PDA

View Full Version : Bolt timing (long and pic. heavy)



Al Nyhus
12-25-2007, 05:44 PM
While we often hear much about 'bolt timing', seldom do we ever get to see an example of this. While there's a lot involved in this whole issue, much of it is subtle in nature and hard to describe without having the pieces in hand and saying: "See????!!!! That......right there! :D

So with all that said, I'm going to put up a couple of pics showing how one specific bolt timing issue was resolved on an action. A little background is in order, I suppose. This action had always been a troublesome unit for it's owner since new. Despite minimal bolt-to-reciever clearance, when the bolt was cocked the bolt shroud and cocking piece would raise upward. The pin tip showed evidence of damage that initially was thought to be caused by the pin tip being retracted behind the bolt face, thus being dinged up as it bounced through the pin hole when the pin came foward. Despite these maladies, the rifle actually shot pretty well although never up to it's owners satisfaction. But it did show promise at times.

Several attempts were made to correct the 'jack up' issue with the shroud and cocking piece...lowering the trigger, a new trigger hanger, several new cocking pieces and some reworking of the cocking piece/sear engagement angle, new firing pin, shroud...you name it, it was tried. And still the issues remained...bolt shroud/cocking piece 'jack up' when cocked and firing pin damage finally culminating in the bolt handle coming loose.

The action finally made it's way into Stan Ware's hands at SGR Custom Rifles where the problem was identified. What was happening was that the locking lugs on the bolt weren't clearing the locking lug abuttments in the reciever before the root of the bolt handle was 'coming up' on the cocking cam angle machined into the reciever. When the bolt was closed, the cam angle on the bolt handle was 'camming' while the bolt lugs were firmly seated against the lug abuttments in the reciever...and since the cam angle on the handle rotated upward as it closed, this caused the cocking cam to raise upward along with the bolt shround. Because of the angles involved, all this happened during the last small amount of bolt closeure, making diagnosing this virtually impossible externally. Essentially, the original bolt handle was just a bit too far foward. By how much...I have no idea.

The original bolt handle did all it's camming on the small leading edge of the bolt handle. It also had the added benefit of a screw attaching it to the bolt body as well as the handle being silver soldered to the bolt body. Because of the 'jamming' that happened between the cam angle on the bolt handle and bolt lugs when the bolt was either opened or closed, the cam angle on the handle exerted tremendous force on the handle itself..in effect trying to rotate the handle around it's axis (the screw) which it finally did when the silver solder failed.

Picture #1 shows the original handle (bottom) and the new PTG handle installed by Stan. Stan recut the cam angle on the PTG handle to work with the angle on the reciever. This new handle spreads the camming load out over a much great area than the original...where the entire camming force was concentrated on the small leading edge of the root of the bolt handle.

http://img.photobucket.com/albums/v467/tenxal/rfdtwobolts.jpg

Picture #2 shows the cam angle on the reciever. If you look closely, you can see a small mark...this is where the 'jamming' was occuring.

http://img.photobucket.com/albums/v467/tenxal/rfdcamangle.jpg

Picture #3 shows the cam angle interface between the reciever and the new bolt handle. Notice that Stan has kept a 'tail' on the bolt handle that wraps as far around the bolt body as possible. This, along with eliminating the bolt handle screw, almost doubles the surface contact area between the bolt handle and the bolt body for more silver solder area.

http://img.photobucket.com/albums/v467/tenxal/rfdnewbolt.jpg

Picture #4 shows another view of the cam angle interface.

http://img.photobucket.com/albums/v467/tenxal/rfdnewbolt2.jpg

After the rework, the bolt shroud/cocking cam 'jack up' is gone. :) The original trigger hanger positions the trigger perfectly in relation to the cocking cam and sear. And finally....no more pin tip damage. What was initially thought to be damage caused by the pin tip being retracted behind the bolt face (and bouncing through it as the pin came foward causing the damage) was in reality the pin tip being 'tweaked' and slightly bent in the pin hole as the cocking piece was levered upward due to the bolt handle/locking lug being 'out of time' with each other.

Certainly there is a lot more involved with the whole topic of 'bolt timing' but hopefully this is of some help. When you get into an area like this, you really need to have someone with true 'gunsmith' or engineering skills to help sort this stuff out.

Hopefully this will start some discussion about 'bolt timing' and related issues. There are actions out there that have a history of never shooting well..no matter how many barrels they've had installed or how many scopes have been on or how many times they've been restocked. Maybe they're suffering from some timing issues and can be straightened out? I know that in conversations with some really good 'engineering type' gurus in the accuracy rifle business..they have all said that bolt timing is an area where occasionally an individual example of an otherwise fine custom action may not live up to their potential.

Looking foward to hearing your thoughts and ideas. :)

Good shootin'. -Al

Wayne Shaw
12-26-2007, 07:03 AM
Excellent post! I have posted about the timing aspect before, where some believe "timing" only involved the trigger positioning fore and aft.There is a whole bunch more involved, as you have shown. Getting the cams in alignment and in time are not as easy as some think. I believe "4mesh" gave a quite good explaination as well on a much earlier post, which I would think could be seen through a search.

