How to tighten up the chamber end lock up of a P-10S and C?

[Joe L]

I have three P-10's, an original C, a late F, and a late S.  The C and S versions have 0.006"-0.008" vertical clearance at the chamber end.  I haven't measured the F clearance since it shoots like it is down to 0.002" or so anyway, and I'm not touching it.  I stopped shooting the P-10C at 100 yards because it was just too loose for that kind of usage.  Not surprising for a service pistol.  The P-10S shot well at times at 100 yards, but has now loosened up enough to where it is almost as unpredictable at 100 yards as the C. 

The biggest issue is vertical spread, due to excessive clearance between the bottom of the barrel and the front locking block insert.  On the C, I was able to temporarily place an 0.005" shim on the insert and it tightened up the lock up nearly perfectly.  I either need a 0.008" oversized insert, or a 0.008" oversize barrel that I could hand fit with a file.  But I don't have a clue who could provide one.  Any ideas? 

Here is a video from yesterday which pretty well documents the problem.  Twenty rounds with the P-10F followed by the last five rounds of 20 from the P-10S.  At 100 yards from a hand rest.

https://youtu.be/Ke2TLkMdrkE

Joe L

[Joe L]

Another change of plan.  I am going to go with some brass shim stock epoxied to the to of the barrel instead of anything added to the front block.   On the S, maybe 0.005" shim and one or two mil of epoxy, on the C, probably 0.008".  If my order arrives this weekend, I should be able to test on Tuesday, maybe on both the C and S pistols. 

If this shim location works, I'll try the F also, possibly eliminating the high left first shot from a slide lock reload. 

Shooting the 97B"E" this week was a good exercise.  Got me back to thinking about good shooter execution.  That pistol is hard to beat from a mechanical standpoint.  But it is large and heavy.  I love it.

Joe L

[Joe L]

My prototype worked well this morning on my old P-10C. 

https://youtu.be/ePCtau5lD_c

Joe L

[Joe L]

Here is the prototype shim installation on my P-10C, after 100+ rounds and two barrel cleanings. 



I started with an 0.006" brass shim stock and some JBWeld quick set epoxy.  I left the tab extension on the shim to make sure I could attach the shim securely.  I chose this location for the shim as there is only clamping, no sliding, at this point of contact with the slide.  If I had added the shim to the locking block or to the bottom lug on the barrel, the shim would be subject to much sliding wear as the barrel locked and unlocked. 

I knew 6 mil plus the epoxy would be too thick, so I planned on manually filing down the shim stock as squarely as I could to get the barrel to clear the lug when reassembling the pistol.  I had to remove maybe half the shim and I obviously didn't get it square.  When I redo this barrel with just the shim on the ledge without the extension, I will use as little epoxy as possible and file more carefully to fit.   Even with my sloppy prototype, I had to go down 6 clicks on the Burris sight to get back even close to zero, so I very definitely took up some of the excessive clearance.  The 100 yard target results also looked good after the modification. 

My P-10S prototype just has a very narrow piece of shim stock epoxied to the ledge without the extension to the round portion of the barrel.  I think that one will be OK as well, but I don't have many rounds through that pistol and I didn't even bring it with me to New Mexico. 

I plan on shooting the P-10C at 200 yards tomorrow, after a good day on Friday with the P-09, which still has a factory barrel and no shim. 

Joe L

[M1A4ME]

Joe, how long do you think the brass will last?  It's not really 'sliding" against the steel of the slide.  More like just snapping up against it.

[Joe L]

I am more concerned with how long the epoxy will last with the thermal cycling over time.  The shim only sees pretty light compression loads so it should not wear. 

I thought about just using the JBWeld steel epoxy and no shim just bare on the shelf and then fitting it with a file.  Even that may last.  Another option is the long set steel epoxy and a brass shim.  I only need a total thickness of 3-6 mil to take up all the slack and still have enough slop to get the barrel lug over the frame lug when putting the gun back together. 

For readers who just stumbled on this thread, please note--none of this is necessary for a pistol in "normal" service!  This is strictly an experiment to see how tight of a group I can get at long distances from an inexpensive production polymer pistol, where the limitation is much more likely to be my eyesight and trigger control once the pistol is tightened up a little. 

My goal here is to get the P-10C and P-10S tightened up enough so that they come close to the average group sizes of the P-09, P-10F, and 97B"E" at 100 yards, when I am shooting well.  I am pretty sure the P-10C with my crude shim is there.  I still have some work to do on the P-10S, I think.  I have to eliminate the eyesight problem before I can come to any conclusions, however. 

Joe L

[Joe L]

I have good "proof of concept" now for the effect of the shim on the loose-from-the-factory P-10C.  It did fine at 200 yards on Sunday after I got the hold over right, and then did fine with both AA and IMI ammo at 100 yards during a 10 round per brand comparison shoot. 
https://youtu.be/chJuVvHYWM4
I think I will redo the shim this week and see if I can be a little more careful with the fit-up.  I also confirmed that the IMI ammo shoots just fine in the 4" barrel P-10C.  Maybe it is only the P-10S with the 3.5" barrel that the burn rate is just a little too slow.  The Atlanta Arms ammo works fine in the 3.5, 4.0, and 4.5" barrels.

This has been a fun week.  Challenging at times.  Can't wait to get new glasses and eliminate some of the vision challenges that resulted in too many poorly executed shots this week.

Joe L

[FakeCZName]

I haven't checked in for a long time, but it is really great to see you are still doing this, Joe! (I got distracted by rifles for a few years.)