I know this has been discussed ad-nauseum, but after going back a ways I couldn't find it. Here's the deal:

military mauser (1908 Brazillian...I know about hardness and such...) rechambered in .280 Rem.

It shot 1.5"-2" originally with good loads.

It had a noticably pitted crown and I wanted to try and see if I could tighten the groups...so I tried a re-crown myself. I chucked it up in a small lathe, cut the crown square/flat, and broke the edge with a brass bolt and lapping compound. Call me Bubba, I know.

Now it's a poor shotgun. It likes to string holes from roughly 6" high and right to 6" low and left, at about a 30* angle from horizontal.

Does a screwed up crown usually display this type of stringing/scattering or should I be looking elsewhere? I've already taken the scope and bases off and remounted w/Loctite, and replaced the scope once. No help. No obvious damage to the stock or bedding. Action screws are tight. Barrel is floated.

Time for a rebarrel??? Sell and get a real rifle??? Chuck it in the Gulf of Mexico???

I don't know the answer; but I would be curious as to what information others may have about whether do-it-yourself crowning is a good idea. Brownell's offers various piloted muzzle cutting, facing and lapping tools for people who want to screw up their own rifles rather than having it done by a smith. I have been tempted to try it; but I don't know what the odds are that the crown would be improved by do-it-yourself techniques.

P.S. : CDH, out of curiosity, did you use a piloted or an unpiloted tool to cut the crown?

The Brownells tools work pretty well. When you
put the barrel in the lathe did you center it based on the outside of the barrel or with a pilot in the bore? You want to cut a crown concentric with the bore.

One crude way to check your crowning job is to look at the pattern of the junk coming out of the muzzle. It should form a uniform star of sorts with crud aligned with the grooves/lands. If it is obviously not uniform then your crowning job probably wasn't too good.

quote:

It shot 1.5"-2" originally with good loads.

Hey CDH, Did you "redevelop" the Load or go with the old one?

'The load' was factory ammo. So no, I didn't re-develop loads for it. I don't think any about of tweaking is going to fix a 12"+ pattern. That big of a jump in group size is, to me, an obvious sign that I really ham fisted it...

I just chucked it up in the lathe without regard for centering. The off-center thing I tried to handle by cutting a square, flat surface with a bit in the toolholder. No radius or taper. That should reduce any effect of an off center bore...but a pair of vernier calipers measuring the thickness at the grooves says the bore is concentric to less than .001" at the muzzle anyways. The lapping tool was a dome head, so it should roughly self center when held loosely against the muzzle.

OEH, I'll look closer at the fouling next time I shoot it, if it doesn't end up taking a bath in the great salt water first!

The scientific problem with improving imperfect rifles is that one change may be over shadowed by another one.

I have done my own crowns. One rifle remains very accurate after being sold to me as a 2 moa gun. That one now has a new stock and it's still very accurate. I have done other crowns and had no change in accuracy.

In my experiance the bedding or something being loose lead the pack in accuracy problems.

quote:

just chucked it up in the lathe without regard for centering. The off-center thing I tried to handle by cutting a square, flat surface with a bit in the toolholder.

There you go. You must dial it in as perfect as you can. The bore must be centered and true. Use an extra center or spud from a bore sighter to dial it in perfect. I use a 4-jaw and a spider. A 3-jaw usually won't cut it. If the breech end is flapping around you are sunk. Dial that end too with the spider.

I use a sickel shaped tool bit on sporters. That will make a rounded crown. Polish with fine sandpaper under power in the lathe. Get the tool bit far out of the way to avoid cutting your hand. It is best to remove it.

Now that you know how to do it right go do it again. Don't get discouraged.

Hey CDH there are a big bunch of people out there that have done some of the same things, you know, the "kick your self in the butt" type things. This is just my opinion, but I would remove all stress and worry about it and take it to a real good gun smith and let hin re-crown it for you. Not that it can't be done your self, but just get it done right and go on shooting with it.

quote:

Originally posted by CDH:
'The load' was factory ammo. So no, I didn't re-develop loads for it. I don't think any about of tweaking is going to fix a 12"+ pattern. That big of a jump in group size is, to me, an obvious sign that I really ham fisted it...

Try not to be so hard on yourself. Once you get mad at yourself, it is difficult to get back on track(or that is the way it is for me).

Moved out of your sequence:

quote:

That should reduce any effect of an off center bore...but a pair of vernier calipers measuring the thickness at the grooves says the bore is concentric to less than .001" at the muzzle anyways.

That sounds good.

quote:

I just chucked it up in the lathe without regard for centering. The off-center thing I tried to handle by cutting a square, flat surface with a bit in the toolholder. No radius or taper.

Let me recommend a slight version of what "Scota4570" posted. I agree with trying to do it once more. And I'm not saying he is wrong at all about cutting it to a "radius", but if you can just get the muzzle cut square (perhaps using his method, or some other) stop and try it. Don't do any Lapping and see how well it shoots.

quote:

The lapping tool was a dome head, so it should roughly self center when held loosely against the muzzle.

OEH, I'll look closer at the fouling next time I shoot it...

Looking at the fouling pattern is a great idea if there is enough of the muzzle thickness to be a reliable indicator.

For what it is worth, I had a "buddy" destroy the crown and manage to scratch the entire length of a 6" barrel on a Target Grade revolver of mine. I could see him getting ready to jam the Stainless "Chamber" Brush in the barrel on a "non-rotating" rod and couldn't get the word STOP out. He must have gotten 10-12 full strokes on it before it sunk in to him that I was headed his way and saying STOP in progressively louder increments as I approached him.

Went from a revolver more accurate than I could shoot to a shotgun. So, with nothing to loose, I chucked up a Round Abrasive Stone in a drill and just held it against the Crown. Groups improved. Did it again and they got a bit better and I stopped. I knew I'd need to replace the barrel to regain the Target Accuracy, but it shoots well enough to kill Deer at 75yds, so I've not replaced it yet.

That incident was about 25 years ago(maybe) and with many tens of thousands of bullets through it since then, I can still see some very faint scratches in the Grooves and atop the Lands, and it continues to shoot better.

However, I really would encourage you to try re-facing the muzzle it "without" doing the Crown Lapping and see what it does.

Best of luck to you.

Wellll, tried again. We'll see. My biggest problem, besides stubbornness (how else do we learn but by making mistakes ), is the equipment. Olllld Atlas lathe with a 3 jaw chuck. No budget for equipment upgrades. Toolholder that wants to flex. you get the picture.

I got a few hundreths shaved off pretty clean, but it left a slight burr. I'm gonna have to lap it a bit to get the burr off...I'm just not comfortable shooting it off!

Really I didn't intend to get into a bunch of backyard 'smithin, just wanted to know if any of you guys had a similar situation that showed similar symptoms.

Tha saga continues...now for some range time.

Hey CDH, How did it do this time? Looking to hear "one ragged hole"!

It's in the truck for a little lunchtime noisemaking today...

I've tried to eliminate all variables, down to taking the best scope I have off of my favorite rifle and mounting it on this POS. It's gonna get it's one last chance...

Well, it's back to the rear of the safe until I get a lot of free time or $$$.

9 shots, 6" wide by 3" tall group at 50 yards. Strangely though, I was shooting 3 shot groups (with 10 min. cooling btw groups) and each 3 shot group was around 1.5" (Still bad, but...) but each 3 shot group was spread out from the others, making a football shaped pattern in the end.

I'm too stubborn to not get this thing figured out, but too stupid (I guess) to outsmart it. Oh, and too cheap to spend real money fixing a cheap rifle...

quote:

Originally posted by CDH:
...but each 3 shot group was spread out from the others, making a football shaped pattern in the end....

I doubt that is a muzzle problem.

Does this rifle have a handguard or two piece stock?

Does the muzzle stick far enough ahead of the stock that you could slide your sand bags way forward and place that portion of the barrel on the sand bags instead of the stock?

The 1.5" groups looks like it is wanting to shoot, but something appears to be moving, shifting or warping.
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Do you have a Strain Gauge on it?!?!?!
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Whipping the problem on a rifle like this will give you great satisfaction.

The stock is the original military stock (same serial # , steel buttplate ) but has been glass bedded and barrel floated. I thought about trying a pressure point but decided that 12" patterns at 100 yds (or my 9" at 50 today) is something major...we're way beyond pressure points and load seting depth! Maybe this winter I'll try re-bedding it, or pick up a B&C stock for it. I just gotta decide if it's worth spending money on...

...and no, it isn't wired for a HSGS and never has been. Honestly, it's a project/beater rifle so I never even saw the point in handloading for it...

I know that a poorly finished crown will surely screw up accuracy but I asked myself what else is wrong as I read this thread. I'd have to re-examine the entire package at this point. And probably get a crown cutter from Brownell's.

If that is the only change you made and it was shooting before, then, I vote for it being the crown.

Rojelio

quote:

Originally posted by CDH:
The stock is the original military stock (same serial # , steel buttplate ) but has been glass bedded and barrel floated. I thought about trying a pressure point but decided that 12" patterns at 100 yds (or my 9" at 50 today) is something major...we're way beyond pressure points and load seting depth! Maybe this winter I'll try re-bedding it, or pick up a B&C stock for it. I just gotta decide if it's worth spending money on... ...

Any chance you might happen to have a "similar stock" on a different rifle that you could try on it?

Putting a "temporary" Pressure Point in and running a few shots through it would provide some interesting insight.

Maybe floating the action up (front and rear) with 3 thicknesses of old Credit Card as a separate test and see if anything changes.

With it shooting 1.5" 3-shot groups and then shifting the entire Point-of-Impact, it sure sounds like something that can be eventually figured out.

I know what you mean about short on time. Best of luck with it.