Tight lockup vs. accuracy

[peacemaker]

I have a SAA that was a little loose in lockup, in that the cylinder could be rotated back and forth slightly with the bolt engaged. The gun shot Keith 454424 SWCs quite well, and the standard 454190 FPRN fairly well.

I decided I could make that puppy nice and tight by fitting a new bolt, so I did. She came out very nicely, but the accuracy changed substantially. The more accurate Keith's now throw way to the left, and the 190s group pretty much as before, which wasn't bad.

The bolt fits perfectly with no pressure pushing up on the cylinder. The width of the bolt head is a close fit to the frame window width, so there was no guess work needed as to which side of the bolt head to favor for fitting the cylinder notches for optimal chamber alignment.

I can only surmise that the chambers are slightly out of alignment with the bore, and the square shoulder of the Keith bullet is more sensitive to misalignment than the round ogive of the 190 bullets. But when the cylinder was a little looser, the cylinder could self-align to satisfy the Keith bullets and give good accuracy.

Has anyone else found their guns to be more accurate when a bit loose when using some types of bullets?

[jimmarch]

Use the flashlight trick. With the gun UNLOADED (check again!) use a powerful flashlight aimed at the firing pin to illuminate the back of the cylinder and esp. the frame at and around the firing pin. A "tactical grade" flashlight is best.

Now look down the barrel. You'll be able to see the alignment between the barrel and the chamber.

If that's off, you've got the bolt "fitted" wrong. Either fit yet another one while making sure this alignment is right, or loosen up the one you have and while doing so adjust the "average set" of the bores so that they tend to fall in line behind the barrel as best you can.

If the gun is set up bad enough it's actually tearing itself apart some on every shot. Having the cylinder locked hard into a mis-aligned condition isn't good.

[COR]

Well if it ain't broke....

[jayhawker]

Put the original bolt back in and shoot it.
Jayhawker Bob

[Fowler]

Tight cylinders are great IF you have perfect alignment. If they are off at all you are asking a bullet to "go around a corner" to get into the barrel and when they do that they get deformed killing any potential accuracy it could ever have. A lot of the Ruger "slop" allows for imperfections in alignment to push the cylinder to the side to allow it to align with the barrel without deforming bullets.

Figure out how to tweak the cylinder back in alignment or more likely but the old bolt back in it...

[2 Dogs]

A good shooting gun is a good shooting gun. I dont have guns built to be "tight" just to have a "tight" sixgun. I build them to be tight WITH lineboring to assure perfect alignment will last LONGER.

[groo]

Groo here
The cylinder does not need to be tight to shoot good,, it just needs to align itself with the
barrel the same way each time..
Colt did this with the Python-The cylinder has a fair amount of play even when cocked,
but when you pull the trigger back the hand pushes the cylinder against the stop so
the alignment as the same for each shot..

[CraigC]

Jun 27, 2010 10:24:13 GMT -5 2 Dogs said:

A good shooting gun is a good shooting gun.

Exactly! Sometimes it's best not to question a good shooting sixgun and leave well enough alone. Sometimes we get so caught up in the numbers we forget that the only thing that matters is the shooting.

[dale53]

Jun 27, 2010 12:15:28 GMT -5 CraigC said:

Jun 27, 2010 10:24:13 GMT -5 2 Dogs said:

A good shooting gun is a good shooting gun.

Exactly! Sometimes it's best not to question a good shooting sixgun and leave well enough alone. Sometimes we get so caught up in the numbers we forget that the only thing that matters is the shooting.

AMEN!

Dale53

[nonpcnrarn]

OK! I'm going to let my ignorance show. Why are the Belt Mounain base pins so popular? Do they increase the tightness previously described, are OEM cylinder pins in the dirt after each shot or are they easier to manipulate (grasp)? Also will an 11 degree forcing cone and Taylor Throating help guide square shouldered bullets from the cylinder throat into the bore?

[rep1954]

I copy-pasted my answer here from my answer on the Colt Forum.
Peacemaker,you are correct in assuming that your chambers mouths are not in alignment with your bore. What you have done is worked backwards to what a custom gunsmith would have in that first he would obtain a minmum movement bolt lock up and then linebore the cylinder to make up for any tolerance build up there might be. When you think of all the different tolerance stack ups there might be it's a wonder we dont see more problems with factory guns than we do. Starting at the crown the bore may be offset to it and then the barrel threads might be offset to the bore not to mention that the forcing cone could be cut off center to both the bore and the barrel threads. The barrel threads and the base pin hole in the cylinder frame could be out of location an allowable amount. Then comes the cylinder mouths location to the cylinder bushing not only could the distance from the center of the cylinder mouths be off center to center to the cylinder bushing but spacing between the chamber mouths can be off a little to each other. Which now brings us to the area of movement and alignment the cylinder bolt stop. The bolt stops in the cylinder may not be aligned to it's mating cylinder mouth as the location of the bolt stop in the cylinder frame side to side could be off a little and you may have pushed it in the wrong direction to make it even worse. Wow, how do they make a factory gun even work? Tolerances may have already had your cylinder pushed to an acceptable limit and with the play you had in the cylinder it allowed the bullet to pass from the cylinder to the bore and help center itself. When a revolver is built to tight tolerances and linebored last it is a very accurate gun.

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[aciera]

Rep1954;
Let's add frame not square to barrel,barrel and base pin not aligned, chambers kanted, oversized base pin hole, or tapered, or basepin not straight, or a frame twisted.

And that's just off a tried man's brain.

[rep1954]

Yeah, like "aciera" said.

[aciera]

rep1954;

Its like a friend that ran a suspention shop was explaining to a young customer when the kid wanted to know EXACTLY the changes he asked for would do.

"Kid when you change ONE thing(drawing a "1" on a paper), and then you change ONE more thing(drawing another "1") you could change 11 things. "

"There are a hellova lotta variables and most interact. BUT I can help you do some things in the right order to get what you want."

If the factory could sort it all out for a good price, there wouldn't be many custom smiths.

That's why this forum is worth so much.


Not a lot of custom 110 volt electric plug smiths are there..........that's why the challange of singleactions is so much fun.

[boxhead]

I bought an early 45 Colt Accusport Bisley used in a west Houston gun shop 6 or 7 years ago that came with throats properly reamed and, overall, a well put together piece. It shot well (2" at 25 yards) but I wanted to tinker. I had purchased a pair of Iowegen's range rods in both 44 and 45 cal so proceeded to "tighten" up the Bisley. I shimmed the trigger pin to reduce side play to near non-existent and all was fine via the range rod. I then took a BM base pin and slid it in and found the range rod "ticking" the edge of the brass. I removed the BM base pin and installed the factory one and took it out to shoot. When I was doing my best it was a 4" gun at 50 yards. I was (am) happy. I had Alan Harton drill the factory base pin and barrel for a locking screw and called it good. The gun is a great shooter and, clearly and not surprisingly, I convinced myself that too tight was not good on a factory gun as has been noted above. It was good to see and work it myself to demonstrate what I thought could happen.