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Very Hot Topic (More than 25 Replies) Vertical stringing.....education needed. (Read 1748 times)
JS47
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Re: Vertical stringing.....education needed.
Reply #15 - Apr 12th, 2019 at 8:29pm
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I'm no expert but I have figured out a few things that work for me. I'm shooting a couple of CPA's, a 52 and a 49. I don't use a sled which means that the rifles are pretty tippy on the bench so free recoil has never worked for me. The muzzle position on the bag seems to be pretty important so I have the sweet spot marked on the barrel with a felt tipped marker. It's also written in my note book. Once I have the sweet spot figured out for the load what always gives me vertical problems is inconsistent shoulder pressure. The method that works best for me is to slide the rifle forward on the bags with my shoulder until the sights are on the the point of aim when the sweet spot is on the mark. I fine tune it with a minor amount of bag squeezing while trying to maintain the same shoulder pressure. Using a bench rest stock instead of an offhand one would eliminate a lot of my problems. Wind can also give a lot of vertical stringing. I didn't realize that until I watched it happen to others as well as myself.

JS
  

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RSW
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Re: Vertical stringing.....education needed.
Reply #16 - Apr 12th, 2019 at 9:13pm
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SBoomer
From the pic you posted of your muzzle rest, it looks like the feet sit on a metal surface. You might consider a 1/4 or 1/2 inch thick Delrin slab cut to fit your bench rest top. Perhaps even an 1/8 inch rubber sheet between the Delrin and bench rest top. A muzzle rest on a hard surface can get some unpredictable bounce from that hard surface, effecting bullet impact point. The Delirn and/or rubber sheet help deaden the surface to eliminate bounce.
  

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JerryH
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Re: Vertical stringing.....education needed.
Reply #17 - Apr 12th, 2019 at 9:21pm
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Inconsistent ignition will string shots also. A broken, dragging, or short firing pin can cause it.

I need to remove the firing pin from my CPA on occasion to clean out any accumulation of brass dust scraped off the primer by the breechblock. Not so much of a problem once I changed to CCI BR-4 primers.

JerryH
  

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JLouis
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Re: Vertical stringing.....education needed.
Reply #18 - Apr 13th, 2019 at 9:36am
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Agree with RSW metal on metal creates allot of undesirable issues all of their own. And then there are the multitude of others that only a process of elimination can sort out with allot of time and effort being spent sending bullets down range. Having a setup that allows you to become 100% relaxed and a 100% comfortable behind the rifle is the first place one needs to start.
  
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Dellet
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Re: Vertical stringing.....education needed.
Reply #19 - Apr 13th, 2019 at 10:06am
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One thing that has helped me, is to keep my thumb on the same side of the rifle as my trigger finger.

This forces a straight press into the trigger, instead of more of a pulling motion towards the thumb through the wrist of the stock by engaging the thumb muscles.


  
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SBoomer
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Re: Vertical stringing.....education needed.
Reply #20 - Apr 13th, 2019 at 10:56am
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If I can ever get this vertical minimized, she wants to shoot. I added 1/8 cork between the rest and sled. I chrono'd Accurate 5744 loads this morning and continued to shoot this string as it was shaping up nicely. The first 4 shots cut the ragged hole with the 5th at 9:30. Very gusty.
  
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joeb33050
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Re: Vertical stringing.....education needed.
Reply #21 - Apr 13th, 2019 at 2:12pm
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JerryH wrote on Apr 12th, 2019 at 9:21pm:
Inconsistent ignition will string shots also. A broken, dragging, or short firing pin can cause it.

