Frustrated and Need help, inconsistent groups

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Barnard308

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Ok guys here is the situation, I am running my .308 target rifle with 42 gr of Vihtori N140, and 155 scenars (lapua), in lapua brass with CCI BR-2 primers at 2760 FPS with about 20 fps deviation. I spent hours doing load development and this seemed to be the most consistent load with the least amount of vertical spread. I know I have the right components and equipment, and I know this rifle will shoot.

If I do my part I can get 5 shot groups under a half inch at 200 yards, but lately the next 5 shoot group has a 3-4 inch random spread on it. I let the barrel cool down between strings, always use tracker bipod and rear sand bag with a bag rider.

Steps involved are tumble brass for 3 hours (corn cob media), neck size case ( lee neck sizing die), trim to 2.006 , re-prime, load powder, seat bullet (foster seating die), bullet is 5 thou off the lands. I clean the barrel every 150-200 rounds with copper gone and ezzox. I should mention the Lapua brass I use I bought new and has been shot about 7 times each with no pressure signs, excessive stretching and no cracking.

I know it has something to do with my loads not the rifle because it will shoot match grade lapua all day in the same 1/2" hole if I do my part.

Now I just started doing the full length re-sizing with a RCBS Gold sizing die in hopes that this will cure my problem. But I haven't been able to get to the range yet to test this theory.

I am completely Frustrated by this and could really use some sound solid experienced advice and thoughts. Thanks guys.
 
Just for giggles.
Try a few rounds with a powder that will fill your case without compression, Varget, 4895, etc.
and see if the problem goes away.
That's assuming the mechanical side of your rifle is not causing it (check your throat for erosion)
If you haven't checked your length to lands for a while, maybe try that.
 
1) Try dropping a bullet in a fired case - if it falls thru, you're good - if it doesn't, your necks are too tight and you'll need to trim them
2) as mentioned above, try a different load (powder or bullet)
 
If your brass is over 7 loadings you may need to anneal, the necks may be getting hard giving inconsistent pull.
Recheck your cartridge OAL, if you've shot over 2000 rounds the throat may have extended 10-15 thou or more and Scenars are sensitive to seating depth.
Give some Hornady 155gr Amax (or SMK's) a try as they're less sensitive to OAL and are quite accurate. My load using Scenars and Amax's is almost identical in 3 barrels.
Are you using Moly or bare bullets? If moly I'd think you're cleaning to often and to recoat the barrel requires about 10 rounds or more before accuracy returns (Moly is worth it in my opinion, far less cleaning) Best of luck.
 
Anneal properly - I do my brass every 2 to 3 firing (PRVI)

Outside neck turn. Lapua brass is already very thick. With most chambers, you will quickly run out of room to expand properly. Turn the brass to 12 thou and likely, the issue goes away. Compare the neck thickness of the factory ammo vs what you have now.

I outside neck turn EVERY firing.

Consider trying Varget. Most Palma shooters are reaching 2900/3000fps with the 155's.

Jerry
 
Bedding and bedding screws. Pull the action out of the stock and make sure it is completely dry. A little film of oil or moisture between the action and bedding can cause the rifle to shoot like lightning (never hits the same spot twice) Also make sure the barrel is free floated all the way to the recoil lug. Barrels are a creature all of their own. Some barrels may need bedding under the chamber, some won't shoot with it. Some barrels need a pressure point at the end of the fore stock, some will not.
 
Does a bullet enter the fired case easily? If not you have tight neck problem. Some match chambers are cut rather tight in the neck.

Failing that, the only thing I see is that your load looks very mild. I load the Lapua brass with 46 gr of N140. I also place bullet 20 thou from the rifling.
 
Mystic Precision said:
Anneal properly - I do my brass every 2 to 3 firing (PRVI)

Outside neck turn. Lapua brass is already very thick. With most chambers, you will quickly run out of room to expand properly. Turn the brass to 12 thou and likely, the issue goes away. Compare the neck thickness of the factory ammo vs what you have now.

I outside neck turn EVERY firing.

Consider trying Varget. Most Palma shooters are reaching 2900/3000fps with the 155's.

Jerry
Click to expand...

Forgive me for questioning you ... but...

Neck turn every firing? Is there anything to shave off the neck after a firing? I can see neck trimming for length, but i havent found any inconsistency in neck thickness after outside turning once that would ever justify re-turning.

Are you on drugs or am I?
 
curseyou said:
Forgive me for questioning you ... but...

Neck turn every firing? Is there anything to shave off the neck after a firing? I can see neck trimming for length, but i havent found any inconsistency in neck thickness after outside turning once that would ever justify re-turning.

Are you on drugs or am I?
Click to expand...

Some people might say it's a bit excessive, but I am pretty sure his logic is, if the brass is flowing (as it does) and you would have to trim *anything* off the end, then that also means that the brass has flowed from the shoulder into the neck. The shoulder is, of course, thicker (and untrimmed), therefore there is going to be a small amount that flows there. Also, if you have the time and want the absolute best ammunition you can possibly make, why would you not go to the extra length?

Is it required to get 1/2 moa accuracy? Probably not, but it certainly doesn't help. If you're going for 1/4 moa, then maybe it's all of a sudden much more worthwhile?

I also suspect that Jerry is using a tight necked chamber? If so, then the neck wall thickness is, of course, more critical.

Just some ideas... don't think anyone's on drugs, but it's probably a little more than an average shooter would do, even most above average shooters. Don't mean its excessive though
 
Question, do you have a runout gauge?

And do you check your resized case necks for runout before the cases are loaded.

Meaning are your dies setup to give you minimum runout.

I full length resize all my cases because this minimizes any influence that case misalignment can have with the bullet and the bore.

