Does runout matter?

[Viperdoc]

I have been working (struggling) at getting the best accuracy out of my 223 AR with a 26in Krieger 1/9 barrel. Got some new Lapua brass, full length resized, ran mandrel, turned necks, resized again with redding S dies, chamfered, and then measured bullet runout at the ogive after loading:

less than 0.002 gave a velocity of around 3070 with an SD of 19 (25.9g Varget, Sierra 69MK, CCI BR primers)
0.002-0.003 gave an SD of 22
greater than 0.003 gave an SD of 25

First conclusion: less runout clearly improved the consistency of the rounds.

Accuracy was generally better with the 0.002 runout group, but a bit hard to say since it was very gusty and windy.

Accuracy was clearly better (and average velocity higher) when neck tension was 0.004 compared to neck tension of 0.002

Still, at least in my gun, it seems to enjoy faster burning powders H335 and TAC with the 69 MK's compared to Varget. Although max speeds are lower, accuracy seems much better. I have not tried downloading the Varget to the level of the faster powders. Have some preliminary results with 2520, which it also seems to like better than Varget.

Is this consistent what others are seeing? I had high hopes for Varget, but it seems like the faster burning powders seem to be better with the 69g MK's for my gun.

The Lapua brass show little run out just out of the box- FL resized, ran mandrel, and then checked runout- not much difference when necks turned or not, usually 0.001 or less. Occasionally did find one greater than 0.002. Is it worth sorting the brass and checking the runout on each case, and then turning just the ones that are over, or would it be faster to just neck turn all, or none?

Need to get at least 1,000 rounds ready for a PD hunt within a few months.

 

[camac]

I was going to suggest a forum thread "Does runout Matter" and try and get some global input. Some believe strongly that it is critical, others fubar it. I personally believe it can make a significant difference especially with projectiles with small bearing surface.
Can we put out a challenge for a few of you with the ability to measure.
Load up some rounds and measure and sort by runout for simplicity we could break it up to < 2 thou (the less the better) and > 2 thou (the more the better). Fire five shots in each and post your MOA results. It would be an interesting pool of information. I bet we would get some with tighter groups, others without and possibly even a few with reverse but would be interesting to discuss.....

Viperdoc - it would certainly be quicker to measure and sort by runout but You will not regret neck turning them all - for neck tension, as well as runout uniformity.

 

[BoydAllen]

Among those who compete, there is a general agreement that straighter is better. Beyond that, the questions are where is the point of diminishing returns, and is anything gained by straightening? I am always a little leery of reported test results unless I am familiar with the shooter. So many don't want to be bothered with really basic equipment and procedures. Kind of like some of the news stand gun writers who are photographed doing it wrong and admit that the test conditions were terrible. Not much can be learned from such data. Generally, I try to limit runout on the bullet to under .002, eyeballed about .150 in front of the case neck.

 

[Viperdoc]

I agree with your statement regarding the role of the shooter, which is why I did not include any group sizes, and only included the objective data of the SD's. I guess the basic assumption is that the lower the SD, the better the group, but this might not necessarily be the case.

Some how, I keep seeing that the ball powders H335, AA2520, and TAC, all seemed to give tighter and more consistent groups compared to Varget. So, now I plan on focusing on these powders- with the next experiment being to use everything the same, with the only difference being whether the necks were turned or not.

Neck runout is obviously better when turned, but the worst new Lapua runout that I saw was 0.0025- the big question is will it make that much difference, if any?

It may be a case of diminishing returns.

 

[johara1]

If you know what a hummer barrel is, load them crooked and watch how the advantage of the hummer barrel goes south. A bullet can't be asleep when you start it crooked...........jim

 

[camac]

I agree totally and fully believe in runout. I also fully agree with you all that some (in fact nearly all) will do it wrong. ie not control variables properly, not do enough replication etc. But one thing I have learnt in my 55 years, is that I can learn something off everybody. I have no doubt that everyone on this forum has seen something in their lifetime that I have not. It is just a matter of filtering out the "b------t". The point is I have one of the most respected shooters in our country telling me he doesn't worry about runout anymore and he still shoots bloody well.

The great thing about these forums is you can get everyone to contibute their "observations" (I will call them observations rather than "facts"). that way each and every reader can make up their mind as to what is real and what is not. The down side is a lot of "misinformation" gets circulated and believed but hopefully in the forum format it generally gets stomped on. I personally think it is better than going to the range and getting one mans opinion..

