Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
yes, the action and bolt are tweaked so that there is zero play at full lock up.
This technique has been in practise for decades.
Jerry
action truing??
- Thread starter wolf300H&H
- Start date
yes, the action and bolt are tweaked so that there is zero play at full lock up.
This technique has been in practise for decades.
Jerry
Actually that is not correct unless an awful lot is removed from the threads in the action... Even if the action is threaded 15 thou over an original barrel can be used... not that I would want to bother with an original barrel (crooked threads, wonky chamber) with a trued action. A trued action deserves a match barrel chambered and fitted as true as the action.
I took that to mean bushing the bolt, but maybe I was wrong. - dan
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Oops, forgot there is another 'bushing' step that can occur
Firing pin exit hole in the bolt faced can be bushed. This is to reduce the gap around the firing pin exit hole. That reduces the amount of primer cratering that can occur under heavy pressure.
Savages used to have a severe problem with this but their new gen actions all use a small firing pin and reduced exit hole in the bolt heads. I have used several of these and the amount of cratering has been almost eliminated. For me, I am OK with a bit of cratering as it is a predictable indication of pressure. Masking all pressures signs sounds good but I would rather keep my fingers, eyes and toes vs gaining another 100fps.
Second is to bush the bolt body/replace with an oversized bolt eliminating the wobble in the action that can happen when the sear is dropped. Just dry fire a Rem 700 and you will see what I mean.
A neat tweak I saw was to hard chrome the orig bolt body to tighten it up in the action. Worked really nicely.
When quality work is done to a Rem 700, many little steps are performed to true and tune it up. That takes skill and experience and 'smiths like Guntech will forget more then most will ever get the chance to learn.
Good stuff...
Jerry
Firing pin exit hole in the bolt faced can be bushed. This is to reduce the gap around the firing pin exit hole. That reduces the amount of primer cratering that can occur under heavy pressure.
Savages used to have a severe problem with this but their new gen actions all use a small firing pin and reduced exit hole in the bolt heads. I have used several of these and the amount of cratering has been almost eliminated. For me, I am OK with a bit of cratering as it is a predictable indication of pressure. Masking all pressures signs sounds good but I would rather keep my fingers, eyes and toes vs gaining another 100fps.
Second is to bush the bolt body/replace with an oversized bolt eliminating the wobble in the action that can happen when the sear is dropped. Just dry fire a Rem 700 and you will see what I mean.
A neat tweak I saw was to hard chrome the orig bolt body to tighten it up in the action. Worked really nicely.
When quality work is done to a Rem 700, many little steps are performed to true and tune it up. That takes skill and experience and 'smiths like Guntech will forget more then most will ever get the chance to learn.
Good stuff...
Jerry
I found out from Bill Leeper this way of 'bumping' a bolt. It is so simple and easy to do...
A dovetail cut in the top and bottom of the bolt when it is in a closed position... and drive in steel inserts and machine them to the correct diameter of your action.
Shown here is the top 'bump'. It reduces the upwards movement by about 3 or 4 thou. The front of the bolt really requires no 'tightening'.
I don't think tighter bolts are that much better than slightly looser bolts in factory actions... lack of movement up and down and accuracy improvement would be something very hard to measure. No doubt it can be one more step towards the best you can get out of an action but unless you have a small accurate cartridge and a match quality barrel correctly installed it would not give a measurable difference... maybe not even then...
Bushed firing pins with a reduced tip diameter can be a big improvement on some bolt faces...
A dovetail cut in the top and bottom of the bolt when it is in a closed position... and drive in steel inserts and machine them to the correct diameter of your action.
Shown here is the top 'bump'. It reduces the upwards movement by about 3 or 4 thou. The front of the bolt really requires no 'tightening'.
I don't think tighter bolts are that much better than slightly looser bolts in factory actions... lack of movement up and down and accuracy improvement would be something very hard to measure. No doubt it can be one more step towards the best you can get out of an action but unless you have a small accurate cartridge and a match quality barrel correctly installed it would not give a measurable difference... maybe not even then...