Gene Beggs
12-26-2007, 10:34 AM
Al, a post like this makes some of us wonder whether or not we can truthfully refer to ourselves as 'gunsmiths.'

Diagnosing and correcting something like this, separates the men from the boys. Well done ! Thanks for sharing that with us.

Later,

Gene Beggs

ArtinNC
12-26-2007, 02:36 PM
I have a XP100 that I bought new years ago and has always been hard to open. And the open cam on the bolt handle never has bumped the cam on the back of the action at all. Who would be a good one to fix this??
Thanks Art

henrya
12-26-2007, 04:53 PM
After the lugs and seats are both cut is it possible to end up with the bolt "out of time"? What do you suppose is the tolerance in the length from lug seat to the cam? How likely is it that you will end up with an extraction cam that no longer cams?

I've been wondering about this for a while as I have two Remingtons that may not be as good as they could be. Slightly "clicky" bolt lift even when there is no apparent reason for it that I can see.

R. G. Robinett
12-26-2007, 05:16 PM
After the lugs and seats are both cut is it possible to end up with the bolt "out of time"? What do you suppose is the tolerance in the length from lug seat to the cam? How likely is it that you will end up with an extraction cam that no longer cams?

I've been wondering about this for a while as I have two Remingtons that may not be as good as they could be. Slightly "clicky" bolt lift even when there is no apparent reason for it that I can see.

Once the space between the rear face of the rear receiver-ring and the front face of the bolt-handle exceeds 0.010", you lose primary extraction - and, due to the compound angles, it goes away FAST!:eek: Further, excessive space exacerbates wear on the bolt-handle cam. :(

Al, it looks like Stan and yourself decoded the script - I wantz my PRECIOUS back! :D :p Seriously, I'd have never figured that one out! I was hung-up on the trigger hanger/sear engagement, the pin coming out of the bolt-head while cocked, and apparent "cock-on-close" issues! Stan's "THE MAN" on this one! Oh, and you ain't less than a moron yourself!:rolleyes: RG

Al Nyhus
12-26-2007, 05:47 PM
After the lugs and seats are both cut is it possible to end up with the bolt "out of time"? What do you suppose is the tolerance in the length from lug seat to the cam? How likely is it that you will end up with an extraction cam that no longer cams?

I've been wondering about this for a while as I have two Remingtons that may not be as good as they could be. Slightly "clicky" bolt lift even when there is no apparent reason for it that I can see.

Henry, this is actually pretty common....more common that most realize. When the back of the bolt lugs are faced off and a cooresponding cut made on the locking lug abuttments in the reciever, the bolt handle moves back..thereby increasing the distance between the cam angle on the bolt handle and it's counterpart angle on the reciever. This reduces the amount of mechanical cam you have for primary extraction. This can result in the dreaded 'click' at the top of the bolt lift. Normal pressure loads can 'feel hot'...even when they're not...because you've lost some mechanical camming that does the initial work of moving the case backwards in the chamber.

Another consequence of the cam angle being reduced is that the 'work' being done by the primary extraction cam angles is now being done over a shorter amount of 'time' and on a smaller amount of contact surface....which in turn causes premature wear on this area (particularly the cam angle on the bolt handle).....thereby making the entire problem worse.

Because of the angles involved, a small amount of increased clearance between the cam angles can cause a loss of quite a bit of mechanical camming, percentage-wise. All but one of my Remingtons have had the bolt handles relocated..and that one is a hunting rig that happened to come from the factory with the handle correctly positioned and it only needed a total of .006 faced off lugs/abuttments..so the bolts cam angle remained in a pretty good relationship with the reciever.

Stan and I have spent lots of time on the road together going to matches. We've dreamed, schemed and blabbered about what we would consider our idea of a 'perfect' BR action to be. The one constant we both agree on would be for the 'perfect' action to have an indexable and adjustable cocking cam angle fitted to the reciever. :cool:

Hey...a guy can dream, can't he? :D -Al

Al Nyhus
12-26-2007, 06:06 PM
Once the space between the rear face of the rear receiver-ring and the front face of the bolt-handle exceeds 0.010", you lose primary extraction - and, due to the compound angles, it goes away FAST!:eek: Further, excessive space exacerbates were on the bolt-handle cam. :(

Absolutely, Randy. It can make a huge difference, can't it? I know you had a Remington that flat out quit camming at an NBRSA Hunter Nationals some years back....good thing you didn't have access to The Red Hammer at that event! :eek:

http://img.photobucket.com/albums/v467/tenxal/BestRFDwreckHolmen07.jpg

If 'Precious' was to come back and live with you..you'd have to promise not to mistreat her and we'd have to discuss 'visitation' rights. ;)

Smilin' in The Forbidden Zone. :) -Al

alinwa
12-26-2007, 10:30 PM
AWESOME THREAD GUYS!!!!!!


Thank you all and al for starting it :):):):)


Heck, I'll even thank WILBUR for letting us play like this.....:D


LOL



al

Al Nyhus
12-27-2007, 07:49 PM
Stan made a video giving a quick overview of the mechanical camming.

