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Old February 17, 2013, 02:45 PM   #26
Picher
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Bart: I know all that, but also have had many years experience accurizing rifles and found what I wrote to be true. Pressure points can reduce amplitude of barrel vibrations, causing different bullet weights and loads to shoot closer to the same POI. As I mentioned, all of my rifles are free-floated, except for my 10-22, which needs a pressure point to keep the rear of the receiver in firm contact with the bedding.

Incidentally, that rifle shot 10 consecutive 5-shot groups on one sheet of paper, averaging .37". There aren't many of those that will do that.
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Old February 17, 2013, 07:08 PM   #27
reynolds357
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Pincher. I actually saw a 10-22 that had the action floated and the barrel full length bedded with no release agent. It also had the barrel bolted to the stock in two places. It also happened to be the most accurate 10-22 I have ever seen. It was also in a custom stock that was basically a piece of aluminum. A 10-22 is a very weak action relative to the huge bull barrel that this rifle had on it.

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Old February 17, 2013, 07:29 PM   #28
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I've got news for you, but benchrest rifles aren't worth a s^#t while NOT on the bench

I have never read such a in-accurate statement in my life. I have 3 bench rifles,One which i take Yote hunting along with my 223 for those 600 yard and farther shots. This rifle is not in a bench while I am Yote hunting. Granted it is in a Rest of some sort (just the front) as it does weigh in at over 14 lbs.

I give your statement half credibility only due to the fact that free handing with a bench rifle would be very tough or the person would have to have increadible upper body strength. Accuracy from a bench rifle does not come from sitting on a rest buddy it comes from the rifle it self
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Old February 17, 2013, 09:49 PM   #29
Bart B.
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Picher, if pressure points can reduce amplitude of barrel vibrations, causing different bullet weights and loads to shoot closer to the same POI, that's interesting. I've never heard of this before.

How did you measure barrel vibration amplitudes to see they were made smaller?

How much closer do different loads shoot to each other with pressure points on the barrel?

Do several loads shoot within 1/2 MOA of each other at 100 yards?

And how do you keep the pressure at each point on the barrel the same force in all shooting positions?
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Old February 18, 2013, 12:55 PM   #30
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Pic shows a page of five, consecutive 5-shot groups fired with a Remington Model 700 VLS .308 Win some time ago. The rifle has the laminated stock and 24-in. varmint weight barrel. The stock trigger is crisp. I had bedded the action with Brownell's Acra-Glas Gel and floated the barrel. The gun would not break 1 MOA before bedding but now occasionally gives 0.5" or less with handloads using the Sierra 168-gr MatchKing or the Nosler J4. I am pretty satisfied with it.
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Old February 18, 2013, 03:25 PM   #31
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There are very few 100%'s when it comes to accuracy, but I feel if the action is bedded "properly", you'll generally get better accuracy with a fully floating barrel. I see pressure points on barrels as more of a cruch for flimsy synthetic stocks or mass produced rifles will less than steller bedding.
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Old February 18, 2013, 03:47 PM   #32
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McShooty, why is group 3 to the right and down a bit from 1 and 2?
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Old February 19, 2013, 10:38 AM   #33
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Quote:
Pincher. I actually saw a 10-22 that had the action floated and the barrel full length bedded with no release agent. It also had the barrel bolted to the stock in two places. It also happened to be the most accurate 10-22 I have ever seen. It was also in a custom stock that was basically a piece of aluminum. A 10-22 is a very weak action relative to the huge bull barrel that this rifle had on it.
That was another pretty good method used by several people, but it fails to stabilize the weak receiver and trigger group. Pulling the trigger can actually bend the action a bit, moving the scope slightly and causing shots to deviate a bit. If a person pulls the trigger exactly the same each time, or if the trigger is extremely light, it's not as much of a problem.

The other thing that the method doesn't do is to provide a bedded trigger guard, which I do. The bedded trigger guard helps provide a bit more consistent hammer energy, especially if trigger pins are at all loose in the trigger mechanism and/or receiver.

The other situation is that barrels tend to lengthen as they heat up, and barrels bolted down in two places can cause the POI to drop, as they tend to bend between screws. Barrels fastened that way can bend more on top than underneath, but such vertical dispersion may only be noticed by shooting benchrest with good technique and using high-quality ammo. Sun warming may be more of a factor than normal target shooting of bull barrels.
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Old February 19, 2013, 11:02 AM   #34
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Quote:
Picher, if pressure points can reduce amplitude of barrel vibrations, causing different bullet weights and loads to shoot closer to the same POI, that's interesting. I've never heard of this before.
If one were to hold a ruler down on the edge of a table with about 9 inches hanging over and stroked the ruler, it will vibrate with greater amplitude and lower frequency than if only about 6 inches hangs over. The sound will also be in a lower key.

Therefore, a barrel will vibrate with less vertical amplitude (but higher frequency) if there is a pressure point with adequate force within the barrel channel. Since the greater barrel vibration amplitude is in the vertical, doesn't it make sense that vertical dispersion will be less when shooting different bullet weights and velocities?

Longitudinal position of the pressure pad within the barrel channel is also a factor in tuning a rifle for best groups.

Again, I still think barrels should be free-floated for most consistency of POI and rest options. Single screw actions are the most common instance for my use of pressure pads, but an older CZ Varmint shot better with one, after eliminating the barrel stud screw.
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Old February 22, 2013, 01:25 PM   #35
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Bart B: It is too long ago for me to remember the details of that day, but I suspect I may have adjusted the scope (B&L Elite 4000 6-24x) a couple clicks between groups two and three. When I saw the rifle was having a good day I probably wanted to see if I could get a good group centered in the bull. Too much of a perfectionist sometimes.
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Old February 22, 2013, 01:38 PM   #36
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I should add that the fifth group used exactly the same load, but with Sierra MK bullets from a different lot, and the group fell to the right. This is an indication of how sensitive group performance is to load conditions. I shoot for groups and I don't shoot in competition but I am sure those who shoot for score take this sort of thing very seriously when preparing for matches.
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Old February 23, 2013, 10:13 AM   #37
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Picher, you're not comparing two similar things in your ruler length to pressure point comments. But a pressure point on a barrel will indeed change the vibration characteristics although the fundamental frequency of the barrel and its harmonics remain constant although the amplitude will change.

The barrel's in a free-fixed holding condition when in a receiver and has a different fundamental frequency than a free-free one that's not fixed at one end. A pressure point on a free-free barrel will have a greater effect than on a fixed-free barrel.
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