Chopped barrel.. How critical is straightness with slugs and smoothbore?

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elano

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I chopped a barrel down from 28 to 20" with a hack saw. I filed on it a bit and got it really close but a tad wavy. Maybe a mm or so off on one part or another. I can't seem to get it perfectly square. I know with a rifle crown, it has to be perfect, but do shotguns have to be?

I put rifle sights on the vent rib and can consistently hit a paper plate at 25 yards however at 50 yards, they seem to open up to maybe 15-20". This is freehand standing with foster slugs. The shotgun is a maverick 88 and williams slugger firesights. I'm just not sure how close they should be. The bead seemed pretty hard to keep steady at that range.

Thanks!
 
It wouldn't hurt to be perfect on a shotgun either!!
In fact, it's just as critical.

Any difference on 'perfectly square' will allow bore pressure to escape first on one side and tip the slug as it exits the muzzle, sending it off on a wobbling flight.

Couple of things you could try at home.

Use a 90 degree square laid, and moved around on the side of the barrel to mark the muzzle exactly square.

Or, wrap a strip of masking tape tightly around the barrel, carefully keeping the front edge perfectly aligned.

Then file off everything that isn't.

rc
 
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You need a large file, preferably at least muzzle diameter in width.

Set the gun on its butt, carefully set the file flat across the muzzle so that it's perpendicular to the bore and make a single stroke (at most two strokes) without altering the angle of the file to the barrel. Be sure the file is perpendicular to the bore before and during each stroke.

Turn the gun very slightly and repeat the procedure. Don't get in a hurry or take a lot of file strokes at one position. Keep doing it until the muzzle is flat--you'll probably end up turning the gun completely around several times.
 
This is all assuming the OP knows how to use a file??

American type files cut on the push stroke.

Trying to cut on the pull stroke dulls and ruins the file faster then you can go buy a new one.

rc
 
So at what point do you call it good?
 
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I've cut a couple using the same technique. They were all filed flat on the end and all shot slugs very well after. Having a sharp blade helps keep the cut straight so you need less filing. I used a small square to check the end of the barrel as I filed. After purchasing some cheap fiber optic sights that clamped onto the rib it was very accurate. I don't have any elevation adjustment but was right on the money with 4" groups at 100 yards. About as good as you'd get with any slug non rifled slug barrel.

Front sight, rear sight in the 2nd photo.

002-4.jpg
003-8.gif
 
If the barrel doesn't have a vent rib, you can use a tubing cutter to score a clean line around the barrel to guide your cut.
 
You also now have a straight pipe with no choke. Choke stabilizes the slug as it leaves the barrel. Modified being the best but I/C works OK. As for crown being as critical as on a rifle, I say no as you are not dealing with the same pressures on a shotgun. On a smooth bore shotgun barrel there is plenty of gas escaping around the load as there is no rifling to form a seal. Have the barrel threaded for choke tubes and cut down by a professional and your issue is over.
 
So at what point do you call it good?
Click to expand...
When you can't tell it's not perfect. If you're patient and don't get sloppy with your file technique you should get excellent results. You'll be amazed what you can do with a file and patience.
 
.
If following AI&P Tactical's advice is cost prohibitive in your situation, then do as JohnKSa suggested, but first, whack a piece of pipe and practice your filing on that... or use the fall-off itself from the barrel cut to practice on. You should have a sharp fine file and something to clean it with every so many strokes. Too, file from all points on the compass, so to speak, treating the crown as a map. Good luck.
 
I have one of these for truing up stuff and have used it for a shotgun barrel exactly as you need here. However, after getting it nearly perfect with this tool I used sandpaper on a hard, glass-smooth surface and finished the job to a factory quality level. I suggest you try to sandpaper on a hard surface.

vertical%20sander_zpsmd2yglks.gif
 
That's a neat tool!

My problem is I can't tell if I'm filing it exactly perpendicular or not. I can tell it's very close, but just can't seem to get it perfect. One side will be off a hair so I file then another appears low so I fiddle with that. Frustrating because I'm a perfectionist lol. My square is not machinist quality. I use a straight edge and check for light and it's just a hair off here and there. Maybe a few thousandths.

4" at 100 yards seems like rifle accuracy!!!
 
You can't intentionally file on one side or the other. Especially once you get close to having it perfect, every single file stroke should be made while attempting to keep the file in contact with the entire muzzle face and perpendicular for the entire stroke of the file. Then turn the gun slightly and repeat.

As you get closer and closer to having it right, lighten the pressure on your file strokes and be super careful about keeping the file in contact with the entire muzzle face and keeping even pressure on the file so you're not bearing down on one side or the other in the course of the stroke.

Remember that my advice was all based on having a file with a width as large as (or at least very close to as large as) the muzzle face. You can get it right with a smaller file but it will be much harder. Turning the barrel frequently is also critical as it insures that the inevitable variations due to uneven pressure, etc. are being distributed evenly over the entire muzzle face.
 
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If, after you get it squared up, you use TruBall slugs, you should have better luck as they have a seal wad and a ball in the base of the slug to keep it centered in the bore. I was quite surprised at the accuracy in a couple of cylinder bore guns I tried with them.
 
I cut down a single shot 12 ga with a hack saw. Then filed it until almost purfect. I finished it with a large sharpning stone I have. I cold blued the cut part and worked the stone over the complete muzzel until all the blue was gone. Then reblued. Really cant tell it was cut. If you use a stone plug the bore with a rag so no grit gets in. Then flush it out with cleaner from the chamber end. Theres no sights on the gun but I can keep Federal slugs on a 6" paper plate at 25yds. I only plan on using shot and buckshot in it. Works great for that. Good luck.
 