Bushed firing pins with a reduced tip diameter can be a big improvement on some bolt faces...
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
Very nice way to solve the problem. Bill, he is a smart one too 
Jerry
Jerry
Tightening up the bolt in the receiver of a Remington, whether by bushing, bumps, or a new bolt, appears to be good for about .040" of vertical at 100 yds. That's 1/25 MOA. The same seems to be true for Winchesters. When bolt clearance is really excessive (more than 6 or 7 thou) the improvement can be more noticeable since the detrimental effect of the sloopy fit is more obvious. I think it was John Fry, a Washington gunsmith, who had the first bushed bolt I saw.
On a Savage, the bolt and trigger design eliminates the deflection of the bolt by the contact between the sear and cocking piece so there is, possibly, less need for a decent fit.
Occasionally, one will see an action with an obvious alignment problem and the correction of the problem will have a marked effect on performance. Just as often, a crooked action shoots fine. After fixing, it still shoots fine. Likewise, we have all had perfectly good rifles which seemed perfect in all respects except that they didn't shoot.
I have always been going to set up an action so that I could deliberately introduce errors in the threads, bolt face, locking lugs, etc. and try to quantify the effects of various defects. This would be a very involved undertaking and I don't know that I'll ever get the time; or the money!
In many cases, action truing is much more effective in the shooter's mind than at the target. Regards, Bill.
On a Savage, the bolt and trigger design eliminates the deflection of the bolt by the contact between the sear and cocking piece so there is, possibly, less need for a decent fit.
Occasionally, one will see an action with an obvious alignment problem and the correction of the problem will have a marked effect on performance. Just as often, a crooked action shoots fine. After fixing, it still shoots fine. Likewise, we have all had perfectly good rifles which seemed perfect in all respects except that they didn't shoot.
I have always been going to set up an action so that I could deliberately introduce errors in the threads, bolt face, locking lugs, etc. and try to quantify the effects of various defects. This would be a very involved undertaking and I don't know that I'll ever get the time; or the money!
In many cases, action truing is much more effective in the shooter's mind than at the target. Regards, Bill.
Mystic Precision
CGN Ultra frequent flyer
- Location
- Summerland, BC
the one thing that definitely improves when all this work is done to any solid bolt front locking action is the ability to resist pressure signs until things get real toasty.
With poor lug contact/bolt face not square to the chamber, things can bend and cartridges can bend. Unfortunately, been there.
With the growing interest in kaboomers in F Open, wonky action and bolt fit will only make matter worse.
The real heart of accuracy is the BARREL and the CHAMBER. Without these being well manf, you could do anything else and it will not shoot.
But all the work done to tune up a solid bolt front locking action doesn't hurt and may resolve other issues that would be too expensive to diagnose and resolve one at a time.
1/25mins added to the normal dispersion of the barrel is just another variable we don't need. With 'field' rifles shooting in the 1's and 2's, every little bit helps if you want to be at the top of the page come Sunday.
One experiment I have wanted to do is to show how well the floating bolt head insulates the lock up and firing of the action from the movements of the moving bolt. It would involve cutting an action in half so I am not in any hurry to do the demo
Jerry
With poor lug contact/bolt face not square to the chamber, things can bend and cartridges can bend. Unfortunately, been there.
With the growing interest in kaboomers in F Open, wonky action and bolt fit will only make matter worse.
The real heart of accuracy is the BARREL and the CHAMBER. Without these being well manf, you could do anything else and it will not shoot.
But all the work done to tune up a solid bolt front locking action doesn't hurt and may resolve other issues that would be too expensive to diagnose and resolve one at a time.
1/25mins added to the normal dispersion of the barrel is just another variable we don't need. With 'field' rifles shooting in the 1's and 2's, every little bit helps if you want to be at the top of the page come Sunday.
One experiment I have wanted to do is to show how well the floating bolt head insulates the lock up and firing of the action from the movements of the moving bolt. It would involve cutting an action in half so I am not in any hurry to do the demo
Jerry
