Hey. It's me. The guy who can't get decent ES/SD from his 6 SLR

[montana_native]

All,



I’ve been fighting an ES issue (50-60 fps over 5 shots) on my SLR since I started shooting it. I posted about this issue last fall. The rifle is used for field precision matches and because most of the targets are in the 4-800 yard range and it doesn’t present much problem at those ranges so I sort of forgot about it. However, my most recent match had a number of targets at 11-1400 yards. At 1400 yards, a 50 fps variation in velocity represents a 23.8” vertical variation on a ballistics calculator and I believe that I verified this at this recent match with unexpected and drastic vertical misses (both low and high); assuming it wasn’t the shooter. I’ve verified the velocities on a LabRadar. I am fairly confident in the Labradar’s velocity variation readings (actual velocity is another story) based on the other readings it gives my shooting partner. Below are the rifle/load specs:



6 SLR – 0.040” Freebore, JGS reamer

RL26, CCI 250, 115 DTAC (old version – pointed) – the average velocity is 3123 fps

Winchester brand brass

Stiller Tac30, Bartlein 7.5 Twist 26” barrel, Elite Iron Suppressor (still an issue without the can)

This load consistently shoots under 0.75 MOA. When I did load development, it was around 0.25 MOA.





Things I’ve tried that have not remedied the issue:

• Benchsource annealing
  
  
• Graphite neck lube
  
  
• HBN coating – this actually seemed to exasperate the problem in my limited testing
  
  
• Varying neck tension
  
  
• CCI200s, BR2s, GM210s, Winchester LRPs
  
  
• H1000 powder was almost 200 fps slower but still exhibited the big ES
  
  
• Seating depth variations
  
  
• Weight sorting brass
  
  
• Deburred flash holes
  
  
• Neck reaming to eliminate donuts which are very slightly evident in this brass even though they aren’t supposed to be per everything I read
  

I’ve noticed that the flash holes in the brass are pretty bad. Some of them are oval-shaped while some are nice and round. Other flash holes seem to have a “chamfer” in the cup area that is about 20-30° of the radius. It’s almost like the pin that created the flash holes came in from an angle. However, I sorted these out as well and there was virtually no effect on ES. As ugly as this brass is, I don’t think it is the culprit.



The Stiller firing pin is fluted and small diameter and I am wondering if this may be contributing; maybe not enough mass to consistently light the primer??? Primer strikes don’t look abnormal. The only reason I thought of this is because I had a worn out firing pin spring years ago on a Winchester 70. When I replaced it, the ES was cut in half.



The only other suspect is my load. Yesterday, when I was experimenting with the HBN coated bullets, my POI jumped about ¾” on the paper at 112 yards with a 0.5 grain charge increase (this was the charge increase to get back the velocity with the HBN bullets). Is it possible I am not in a node? The rifle is very accurate, during load work-up, I don’t recall anything being over an inch at 100 yards. My notes weren’t good enough to go back and determine if there was a POI shift while I was doing load development.

 

[expiper]

try 4831...Roger

 

[pacificman]

Wow...all your reloading sounds very consistent so it seems you should have better ES/SD. The only thing left
that I could think of would maybe try some lapua brass. On another note...I have an old Nosler reloading
book that mentioned components to change if you have flyers or UN-exceptable groups. I remember those
components were either bullet or powder change. ....Just throwing some suggestions out there as this would
be what I would consider if it were one of my rifles.

 

[Milo 2.0]

What is your actual load and coal? .040" freebore is not much, here is a reamer dia print of mine and we throated .015" more.
You can try anything you want but until your platform likes what your putting into it, your numbers can't tighten up.

 

[savagedasher]

What is your actual load and coal? .040" freebore is not much, here is a reamer dia print of mine and we throated .015" more.
You can try anything you want but until your platform likes what your putting into it, your numbers can't tighten up.


View attachment 1012542

I think to get low Es you must first have the internal volume to be the same . Not weight of the cases but the volume . Then you must have a primer that starts the ignition the same . I have primers that I get 20 foot with and other that I get 5 . Premium brass is a good place to start
Larry

 

[montana_native]

Thanks for the replies so far. My load is 46.3 grains of RL26, CCI250, with the COAL at 2.185" to ogive using a Hornady Tool. If I recall correctly, it is jumping about 0.030".

