Seeking input on shotgun barrel liners.

[KeithB]

Bill - I'm sure not going to discourage anybody from doing a computer simulation of this issue, that would be great! As long as the software accurately models the actual situation, i.e. expansion of gas from a small to a large cylinder. I'm not familiar with the software someone might have to do this. Your reasoning process was what I went through, reduced gauge reduces head thrust and the stress on an old action, full length liners should not transfer pressure to the outer barrels (which are pitted internally).

I understand that liners will up the gun's weight and change the balance. Shortening the barrels changed the weight and balance also, moving the CG to the rear and putting more weight between the hands. Adding a liner will move the CG forward just a bit and increase the weight, all immaterial in a confined spaces self defense weapon.

 

[Ian]

Quickload only models metallic cartridges.

You didn't say it was a coach gun for home defense, by all means put full-length barrel liners in it in that instance. I personally would never wish to wield a full-length double in the field configured as a 10-gauge with 28-gauge full liners, that would add several pounds to the wrong end.

Dan, I'm still scratching my head over the mid-barrel pressure peak remark with smokeless powder. I think pressure probably peaks at the forcing cone. Any pressure/time data out there we could reference?

 

[Ian]

OK, have a look at this chart I copied from Shotgun World, comparing distance/pressure curves of two smokeless and two black powder loads in a 12-gauge.

 

[Tony]

Damascus barrels in as new condition are stronger than a lot of people seem to think. The problem is that they can rust in places not easily seen and let go at inopportune times. Briley Mfg. is an excellent source of information on sub bore liners.

 

[fiver]

the only 'problem' with that chart is the only powder still made on it is the black powder.
the info is still relevant even with other newer powder types in that burn range.

now you can cheat the system in this case.
new hulls from Europe and some American made hulls are super duper close to .750 internal diameter.
Rio, and brass headed Estates are two that are that Large.
the Federal Top Gun hulls are also that big internally but have less case Capacity.
the base of a 12Ga. wad will blow out and seal a 10ga. Barrel.
[a 20 will fill a 16ga. too it was common practice to load 16ga hulls with 20ga. wads]
it used to be pretty common practice to use 12ga. duck loads in 12 ga. shotguns, especially those with the 2-7/8" chambers.

a 3 to 3-1/4 dram load under 1-1/8 oz of #2's or #4's would be pretty good at clearing bout anything across the room.
it could also be lower pressure than the chart above.

 

[Pistolero]

A point of useful comparison, for discussion purpose, not trying to convince Keith to do
anything that is against his judgment, might be to look at the pressure vs distance situation
for a similar pressure .45-70 or .50-70 load (just because they are larger diam, so scale will
be closer to a shotgun situation than a .38 Spl) with some real shotgun powder like Unique or Red
Dot.
It would seem that if you are looking (simulation) at large diameter cartridge, operating at the same
15,000 psi (or whatever it is, I think I have read that peak shotgun pressures are something like
15Ksi, I am no shotgunner) peak pressure range, examining how far down the bbl the pressure is still
a substantial fraction of the peak would give an idea how the pressure in the unsupported original barrel
would vary. Also, stepping off of the liner into the larger diameter has to substantially lower
whatever the pressure was at the end of the liner, just gas laws effect. Directly proportional
to volume change. P1V1=P2V2. If you go from 20 ga to 12 ga, the volume is proportional to
the area of some fixed axial length, so you would again see a drop of pressure immediately to
75% of what it is at the end of the liner, same effect as the head thrust calcs.

IIRC, Unique pistol loads, (perhaps in that pressure range?) are dropping to really, really lower
value within a couple of inches, like to maybe 30-40% of peak or so, but that is just memory, a look at
a .50-70 load of Unique,Green Dot, or Red Dot simulation would be interesting. If you use the
chart that Ian showed, and a 6" insert, the pressure at 6" is ~ half of breech pressure for any of them.
drop that by 0.75 factor due to area increase, and you see ~38% of breech loads on the unsupported
bbl at 6".

As a real solution, what about loading blackpowder shells? Can you load modern shells and wads and such
with black and get the same lower pressures of the originals, or do the components not work with
black? I have a Lee cheapo shotgun loader and have loaded maybe a thousand shells years ago, but
just blindly followed some recipe that worked then for practice shells on the cheap. No real knowledge
on that subject. Might hinder things, but perhaps a good tactical smoke screen effect may
help in a self defense situation, too.

Again - obviously, Keith needs to do what HE thinks is safe. Not trying to convince him of anything,
just a guy who spent a 40+ yr career getting paid to calculate things like this thinking out loud.

Bill

 

[300BLK]

BP can be loaded in modern cases, but different wads are generally used. I have loaded some and they are LOUD, but they sometimes burn through WW AA plastic hulls.

IMO, its not worthwhile to load BP for this particular shotgun. The pitting in the bores will collect the fouling and make cleaning more problematic unless full length liners are used. I would use the chamber inserts and call it good. 20ga are under 12K psi peak pressure anyway.

 

[Ian]

10-gauge loads are limited at around 11K psi, due to case head size. Net backthrust is about the same for all gauges. FWIW I agree 100% with 300BLK.

 

[KeithB]

Bill, I really appreciate your thought processes. If you (or anyone else) ever convinces me to do something, it will be the way you do it - through logic and reasoning based on facts and provable data.

One of the reasons this gun had its barrels cut short was because of pitted bores that were very bad at the muzzle. I was going to be happy not shooting it and making it a wall hanger until I recalled reading about liners and chamber inserts. I have no experience with these but figured some of the folks here might. I have other guns available for self defense purposes but configured as a coach gun with big loud-cocking hammers and impressive barrel openings this gun has a real intimidation factor going for it. I'm pretty sure that if a wild eyed guy shoved that gun in MY face and cocked the hammers I'd have bowel and bladder control issues.

