Inconsistent groups.. How to troubleshoot?

[2506]

The second target indicates vertical stringing.. the target could well have been hung sideways but that's bad practice for archival purposes.

Ha! Yes it does, now that I'm looking at it on my computer not my phone.

 

[Green Rabbit]

Thanks all
I figured light/inconsistent firing pin strikes will be the first problem to troubleshoot. It looks like the firing pin is just worn out, it easily can be 70 years old.
One thing I could do it to try to mess with it - like dremel around the firing pin stop to make the pin protruding few thousands of an inch more hitting the primer a little harder.
But instead I just placed an order on Tubb SpeedLock - it claims to be 70% lighter, so should greatly help with the lock time, too
If it arrives before the weekend, I'll give it a try on the next trip to the range.
I'll keep the thread updated on my progress

 

[Certaindeaf]

It sounds like you're getting it well sorted.. I'll be interested in the results as well and won't be surprised if that comes to be a sub MOA rig with just better primers/primer smasher.

 

[MarkAd]

I can't tell, but is the bell of your scope touching the barrel?
Is there any crimping involved with this cartridge?

 

[Green Rabbit]

I can't tell, but is the bell of your scope touching the barrel?
Is there any crimping involved with this cartridge?

Scope is not touching the barrel - there is some (little) clearance.
And there is no cartridge crimping,

 

[Green Rabbit]

Made some progress today - I figured out the cause of light primer strikes.
It wasn't short firing pin - it was the bolt not fully closed. It appeared the stock came in contact with bolt handle stopping its rotation before. No idea how I missed it.. Other than unreliable primer ignition, the cocking piece was also hitting the bolt at the same time then hitting the primer - seems like a good reason for larger groups
Didn't make it to the range yet, that's left for the weekend

 

[Certaindeaf]

Dang.. good find. That's terrible but good that you found it.

 

[Green Rabbit]

Some "brass porn" my wife took pictures while I was prep'ing the cases

 

[Certaindeaf]

Did you go shooting yet?

 

[Velzey]

Your bolt not being closed all the way could very well be part of your problem!
As you can see from the light primer strikes that it was not fully into battery. Allot can happen when the bolt is not fully closed, brass stretch, bullet jump, light strikes, excessive headspace, etc etc.

I would go back to the load in the first decent target and start there!

As for three screws in the mount, I would drill them out and re tap them to 8-40!

 

[Green Rabbit]

Well, SpeedLock came in on Friday. While (after buying it) I realized it's not the firing pin to blame for light strikes, I installed it anyway - it should not hurt. Looks very nice and installation is fairly easy (not exactly a drop in, but all I had to do is to open a little the hole in the cocking piece).
Here is the speedlock next to original firing pins (I should have put them on a scale - the speedlock feels much lighter)

Sure thing I also made sure bolt handle has enough clearance in the stock and closes fully
On Saturday I went to the range... and still got quite disappointing results. Here are five groups:

No more duds, and most holes are under 1 MOA - however there were 2 flyers opening two groups to 1.2-1.7 inch

Sometimes frustration give me energy to do things so I spent most of the Saturday night in the garage redoing the action glass bedding. Since lack of stiffness of the action is one of the main Mauser drawbacks in the accuracy department, I decided to do full bedding (I only had acraglass under front and tang screws before).
Let it harden overnight and went to the range once again, additionally cleaning bore between the groups.
This time I liked result better:

There are only 3 groups - others 3 I shot with Remington bullets. Didn't like them at all - they shot like 2 inch lower and all groups are in 1.5 inch range.

So I believe there were 3 problems:
1) Obviously, the bolt not fully closed
2) Full action bedding seems to hold better than just front and back
3) Cleaning between groups seem to help


Still want to bring it to 0.5 MOA range. Things I plan to try next:
1) Buy and shoot lapping (abrasive) bullets. While I was (unfortunately) not recording group sequence and cleaning in between, frequent cleaning seem help for better groups. For me this is an indication of rough bore and lapping should help
2) Try other bullets - probably SMK. Running out of my Lapua anyway
3) Try different powder

Thanks all for your support and suggestions. I'm learning a lot.
Is there a good reading on developing best handload for given rifle?

 

[Certaindeaf]

It's just my opinion but I wouldn't use any of those fire lapping bullets/procedures.. however, I don't see how a few passes with JB bore polishing paste would hurt.. the smallest container will last many lifetimes.
A good site, though perhaps not distilled/focused like you might like is 6mmBR.com
http://www.6mmbr.com/index.html
edit.. here's a pretty good bedding tutorial there.. there's a lot of good stuff there but it's kinda hard to find stuff/navigate.. I just used the search function on bedding for example to find that..
http://www.6mmbr.com/pillarbedding.html

 

[Green Rabbit]

Thank you for the link, this is actually very helpful reading. I tried to do stress free bedding, but I used different technique and I don't think it was as good as the one described.
Mauser receiver is very different and it's front piece does not rest on a pillar - it rests on the trigger guard assembly.
However, I also read somewhere recommendations to cut off the tube extension from the assembly and make a pillar out of it.
Sounds like an interesting idea... chances are it will keep me busy next weekend or two

Any particular reason why you would not recommend fire lapping bullets?

