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WHY is my first shot high?

Discussion in 'Handloading and Reloading' started by docsleepy, Apr 7, 2013.

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  1. docsleepy

    docsleepy Member

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    My "cold" first shot on a 7mm08 Savage is consistently 2" higher than the group that follows, beginning with the 2nd shot. It is very notable, as the groups (4 or 5 shots beginning with the 2nd shot) will be around 1".

    Handloads, 42 grains Varget, 120 grain spire point Sierra, if any of that is important. I'm using a Rock BR front rest, and leather rear bag, using a wooden shim around the rounded forearm so that the rifle slides just like my 6PPC benchrest gun, which achieves in the range of 3/8" groups. The action is bedded. The lug is precision.

    It is ALWAYS verticle stringing. The horizontal spread of all the shots is virtually always within 1". The first shot is just high.

    I've tried shooting it uncleaned.
    I've tried shooting it minimally cleaned.
    I've tried shooting it extensively cleaned and de-coppered.

    They are always high.

    I can go up or down 1 or 2 grains of powder and I don't get near that change in verticle point of impact.

    WHY? Can anyone give me a explanation for WHY that first shot is HIGH rather than LOW or RIGHT or LEFT?

    I have a Mosin Nagant that is now down to 1" groups and its first shot is dead on. My benchrest 6PPC with a Shilen stainless match barrel - first shot is identical to others. My AR15 and AR10 -- no difference in first shot.

    Any ideas?
     
  2. NeuseRvrRat

    NeuseRvrRat Member

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    it's not unusual for the cold bore shot to have a different POI
     
  3. docsleepy

    docsleepy Member

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    Here is a representative group, where the 1st shot was actually 3" high. In this case the outside temperature was 65 degrees and the rifle uncleaned. On a warmer day (75 F) with a decoppered bore, the first shot was more like 1.5" high. Statistically these might be identical.
     

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  4. docsleepy

    docsleepy Member

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    but why? why high? and not low? or right? or anything? All the other shots are grouped reasonably well. If it is powder, why doesn't the uncleaned bore shoot the same cold? If it is temperature, why don't the 3rd 4th and 5th shots move farther?
     
  5. MErl

    MErl Member

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    You say you tried cleaning or not and it didnt change this.
    How about a quick cleaning after every shot?
    Have you tried shooting a group and letting it sit untouched for an hour to get back to 'cold bore' temperatures? would it string again.

    A guess, something is shifting in transport and storage which gets reset on that first shot. A little imperfection in the bedding or scope mount, possibly even the scope itself? That is just a guess though, you probably know more about it than I do.
     
  6. docsleepy

    docsleepy Member

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    When I waited an hour, it shot at the top of the bottom group, but not nearly as high as the first shot. Your thought about something changing in transport is intriguing. I wondered about sharply banging the butt of the stock on my foot or the ground.
     
  7. docsleepy

    docsleepy Member

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    I could try a different scope.
     
  8. dvdcrr

    dvdcrr member

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    For safety I would never get in the practice of sharply banging a gun on the ground. One day if you forget a round in the chamber you could end up blowing your head off. What I would is sight in using a slow five shot group. Center that group on your point of aim and " draw a fine bead" always on your first shot unless its way out there then aim dead center. I know you are wondering why and I don't know why but if the overall group is small and well zeroed it doesnt matter especially if you practice a lot and know where your gun shoots. Also let a couple buddies shoot it and see if it does the same for them. It might not be the gun, maybe after the first shot you are snugging up tighter to the gun or something.
     
  9. kBob

    kBob Member

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    In a class I took from EJ Land, he warned that the first shot from a cold barrel will seldom go where the following shots go and had us shoot from cold bores several times. He insisted this was one of the reasons a good shooter keeps records in a journal, so you can predict this and take it into account when that first shot has to count.

    Oddly if a many times national champion and world famous sniper thinks this is a common event that one should take into account and I see it demonstrated time and again I tend to think it is normal

    Consider for a moment that many competitions allow for a "fouling shot" or two before the scored portion of the relay. What does that tell you?