A full length resized case is supported in the rear by the bolt face and by the bullet in the chamber throat. This means the body of the case does not touch the chamber walls and is eliminated from centering the bullet in the bore. The late Jim Hull of the Sierra bullet test lab and competitive shooter jokingly said the following about full length resizing his prefered method of resizing cases.

"I get the best accuracy when the cartridge fits the chamber like a rat turd in a violin case"

Below is the rat turd in the violin case, again the base of the case is supported by the bolt face and the front is supported by the bullet in the throat, and the body of the case does not touch the chamber walls.

chamber-neck-diagram-with-cartridge2x_zps7395df40.jpg


Read below about neck sizing, partial neck sizing and full length resizing and bullet alignment with the bore.

The Rifleman's Journal

Reloading: Partial Neck Sizing
http://riflemansjournal.########.com/2010/06/reloading-partial-neck-sizing.html

"a full-length sized case in which the neck is also fully sized. There is clearance at the neck and in the body of the case, the closest fit anywhere is the bullet in the throat. If the neck to bullet concentricity is good (although it needn't be perfect), then the bullet will find good alignment in the throat and the case body and neck will have minimal influence. Let's not forget that the base of the case is supported by the bolt face or the extractor to a certain degree as well; this is yet another influence on alignment. As you can see, there are several points from base to bullet that can have an effect. My procedure is to minimize the influence of those that I can control, namely the case body and neck, and let the alignment be dictated by the fit of the bullet in the throat and to some extent by the bolt's support of the base. Barring a seriously out of square case head, I don't think the bolt can have a negative effect on alignment, only a slightly positive effect from minimizing "case droop" in the chamber. Given that a resized case will usually have a maximum of 0.001" diametrical clearance at the web, this isn't much of a factor anyway.

In conclusion, I believe that allowing the bullet to find a relatively stress-free alignment in the throat by full length sizing (including the neck) and turning necks to enhance concentricity gives the bullet the best probability of a well-aligned start into the rifling."

The Rifleman's Journal
Germán A. Salazar

Below, Kevin Thomas Team Lapua USA
KTLapua-b_zps8d1abc2c.jpg
 
Biged, while you are absolutely right, I can't see the neck sizing being the problem. It would mean that the first five shot group should be bad too.

I wonder if the barrel has developed a problem with fouling, and as such fouls up quickly? Also wonder if it is being cooled down enough, though I would think this wouldn't crop up suddenly like this?

I'll leave this to more experienced shooters, but to me, it sounds like, while the ammo isn't being worked in the best fashion (no body/full length sizing being done), this should show up, if it was causing a problem, with all the loads not just the second set of five, no?
 
Not saying this is the case, but I had exact same issue, after wasting components for 100 shot and frustrating 3 range trips I found out that base screws were coming loose and load that I thought was good node was actually scatter node.
 
Barnard308 it sounds like you have previously had good success with this ammo in this rifle (though I agree with Ganderite's comments that it is quite a mild load.... target rifles usually use 45-46 grains of N140 in a Lapua case with Lapua 155s). Therefore it should still work.... there's no way you should be getting 3-4" groups with it at 200 yards. If you are getting awful groups like this, something BIG is wrong, which is actually good news because it means it should be easy to find and easy to confirm that you have fixed it.

You should check the bedding as per Maynard's posting.

Does your rifle have iron sights or a scope? If it is a scope, that would automatically be my suspect. Take off the scope you are currently using and temporarily install another scope that has shot good groups on another rifle. See if changing the scope solves your problems.

EDIT to add: also, be sure to check your sight mounting screws (iron or scope) for tightness, make sure they have not come loose on you! Grab your rear sight, or scope, or front sight, and give it a firm wiggle; it shouldn't move.
 
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Is it likely to give good groups for the first five shots then get worse after that though, if the scope was the problem?

Barnard.... does this act this way every range trip lately? After you clean ur does the next group shrink? What if you let it cool off for like half hour or more?

If it was me I'd be at least having a Smith with a bore scope looking at the barrel. In my mind, if it groups well then bad, it seems that something is happening between the first few shots and the next ones.

If it was your load it would be expected to be bad regularly. Though one still anneal those necks, check your action screws and scope/mount screws, those things would be more likely to cause regular issues not good then worsening results
 
has been shot about 7 times each with no pressure signs, excessive stretching and no cracking.
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Anneal properly - I do my brass every 2 to 3 firing (PRVI)
Click to expand...
A headscratcher for sure OP.
Most often, when my most accurate rifles do go haywire, It's caused by work hardened necks, or, needing a trim/a bit more neck clearance, or, runout.
Have you any fresh brass to try out? ... to determine if it's a case related problem?.
Does your rifle put the first 5 from cold bore into a nice cluster ... then go south as the barrel warms?.
 
Actually mine would do just that, one good group here, one good group there but then same load was two holes together and other two together but 2" away and finally it went shotgun pattern and that's when I removed the scope to find loose base screws. Torqued them up and she shoots .6-.7 moa everytime. No way I'm saying this is the problem but that's my personal experience.

krprice84 said:
Is it likely to give good groups for the first five shots then get worse after that though, if the scope was the problem?

Barnard.... does this act this way every range trip lately? After you clean ur does the next group shrink? What if you let it cool off for like half hour or more?

If it was me I'd be at least having a Smith with a bore scope looking at the barrel. In my mind, if it groups well then bad, it seems that something is happening between the first few shots and the next ones.

If it was your load it would be expected to be bad regularly. Though one still anneal those necks, check your action screws and scope/mount screws, those things would be more likely to cause regular issues not good then worsening results
Click to expand...
 
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