spots as well as measure the lands and grooves using Bill's methods.

Bob

 

[Eddie Harren]

I fully agree. The best 6mm barrel, that I ever owned, was a HS Precision 10X that a customer paid me to replace, after bore scoping it. I put it on my Rem actioned Varmint Hunter rifle and set 2 records as well as making IBS "shooter of the year". That barrel fouled worse and shot better than any barrel I've ever owned.

 

[alanfuge]

A borescope can detect imperfections in the barrel,tool marks, lapping, copper, fouling) but cannot accurately measure tolerances in the bore diameter.
Using a lead slug does give an idea on the consistency of the barrels bore diameter but again too many variables with pressure of the rod, this is only a rough indication.
I personally grind pilots to the diameter of the bore same you would for chambering,.0001) then by adapting theses to a rod and gently easing down barrel you can accurately measure the bore diameter if the pilot stops you no of a tight spot if the pilot becomes loose you know of loose spot,barrels must be clean for this process. And as i do own a bore scope this process does not damage the barrel much care needs to be taken in the process no force is to be required.

Alan

 

[sjk]

Alan,
I used to do the same but adapted the slug to an air cylinder and air gage. The borescope is a great way to go visually, but the air gage is one of the most accurate means of measuring ID's we have. It will detect variations of .00005 if you really want the nitty gritties. These gages are not at all hard to make in your shop and they're worth their weight in gold. Pushing a slug down the bbl only tells you that it's looser or tighter in one or more spots, but not how much the looseness really is. The how much is what most shooters are after.