Assuming a properly chambered barrel, a blueprinted action (lug faces, threads, receiver face) and a trued bolt (bolt face, bolt nose, lugs), how much affect is the slop in the bolt tolerance on accuracy? We're building a rifle that we'd like to be sub MOA if possible. I measure the bolt body to be 0.696". I haven't mic'd the action yet, but for the sake of the question we'll assume 0.700. If the lug faces on both bolt and action are trued properly, how much will the bolt slop affect things? Is sleeving a factory bolt worth it, and what are the downsides - Im assuming that the tolerance helps when the rifle faces "bush conditions" (grime and dirt, temperature fluctuation, etc.)
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Bolt Body to Action Tolerance > Affect on accuracy?
- Thread starter mikemaat
- Start date
- Replies 13
- Views 10,490
paracongo308
Banned
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- Jan 16, 2014
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- Green Lane, Pa.
If your referring to a Remington 700 receiver, they will measure .702+ inside. I had a factory Rem. 700 308 Win. That would shoot on average .680 groups with factory Federal medal ammo and with handloads for the 1st 1,500 rounds before the group's started opening up. When I pulled that barrel after 3,000+ rounds on it and checking the dimensions the receiver tenon threads were out of concentrity with raceway .005 (.010 tir) the face was out .002 out of square, and the inside lug abutment was out .002 the bolt to raceway clearance was .006 so don't believe if the receiver dimensions are cockeyed that the gun will not shoot. 90% of the accuracy is attributed to the quality of the barrel. After the barrel was removed the receiver dimensions were machined pirpundicular & square I installed a PTG bolt running .003 clearance and a Bartlein 6.5 cal barrel was installed and chambered in 260 Ackley.
Paracongo is quite right. The projectile is pushed through the barrel by a column of expanding gas. That gas does not care about any mechanical details. Any irregularity of the breech is accommodated by the case which conforms to it due to the gas pressure.
Many years ago the American Rifleman had a article on barrel erosion which cited a test done by Springfield arsenal. They had fired an astounding number of rounds through 2 groove Springfield barrels to determine the effects of erosion on accuracy. Much like Paracongo's barrel above, there was a slight deterioration after a thousand or so. The accuracy remained serviceable until the erosion was within a few inches of the muzzle, which would indicate that the last few inches are where your accuracy lies. Those last few inches are the last part of the rifle to have an effect on the bullet. I suspect cleaning from the muzzle end has way more deleterious effects than any supposed irregularity of the breech end.
Many years ago the American Rifleman had a article on barrel erosion which cited a test done by Springfield arsenal. They had fired an astounding number of rounds through 2 groove Springfield barrels to determine the effects of erosion on accuracy. Much like Paracongo's barrel above, there was a slight deterioration after a thousand or so. The accuracy remained serviceable until the erosion was within a few inches of the muzzle, which would indicate that the last few inches are where your accuracy lies. Those last few inches are the last part of the rifle to have an effect on the bullet. I suspect cleaning from the muzzle end has way more deleterious effects than any supposed irregularity of the breech end.
glbreil
Cast Iron
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- Feb 10, 2008
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I think it all depends on the level of accuracy that you are trying to attain. It would not do you any good to go to a benchrest match with a rife that would shoot .680" groups.
With that said I think that concentricity has more to do with accuracy than the bolt body tolerance does. But then again a benchrest shooter would want it a tight as possible with no play what so ever because they can see a difference on the target,but for sub MOA it probably doesn't matter and a nicely fit quality barrel would do it for you.
Gary
With that said I think that concentricity has more to do with accuracy than the bolt body tolerance does. But then again a benchrest shooter would want it a tight as possible with no play what so ever because they can see a difference on the target,but for sub MOA it probably doesn't matter and a nicely fit quality barrel would do it for you.
Gary
Spyderedge
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Let it be. If it's problematic, you can redo it later.
There is a tale of a hunter who went up to Alaska (Or other cold region), got the best animal he's ever seen in his sights....applies pressure.....and nada. He has his trigger overtravel stop set for warm conditions, the cold trigger changed dimension and was not able to function properly.
.004" ID/OD slop looks bad, but over 3-4" of action it's really very little play. And the angle change on the bolt face would be around half a thou. Much more deviation in the brass itself.
Maybe you could add small brass tipped screws, and have a similar setup to a K.O. Lee air bearing (with those graphite pads)
There is a tale of a hunter who went up to Alaska (Or other cold region), got the best animal he's ever seen in his sights....applies pressure.....and nada. He has his trigger overtravel stop set for warm conditions, the cold trigger changed dimension and was not able to function properly.
.004" ID/OD slop looks bad, but over 3-4" of action it's really very little play. And the angle change on the bolt face would be around half a thou. Much more deviation in the brass itself.
Maybe you could add small brass tipped screws, and have a similar setup to a K.O. Lee air bearing (with those graphite pads)
paracongo308
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And you never mentioned what the average group size this rifle is currently shooting? If you take your barrel off and the receiver threads were out .004-.005 and you decided to recur them you will either have to cut the existing barrel tenon of and start again to fit your new receiver threads. Or you might want to install a new barrel. All the receivers I make have .003 bolt clearance and use PTG bolts. If you are going to build a custom rifle your better off buying a new receiver such as a Stiller, Borden etc. and start from there.
