Help determining choke restrictions on a Spanish Laurona shotgun?

james01

james01

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Hoping someone here can help me. I bought a used Laurona Eibar sxs shotgun, and I'm having trouble figuring out how the barrels are choked.

I think I have the proper choke indicator barrel stamps figured out, but don't know how to calculate the restriction.

One barrel (the left)is stamped 17.3 with an 18.6 under it.

The other barrel (right) is stamped with what appears to be either a 15 or a 1S over 18.6.

Any help would be appreciated.

Thanks,
J
 
Choke is the difference between the bore diameter and the minimum choke diameter expressed in millimeters or thousands of an inch. The larger figure (18.6) is the original bore size in millimeters at proof. The smaller number is the choke diameter in millimeters at proof. Subtract the smaller from the larger and you will have the original factory choke in millmeters. At this point you may need to convert your metric restriction to thousands of an inch, simple math. Look on a restriction chart for any of the choke manufacturers and you should be able to put a name ( such as full) to your choke constrictions. Note that if the bore has been honed at some time to remove pitting the bore will be larger than the stamped number, the choke constrictions could also have been altered. Either way the stamped sizes no longer apply. Only with careful measurement with a bore gauge can you be sure of what you have. Another note, older guns were choked to get the desired results with ammo that normally didn't have our modern shotcups which effectively tighten patterns so they tended to be choked tighter for a given result than modern guns.
 
Ashcroft said:
Choke is the difference between the bore diameter and the minimum choke diameter expressed in millimeters or thousands of an inch. The larger figure (18.6) is the original bore size in millimeters at proof. The smaller number is the choke diameter in millimeters at proof. Subtract the smaller from the larger and you will have the original factory choke in millmeters. At this point you may need to convert your metric restriction to thousands of an inch, simple math. Look on a restriction chart for any of the choke manufacturers and you should be able to put a name ( such as full) to your choke constrictions. Note that if the bore has been honed at some time to remove pitting the bore will be larger than the stamped number, the choke constrictions could also have been altered. Either way the stamped sizes no longer apply. Only with careful measurement with a bore gauge can you be sure of what you have. Another note, older guns were choked to get the desired results with ammo that normally didn't have our modern shotcups which effectively tighten patterns so they tended to be choked tighter for a given result than modern guns.
Click to expand...

So, for example: 18.6 subtract 17.3 = 1.3 mm

1.3mm divided by 25.4 to get the fractional equivalent (thousandths of an inch) = .051" choke restriction?

According to the chart below, this barrel is tighter than extra full??

TeagueChokeDimensions.jpg
 
18.6 = .732 this is your bore measurement
17.3 = .681 this is your choke measurement
Total = .051 constriction

As your chart suggests you have a bit tighter than XF if indeed 18.6 is your true bore size. .051 constriction is alot of constriction!
 
Back to my last sentence, older guns were frequently choked tighter than today. Modern ammo doesn't require as much restriction to get a desired amount of pattern result so modern guns reflect that by having less construction for a given choke. Older guns from about pre 1970 or so often have very tight extra full chokes by modern standards, .051" would not be unusual. Pattern results can be very erratic in these guns with modern ammo, especially with larger shot sizes.
 
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