Bolt Diameters

[TK 1985]

Looking at PTG bolts, and they wiill make the bolt body to a custom diameter to your specification, that way you reduce slop in bolt going down the raceway. My question is that while good in theory on a bench rifle, on a hunting rifle, especially in the conditions I experience here in Pennsylvania, would that not be a bad thing?
It was brought up to me today, that with such close tolerances, in our climate, if any moisture gets in there and then freezes, it could lock the bolt in the rifle. Is this a real concern with making such a tight fit? I have never experienced it but I also have only always hunted with factory rifles.

 

[Joel Russo]

Going too tight on the bolt body to action body tolerance can and will be detrimental on a hunting rifle. In designing our custom actions, we found that .004" was the magical number. I have an early BAT action that was closer to .002". If felt butter smooth when you cycled the bolt on a cold action. I used this particular action on a comp rifle, and after a few shots, the heat from the chamber would migrate through the tennon and into the action body. It tightened up the bolt and rendered the rifle inoperable. I used some lapping compound and opened it up a few thou. On an action, I highly recommend going with .004" clearance.

 

[Edd]

..... after a few shots, the heat from the chamber would migrate through the tennon and into the action body. It tightened up the bolt and rendered the rifle inoperable....

Why did heating the action body made it tighter instead of looser?

 

[Sully2]

Why did heating the action body made it tighter instead of looser?

The "OD" of the action will get larger whereas the "ID" of the action grows slightly smaller

 

[Edd]

The "OD" of the action will get larger whereas the "ID" of the action grows slightly smaller

Nope, a ring grows when heated. The circumference of the ID and the OD both get longer.

 

[J E Custom]

Looking at PTG bolts, and they wiill make the bolt body to a custom diameter to your specification, that way you reduce slop in bolt going down the raceway. My question is that while good in theory on a bench rifle, on a hunting rifle, especially in the conditions I experience here in Pennsylvania, would that not be a bad thing?
It was brought up to me today, that with such close tolerances, in our climate, if any moisture gets in there and then freezes, it could lock the bolt in the rifle. Is this a real concern with making such a tight fit? I have never experienced it but I also have only always hunted with factory rifles.

All bolts have to have some clearance. As Joel stated, you can go to tight and have problems.

Most bolts have .003 to .004 clearance and that Is about right. Some of the older or used actions may have more but that Is not a problem ether.

I have seen bolts with taper (Bolt would be smaller at one end or the other) that shot fine, they just felt bad.

With good headspace and proper sizing of the cases, the bolt fit doesn't hurt accuracy because of the lock up on the front of the bolt. If the head space is to much it will allow the bolt to lay in the bottom of the action and move when the firing pin drops. (You can see this when you dry fire any
bolt action. But when a properly sized and head spaced round is placed in the action and the bolt is closed, there is little or no movement of the bolt. (You can see this if you load a dummy round (No powder or primer) that has been sized only enough to close the bolt, there will be no bolt movement when the firing pin drops.

When you go to an oversized bolt, you have to ream the receiver and end up with .003 to .004 clearance (Right back where you started from). There are probably times that bolt should be replaced for one reason or the other but normally the problem is poor or no lubricant, or poorly sized
ammo.

In a perfect world, zero head space will cure this, but with loads of all different sizes, some head space is required to chamber all rounds. My recommendation would be to concentrate on loading
quality, perfectly sized ammo and bolt fit will only be a mechanical issue not an accuracy issue.

Just my opinion

J E CUSTOM

 

[Canadian Bushman]

Nope, a ring grows when heated. The circumference of the ID and the OD both get longer.

More often than not this is how it works.

I have a ptg bolt in a rem 700 running just under .001" clearance. Ive never locked it up but its a pretty tight fit and requires a bit of extra attention.

I was under the impression bat borden and defiance all produce actions utilizing .002-.003" slip.

 

[Edd]

More often than not this is how it works.

I have a ptg bolt in a rem 700 running just under .001" clearance. Ive never locked it up but its a pretty tight fit and requires a bit of extra attention.

I was under the impression bat borden and defiance all produce actions utilizing .002-.003" slip.

BAT says HR and VR actions have .0025" clearance and their benchrest actions have .0015" clearance. I have an HR action. I don't have gauges to do a proper measuring job but with the gauges I have it appears to be right at the 2.5 spec. I wish I had a good way to turn the bolt slightly smaller. I'm going to rig something and reduce the diameter of the bolt about .0015" so I can coat it with something. Just from eyeballing the lugs and the lug raceways on my action, I think the lugs are also going to require a little work to accommodate a coating.

Surgeon actions are made with consideration for Cerakote. I also have one of those. The bolt on a Surgeon action has a .005" step on it. It is a lot tighter when closed than when being cycled. The lugs and the lug raceway have enough clearance for a double layer of coating.

 

[Canadian Bushman]

BAT says HR and VR actions have .0025" clearance and their benchrest actions have .0015" clearance. I have an HR action. I don't have gauges to do a proper measuring job but with the gauges I have it appears to be right at the 2.5 spec. I wish I had a good way to turn the bolt slightly smaller. I'm going to rig something and reduce the diameter of the bolt about .0015" so I can coat it with something. Just from eyeballing the lugs and the lug raceways on my action, I think the lugs are also going to require a little work to accommodate a coating.

I had my bolt coated with TiAlN for that exact reason. It grew aprx .00015-.0002 on the diameter after the treatment.

 

[Edd]

I had my bolt coated with TiAlN for that exact reason. It grew aprx .00015-.0002 on the diameter after the treatment.

I'm wanting to have my bolt and receiver coated with NP3. They told me the coating would be about .0003" thick on each surface. That would consume half of the clearance I currently have. I don't want it that tight.

 

[bigngreen]

The best way to take cleance out of a Remington is to cerakote it IMO, I avoid Kiff bolt like the plague, saw two more bad bolts machined so out of whack it was crazy!! I've also seen bolts lock up from heat but it was not the bolt expanding it was the bolt bending because of poor heat treat, you could have it measuring straight and just pooring hot water on it would make it move.

 

[Edd]

... I've also seen bolts lock up from heat but it was not the bolt expanding it was the bolt bending because of poor heat treat, you could have it measuring straight and just pooring hot water on it would make it move.

Maybe that is what was happening to Joels receiver. Maybe it was becoming curved when heated.

 

[Canadian Bushman]

I think edd is trying to coat his bolt and not encroach his already tight clearance, unless i misunderstood.

I guess i got lucky wit my PTG bolt, it was cut pretty square and true. A little fitting and it ran just as good as the factory bolt. With .007" less clearance im getting better accuracy out of the rifle, and i can eject br cases.

What kind of bolt was it that was warping from hot water?

 

[Sully2]

Nope, a ring grows when heated. The circumference of the ID and the OD both get longer.

Not metal rings! I spent too many years doing stack-ups on jet engine hardware to assume that BOTH the ID and the OD grow larger