On military bolt rifles, the bolt is often rather loose. I have a 7mm Chilean Mauser with a close fit bolt and a 6.5mm Swedish Mauser were the bolt has more clarence. Both rebuild with good new barrels, triggers, lapped faces, etc. Hand-loaded rounds. The Swedish is more accurate (at 300 yards). Obviously there are other factors that are more critical.
".004" ID/OD slop looks bad, but over 3-4" of action it's really very little play. And the angle change on the bolt face would be around half a thou. Much more deviation in the brass itself."
And with the bolt closed and a cartridge in the chamber it is practically nonexistant. If you are really after that last gnat's ass then you would be neck sizing your cases and they would be virtually a perfect fit in the chamber.
And with the bolt closed and a cartridge in the chamber it is practically nonexistant. If you are really after that last gnat's ass then you would be neck sizing your cases and they would be virtually a perfect fit in the chamber.
As well keep in mind that with a close fit, any dirt or grit will making closing difficult or impossible. This was the sad lessons in WW1 with the very accurately made Canadian .303 Ross. I had a pristine condition Ross, probably never issued. The bolt (straight pull)fit was as close as a spindle in a machine tool.
300sniper
Hot Rolled
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- Nov 14, 2006
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- Greenwood, Ca
My personal 700 match rifle has a sloppy .007" clearance between the bolt body and receiver bore. It shoots great and do not feel I would see any accuracy improvement by tightening that clearance up.
If it were a bench use only rifle and I was trying to remove every last variable, then I'd probably have a different opinion.
If it were a bench use only rifle and I was trying to remove every last variable, then I'd probably have a different opinion.
hanermo
Titanium
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- Sep 28, 2009
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Fwiw..
I went back to the air force for compulsory re-training 5 times (conscription in Finland, voluntary special forces like us had special rules).
We shot the local "RK62", 7.62 assault rifles.
Its an upgraded, H&K quality Finnish made version of an AK47.
Its the most accurate AK-type-version in the world.
Last time, prone 150 m (==170 y).
93 /100 first time.
92 /second time.
I was first / 150 men first time, second/150 second time.
The rifle was made in 1968.
Group was about 12 cm or so.
On iron sights.
I went back to the air force for compulsory re-training 5 times (conscription in Finland, voluntary special forces like us had special rules).
We shot the local "RK62", 7.62 assault rifles.
Its an upgraded, H&K quality Finnish made version of an AK47.
Its the most accurate AK-type-version in the world.
Last time, prone 150 m (==170 y).
93 /100 first time.
92 /second time.
I was first / 150 men first time, second/150 second time.
The rifle was made in 1968.
Group was about 12 cm or so.
On iron sights.
This will be with a brand new chambered barrel, so current average group is moot. We have a rem 700 donor action already in hand and trying to see how accurate of a gun we can make without going with a custom action.
Thanks to everyone for all the replies, they answered my questions perfectly. On this rifle we will leave the bolt raceway alone and just square up the faces and threads. Cheers!
Alpacca Fortyfive
Stainless
- Joined
- Nov 16, 2007
- Location
- Leinster, Ireland
Have you read Vaughn, rifle accuracy facts?
About the only way that bolt body to rcvr bore fit affects accuracy, is if the uplift of the rear of the bolt due to the pressure of the cocking piece on the sear, lifts the top lug off its seat.
When you fire, the lug hitting the seat, adds to barrel vibrations.
There's a name for small bumps dovetailed or stuck to the rear of the bolt, to prevent it from tilting up due to the force of the cocking piece.
A name I can't recall...
Beyond that, go as tight or loose as you like. A commercial 700 receiver ring has bedding screw, scope mount and superfluous vent holes, all of which cause aesymetric stretching and barrel vibrations, as does the recoil lug that is aesymetric to the centreline.
Group size is controlled by the root mean square of all of the upsetting factors, so each individual factor that you correct, makes a relatively small contribution to reduced group size.
Hence competitive bench rest smiths using actions that are built from scratch to be straight and true, rather than messing around to true up mass produced actions.
About the only way that bolt body to rcvr bore fit affects accuracy, is if the uplift of the rear of the bolt due to the pressure of the cocking piece on the sear, lifts the top lug off its seat.
When you fire, the lug hitting the seat, adds to barrel vibrations.
There's a name for small bumps dovetailed or stuck to the rear of the bolt, to prevent it from tilting up due to the force of the cocking piece.
A name I can't recall...
Beyond that, go as tight or loose as you like. A commercial 700 receiver ring has bedding screw, scope mount and superfluous vent holes, all of which cause aesymetric stretching and barrel vibrations, as does the recoil lug that is aesymetric to the centreline.
Group size is controlled by the root mean square of all of the upsetting factors, so each individual factor that you correct, makes a relatively small contribution to reduced group size.
Hence competitive bench rest smiths using actions that are built from scratch to be straight and true, rather than messing around to true up mass produced actions.
JMO...What Gary said above.
You're going down a road that's unnecessary. Bolt lift is typically one of the smallest factors affecting accuracy- and you're looking for no better than OEM, off-the-shelf accuracy.
No herculean efforts need be taken here. A $300 Ruger American will shoot sub-minute off the shelf. Any quality match barrel, correctly chambered and fit to the action with just the basic "requirements" met (good trigger, stock fit/bedding/recoil block/etc., will shoot under a minute with match ammo- no blueprinting required.
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