doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Question about bore

I just had a L.C. Smith Gr. 2E delivered. Seller said chokes were .006 on right and .018 on left. I checked the bores using my Skeet's gage and inserted into breech end and once past chamber and forcing cones, read .729 in right and .730 in left for the length of the gage which is 12". Inserted into muzzle and read .718 in right, withdrawing until out, still read .718. Left barrel, .719 and withdrawing until out, read .710. Both were inserted for the full 12" and were zeroed again with the .700 ring.
Question is where do you determine choke, from the muzzle bore or half way down the barrel bore? If it was assumed bores were .732 past choke, then his readings were right, but bore wasn't that past choke area.

Barrels are 28"

Assuming hypothetical .732" bores adjacent choke area and exit diameter muzzles as .718 and .719" respectively, the barrels would hypothetically be choked 14 and 13 points respectively. Which they ain't so they also ain't. I'd say the thing's choked cylinder and 9 points on the front end and has big jugs at the rear. Perhaps aggressive pit removal leads to progressive choking. Maths can be difficult what with the possibility of getting adtraction mixed up with subdition. Could be the unmistakable is the number of inches of length removed from barrels.

jack

Jack, nothing removed from barrel length.
I'm confused, if you remove material from inside diameter, the balls in the gage would not compress, they would expand and give you a higher number, not a lower number, as seen with the area of choke.
Turning the o.d down gives you smaller, turning i.d gives you larger.

Am I missing something.

Whatever the bore is for the last several inches leading up to the taper just before the choke (muzzle), minus the choke ID, will determine the choke. What the bore ID is, way back toward the chambers, is not relevant.

If any material was removed from your 2e, it was most certainly on the ID of both barrels from the cones to the depth your Skeets bore gauge will reach (about 12") or perhaps a bit further. As your Skeets enters fromn the muzzle end to the same depth and you're getting .718-.719 ID in that forward area, you have surveyed ID except for the midway 4" of length. Be interesting to know the nature of the bore wall in that transition. Is a step? A taper? As to what the indy balls do on a bore gauge, they are ALWAYS compressing against their springs while in the bore relative to their "free" diameter outside the bore. I also am confused as to the relevance of the mechanical principle of the gauge and its influence on or received influence from bigger or smaller bores. It simply measures one thing or another. It will "measure" absolutely when indexed to a standard (the .700 ring gauge) or, in the case where relative choke constriction is all that is desired, it simply "counts" reduction in diameter in 1/1000s of an inch if the bezel marker is zeroed while the gauge is inserted in the bore. Everything should be made as simple as possible, but no simpler, at least in my case. I don't know what you're missing but exit number subtracted from bore number is points of constriction of choke (reduction in ID size. As for the relevance of .730" ID back by the cones and some distance forward, you need another "assumed" hypothetical, to wit, a gun with the "major" bore pretty much adhering to one single diameter to all its length between cones and chokes. Since that hypothetical is the customary case and expectation in an unmuddled gun, choke is simply relative to the ID of the entire bore.

Hope this helps one of us understand the other, JD, but I'm not counting chickens yet. More like candling eggs.

jack

Thanks Jim and Jack, I'm still confused. I understand what you are saying Jim, whatever choke there is would be from the area before the choke. In this case it would be .718 and .719 on the Skeet's gage, and if you zero it at that reading, you would read zero coming out the right barrel and -9 on the left barrel.

To make things more confusing, from the breech, a .724 plug gage went in 22 7/8" and stopped in the right barrel, a .726 went in 9 3/4". I'm going to make a .718 tomorrow and see how that fits.

It's not relevant unless you were measuring an English gun with a tapered bore.

You need to get access to a Stan Baker bore gauge....I'm with the Rabbit there's been some honing going on somewhere.

Get your bore gauge into the muzzle. Measure the bore four inches back.

As you pull the gauge out, you will probably find you can't as the chokes will be tighter than the bore. In order to get the gauge out you will need to adjust it downwards.

The adjustments will show in thousandths of an inch. When you manage to remove the gauge, look at how many thou you had to reduce the gauge by to do so. That will give you your choke reading.

Why not try it on a pattern plate and see what it throws?