 

[BoydAllen]

Consider this. I have a 6PPC with a .262 neck and .060 freebore that is a few tenths over bullet diameter. Typically I load to a length that is a few thousandths longer than "touch". My FL die barely reduces the case at all. Once, as an experiment, I bent a loaded round to a runout of a little over .004, and then chambered it, closed the bolt, extracted the loaded round, and then remeasured the runout. It was .0015, about .150 out from the end of the neck, about what my dies produce. I would not expect this result with a factory chamber of much more generous dimensions. My point is that one should make sure that one is speaking of the same set of conditions when making comparisons. My Benchrest rig is, to as great degree self straightening. My factory rifles are not, so it may be that what is true for one, with regard to the importance of runout, may not be true for the other. Your respected shooter may be shooting rifles that are like my PPC, so for him, it may not matter, but not necessarily for everyone.

 

[camac]

Boyd, I imagine if you extracted the round and measured such low runout - then with a bit of springback would have meant your chamber is holding your bullet with even less runout than this. .

 

[camac]

OK, thought I would post a pic - went out this morning with my 6BR varmint 1 in 12 twist (as I am confident runout does matter in this rifle) and shot two groups at 100 yards. Headwind of around 10 knots, 80 gr custom flat based bullet with Varget (ADI 2208) and BR4 primers doing 3080fps. Two 5 shot groups shot round robin to try and minimise variables such as barrel heating, wind changes etc on groups. Left group (0.172" c-c) had less than 0.0005" runout measured at ogive about .4" forward of neck, Right group (.426" c-c) had .002-.004". Low runout was loaded by two step neck sizing using tapered bushings as described in other threads, others were loaded and selected with standard bushing, one step neck process. I know a single comparison of 5 shot groups is not statistically concrete but worth a mention.

 

[BoydAllen]

Look...you have broken one of the most important, unwritten rules for this kind of internet discussion. You actually did something, to see what would happen. What is the world coming to?

Seriously, thanks for the information, and picture.

 

[camac]

No worries Boyd, I would love to try a replicated experiment on my 6.5 x 284 (ie 3 lot's of 5 shots in <0.0005, 0.0005-0.002, and 0.002-0.004 and 0.004 plus but for damage to barrel life and cost (ie 60 shots all up). My theory is it does make a difference, for some rifles and projectiles more than others. But like the guy says, at a point the chamber and throat might start to take over to straighten them up presumably more so in my 6.5*284 match barrel with long throat and bearing surface. I would suspect at some point it doesn't get any worse though due to this (also different in every rifle).
But hey, anyone who has some rounds with excessive runout that they don't want to use for a match please help and run the experiment as well??????

 

[clmayfield]

This is a fascinating discussion. I have sorted 500 .308 Federal Gold Medal Match 175 gr cartridges on runout. They are for a gun that is not yet in my possession. When I get it, I will report the results ranging from the highest to lowest runout. This will give us a data point on no-turn neck chambers and FGMM should be pretty consistent in all the other variables.

 

[JERRYHM]

I have a DIFFERENT view on runout. My loads have very little runout, but it is not something I worry about.


One very important item left out of this discussion is neck clearance! I have found from MANY years of testing run out that : the tighter the neck clearance the more perfect the loaded round needs to be. I use tight throats (0.0002" bigger than the bullet) and a neck clearance of at least 0.004", up to 0.012". Testing 308 loads with a tight throat and 0.010" of neck clearance; comparing loads with 0.001" or less and loads with a runout of 0.012" there was NO difference in group sizes. The high run out loads were also shot with the high side at 12.3.6.and 9 o'clock in the chamber, also no noticeable change in group size as compared to the low runout loads.
I believe one of the reasons that improvements in accuracy is seen when neck turning the brass is the increase of neck clearance more than an improvement in the brass....

I have NEVER found in my testing that increasing neck clearance had any ell effects on accuracy.

 

[camac]

Very interesting Jerry, and probably more in line with viperdocs original observations. Is the runout interaction BETWEEN throat and neck (or indeed other parts of chamber) more important than actual runout itself? I imagine I understand how a tight throat, loose neck chamber could minimise any effects of runout
To quantify the above 6BR then, it is a .272 neck with .267 loaded round (very minimal neck turning). But perhaps it does not have as tight a throat?? I will probably try a little more on this rifle as I have all sorts of projectiles and am not as "worried" about the barrel.

As a similar point I know the person I mentioned above that also doesn't worry about runout has a 6.5*284 for his 600 metre shooting (same as I) but in discussions with him he full length resizes every time and has 5 thou neck clearance in his 6.5x 284 (believes this is the minimum required for this round) - not sure about his throat. So , I certainly could imagine he has similar observations to yourself though.

0.0002 clearance on the bullet could really be the big difference.......and letting the shell or neck float a little behind it. Very good.