It wouldn't take much to make some 20 gauge chamber inserts. I'd be willing to bet the gun by test firing it from a safe location. But only if it passed that test would I consider getting it near my body and touching it off. I would have no such worries with a full length liner.

Bill, none of this is questioning your logic or good judgment. I just have no idea how strong the pitted twist barrels are on this gun. And I have no real reason to do anything even remotely unsafe when I have other guns/choices.

 

[Ian]

If the barrels are in that poor of a condition, maybe you'd better line it in 20-gauge. You could even thread the liners for chokes....one IC, one Blunderbuss! Too bad you don't know anyone with a good lathe, following rest, and machining skills..........

 

[KeithB]

Ian, I was thinking that if I made full length liners (well, I'd stop a little short of the muzzle to preserve the full diameter look of the 10 gauge bores) I would put about a 10 degree expansion cone in the muzzle end to spread the shot charge just a bit. There is no shot in my house that exceeds 30 ft/10 yards, and that is down a hall and into another room. No room is more than 18 ft on a diagonal. Anything to help.

 

[300BLK]

From a cylinder bore, the shot charge will expand about 1"/yard, so 10" pattern down your hallway, but it might actually spread more.

 

[fiver]

just put a choke in the liner.
you should be able to pick up factory type chokes from say Winchester or Remington on the E-bay for like 10$
threading the barrel and screwing them in shouldn't be an issue.
for a 20 ga. the larger diameter shot will perform just fine in a cylinder or improved cylinder choke.
with the larger shot sizes you get tighter patterns than the choke indicates anyway.
in a 20ga #4 in a cylinder choke will pattern closer to modified at 30 yds.

I made a mistake in the above post.
I meant to say they fired 12 ga. shells in 10ga. shotguns.

 

[quicksylver]

Ian ...the only reference I have on pressure curves are old articles showing blown out damascus barrels that had smokeless shells fired through them....

The comment on Green Dot comes from split liners that started to show up on the skeet fields..

 

[Pistolero]

Stay safe, Keith. Only you have seen the condition of the bbls, plus you are absolutely correct that
risking anything isn't a good choice. Besides, with your machining capabilities, no reason you can't make
really nice 20 ga liners. If you really want it to spread, I would think a gradual bore increase for 6 inches or more at the muzzle
might help, but I really know nothing about how chokes and such really work, only what seems reasonable,
sort of a nozzle effect.

I should mention that I have one of your Lyman 450 die nut starting tools, and every time I use it, I
am pleased with it's simple, elegant design and how well it works. Thanks again for that very useful,
well appreciated tool.

Bill

 

[fiver]

green dot is an odd powder.

I might be able to explain their issues with it since I have used a lot of it over the years.
it is the only powder I have been able to get to replicate how a SEE event would occur.
if you take a shell add about 19grs of green-dot a wad and fold the crimp down and over the wad fingers with no shot and fire it. [generally with a little room between the front of the petals and the roll over of the crimp]
you will get a poof.....bang.
the bang is a full pressure boom not the usual pop sound you get from other powders.
and it is a distinct poof hesitation then boom.
now if you add an ounce or more of weight to the front of that happening I could easily see a pressure spike occurring, and it would occur right about where the barrel and mono-block are soldered together.


a longer crush section gives more room for the powder to expand before pressure is built.
this is why a 1oz load wad requires more powder to reach the same velocity's as a heavier 9/8oz. payload does using the same wad.
and why the lighter shot weight can reach velocity's much higher with the same pressure Cap. when using the same powder.

 

[Pistolero]

That sounds kinda scary. Fortunately I have never had any Green Dot in stock, sounds like I will continue
that trend.

Bill

 

[freebullet]

Just get a blunderbus

 

[KeithB]

My knee feels good enough now (arthroscopic knee surgery is a wonderful thing) that I'm able to get around without any real impediment. Went downstairs to my armory and got these photos.

You can see the coach gun configuration. (Boomer my cat just HAD to get in the photo.)

My BIL left the action in the white, I rather like the gun metal gray finish.
Here is a shot of the patent date.

The stock had one glaring defect. The diamond inlay is nicely done IMHO.


Couldn't get a good shot of the interior of the barrels but they are pitted enough to make me cautious about using it w/o a strong sub-gauge liner.

 

[Ian]

I'm not sure what you have there.

The patents are William H. Baker's, the first for the lock, the second for the method of forend attachment.
The hammers are very unique in shape and are most probably Baker hammers, from early 1880s, similar to those used on the Baker triple barrel gun.

BUT, Baker guns never had a thumb break, using the front trigger to release the action instead. The LC Smith doubles used a thumb break, but had different hammers and always had side plates....maybe this is a transitional model from 1882-4, in fact that is most likely except for a couple of other things.

The serial number is either 1898 or 1918, which doesn't jive.

None of the rifles related to Baker or Smith were ever made or stamped "Ithaca, N.Y.", they were made in Syracuse....

The recoil shield shape around the firing pins has either been re-shaped, or this is an Ithaca gun, not a Baker or Smith, but the patents are clear enough, and I think in the end this must be one of the first runs of the WH Baker doubles, probably around 1880-81, and being a double instead of a triple, is probably in that group of only 260 ever made.

I'd like to know what the markings on top of the barrels, if any, read. Also, a photo of the forend from the bottom could help, and if the barrels are Damascus or twist steel, which were options on the later 1896-98 LC Smith models. Still, though, due to the hammer and lack of lock plates, this just about has to be one of the very first Baker doubles, even with the thumb break being there.