Bolt shroud gizmo

[AlNyhus]

Boyd Allen and I were talking the other day about shroud fit relative to bolt movement and he had a good idea for a checker. I used a piece of 1" Delrin round, milled a flat, milled a 3/8" hole in the flat to accept a dial indicator and used a 1/4-20 Nylon screw epoxied into a round ball as a locking screw. With a 30mm-1" ring spacer, it will work on both sizes of rings.

Thanks to Boyd for the idea! -Al

 

[Hal]

Great idea. Swap it around and check the bolt play on some open topped actions.

Hal

 

[LVLAaron]

Al that looks like it needed a lathe!

 

[VA_XTC_Shooter]

Dumb question - what are you measuring? As you operate the bolt to see if the shroud moves up and down? Or for flex in the system?

 

[AlNyhus]

Dumb question - what are you measuring? As you operate the bolt to see if the shroud moves up and down? Or for flex in the system?

I want to see how shroud fit in the bolt changes firing pin drag. -Al

 

[AlNyhus]

Al that looks like it needed a lathe!

Now, don't be dissin' my hack saw and file machining method!

My little gun room lathe is down with a bad case of electronic flu. The control board has been repaired and is wingin' it's way back home.

 

[LVLAaron]

Keep us posting with your learnings

 

[AlNyhus]

Keep us posting with your learnings

I'll probably learn that I don't know too much.

 

[V35]

I'll probably learn that I don't know too much.

I find myself in that position often.

 

[LVLAaron]

Do we know how much clearance we do or dont want? I have a 700 on the bench with something like 40 thou of gap between the shroud and bolt. I'm wondering if it warrants a bushing somehwere

 

[DaveTooley]

There were questions I got asked over the course of my career about various new techniques, approaches, etc. My usual answer was I'll tell you what I think about it and in two years I'll tell you what I know about it.

 

[BoydAllen]

In a rifle that otherwise is capable of fine accuracy, too loose of a shroud thread fit can degrade accuracy. Many years ago, I asked Wilbur Harris what he knew about this. He told me that when his rifle that had a panda action that had a lot of rounds on it, started losing accuracy for no apparent reason, a new shroud fixed the problem. Another time, a fellow posted on Benchrest Central about a problem with one of two identical rifles, built with top components, using the same action. When he first got them, they both performed as expected, but after a while one of them became inconsistent. In a PM I suggested that he try wrapping the shroud threads with a few tight wraps of plumbers' teflon tape, It worked. Later he measured the threads of the shrouds of both actions and the one that acted up was several thousandths smaller. My guess is that it was borderline when new and a little wear took it over the line. You may note that based on an original request from Speedy, some years back, that Pacific Tool makes an oversized Remington shroud that requires fitting, and recently I believe that Eric Cortina has started offering shrouds. For a while, for Bats, I believe that Alex Wheeler offered a shroud that required fitting. Just a theory, but I believe that one of the issues is not so much binding, but rather vibration. My thought is that with a tool to look at shroud movement, we can start to investigate how this might correlate with differences in accuracy. I believe that the same tool can be used to look at bolt fit in the receiver.

 

[LVLAaron]

For the one I have that's super bad, I might craft a delrin bushing just to play with it.

 

[DaveTooley]

On 700's you're assuming the treads in the bolt body are true.

 

[STS]

On 700's you're assuming the treads in the bolt body are true.

And many of them are very definitely not.

 

[WSnyder]

Do we know how much clearance we do or dont want? I have a 700 on the bench with something like 40 thou of gap between the shroud and bolt. I'm wondering if it warrants a bushing somehwere

I have soft soldered a ring to shrouds right behind the threads and then turned to fit.

I fit the PTG fairly tight. I use a sacrificial mandrel in the lathe to mount the oversized shrouds for fitting. As I measure and cut I can fit the bolt to the shroud and sneak up on the fit. I fit them more by feel than actual measurement. I fit as tight as possible but eliminating any drag when the bolt goes through it’s 90° rotation. The RR action bolts are fairly consistent and fairly straight, more so than some earlier bolts. If you plan to nitride or Cerakote after fitting leave sufficient clearance in the fit. Yes nitride will add tenths to the parts and if a little too tight before it just might get squeaky tight after nitride.

To check the back end of the bolt for true, cut and thread a sacrificial mandrel in the lathe to fit the bolt. Once fit rotate bolt and see how bad it flops around or not.

 

[AlNyhus]

My original (pictured) has .009 clearance between the shroud shoulder (.495) and bolt counter bore (.504). It showed .005 movement when the trigger is pulled.

With a new shroud that gives .002 clearance between the shroud shoulder and bolt counter bore area, shroud movement is .002 when trigger is pulled.

With some black Magic Marker on the pin tip, the slight rub marks appear the same with each shroud. The flats on the bottom of the 'tight' shroud are lower (from the center line) of the pin than the original shroud. Thread fit to the bolt body with both shrouds is excellent.

Am going to set up two pin assys. and see if there's any difference on target.

 

[BoydAllen]

For the one I have that's super bad, I might craft a delrin bushing just to play with it.

Back in the days when Gene Buckys and Jackie Schmidt were shooting buddies and both were shooting Farley actions, Gene made them shrouds from some sort of dry lube filled plastic. This allowed a tighter fit than would have worked with a metal to metal fit. Both had fair to midlin' records as shooters. Jackie still is, and from time to time we are blessed with his wisdom.

 

[WSnyder]

dry lube filled plastic

PTFE impregnated delrin. I made a couple, still have a couple of feet of stock. Jackie posted a picture of one of his in another thread this week. Time consuming to make. When PTG started offering the Speedy that was the easy button. A fitted, nitrided, modified, stainless Speedy is as slick as they come. The Cortina I think might be the easy button now.

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Jackie's (Buckys) shroud

 

[BoydAllen]

Back in the day, a fellow named John Illum made actions under the Ram Pro name. They had shroud threads that were LH for right bolt and RH for left bolt, that were precisely timed, so that with the bolt handle turned the shroud screwed into the bolt body to the point where the gap between the face of the shroud flange and the back of the bolt body was almost nonexistent. At the root of the flange the inside corner had a angled fillet that fit into a matching shape in the bolt body. 'Ol John was quite a machinist, and CNC operator.

The Ram Pro name came from his scratch built bolt action silhouette pistols. He would buy straight contour top grade barrels and cut them in half to make two pistol barrels. This gave him unique information on how well centered the bores of various manufacturers were in their ODs. He kept a list on the wall of each one he cut. I forget the numbers, but I do remember him telling me that the cut barrels tended to be better in that respect than the buttoned ones., but of course when he contoured them, most of that went away.