Forcing cone erosion - when to fix?

[wbrco]

I've only been reloading metallic .38/.357 for about a year. As part of doing my load development, I try to test accuracy. I do have a chony, and I really been focusing on cast bullets (store bought at the moment).


But I've been having a lot of problems with accuracy, particularly with my Blackhawk. The question of course is where is the problem - the load, the gun, or the shooter? I've been focusing on .38 loads, not 357's. I also use factory loads as a control for evaluation.

So researching the problem I did several things, first of which is a though cleaning using JB paste, a .22 patch and a 1/4" dowel rod for a very tight fit. After removing ribbons and chips of lead from the barrel, and making sure I could see the machining marks in the cylinder throats, things improved, but not as much as I expected.

Further reading lead to questions on lockup and forcing cone issues. But I've not been able to get a good reference of when the erosion is at a point where repair is advised. I also am questioning the amount of play is excessive in the lockup.

As background, I've owned this firearm since the mid-80's, and it has been fed nothing but factory loads. This was the first hangun I owned, and has had several thousand rounds through it.


Is the erosion in the photos to the point that it should be adressed?

7672976730

[Outpost75]

Get the appropriate Brownell forcing cone gage for your .38/.357, based upon angle of existing forcing cone, and if it drops in to "No-Go" then it is time.

http://www.brownells.com/gunsmith-tools-supplies/handgun-tools/barrel-tools/chamfering-tools/barrel-chamfering-plug-gauges-prod626.aspx

Eyeballing your photos it looks like it is time to set the barrel back a thread, reface, ream forcing cone and if necessary refit a new cylinder bushing to remove end shake, if you can measure it at >0.002"

[fecmech]

If you are removing "ribbons and chips of lead from the barrel" I'd suggest clearing that problem up first before doing any work on the gun. The forcing cone on my Ruger .44 mag makes yours look like new and it's a very accurate gun. Size your bullets to your cylinder throats, use a good lube and powder appropriate to the desired velocity. That would be my approach.

[wbrco]

@fecmec - Done. Was first thing I did. Kept going with JB Bore paste until no more chips or black streaks. I'm not casting my own, so I don't have a sizer/luber. As to what I shot as factory lead loads in the past, who knows, but my own loads are Suter's 158 swc from Graf's, which has a blue lube, and Precision Delta 158 swc, which has a moly lube according to the web site.


I did measure my bore, but not the cylinder. Bore measures .3575 if I'm reading my used Brown & Sharpe micrometer right. The highest velocity lead loads I've developed are all less than 900fps.


@Outpost75 - Can/do you measure that between the cylinder and the frame where the cylinder pin passes through the cylinder? Do I measure that with a feeler gauge? What in the image causes you to think the barrel should me moved in? I certainly can measure the cylinder/barrel gap. I don't know what it should measure. I can also take a photo of the cylinder and post it.

[fecmech]

Done. Was first thing I did.
I evidently was not clear in my post. I did not just mean clean out the lead and chips. I meant have the properly sized bullets with a good lube so that at the very least you were not leading your barrel to start with. It's a foregone conclusion that you can't have accuracy when you have a lot of leading. If you are only able to use commercial bullets you are somewhat restricted. I would try to get bigger( .358-.359) and softer bullets if all you are looking for at this point is .38 level loads. I believe Missouri bullet has softer bullets available for purchase.

[EMC45]

Bigger bullets. Maybe even bigger softer bullets........

[Outpost75]

@Outpost75 - Can/do you measure that between the cylinder and the frame where the cylinder pin passes through the cylinder? Do I measure that with a feeler gauge? What in the image causes you to think the barrel should me moved in? I certainly can measure the cylinder/barrel gap. I don't know what it should measure. I can also take a photo of the cylinder and post it.

Measure cylinder gap inserting an ordinary automotive blade type feeler gage completely through the frame opening so that it pokes out both sides of the cylinder. The largest size feeler gage which you can pass completely through the opening and then cock the hammer and rotate the cylinder past all six charge holes, WITHOUT resistance is the "PASS" measurement.

Then determine which larger size blade gage, when inserted through the opening and protruding out both sides of the cylinder, does not permit you to rotate the cylinder completely around all six charge holes. That is the "HOLD" measurement.

Now, with the "HOLD" gage left in place, force the cylinder back, and insert a 0.060" "GO" (for .38 Spl./.357) headspace age, which should enter without any resistance.

http://www.brownells.com/gunsmith-tools-supplies/measuring-tools/headspace-gauges/revolver-cylinder-gauges-prod685.aspx

Next, remove the front "HOLD" gage, and try to insert a 0.066" "No-Go" rear gage between the frame bolster and the rear of the cylinder. DO not force the gage, any resistance is OK. But if the gage enters easily, without resistance on the 0.066" gage, headspace is excessive.

The difference between two "PASS" measurements taken first with and again without the .060 rear "Go" gage in place is the cylinder "end play" or "shake." More than 0.002" movement will cause peening of the frame bolster where the cylinder slams against it and gradually increase headspace further.

Your photograph shows apparent peening of the frame bolster to visual inspection. I would perform the above checks and if necessary return your revolver to the factory for refit if it is still under warranty. If you are the original purchaser Ruger will probably do this either for free or for nominal cost. At least, that has been my experience.

[wbrco]

OK - so after doing some measurements, and assuming that I can properly read my swap meet Brown and Sharpe vernier caliper as well as my off shore feeler gauges normally used for spark plug gaps...

The forward cylinder travel is somewhere between .002" and .0025", with gap between the cylinder and barrel varying between .004" and .0045" depending on the play of the cylinder. I would categorize the feel as the boring of the hole through the cylinder for the cylinder pin having worn at the front of the cylinder, i.e., it wobbles, even when cocked.

I could actually measure the gap between the front of the frame and the cylinder bushing with the feeler gauges as .0025 running the edge of the gauge right up against the pin.

I also attempted to measure the throats and the barrel.

Lesson #1, using regular cast bullets, it's possible to break a 5/16" oak dowel rod when driving at bullet down the barrel.. Next time use something softer!

However, the cylinder throats measured .3584" (new bullet for each one) and the barrel measured .3575"

Since then, I've also done some additional reading. Given that it seems to be more "wobbly" around the cylinder pin than back and forth, would this be a good candidate for an oversize cylinder pin? Can I assume that the wear is symmetrical and the cylinder/barrel alignment would not change?

[Outpost75]

Oversized cylinder pin is easy fix.

[MtGun44]

A bit of cyl wobble is not a big issue. Too hard and too small boolits
IS a big issue. Go to .358 or .359 and softer, good design and good lube.

Bill

[wbrco]

Know this old thread but wanted to follow up.

After delaying and then waiting, my new oversized cylinder pin arrived. Helped a lot.

I also bought Kuhnhausens book. Way overkill for my skill level, and tool availability but I did learn some things. I need a bore alignment rod before doing just about anything else.

I also noticed that there is a tool to swage the cylinder bushing instead of machining a new one in, or replacing the cylinder.

Thanks for all the help guys!

[paul h]

Did you ever slug the barrel to see if it has thread choke? My 357 suffered from thread choke, a constriction in the barrel where it threads into the frame and it would not shoot cast bullets worth a hoot. I ended up cutting in a Taylor throat to get rid of the constriction and it make a huge improvement in accuracy.