Hope this helps....please post your thoughts on this if you'd like. Good shootin'. -Al :)

http://www.sgrcustomrifles.com/us/custom-rifles/bolt-timing-video-36.html

crb
12-27-2007, 08:17 PM
On the rifle in the original post would it have not been obvious there was a severe timing problem if you removed the firing pin assy and worked the bolt in the action a few times? With the FP out the bolt should cycle absolutely freely.

I recently picked up a 40x for a project and disassembled it immediately upon getting it home. A few days later I needed to check the trigger pull wgt so I reinstalled the trigger and cycled the bolt a few times while checking the trigger pull.

When opening or closing the bolt it felt like there was a tremendous out of time situation. It felt like the primary extraction surfaces were just about locking up the bolt handle. I removed the FP assy and the problem went away and the bolt was totally free.

I inspected the FP assy and the threads of the bolt shroud were really bad. They had very sharp peaks and that area of the threads also looked like the threading tool hadn't properly picked up the previous cut. I cut down the peaks and the 'timing' issue was better. I lubed up all the rubbing surfaces of the FP assy and after that the bolt lift and closure were smooth with no more binding.

bglenn
12-27-2007, 09:23 PM
Al
How about a vido on the other areas of bolt timing?
Thanks

Glenn

robertb
12-27-2007, 09:31 PM
Great thread...Enjoyed this immensely.

henrya
12-27-2007, 09:37 PM
Good job on the video!

Great thread - thanks for starting this.

wnroscoe
12-27-2007, 10:06 PM
Al,

Thanks for the video link and your info. It got me to thinking so I started looking at my 700's and one that belongs to one of my friends. Mine are fine but, my friends bolt, bolt handle and receiver cams are obviously out of time. There's about a .045" gap, not the .010" gap between the handle and receiver. There’s a small shinny spot on the receiver cam and bolt cam where they've been contacting each other over time. This spot is really small, it's at the rear of the cam on each, as far back as it can get and still have the cams touch. Man this thing must have been a pain to cycle. This post has really opened my eyes to something and started me to thinking. Thanks again for sharing this info.

William

robertb
12-28-2007, 09:28 AM
What is the dreaded click you hear when you open the bolt on an un-timed action?

RL Weikart
12-28-2007, 09:03 PM
i really appreciate this discussion, probably would be a good time to remind every one to put a little lug lube on the contact angle of the bolt when greasing the lugs.

:D

taxman
12-30-2007, 09:30 PM
Hi all,

My first post and a disappointing one at that.

I just had a brandy new 700 stainless "trued" with a new Kriger barrel installed. Have been shooting it for about a month now. Today, I found a pretty good load.

I read this thread, watched the video and decided to take a look at my new piece. Low and behold, I have little to no caming action and a loud click at the top of opening up the bolt. I feel real happy about learning all of this.

But I would like to thank all of those in the know, for letting us know the difference.

Thanks!!!
Tony

gundecking
03-23-2008, 09:59 PM
Hello all. Great information here, and I have only scratched the surface.

How is the out of time issue solved? Just reposition the bolt handle? :confused:

abintx
03-24-2008, 11:25 AM
by Fred Moreo. Here's what Fred (the Savage Guru) has to say about Truing and Timing the Savage Action. (I know it's not a benchrest action but his explanation conveys a timing procedure nonetheless that resolves the problem for a specific action.)

When I build a rifle, truing and timing the action is a standard procedure. Shooters understand truing, but not "timing".

When an action is out of time, the bolt operation is stiff, bolting or unbolting.

This is caused by the cocking ratio being out of balance, and the sear engaging too early or too late. The lead-in ramps and the primary extraction are not synchronized.

When we true an action, the lead-in angles (the ramps that lead into the lug seats) are re-cut to a true helical cam. Factory cuts are made with an end-mill, and are not helical. A helical cam is like a spiral staircase, and I have developed tooling to precisely cut the lead-in angles to engage the whole width of the bolt lugs. The receiver face and the lug seats are machined to square them up relative to the receiver threads, not to the bore of the receiver. The reason for this is the barrel will be square to the bolt face.

Concentricity behind the bolt head is not critical, as the "float" in the bolt head allows the bolt body to be off center as much as .045" in any direction, and still get full lug contact, although I've never seen one that bad.

The bolt head is squared, front and back and the firing pin protrusion is reset to .040" +- .005". After this the firing pin travel is corrected and timed with the sear and trigger. At this time the cocking ratio is corrected to avoid over cocking and hard bolt lift. The cocking ramps are reground to the correct angle, and the barrel nut is faced for 100% contact.

After the above work was performed my action was smooth and precise. Fred can be contacted at Sharp Shooter Supply, 4970 Lehman Road, Delphos, OH 45833, Phone: (419) 695-3179

gun-rx
03-25-2008, 10:34 PM
Just a note to expand on the timing issue. The bolt cam timing is also in direct proportion to the fit of the extractor. I've seen a number of Sako style extractors that have been installed with a vast amount of gap between the extractor claw and bolt face. The larger the gap, the more cam action that's lost. We sometimes try to make the world more perfect by holding such tight tolerances. The best action available needs to have at least a minimal tolerance as pointed out in Stan's thread.