deltronic pins for measuring bore

P

philipbrousseau

Member
I mainly purchase .308 cal. barrels and was wondering about checking bore diameter. if this is a suitable method what sizes smallest to largest and in what increments would you suggest. also the palma barrels i think are smaller so please include them in the diameters to be measured. thank you for your thoughts on this.
 
Deltronic pins are usually sold as 'kits' that surround the size you'll need - so you'd grab a .308 kit and it would cover .3068 to 0.3092" in 0.0001" increments. I don't know how valuable they'd be for "measuring" the bore - what are you trying to accomplish? They'd probably do more harm than good to a finished barrel, and an unfinished barrel will have larger ends (the only place you can gauge with pins) than bore.

Good luck!

GsT
 
In the gunsmith or home shop the only method of checking the bore dimensions is by slugging with a lead slug. Pushing a slug through the bore is kind of like walking through it and looking around. The feel will tell you if the barrel is different in diameter from the bore to the muzzle. On a rimfire bore being very slightly tighter at the muzzle is desired. On rimfire or centerfire bores a larger diameter at the muzzle is a big no no.

One other thing slugging will tell you is if there is a place in the bore that is larger than the rest of the bore. Some bore lappers will try to lap out a void down the bore. When this happens the oversize portion will allow a gas blow by and cause copper fouling at that point.

Pushing a hardened pin down the bore would only detect an unusual tightness.

Why does Bill Calfee get up to $3,000 for his barrels, just the barrel, because he has slugged and relapsed the factory bore.

IMO, a gunsmith who does not slug a new barrel before he puts a tool to it is wasting your money and his time.

.

.
 
Last edited:
Jerry,
A friend of mind does about the same thing by casting a pure lead "lap" in the muzzle of barrels. He does this to "map" barrels, to see what he is dealing with, and from our discussions, I would have to say that I agree with you 100% on this. Even big name barrels have been discovered to have issues that prevented them from giving top performance. He also does some lapping, quite a bit actually. Beyond what can be done at the groove diameter, he has also discovered that the bore dimension (diameter at the top of the lands) can have issues that require separate treatment of their own. Because he does not use the internet, early on, I was able to help him with some research on lapping, and since then I have been privileged to be kept up to date on his work in this area. While slugging. or casting a lap is not really a big deal, once you have done it a few times, relapping barrels, especially those that have been chambered is not for the faint of heart, or technically backward.
Boyd
 
philipbrousseau said:
I mainly purchase .308 cal. barrels and was wondering about checking bore diameter. if this is a suitable method what sizes smallest to largest and in what increments would you suggest. also the palma barrels i think are smaller so please include them in the diameters to be measured. thank you for your thoughts on this.
Click to expand...

IMO the nominal bore size of a 308 is .300. I can't imagine you needing many outside of the .299-.301 range.... Palma goes down into the .297 range I guess.... maybe I'm missing something here?

I've only got a very few, I use PTG reamer bushes instead, and I'm a lead lap/feel/measure guy when it comes to "the bore"......I even cringe a little sticking the reamer bushing into the bore....
 
You need an 'air gauge' to measure the ID of long (or deep) precision holes.

Pass the head of the air gauge down the bore after calibrating it in some precision holes.

When done very carefully you can detect variation in the bore of 1/10,000 of an inch.


The back pressure shows hole changes.

http://www.qualitymag.com/articles/84748-quality-measurement-why-air-gaging-still-matters

For occasional use you can rig it up.

A simple block clamped on the tubing and a nice long steel ruler are enough to get distance locations without resorting to expensive equipment.

http://www.threadcheck.com/content/mahr-federal-air-gages.asp

Look in the catalog.

Page 3 has a setup diagram.
 