    Any changes in condition can change POI. Dropping the rifle should cause one to expect a change in POI......and drop and give me fifty.... and one for Mom.....and one for the Ranger in the Big Blue Sky.....etc.

    -kBob
     
  10. Caliper_Mi

    Caliper_Mi Member

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    How are the rounds being fed into the chamber? Do you load all five into the mag and feed from there or single load?
     
  11. ironworkerwill

    ironworkerwill Member

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    You may be on the right track. I would suspect the scope first. However, just like barrel harmonics the scope will experience vibrations when shot. Also saying you get more vertical stringing from a cold bore with that load. I may just be a load development issue. I started using Re 17 in my 7mm-08 and have seen groups shrink. Using 45gns of H414 and 130 grn sie mkings and 2+'' to 45.2gns of Re17 and 160grn gkings with 1.25'' groups. I expected more recoil from the latter but seen it to be noticably milder. Go figure that one.
     
  12. drcook

    drcook Member

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    If you all watch the shows on the Military Channel that documents the US military's precision shooter (ie: sniper) contests, you would see that one of the competitions is the "cold bore" shoot.

    Military precision shooters are taught to find out where the cold bore shot goes, because that is typically what their first shot is.

    Having the first shot go into somewhere different is not a fault of the gun, nor of the scope, nor of the shooter. It is just a fact of life concerning metals and firearms.

    Even my BPCR rifles shooting lead cast bullets and black powder and weighing almost 15lbs due to their barrel size don't shoot the first shot where the rest of them go.
     
  13. Col. Plink

    Col. Plink Member

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    I think I can echo what's been said, mainly with respect to coldbore shots. They are largely unpredictable versus the following shots, but if you get predictable coldbore POI that's a good thing (predictable!).

    In terms of cleaning cylcles, a seasoned distance shooter described to me how many times shooters will never really isolate a problem with accuracy because they change more than one variable at a time.

    He recommends taking a log of performance from a cold, clean barrel going forward. As the initial fouling takes place, the groups will tighten-up until the fouling begins to force them back out again. The sweet spot lies somewhere in between a clean, cold barrel and an over-fouled one. You can conceivably do a light cleaning (no de-coppering) and keep the sweet spot longer, until the copper fouling starts to take over.

    Basically, if small variances in accuracy are really a problem, a full-process approach to logging shot info and cleaning frequency is the way to go.
     
  14. Float Pilot

    Float Pilot Member

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    1. try another scope as mentioned.

    2. Try only cold bore shots.

    3. Make sure the rounds in the magazine are not having their COL changed by the recoil. ( bullets being pushed in or out of the case slightly while banging around in the magazine)

    4. Try single load vs magazine load.

    5. CHECK THE TORQUE on your action screws.

    6. You might have a pressure point in your fore-arm channel of the stock that seats better after recoil or when it gets a little warmer. You can sometimes wedge a business card between the stock channel and barrel and get some interesting results.

    7. Remember that some powder is Temp sensitive and if a cartridge sits in a hot chamber for 10 seconds the powder is now a hundred or more degrees warmer than the first shot's powder.
     
  15. docsleepy

    docsleepy Member

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    Thanks guys for all these ideas!

    1. I always individually hand load each shot; I don't use the magazine.
    2. I have been keeping records for years. I started the "cold bore" records on this gun after the last work I did on it and picked this up.
    3. I think the barrel is not fully free floated -- I will work on that. THis may have a change during first/second shots due to mechanical changes.
    4. Just bugs me that my $130 Mosin Nagant does NOT have this problem.

    I'll report back.

    Thanks!
     
  16. The-Reaver

    The-Reaver Member

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    Dunno, aim two inches low when it counts
     
  17. nathan

    nathan Member

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    Locktite those mounting screws.
     