 

[Certaindeaf]

It seems heavy handed and uncontrolled. If the barrel was very neglected and fouled, I'd remove all copper fouling and if it was pitted, I'd use a few strokes of JB.
There's a lot of info out there.. the only way I'd use the fire stuff is if I wanted to appreciably enlarge the bore diameter for some reason like if it was too small to begin with.. but still.
Here's one guy's thoughts on breaking in barrels..
http://www.6mmbr.com/GailMcMbreakin.html

 

[AMProducts]

The mauser originally had a steel pillar that was sideways through the stock, however I don't think bedding is your issue here...

In reading the OP and the responses, after figuring out that bolt closing issue (that's kinda've a big one) there are two things I would recommend:

1) Load cartridges to factory OAL - I have never found any preferential results from loading bullets long (except in cases where I needed extra powder capacity) in fact it's something I consider generally negative to accuracy. Granted, I'm not a bench rest shooter so I will never realize any advantage to doing this. The key to accurate shooting is consistent performance, I generally find that the key here is consistent loading procedure, not components. While the component selection is important, it is not the determining factor to good performance.

2) The cartridge you're loading is high velocity... this means added stress and likely copper build up which will ruin accuracy quite quickly. I would not recommend fire lapping or any of the other fancy things you read about in the gun rags... Clean the gun every 5-10 rounds with a copper solvent (I like sweets 7.62, but anything containing ammonia will work) followed by a conventional bore solvent. Start with a mop (looks like a brush made of cloth) use this to soak the bore, then a brush, then patches. The barrel break in process is achieved by "wearing" your barrel in. This can be done either the fun way (by shooting) or by the expensive and perhaps disaster by using firelapping, bore paste, or any other number of wunder-tech that probably isn't what you need. Most of these solutions seem like a dremel tool when what you need is a whetstone.

 

[Otter]

My advice would be to keep your perspective on what this rifle is capable of doing. Many hunting rifles like this are lucky to shoot honest 1 inch groups. Big difference between Internet groups and what kinds of groups people are really shooting. With my medium caliber hunting rifles I'm quite happy to shoot groups in the 3/4 inch range and in the case of my 30-06 feel lucky when it does 1 inch groups. I have a high end Remington model 700 .223 and it averages 1/2 inch groups, and to be honest I'm surprised it will even do that. It was only with a lot of load tuning and tweaking have I been able to get it to do that consistently. I have target rifles in 6BR and 6PPC, and only with those rifles can I get groups in the 1/4 inch and smaller range. Yet if you read the Internet postings, lots of people do that with their hunting rifles, all day long.

 

[rutilate]

Have you done a ladder test to determine your optimal charge weight? Barrel harmonics can affect accuracy. By tuning the load you can stabilize the harmonics such that the bullet is not slowed by harmonic waves returning from the end of the barrel. To do this you first vary your powder charge to see how the groups perform on paper, then you vary your COAL to further dial it in.

Here is some good reading for you:
http://optimalchargeweight.embarqspace.com/#
http://www.6mmbr.com/laddertest.html

 

[AMProducts]

Have you done a ladder test to determine your optimal charge weight? Barrel harmonics can affect accuracy. By tuning the load you can stabilize the harmonics such that the bullet is not slowed by harmonic waves returning from the end of the barrel. To do this you first vary your powder charge to see how the groups perform on paper, then you vary your COAL to further dial it in.

Here is some good reading for you:
http://optimalchargeweight.embarqspace.com/#
http://www.6mmbr.com/laddertest.html

While barrel harmonics do come into play, the larger target generally should be optimum powder load. One thing I've observed many a time is you will have a load that will have a standard deviation of 50-100, and as you move up (or down usually) you will find all of the sudden your SD drops down into the single digits. Typically this is a function of the powder bullet interaction rather than barrel harmonics. (as you can take the same load, put it in a very different gun, and get the same performance)

My advice would be to keep your perspective on what this rifle is capable of doing. Many hunting rifles like this are lucky to shoot honest 1 inch groups. Big difference between Internet groups and what kinds of groups people are really shooting. With my medium caliber hunting rifles I'm quite happy to shoot groups in the 3/4 inch range and in the case of my 30-06 feel lucky when it does 1 inch groups. I have a high end Remington model 700 .223 and it averages 1/2 inch groups, and to be honest I'm surprised it will even do that. It was only with a lot of load tuning and tweaking have I been able to get it to do that consistently. I have target rifles in 6BR and 6PPC, and only with those rifles can I get groups in the 1/4 inch and smaller range. Yet if you read the Internet postings, lots of people do that with their hunting rifles, all day long.

While I don't much disagree with your assessment, he's built himself a new rifle on this action... a brand new ER shaw heavy barrel should be much more capable of delivering bullets accurately than a stock barrel (don't get me wrong, there are some amazing stock barrels out there, but that tends to be more luck than intention). Much of this is going to come down to tuning.