Last edited:
Boyd, I wonder

Boyd Allen said:
Jerry,
A friend of mind does about the same thing by casting a pure lead "lap" in the muzzle of barrels. He does this to "map" barrels, to see what he is dealing with, and from our discussions, I would have to say that I agree with you 100% on this. Even big name barrels have been discovered to have issues that prevented them from giving top performance. He also does some lapping, quite a bit actually. Beyond what can be done at the groove diameter, he has also discovered that the bore dimension (diameter at the top of the lands) can have issues that require separate treatment of their own. Because he does not use the internet, early on, I was able to help him with some research on lapping, and since then I have been privileged to be kept up to date on his work in this area. While slugging. or casting a lap is not really a big deal, once you have done it a few times, relapping barrels, especially those that have been chambered is not for the faint of heart, or technically backward.
Boyd
Click to expand...

why more people aren't like your friend? Something I have found is barrels that are tired can be brought to life again by simply lapping what looks like Firecracking out of them. Have done it enough so that I know it works. Actually, It's not something I discovered but learned from Jon Newman, who left us a couple years ago. Just some compound on a tight patch is all it takes. I believe what most folks think is firecracking is actually carbon. It comes right off quite readily, especially when using 180.

Pete
 
It is precisely because each rifling configuring within each caliber requires its own expensive plug that air gauging is not a practical answer for end users of rifle barrels. Beyond that, in my discussion with a well known top barrel maker, he admitted that a lead slug allows one to feel things that may not be readily apparent when air gauging. On the other hand, I know of no barrel maker who would use slugging to do QC on all barrels produced. This leaves it to the gunsmith to do, and report back problems found through that method. By taking a "look" before machining is commenced, a lot of labor, shooting time, and components can be saved if a problem is discovered. Also, if the barrel is to be used for an application where some choke at the muzzle is desirable, the amount of constriction and its length can be determined. While relapping a barrel is a labor intensive task that must be done with great care, simply slugging or casting a lap for measurement purposes is much less time consuming. Useful information can be obtained in a half hour or less.
 
Back to Deltronic pins. I have them in sets of 25 for each chamber diameter that I chamber, only 6 calibers in my case. Take the 308 for example, as Al said, the nominal is .300. My pins come in 12 ea. in .0001 diameter increments below and above the .300 nominal. I don't beat them down the bore either. I chamber in the headstock and use them to get my initial dial in before chambering. We all have our own methods on chambering. If I want to feel the whole bore for any reason, I slug them.
Did the OP say why he may have wanted them?
 
Butch Lambert said:
Back to Deltronic pins. I have them in sets of 25 for each chamber diameter that I chamber, only 6 calibers in my case. Take the 308 for example, as Al said, the nominal is .300. My pins come in 12 ea. in .0001 diameter increments below and above the .300 nominal. I don't beat them down the bore either. I chamber in the headstock and use them to get my initial dial in before chambering. We all have our own methods on chambering. If I want to feel the whole bore for any reason, I slug them.
Did the OP say why he may have wanted them?
Click to expand...

Make sure you chamfer both ends of those pins.

Mine are pretty sharp and hard steel.

Not good for the often softer steel of a barrel.
 
Butch, i had read of smiths using them and was curious as to what i would see by just dropping them down a barrel. i would never force one down the barrel. appears slugging is the way to go. alot of good input on my question, thanks to everyone for their replies.
 
philipbrousseau said:
Butch, i had read of smiths using them and was curious as to what i would see by just dropping them down a barrel. i would never force one down the barrel. appears slugging is the way to go. alot of good input on my question, thanks to everyone for their replies.
Click to expand...

Phillip, I've never tried it and would be hesitant to try.
 
Butch Lambert said:
Back to Deltronic pins. I have them in sets of 25 for each chamber diameter that I chamber, only 6 calibers in my case. Take the 308 for example, as Al said, the nominal is .300. My pins come in 12 ea. in .0001 diameter increments below and above the .300 nominal. I don't beat them down the bore either. I chamber in the headstock and use them to get my initial dial in before chambering. We all have our own methods on chambering. If I want to feel the whole bore for any reason, I slug them.
Did the OP say why he may have wanted them?
Click to expand...

A couple of the better rimfire smiths swear by them. One in particular had them down to .00005" primarily to map out how progressive a taper gets lapped into a bore. The thinking is that you do not want one dimension for too long, longer than, say 2-3". It is not that easy with a slug. You can feel a slug tighten, or loosen in a bore, but that is still less precise.
 
You must log in or register to reply here.
Back
Top