PRIMER TESTS
C. Dell

"I have been told many times down through the years that if a gun has a light hammer fall the groups fired with that gun will string up and down. I had always assumed that this was true as the persons reporting this effect were very respected men who had done a lot of really serious shooting.
Back before the primer shortage developed, I had made a test rig to test primers all by themselves (a standalone test of primers). Basically, I was able to hit primers with a very repeatable force and was determining how much force it took to reliably fire them as well as the velocity that they would impart to a specially made pellet. Results were determined by measuring the velocity of the pellets about fifteen feet from the muzzle of the test rig.
This testing was discontinued when the supply of the desired primers for testing dried up.
These tests have not at this time been resumed. Two observations were, however, made from the data collected at that time. One: the observed average velocities were not affected by how hard the primer was hit. Second: about one primer in five regardless of make or grade was to a noticeable amount deviant from the group average. This took the form of either being significantly higher OR lower in velocity than the average.
These properties were discussed with various shooters during the time that supplies of the various primers were not available. I was often asked if the same results would be observed if I were actually shooting cartridges loaded with powder and bullet. There was at that time no practical way that I could test this idea. As a result, the question was left hanging with no real answer.
Recently a method was conceived that would readily permit study of this as well as other questions. I had a spare Douglas 32-40-barrel blank with a 1-12-inch twist that could be devoted to a test program. A breech system was devised that would permit various firing pin impacts on the primer to be studied. It is not a fast system but permits one shot to be fired about every two minutes. Bullets are weighed, lubricated and swaged so that they are as uniform as can practically be made. All of the shots in the test were fired from my rail gun at a range of 100 yards. This test was designed to equate obtained accuracy with primer impact.
It was determined that six five shot groups under three different striker impact forces would be studied. The cartridge case was my 32-357 Magnum which was developed back in about 1971 but not really used until about 1993 when I received a barrel blank from Ken Bresein that was cut with Pope style rifling. It is the cartridge that my current competition gun is chambered for. The bullet is a 200-grain basic bullet from a Colorado Shooter's Supply mold. the bullet is subsequently lubricated and swaged before shooting. The swage is one of my own design and build. The powder charge for this test is 8.1 grains of Accurate Arms #7. Primers for this test were the Remington 7 1/2. One cartridge case was used for all shooting in this test. Powder charges were cast from a Redding M 3 BR powder measure and not individually weighed. Groups were evaluated by two methods, extreme spread of the two widest bullet holes and by the mean radius concept which studies all of the shots in the group.
In studying the velocity of all the shots fired on the record groups it was interesting to observe that about one shot in five was deviant from the group average by more than five feet per second. As most groups did not have an extreme velocity spread of more than ten feet per second this was considered significant. The deviance occurred both ways from the average velocity of the group. Some deviant shots measured a low velocity and others a high velocity. When more than one deviant shot occurred within a given group of five shots it would raise or lower the group average. Because of this, all comparisons were to the overall average velocity as all shots were fired under basically the same conditions of loading, temperature and load.
I will report the average velocities of each of the 30 shot study groups and the final
average velocity for the total 90 shots of the test.
In a similar manner I will report the average velocity spread within each set, the average
standard deviation, the average extreme spread and the average mean radius. All averages taken on six five round groups.
     Phase I      Phase II      Phase III      
     Light      Moderate      Heavy      Average
     Impact      Impact      Impact      Overall
Average Vel. (fps)      1227      1227      1228      1227
Avg. Velocity Spread (fps)      8      9      11      9
Avg. Vel. Std. Dev. (fps)      4      3      4      4
Avg. Extreme Group Spread (")      0.695      0.700      0.750      0.720
Avg. Mean Radius (")      0.281      0.252      0.276      0.270
This I believe shows beyond any reasonable doubt that accuracy is not affected one way or another by the force of the firing blow. If the primer goes off it goes off and the amount of energy transmitted to the powder is not affected by the impact energy of the firing pin. Even those primers that had to be hit twice in order to initiate ignition showed no difference from those that went off on initial impact.
While I believe that this eliminates one source of alibis for groups that are strung out up and down, it is one less thing that we as shooters of various old and new guns have to be concerned about. After completing this series of tests, I can say without hesitation that accuracy is in no way affected by the force of the firing pin impact on the primer."



I need to remove the firing pin from my CPA on occasion to clean out any accumulation of brass dust scraped off the primer by the breechblock. Not so much of a problem once I changed to CCI BR-4 primers.

JerryH

  
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Nero
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Re: Vertical stringing.....education needed.
Reply #22 - Apr 13th, 2019 at 4:31pm
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I am hesitating to put my two cents worth in here after reading your interesting post on primers but after spending so much time on the preparation that you did not weigh all charges.
  
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Re: Vertical stringing.....education needed.
Reply #23 - Apr 13th, 2019 at 6:56pm
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Oops, I meant to post this pic and details to this discussion but added it to the 25/20 Wads thread. Making progress on reducing vertical spread. Lots more shooting tomorrow.
  
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John in PA
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Re: Vertical stringing.....education needed.
Reply #24 - Apr 15th, 2019 at 12:28pm
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I remember reading many years ago about locating barrel vibration nodes.  Secure action in a padded vise, hang u-shaped wires along the barrel every couple inches or so, and tap the muzzle with a lead, copper, or other non-marring hammer.  Wires will migrate along the barrel to bunch at the nodes.  I'm *guessing* that the sweet spot to rest would be at one of the nodes.

