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Help - grouping question

 
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  #1  
Old 08-10-2009, 09:24 PM
tlk tlk is offline
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Help - grouping question

Getting my 30-06 dialed in with powders, etc. Now that the groups are getting smaller I cant figure out whats going on:

First three shots were a 1/2" group. Fourth shot was low and to the slightly to the right, making a 1 1/8" group. Fifith shot was lower still and to the left, making a 1 5/8" group. This is all center-to-center measuring (not sure if that is correct way to do it).

What gives with the last two shots creeping down so much?

Stats:
30-06, SAAMI chamber
58 gr. IMR4350
Fed Primer
SMK, 168 gr.
Lapua brass, fired 2 times previously
runout on finished rounds: < .003

Thanks
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  #2  
Old 08-11-2009, 02:50 AM
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Re: Help - grouping question

I'd take a look at shot duration, first three, barrels warming up, might tend to walk after that. I've had that happen with a couple different rifles,,,,,just went to 3 shot groups between cool downs

If its not free floated than I'd say that is the issue, I have a 22-250 with a light barrel and likes tip pressure. It won't group more than 2 shots, but will drive holes if I give it time between shots

I'd like to shoot cold bore everytime, but don't have that backyard range that allows it!

Much more experienced fellas here, just my 2 cents,
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  #3  
Old 08-11-2009, 05:33 AM
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Re: Help - grouping question

+1 on the barrel warming up and affecting the last 2 shots.
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  #4  
Old 08-11-2009, 11:04 AM
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Join Date: Jun 2009
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Re: Help - grouping question

The barrel warming up idea holds merit...it is obviously a dynamic issue that occurs in some shots and not others (eliminates a whole host of possibilities that would affect ALL shots and not just some). Luckily, this is also easily tested:
1. Fire a 5 shot group with adequate time between each shot (10 minutes is more than enough) and see if the creep exists.
2. Fire another five shot group after the first is completed and significantly reduce time between shots. Start this immediately after the fifth shot in #1 (at a fresh target). As soon as you are ready to fire, fire away.

This approach will ensure a cool barrel for each shot in #1 and a increasing barrel temperature in #2. Of course, this assumes that all else is constant and equal (or as equal as you can make it!).

Good luck! If you try this approach, let us know how it goes!
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  #5  
Old 08-14-2009, 10:42 PM
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Location: Jackson Ms
Posts: 316
Re: Help - grouping question

Funny you have this problem today. I have had it aswell. First two shots pretty close. Sometimes touching. Third and fourth just about in the same hole.

Below two groups are the same load shot a few minutes apart. 200 yards. The top was shot in about a minute. The bottom shot over fifteen minutes. Same load, same shooter. Cant be all luck
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  #6  
Old 08-15-2009, 09:59 AM
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Re: Help - grouping question

Unless you are getting consistent results over time, then there is a variable in your process somewhere or the rifle is not capable of shooting five shot groups as small as you would like. A common problem with factory tubes and rifles for that matter.

How long are you letting the 4th and 5th round sit in the chamber before you are pulling the trigger? When I am competing, the round is only in the chamber maybe 2 seconds so any heat transfer will be kept to a minimum.

Bench technique has a large part of being successful at shooting small holes as well and as a factory or some custom tubes heat then stress is introduced which will shift POI and compounded by inconsistency in you bench technique.

I have a sporter that by putting excessive torque the front lug will cause a change in POI as the barrel and action heat up. Granted it is a B/Ped Remington that will shoot .3 if I do my part but put 20 lbs more on that front lug and it went to a garden sprayer shooting right at an inch. The rifle is a 6.5 284 built to the same specs as my match tubes using the same reamer and ammo so the only variable was 20 lbs of TQ.

There are so many variables in this equation not knowing how your rifle was built that it is almost impossible to diagnose accurately. Just a FYI but after I started getting Speedy to make all of my dies with the reamers being used for the tubes oh and the seating die is a Wilson that goes into the arbor press my run out problems vanished completely. A very often-overlooked part of the precision loading process is the consistent application of sizing lubricant to the brass. Spring back or the lack thereof on part of the brass when it comes out of the sizing die can account for quite a few problems in and of itself. Hope this is not too much information but when preparing ammunition ANY VARIABLE in the process has, the potential to cause erratic results all other thing being equal.
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  #7  
Old 08-15-2009, 11:39 AM
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Re: Help - grouping question

Hoss- where do you put lubing when you resize your brass. I usually just put it on the base of the brass and slowly run it through the RCBS DIE. I know the expanded ball can cause trouble but most of my loaded ammo has a average runout of 5 thou. Measured on the shank of course.
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