I use a 1" grit ball grinder thingee that I bought at Home Depot for chucking up in a drill, and gently spin it by hand in the muzzle. It naturally self-centers and puts a light radius on the cut, and I can then look at the remaining 'flat' of the muzzle crown and see where I'm high/low.
 
243winxb Bore is now oversize. No it's not!
Choke is gone. ok
Any slug accuracy went with the choke. Then why are most smooth bore slug barrels made with cylinder (no) choke?:banghead:
 
FANTASTIC REPLIES!!

JohnKSa and RCmodel WIN the best replies! I took a different approach and was amazed what I was able to accomplish. It's now perfect as I can tell though I'm sure it's not machine perfect. What I did was change my technique. Took my time and made even swpies. About 3-4 strokes/pushed (I had no idea files only cut one way). I rotated the barrel 1/4 turn and did another 3-4 strokes. Between complete turns, I used a sharpe marker to determine if my strokes were even or where the high points were. I figured out that when it's really close it will grab the file so you must use light pressure towards the end as it gets near perfect. It is now 10x better than it was on my first attempt. BTW on my first attempt I used a file smaller than the muzzle width. Once I stepped up to a 1" nicholas black diamond file it worked much better.

THANKS AGAIN ALL!!!!!

BTW, here were the best posts...

JohnKSa...

You need a large file, preferably at least muzzle diameter in width.

Set the gun on its butt, carefully set the file flat across the muzzle so that it's perpendicular to the bore and make a single stroke (at most two strokes) without altering the angle of the file to the barrel. Be sure the file is perpendicular to the bore before and during each stroke.

Turn the gun very slightly and repeat the procedure. Don't get in a hurry or take a lot of file strokes at one position. Keep doing it until the muzzle is flat--you'll probably end up turning the gun completely around several times.
Click to expand...

You can't intentionally file on one side or the other. Especially once you get close to having it perfect, every single file stroke should be made while attempting to keep the file in contact with the entire muzzle face and perpendicular for the entire stroke of the file. Then turn the gun slightly and repeat.

As you get closer and closer to having it right, lighten the pressure on your file strokes and be super careful about keeping the file in contact with the entire muzzle face and keeping even pressure on the file so you're not bearing down on one side or the other in the course of the stroke.

Remember that my advice was all based on having a file with a width as large as (or at least very close to as large as) the muzzle face. You can get it right with a smaller file but it will be much harder. Turning the barrel frequently is also critical as it insures that the inevitable variations due to uneven pressure, etc. are being distributed evenly over the entire muzzle face.
Click to expand...

Rcmodel....

This is all assuming the OP knows how to use a file??

American type files cut on the push stroke.

Trying to cut on the pull stroke dulls and ruins the file faster then you can go buy a new one.

rc
Click to expand...

In case someone else stumbles on this thread, those were the posts which helped me most. I had no technique with the file. My whole life I've been filing wrong LOL I just ground away in both directions briskly. No wonder I've damaged my files.

Anyway thanks again yall!!!!
 
JohnKSa said:
When you can't tell it's not perfect. If you're patient and don't get sloppy with your file technique you should get excellent results. You'll be amazed what you can do with a file and patience.
Click to expand...
I agree with the patients method. If you take your time and have things handy like a square. A piece of some kind of (softer than steel) rod that just fits in the barrel, you will get it close enough. I cut off a shotgun one time and took it to a machinist to have him throw it in a lather to crown it. He talked me out of it. He did it with a file also. I disagree that it is critical as a rifle crown. With plastic wads a tiny tiny tiny bit of gas escaping unevenly shouldn't make any difference. BUT, that is just my opinion.
 
243- You need to study slug guns.

How does cutting off the choke make the bore over size? ( hint the bore is the inside diameter of the barrel between the choke and chamber)

Most smooth bore slug guns come with no choke so how does cutting off the choke remove accuracy?
Accuracy comes from some type of adjustable sights; scope, red dot, rifle sights and finding ammo your gun likes!

In case you think the slug wobbles down the barrel, riffled slugs have ether a hollow base that expands to fill the bore centering the slug and preventing gas blow by or a felt base that preforms the same thing.
 
Choke stabilizes the slug as it leaves the barrel. Modified being the best but I/C works OK.
Click to expand...

There is really no hard fast rule for this, and often, the less choke the better. Your ammo will make a huge difference. Sure, you need your cut to be as square as possible, but I would not accept the results of one type of ammo. It's not uncommon to have to experiment with a half dozen different foster slugs to find the one that shoots well in your gun.

I have a 1200 Winchester and get super grouping with Federal slugs out of a the unchoked 18" Defender barrel. None of the other slugs I tied come close. In my son's 870 20 guage we tried 8 slugs and wound up with Brenneke shooting tightest from a screw in improved cylinder choke. Nothing shot as well with the modifed choke.

Ohio was a deer by shotgun only state for many years. The first "slug barrels" where a smooth bore with a front and rear sight. They were not choked.

I sometimes takes a lot of trial an error to find the right slug for your shotgun.
 
"...a straight pipe with no choke..." Is called Cylinder choke. Slugs work just fine with cylinder bores. Factories use it.
Anyway, file it flat. Bastard file is very coarse and will remove metal fast. Then use a finer file to finish. And don't forget to deburr inside and out. Harbor Freight has a 12" set on sale right now for $7.99 that'll do nicely. Use a padded vise to hold it still.
Yes, it is easier said than done, but it's not out of the realm of possibilities even for a guy who has never done it. It's one of the few times that patience just might be a virtue.
 
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