Comments on theory or refining the procedure?
  

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JS47
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Re: Vertical stringing.....education needed.
Reply #25 - Apr 15th, 2019 at 9:33pm
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I've tried what you suggest about finding the node or dead spot on the barrel and it has corresponded within a fraction of an inch of the location of the sweet spot to rest the barrel. It may vary a  little depending on the load. This is the case with two 22rf barrels and one 32-20.

JS
  

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texasmac
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Re: Vertical stringing.....education needed.
Reply #26 - Apr 16th, 2019 at 12:45am
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In response to JerryH's posting of C. Dell's primer impact conclusions I offer the following.  In a BPCR silhouette match this past weekend I shot with an experienced shooter that was using a Sharps 1874 #1 Sporter in .45-70.  In a 40 round match he typically turns in AAA or master scores (26 to 31 out of a possible 40 - keep in mind that the chickens are shot off hand at 200 meters so hitting 4 or 5 is considered excellent and no one has every shot a 40 that I know of).

Anyway, he had a terrible day, ended up with a total score of 14 which was the lowest score of all the shooters by far.  He had no idea what was going on.  All the misses were high or low and all cartridges fired with no apparent problems.  After returning home he disassembled the receiver and found a broken firing pin.  This is clearly an example of very poor accuracy (significant vertical dispersion) due to inconsistent primer striking energy.

BTW, this is not a rare occurrence.  Other BPCR shooters with broken firing pins have reported similar results.

Wayne

« Last Edit: Apr 16th, 2019 at 1:04am by texasmac »  

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Re: Vertical stringing.....education needed.
Reply #27 - Apr 16th, 2019 at 1:05am
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texasmac wrote on Apr 16th, 2019 at 12:45am:
In response to JerryH's primer impact conclusions I offer the following.  In a BPCR silhouette match this past weekend I shot with an experienced shooter that was using a Sharps 1874 #1 Sporter in .45-70.  In a 40 round match he typically turns in AAA or master scores (26 to 31 out of a possible 40 - keep in mind that the chickens are shot off hand at 200 meters so hitting 4 or 5 is considered excellent and no one has every shot a 40 that I know of).

Anyway, he had a terrible day, ended up with a total score of 14 which was the lowest score of all the shooters by far.  He had no idea what was going on.  All the misses were high or low and all cartridges fired with no apparent problems.  After returning home he disassembled the receiver and found a broken firing pin.  It's clearly an example of very poor accuracy (significant vertical dispersion) due to inconsistent primer striking energy.

BTW, this is not a rare occurrence.  Other BPCR shooters with broken firing pins have reported similar results.

Wayne


I would be interested to know if it is a due to a different energy level on striking, or more likely a longer or more erratic time between trigger pull and ignition.
  
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JerryH
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Re: Vertical stringing.....education needed.
Reply #28 - Apr 16th, 2019 at 1:40am
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JerryH wrote on Apr 12th, 2019 at 9:21pm:
Inconsistent ignition will string shots also. A broken, dragging, or short firing pin can cause it.

I need to remove the firing pin from my CPA on occasion to clean out any accumulation of brass dust scraped off the primer by the breechblock. Not so much of a problem once I changed to CCI BR-4 primers.

JerryH


Wayne (and everyone else),

The above is my original post. joeb33050 inserted Charlie Dell's primer test in the middle of my post trying to imply that what I posted was wrong. I have seen the same thing happen in BPCR Silhouette that Wayne described.

joeb33050,

I have no problem with you quoting my posts, but please do it in a way so it's clear what I posted and what you're adding to it. I would appreciate that courtesy.

JerryH
  

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joeb33050
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Re: Vertical stringing.....education needed.
Reply #29 - Apr 16th, 2019 at 5:19am
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Sorry, Jerry H, I'll be more careful in the future.
Wayne;
Until I see test results contrary to Charlie Dell's experimenting, every test I've done confirms that lighting the fire is a digital event-either it's lit or it's not. The force that a primer is hit with does NOT vary velocity.
Small vs Large primers don't affect accuracy.
Primer brand/model does not vary accuracy.
Rem LP primers, used religiously in my day, do not improve accuracy.
I've been looking for that magic primer for 50 years plus, never found it.

Harry Ricardo, in The High Speed Internal Combustion Engine, said that his testing found no difference in power with variation in spark voltage. It's either lit, or not.

I'd love to see test results that show me and Charlie to be wrong.
joe b.
  
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