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A gun question: in a recent post there was mention of a torque or twisting of a high power rifle action. I am not familiar with

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  • #16
    Phw - Affirmative. And that is the reason that Smith&Wesson pinned their barrels to the frame, up until about 1982, when they developed a crush fit so the barrels could not unscrew.
    Colt pistol barrels had a right-hand twist and did not have this problem.

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    • #17
      I hope the crush collar was on the barrel and not on the receiver?

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      • #18
        jimbo - The Winchester Model 70 Owner's Manual specifies that the two action screws should be torqued to 35 inch pounds. The manual doesn't mention it, but I think the middle screw is to be tightened last, though not as snugly.

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        • #19
          Phw - "Crush fit" means that the threads are over-tightened to the point of "crushing," thus eliminating the need for a pin.

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          • #20
            Holy smokes, makes more sense. I was wondering how they got such a large piece of technology in such a small area.

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            • #21
              Funny and you guys say nothing about soft nose bullets in hunting. On my ’06 the tiny soft none is slightly deformed on feeding from the magazine. Creates Just a small flat area on one side. On longer ranges, that deformity catches air and increases the size of the bullet rotation and the center line it rotates around. So every round flies slightly different. The longer the distance the bigger the arc. Why is that important? That has a whole lot more effect on accuracy downrange than bullet torque going down the barrel.

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              • #22
                99,
                Check this out. Tightening stock screws. 50 to 55 lbs.inch.

                www.weatherby.com/support/faq/item/view/44349

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                • #23
                  Rocky,
                  If I find a deformed tip I just take a file and smooth it over. For hunting ammo I use protected tip bullets or lately the polymer tipped bullets.

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                  • #24
                    chuckles, many thanks for verifying that for us! As Barnaby said, the heavier the projectile, and the faster the acceleration, the higher the torque. The .458 is a pretty good test of that theory but of course the recoil force is still much higher than the rotational force.

                    Regarding the effect of this torque on actually twisting the receiver... this twisting force ("torque") is definitely applied to the receiver. The question is, "Is it sufficient enough force to cause impact to the accuracy of the bullet?"

                    There is debate on that but I can tell you that bench rest receiver manufacturers do everything they can to solidify the receiver so that it cannot twist. They have reduced the size of the ejection port, eliminated the magazine port underneath and enclosed the entire top of the receiver in order to add strength to resist this rotational force (or it may be a marketing ploy because that seems to be what the shooters feel they need. Of course this is in an application where rapid repetition of fire is not important but .001" in accuracy IS.

                    The Mauser style receivers were specifically designed to reduce the effect of both recoil and torque with their large flat base and large integral recoil lug. They did that effectively but they were just more expensive to manufacture than the tubular steel style receivers that are so common today.

                    In my long range rifle, I’ve done a lot of things to make it behave a little more like a drill press. I’d say the top 10 are:

                    1. It has a 6.5 pound barrel to reduce sine wave vibration and rotational torque due to the rapidly accelerated heavy (215g @ 3250 fps) bullet. Heavier barrels are better and some shooters use 15-25 pound barrels, but mine is for hunting and I still have to be able to carry it. It does not have barrel fluting to aid in the consistency of its response to torque. The total rifle with scope comes in at 12 pounds. If Chuckles added about 10 pounds to his barrel it would feel much better when he shoots it sans stock.

                    2. I’ve done my best to ensure 100% perfect alignment of my chamber to the bore to eliminate bullet deformation as it slams into the lands (more on the effect of bullet deformity in my answer to Rocky below).
                    3. I use a very high tensile strength (original M98 Mauser) with the flat base/large integral recoil lug to resist movement from both the forces of torque and recoil. It is perfectly glass/pillar bedded within the stock to reduce or eliminate movement due to these forces. The pillar bedding allows me to apply the highest possible torque to the screws without crushing the stock. This provides a real tight and consistent fit of the receiver into the stock. My personal theory is that rotational force is not sufficient to require a special bench rest receiver as long as you hold the receiver in place effectively. I can also benefit from the receiver openings needed for hunting with minimal effect on accuracy.

                    4. I test numerous powders, charges, primers and bullets to find the specific acceleration and velocities that are harmonic with my barrel and receiver vibration/torque so that the bullet exits the barrel at the same clock position every time (e.g. 12:00). This takes a lot of load testing but when you achieve the Holy Grail, groups size comes way down.

                    5. I test multiple harmonic velocities and chose the lowest velocity that produces accuracy to reduce the forces of recoil and torque and thereby improve shot to shot consistency. It also reduces barrel motion during the acceleration of the bullet down the barrel, improving consistency.

                    6. I use highly accurate bullets; weigh every case, every bullet, and every charge for consistency.

                    7. I use a unique cartridge (.300 Dakota) that has a case designed for consistent pressure from shot-to-shot (like the 6PPC).

                    8. I trim the length, turn the necks and debur the flash holes at least every couple shots in every case to aid in consistent pressure from shot-to-shot.

                    9. I perfect the cases. I anneal cases every couple shots to avoid cracked necks that could reduce pressure during a specific shot. It also makes the cases last longer. I neck size all fire-formed cases to eliminate variance in pressure as the brass is pushed out to the chamber walls.

                    10. I test bullet seating depth to find the most accurate depth for each specific load. I rotate the cartridge as I advance the ram in my seating die to improve bullet concentricity. I measure the overall length of every cartridge to ensure it is consistent.

                    While I don’t consider this a secret to success, I would also note that I only pass around pictures of my better groups. All those 4” groups I’ve shot while working up loads usually don’t get pictures.

                    I know this is a long post but thought it might be of interest to those aspiring to be more accurate at long range.

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                    • #25
                      Rocky, you are very right that deformed bullets cause inaccuracy at long ranges. Although they DO cause a little more turbulence at the tip, the primary physical force that sends them off target is “angular momentum” or the gyroscopic force that keeps a top spinning.

                      Upon its exit from the muzzle, a bullet may be rotating at approximately 250,000 revolutions per minute. It is rotating on the center of the bore’s axis and that gyroscopic force will keep it in line with the bore exceptionally well for at least a couple hundred yards.

                      At about 250 yards or more, the bullet transitions from rotating on the axis of the bore to rotating on its own “center of mass”. If the projectile is not PERFECTLY concentric, this transition will cause a bullet wobble that may even be serious enough to de-stabilize a very long VLD type bullet. This is why hollow point and polymer tipped bullets have been so successful for long range shooting. They really have helped in the tip deformity issue as it applies to long range shooting.

                      This is also why PERFECT chamber alignment with the bore is so important in long range shooting. If the chamber is even microscopically out of line with the bore, the bullet will be slightly deformed as it hits the rifling. The lands may gouge a little deeper groove on one side over the other or in extreme cases; the lead core in the bullet may be slightly “squashed” (to use a technical term).

                      I always do my best to see that chambers are perfectly aligned for long range shooting. I often use lead tipped bullets for hunting out to 250 yards though because of their relatively low cost and excellent high speed penetration / expansion. They typically don’t fragment at high speed nearly as much as most other tip styles. I may file them to improve concentricity if they get really deformed but I don’t worry much about them knowing that gyroscopic force holds them within a hundredth of an inch or so of the aim point at 100 yards. However, if I expect shots to reach out beyond 300 yards, I prefer polymer tipped bullets or hollow points that are designed for large game hunting.

                      I would also note that this transition to center of mass is an important reason that normal hunting bullets don't work well for long range shooting. Most such bullets are just not made to be so concentric. That is why some good long range VLD bullets can hit a Coke can at 1000 yards consistently while most hunting bullets would have trouble hitting a dump truck at that range.

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