Swamped barrel accuracy

[squirejohn]

A friend of mind has a 42" swamped barrel flinter that shoots about 8 to 10" low at 40 to 50 yds. in the winter. During the rest of the year it shoots "right on". Another friend sold his 42" swamped barreled gun for the same reason.
I don't think the cold weather here during the Vermont winter is the problem and I suspect it may be drying out of the stock due to low humidity. This is just a guess however. Has anyone had or heard of this phenomenon?

 

[Birddog6]

I have heard of that happeing to an extent, but not that much. Usually such a condition involves a stock that warps with humidity or vica versa. And easy way to tell would be to lay a straight edge on the barrel & make a few critical measurements, however if it was me, I would remove the barrel & then look at the stock & see if it is twisted. If so I would relieve it a lil & dampen it & twist the the opposite & get it back to straight. Then I would bed it in acruglass or microbed, then relieve the pin holes in the tennons so the barrel can move slightly forwards & backwards, but not up & down. If the stock was warped to an extreme, I would scrap the stock & rebuild the rifle. This is one reason it is critical the grain run true down the barrel channel, to eliminate warpage. Also, the thinner the swamped barrel the easier it will pull & thus I don't use A class barrels, but use B sometimes & really prefer a C in some instances.

 

[musketman]

Is this a full or half stock muzzleloader?

If full, maybe he can make a half stock muzzleloader out of it, cutting away some of the warped stock that touches the barrel.

Glass bedding the stock would be like putting lace curtains on a broken window, so that would be out of the question.

If it is a half stock muzzleloader, try adjusting the stock's nose cap, it could be putting too much pressure mid-barrel.

This will show up as brass marks on the barrel where it touches, the two different metals will flex differently under extream temperatures.

 

[Birddog6]

That all depends on the type of rifle it is, class of barrel, and how the barrel channel is cut. I have seen rifle with swamped barrels with 1/4" of clearance in the barrel channel & if this would be the case, a 1/4" of acruglass down a barrel channel is Extremely strong & could possibly cure the problem & definately worth a try, tho some think it may be a waste of time. Also if the rifle is taking moisture it tells me the stock is not sealed well & the rifle is being kept in damp conditions & appropriate measured can help that also, such as sealing the stock & barrel channel & lock & trigger area, under the nosecap & buttplate & etc. Keeping the rifle in a moisture controlled enviroment would help also. If the rifle is sealed up good, going hunting & shooting it will not enough absorb moisture to cause a problem as it takes a long time to absorb it. However, unsealed & submitted to dampness all the time & problems do occur.

The correct thing to fix the rifle IF the stock is warped is to restock the rifle, however, this may not be a option $ wise for the owner of the rifle.

As far as halfstocking it, a halfstock with a swamped barrel don't look good however I have seen them shortened & cut the swamped end off.

 

[squirejohn]

Thanks for the info re swamped barrel accuracy; I'll pass the word along. Since neither of us are adept at doing even minor gunsmithing work he will have to take it to a gunsmith in order to correct the "problem". Since the flinter is very accurate most of the year (don't do much winter shooting) and it gives him the "excuse" to shoot his Hatfield or fusil de chasse, I expect he'll leave well enough alone. It's an exceptionally fine piece with some antique furniture (quill holder) installed.
I might try making longitudinal slots in one of my thin-barrel smoothbores if I knew how to do it; i.e make a horizontal slot out of a tenon hole without increasing the vertical height. Four of the flinters (don't know about the fifth - never had it apart)I own have tenon holes - not slots.
I find it somewhat curious that of the many, many articals I've read concerning accuracy, most all go into agonizing detail about working up optimum ball & patch size and grains of powder - even to the 1/2 grain! Sights and the affect of the sun are also discussed at great length. However I cant't recall ever reading anything about humidity affecting accuracy. It cartainly makes sense though.
P.S. I take that back - Caywoods brochure mentions slotted tenons beings installed to account for accuracy re the barrel heating up and HUMIDITY.

 

Squirejohn, part of the problem will be that the powder has less power in cold wheather. With smokless cartridges, a handload developed in 32F that are hot but show no excess pressure signs will blow primers out in 90F temp. It's just not as easy to determine with a ML because you don't have a cartridge to examine. If he's useing light loads to begin with, maybe 30-40g the drop in pressure/velocity could result in a substantial drop.However, 8-10" sounds like alot. If you have access to a chronograph, check the velocity now, and again in the winter. Increase powder charge until you get the same velocity as the summer reading and I think you'll see it shoots fine.I'd be surprised if wood warp would cause the problem you are describing.

Cody

 

[Birddog6]

When removing the barrel pins to take the barrel off, you must take great care removing same pins, clean out the pin hole around the pin & extreme caution & go very slowly taping with the correct size punch & insuring the pin is not catching wood as it comes out & thus chiping out the wood. Always look to see if one side or the pin or the other has a rounded head, & if so that is the one you want to come out. I always round Both sides on mine when I build one but some leave them flat or round one side. Go back in with same rounded end of the pin. Also you must be careful when you bring the barrel out in the tang area as not to chip wood or whatever there also. Some bounce the butt on their leg or knee, I prefer to hold mine close to the carpeted floor & tap the butt to loosen the tang area. As for elongating the hole they make very small sets of files about? 5-6" long with a tiny round file in same set & that is what I use. If you relieve it 1/16" each way of original hole (mark with a marker) that is adequate for lateral movement.
Also keep in mind that moisture going into a piece of wood is mostly absorbed thru the end grain, thus the butt end, muzzle, where trigger goes thru etc exposes the end grain & this is where it needs to be sealed up. Small paint brush & some Q'tips & some True-Oil will seal this up & works pretty good. Usually not much moisture. If you want a non-glare dull finish on the true-oil in these areas, just touch it with any cotton cloth before it is dry & the shine will dull usually.

 

[tg]

The drop memtioned does seem extreme at that range, one might check the history of the situation, was this a one winter experience or something that was noticed over several years? different types/lots of powder? or any possible variables that may have been overlooked.

 

[squirejohn]

Thanks for all the feedback re "swamped barrel accuracy". Since this has been a chronic condition and he shoots a pretty stiff load (75g 3F in .50c), The problem definitely seems to be related to stock warpage. Thanks for all the solutions ranging from simple - store in unheated bedroom, basesment etc. to drastic - cut off or replace stock. Still, it seems pretty amazing that a little skinny peice of wood could bend the barrel that much. If my math is correct, and it may not be, an assumed sight distance of 30" between the front and rear sight, would have to bend the barrel 0.13" to effect a point of impact change of 8" at 50 yds.

 

[Randy]

Most A and B weight swamped barrels, especially in the larger cal. can be warped or bent surprisingly easy. They usually spring back straight when the pressure is taken off.

Your calculation would be divided in half since the bend or warp will occur near the middle of the barrel. .065" isn't that unbelievable.

Horse Dr.

 

[No Powder]

Squirejohn
Not if the warp is also moving the sight, especially the front sight is susceptible to small movements.

 

[LRB]

I don't see much good in slotting the pin holes if you do not do the same with the tennon inlet. I see some are and some that aren't.

 

[Birddog6]

Guess I should have stated that. I try to hve about 1/16" to 1/8" clearance on front & back of the tennon & just barely clear the wood on the sides & bottom of the tennon.
I don't want them tight as I am afraid if the gun takes a hard knock over it that it may crack or split the wood.