Technical Question / Discussion (NOT hc/pc discussion)

[Lonegun1894]

I know this is not completely identical as this is relating to a modern breechloader, but maybe it will help anyway--or possibly confuse the issue further.

I have Mossberg a 500 and a 835, both in 12 gauge. The 500 has a straight-bored barrel til it gets to the screw-in choke. The 835 however, has what Mossberg advertizes as a 10 gauge barrel (as was mentioned above,) with a 12 gauge chamber, and then a screw in choke on the muzzle end. It seems to me that this is, in effect, a jug choked barrel seeing as it goes from 12 gauge to 10 gauge, and then back down to whatever the choke constricts it to. Here is the part that has me scratching my head though: I have several chokes for it, with the most open being "cylinder" which should be .729(ish), and the tightest squeezing everything down to .610--if the markings on the choke can be trusted. If this is all correct, then this shotgun starts as a 12 gauge, then is jug choked to a 10 gauge, and then the muzzle constriction with the tightest choke brings it back down to just (very) slightly under a 20 gauge. I would imagine this would be a serious pia to load if it was done to a ML, but it works well in this suppository gun, and proves that the jug choking can be extended out further back than I would have imagined, and then tightened down to smaller than bore diameter. I hope this doesn't hijack the thread as that is not my intention, but just to add another option/possible variable that we may have to consider with some guns out there. I may have to load some shells with cloth "shotcups" into this thing to experiment with the performance difference as opposed to the plastic shotcups that factories use. As is, with it's preferred factory load of a Federal 3" loaded with lead 4s, it will keep all it's shot in a 8 inch circe as 40 yds, with the main charge in about 4-5 inches and the rest of the pattern being flyers.

I apologize for the transgression of bringing up suppository guns, but thought this variation and it's similarity to jugchoking may be worth bringing up for this conversation, and hopefully will help with some of the theories involved here.

 

[roundball]

No apology necessary...I clearly identified this as a technical discussion and this subject is illusive enough that I personally don't see any problems with occasional comparisons to modern things that we're more familiar with to make a point of clarification.
What you described is called "back-boring"...my Remington model 1187 .12ga trap gun is back bored the full length until reaching the choke area. It is often found on trap guns where large volumes of shooting large gauges is done to reduce recoil...and a by product of it is also the Jug Choke side effect.

Ordinarily a Remington 1187 comes with three choke tubes marked Imp.Cyl., Mod, and Full. The 1187 trap gun also comes with three choke tube..."marked" Trap Full, Trap Extra Full, and Trap Super Full...BUT...they are exactly the same three standard chokes, just marked differently.
The trap marked chokes aren't tighter, the back boring Jug Choke effect simply creates the additional choke usually needed for trap shooting, in addition to its main purpose of reducing recoil.

I first discovered this when cleaning one day by realizing I had just shot a few rounds of Trap with the Imp.Cyl. choke I'd accidentally put in the barrel after the previous cleaning, yet I'd had my normal scores on all the rounds.
I then confirmed this by measurements and got official confirmation with a call to Remington's Service Manager.
To prove the point to my trap shooting colleagues I actually leave the standard choke marked Imp.Cyl. in my 1187 permanently and whenever the discussion comes up I just spin it out and show them.

 

[paulvallandigham]

Unless you have actually measured that tube that you say is .610" I suspect that its either mismarked, or that it measures +/- .690".

A Full-Choke is historically considered .040" of constriction, or "40-Points" of constriction down from the bore diameter of a 12 gauge shotgun barrel.

You are correct that the "NOMINAL" dimension for a 12 gauge barrel is supposed to be .729". Subtract .040 from .729" and you get .689". However, a lot of modern "Full Choke " barrels often measure out at .730". So, subtracting .040" from that would give you the .690" dimension for that tube.

I don't know how you could pass a 12 ga. plastic wad/shotcup out of a 20 gauge tube, even shooting it. It would be next to impossible to pass a modern 12 gauge plastic wad/shotcup through a 16 gauge( .662) barrel/choke tube.

For conversation sakes, a 14 gauge is nominally .693". Notice how the usual "40 points" of constriction in a 12 gauge reduces the bore diameter down TWO Gauges to that of a 14 gauge. Sounds very much like the information from those old articles from Spain. NO? :idunno: :hmm: :thumbsup: :thumbsup: