Crown Effects on PB Bullet Accuracy

[Bass Ackward]

Well this has been my last .... my most recent, focus for experimentation. Spurred on by my bad forcing cone in my Redhawk, I decided to recut the crowns on that 7 1/2" Ruger along with a 4" Smith that I owned that looked like it was cut with a poket knife. Some interesting things came to light.

While I slug for bore measurements often, I rarely worry about rifling height in a wheeler because of the velocity ceilings involved. The Smith was never fire lapped and had plenty of slop with the .416 pilot of the cutter. So much so that I started to re-evaluate my decision to proceed. I went ahead and let the cutter follow what was already there until it cleaned up. The stainless cut like butter. So I have no idea if it is true with the bore or not, but it does pass the eye test now.

So I went to the Ruger with the .4305 bore. This has been lapped and relapped and finally lapped again. Surprise! I could just barely get the pilot in and only after liberal lubrication. The cut was fairly clean with the origional crown out so bad that I was sure it just had to improve. Only a hint of chatter from the hand powered reamer as the steel was slightly harder.

Results? Well there was no noticeable difference in the Ruger what so ever. Bummer. But it was shooting PB slightly better than the Smith before I did this anyway. The Smith was the surprise as it jumped way ahead in performance to about where the Ruger is now. At least with the level of accuracy loads I was using in this instance.

Conclusion? While I have seen crowns do dramatic improvement in rifles, there appear to be too many variables in a wheeler to "expect" improvement. I had high hopes for the Ruger seeing how much it was actually out and how well it shot origonally. Evidently, unless there is an actual problem caused by the crown which I don't believe either of these had, handgun pressures just don't make that much difference in longer barrels.

This is just FYI for those perfectionists out there that may look at their crown and be wondering. I would still watch my cleaning rods though, as I am sure there is a limit involved. :grin:

[felix]

BA, yes, revolters are hard to make shoot straight when talking about the barrel exclusively. The gap between cylinder and forcing cone, right? Gas pressure is diverted out of this location, and is likely to ever be more than at the crown of the barrel, no matter how long. Revolters tend to shoot well when the bolt locks up the cylinder holes center line straight. ... felix

[Char-Gar]

Crowns on sixguns can be very important if they are damaged. I bought an excellent Smith Brazilian 45 ACP, and it had a small ding on the crown. It didn't look big enough to make any difference.

Groups were two to three FEET at 25 yards. I bought the correct pilot to recut the crown, but it would not even go in. Even though I could not see it, metal had been moved in front of the bore. I had to go to a 44 pilot and tape it up until it fit and remove the offending metal. I then used the correct 45 pilot and squared and recut the crown.

The groups shrunk from two to three feet to two to three inches!

[StarMetal]

John,

Maybe all along the bullets fired out of the Smith were being led into the barrel in just about perfect alignment with the cylinder, as Felix mentioned about the bolts locking the cylinder up as it should be, in alignment. So maybe then the Smith did have bad crown and when you recrowned it, you fixed it, and as it was, everything else must have be right. You saw an improvement. Ah, now the Ruger...maybe it's not feeding the bullet in perfect alignment from the cylinder and the crown isn't going to make a whole lot of of difference.

To give folks an idea of what a crown imperfection can do, I got an old Remington semi-auto 22 rimfire in my shop oneday when I was doing some part time gunsmithing. It had a little divet or dent in the crown. Wanta know how far it threw the bullet off? One foot...IN JUST A FEW FEET FROM THE MUZZLE!!!!!!!!!!!!!!!!!! I couldn't believe it. Worst I've ever seen. Well chucked it in the lather and recrowned it and that was that.

Joe

[Bass Ackward]

Ah, now the Ruger...maybe it's not feeding the bullet in perfect alignment from the cylinder and the crown isn't going to make a whole lot of of difference.

Joe,

Are you trying to insinuate that Ruger might put out a product with less than perfect dimensions? :grin:

I intend to see more of what results cleaning up the crown has done. Remember these were what I would refer to functional crowns before I started as opposed to an impeeding crown that will cause problems. The base of the bullet just wasn't breaking true. I was guessing that the lead base was paying a price for that which .... really .... didn't pan out as a theory.

I am not finished in this area yet. Maybe higher pressure loads will still show improvement in the Ruger. Certainly, the pressure at the muzzle was higher in the Smith than in the Ruger because of the 4 vs 7 1/2" barrel. Also the tollerances are .... a .... little tighter on the Smith for some reason. [smilie=1

But some side issues provided education as well. The Ruger had rifling at least .005 tall AFTER fire lapping? So either they make really tall rifling which I doubt or fire lapping doesn't remove as much metal on rifling height as is customarily believed. And I would have never believed that Ruger rifling was taller than in a Smith. That was a shocker.

[44man]

Ruger makes a decent barrel and they are hard. It takes a LOT of fire lapping to make a difference. The only time I would lap is if there was a constriction where the barrel screws on.

[StarMetal]

John,

I'm not saying Ruger puts out an inferior product. All manufacturers have a lemon one time or another.

If you think about fire lapping the lands in the barrel are sticking up ridges. The grooves are just where there aren't no lands. With that said, when the bullet starts into the barrel it encounters more resistance from the lands, even though they have a tapered beginning. What I'm getting after is, wonder if the lands push the lap media down the bullet, like a blade on a road grader and the groove don't push as much away because they aren't a big obstacle for the bullet? I know the bullet will be oversized to the groove. Just a thought. If that thought is true, then the groove would get more lapping effect.

Personally I never thought of Smith and Wessons rifling as deep.

Joe