  18. Kachok

    Kachok Member

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    Had a similar glitch with a Savage, my brother somehow managed to twist the stock until it was pushing against the barrel, don't know how he did it but I shimmed some folded paper between then pushing the stock out and left it for a week, problem solved.
     
  19. chaser_2332

    chaser_2332 Member

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    It's just your cold bore, learn it and compensate for it. Some guns are worse than other. As long as its repeatable whats the problem. Adjust your scope for the cold bore then back for the following shots, shouldn't be an issue. Alot of matches have a cold bore shot for this very reason. It's all about knowing your rifle and scope.
     
  20. Andrew Leigh

    Andrew Leigh Member

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    Not discounting the effect of the cold bore throwing the first round off, one must not discount other possible causes.

    Vertical stringing is indicative of poor breathing control and can also be diagnostic of a broken / malfunctioning firing pin.
     
  21. jim243

    jim243 Member

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    As you heat up the barrel and chamber the metal will swell to give a tighter fit to the stock, some times this can be corrected by making sure the mounting screws are tourked correctly.

    Jim
     
  22. BluegrassDan

    BluegrassDan Member

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    Torque wrench. I would suspect the front action screw or the scope mounts. Most likely tge front action screw.
     
  23. docsleepy

    docsleepy Member

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    OK. Here's an update.

    I removed the stock and used sandpaper on PVC pipe to create enough clearance to guarantee that it was completely free floated.

    In the process I verified that the actions WERE tight, and they HAD BEEN Loctited.

    The bedding looked perfect. There was a tiny spec of epoxy jutting out from the stock just in FRONT of where the barrel lug would be; I knocked that off. I also added some epoxy to the forearm to perhaps make it a tiny bit stiffer.

    I decided to put a tiny dab of RTV clear on the rear of the barrel lug (where it will contact the bedding). I also installed a small bit of RTV on the outside of the action screws where there are no threads (to make them snug in all directions) and loctited the recesses of the action threads. Put it all back together.

    Created annealed, full length sized, then neck sized, 42 grain Varget, 120 grain Sierra SP ammo as always. The COAL was selected after several tests of grouping.

    Pounded the butt on the ground a couple of times firmly but not destructively before placing rifle in the Rock BR front rest, and leather rear rest. As always, verified good fore n aft movement of the rifle in the bench rest, locked down the front rest before each shot. 16X scope, able to keep the cross hairs still on the target with less than 1/4" observable error in sighting, parallax removed with AO. Bore was NOT cleaned since last session couple days ago. 100 yard target.

    As expected, the zero had shifted slightly due to all this taking off / putting back on. The first shot was 2" higher than the 2nd shot, and then the 3rd and 4th were touching/on top of each other one inch further down and slightly more leftward. I readjusted the scope based on the last shots, and the next shot was perfect. I proceeded to hit 3 out of 3 4" clay pigeons at 215 yards on the berm. No misses. Of course, there was no way to do another "cold shot" so that testing was done for the day.

    This weekend I may have a chance to try it again, and see if the new zero is holding and whether the cold shot is still repeatably high or not.
     
  24. fdashes

    fdashes Member

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    Could be very simple reason and fix. Marksman know all about the first shot from a cold barrel and many preach the "fouling" shot. It may be caused by a too clean barrel. Are you cleaning the rifle between each and every range visit. Try not cleaning the rifle on a return trip and see if that does it for you.
     
  25. BCRider

    BCRider Member

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    I'll bet that if you log the temperature of the barrel through the seasons you'll find that the cold bore elevation change varies with temperature as well. On a hot summer day if the gun sits in the sun for a while there may not be much shift at all. But on a cool day you'll likely get this much or more until it warms up.

    An hour SHOULD be long enough to cool off but what if it's sunny that day and you had the gun sitting protected from wind and in the sun? That could prevent it cooling off that far.

    You may want to add a column to your cold bore log which is for "barrel metal temperature". Log that and the elevation changes for "cold bore" and I would not be surprised if you don't get a repeatable pattern to emerge. Of course you'll need to find something to measure the metal's temperature accurately.
     
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