 

[BoydAllen]

On an unrelated matter, virtually every AR shooter that I have seen at any range has had serious issues with how his rifle interacted with the sand bags that it was resting on. The list of problems is a long one. Typically they want to shoot smaller groups but don't want to change much about their setup. From what I have seen, this is a major limiting factor. The one exception to this is the rifle featured in the Gun of the Week article on the 20 Practical, that shows a rifle that has pieces mounted front and back to better fit the bags.

 

[Viperdoc]

My original post was regarding AR's in 223. In search of improved accuracy, I tried taking new Lapua brass, FL resizing with a Redding S die .246 insert, run mandrel through, neck turn on Gracey, resize, trim/chamfer in Giraud, then primed with CCI BR primers. Loaded with Sierra 69MK to same head-ogive length.

Using the same brass, then tried Varget, TAC, and AA2520. Neck tension was around 0.003. Sorted each finished shell by bullet runout >0.004.0.002-0.003, <0.002.Did learn as suggested that bullet runout can be decreased somewhat by seating around half way, and then turning bullet.

Testing was on a bad day, too windy and gusty. Shooting AR with 26 Krieger 1/9 and free float tube off a heavy sinclair rest,but have yet to find a good flat adapter that will fit the rail on the free float tube. So, round peg in square hole, plus gusty and windy- not able to make any conclusions. Still did have fun blasting away.

Only lesson learned was that I miked some cases after returning, and the average runout was less than the new cases- no surprise there. One x cases are now being processed by decap, clean, FL resize, mandrel, resize, and then chamfer (cases after only one firing did not lengthen at all, and runout was consistently less than 0.001.

So, back to original question- how can I get more accuracy out of the gun? It is hard pressed to consistently shoot less than 3/4 to one inch with the 69 match kings, and does do better with the 53 FB matchkings. Varget seems to consistently do worse than some faster burning powders like H335 or TAC, but AA2520 is also better in terms of group size.

Is it worth trying heavier bullets like the Sierra 77's or possibly lighter like the 62Bergers? Any other tips or tricks I'm missing?

 

[TonyR]

Viperdoc
I have never owned an AR but I shot a Space Gun once in a 600 yard prone match and was amazed at the accuracy. That interested me enough to buy Glen Zediker's book "The Competitive AR-15, AR-II" which deals with more opportunities for improvement than I ever thought possible. It might help you sort your gun out or at least give you some things to think about.
Good luck with your project.

 

[Viperdoc]

I do have his books, and they are a great source of logical information, although a little wordy and repetitive. I think I have tried everything in his books. My only basis for comparison is my bolt action 6.5 Creedmoor, which even with factory ammo is unbelievable in terms of accuracy. The bullet selection is somewhat more limited, but it seems like the Berger 140VLD's with 4350 or Reloder 17 were great.

However, with the AR, even with a top notch barrel, I still struggle to get better than 3/4 in groups, and expect it to do better.

 

[camac]

Viperdoc, sounds like your issues are getting beyond runout alone and probably this thread (although being read by many) may not be drawing the experience you require. (I personally have no experience with AR platforms - we are not allowed them over here in AUS). Perhaps we can still talk about runout on this thread but can I suggest you also start another directed at AR accuracy issues that might draw in the AR experience you require. Getting less than 2 thou runout should see you better accuracy than that in good barrel, well bedded etc. I know the AR platform can deliver pretty amazing accuracy so you might get some great tips.
ps did you see any accuracy differences in the runout sorting???
CAM

 

[camac]

from MANY years of testing run out that : the tighter the neck clearance the more perfect the loaded round needs to be. I use tight throats (0.0002" bigger than the bullet) and a neck clearance of at least 0.004", up to 0.012".

Once again Jerry I believe you may have hit the heart of the difference as to why runout sometimes matters and sometimes doesn't. I have been thinking about this with reference to my own rifles/barrels and which I believe are worst affected by runout. I have measured some of my reamers and decided I will go back and "cast" some of my chambers to have a look. Indeed I have more than 0.0002 throat clearance (although necks appear ok with my neck turned shells).

An interesting twist on this is, even though I have some of my own reamers, if your points prove correct (and I believe they should) then I would have been far better off redesigning my reamers (pretty simple to take some off throat diameter - harder to add to neck but my diameter is OK - or as you pointed out I can simply neck tuirn to create more room), than going to all the work on the dies (and sometimes spending big money chasing wilson and redding competition dies, and then accurizing them). If, in fact 12 thou runout does not matter, you could have the cheapest dies available. Though that being said I enjoy the precision of all this so personally would not go down that path. Just a point being made.
CAM