 

[DHuffman]

I think to get low Es you must first have the internal volume to be the same . Not weight of the cases but the volume . Then you must have a primer that starts the ignition the same . I have primers that I get 20 foot with and other that I get 5 . Premium brass is a good place to start
Larry

I'm with Larry on this one. I would say it's not quite in the node so if it's not your powder charge I would lean towards inconsistent case volume giving inconsistent pressure on ignition/burn.

I pretty much exclusively use Lapua brass and have never weighed or measured internal volume but easily get single digit SD and usually 9-16 for ES, I can usually get the ES to 12 or less but the smallest groups are usually @ 14-16 ES. This has been true for several loads in several rifles for me. Smallest numbers not necessarily the smallest groups.

I know nothing about the 6 SLR so have no comment on your powder or primer choice.

 

[Milo 2.0]

Thanks for the replies so far. My load is 46.3 grains of RL26, CCI250, with the COAL at 2.185" to ogive using a Hornady Tool. If I recall correctly, it is jumping about 0.030".

With 46.3gr of RL 26 and a magnum primer, you must be 3250+ fps?

 

[Milo 2.0]

Thanks for the replies so far. My load is 46.3 grains of RL26, CCI250, with the COAL at 2.185" to ogive using a Hornady Tool. If I recall correctly, it is jumping about 0.030".

Take a pic and post of your rd, that bullet must be in the case a ways, not good either.

 

[watercam]

I also think you should try H4831...

 

[XTR]

N160
IMR7828ssc
H4831

I also found H1000 to be too slow for my SLR.

.040 freebore is crazy short for running 105/107 class bullets. You have got to have a lot of bullet in the case. You can load to mag length in a n AICS at .125 with most bullets n the class.

 

[boltfluter]

With such a short free bore I would do a test with a much lighter bullet as an experiment to see if it comes around. Good luck.

Paul

www.boltfluting.com

 

[Mozella]

As someone trained in the sciences, I like to believe that precision shooting is not all about luck and black magic. I believe that we can zero in on a nice precise load in a scientific way at least to the point that losing a match will be the fault of the shooter in many, if not most, cases.

You seem to be devoting some effort to improve your load precision and that's good. However, you also say "If I recall correctly........." and "My notes are not good enough..........". That tells me that you might consider spending a little more time and effort when gathering and analyzing your data.

I believe it's hard to reach your goal if you don't know where you are at the moment, if you get my drift. In other words, without solid data it's hard to discover exactly what the problem is and if you don't know that, problems are hard to fix simply because we shooters are dealing with so many variables. What's worse, is quantifying the effect of these variables isn't easy.

When I do load development I like to produce a load recipe sheet for each test session listing every variable along with some notes about how the ammo was produced; i.e. bullet type, powder type, charge weight, COAL, predicted temperature, etc. The notes mention if the bullets were pointed or not, if the cases were sorted, and so-on. When I return from the range I scan my targets and measure the data using On Target Software. This gives me precise measurements of many parameters; group height, group width, group size, variation from aim point, average-to-center, etc.

I also pull up the load recipe sheet and comment on the test session including things like actual temperature, wind, and general comments about that particular load. Then I save that sheet with a sequential reference number and also print it out.

I like to put the collected data for each 5-shot group into a spread sheet. This is a simple matter using On Target. Then I add other information including a test reference number, bullet weight, bullet type, powder type, muzzle velocity, SD, and so on. I have even developed a formula to normalize the data collected at 100 yards to that collected at other ranges so I can compare my 600 yard competition results with my 100 yard testing results. I've done the same with shots/group so I can compare 5-shot groups with 3-shot groups for instance.

Once I have the carefully measured data in the spread sheet, M.S. Excel gives me the ability to sort and sift this data eight ways from Sunday so I can compare one test with another. For example, if sample #607 (my personal reference number sequence for 6mm BR) used a neck tension of .0010" and sample #608 used .0015 I can then see if one sample produced different results. And I can see, for example, if the resultant reduction in the SD correlates to a smaller MOA or tighter Mean Radius, or not.

Or, to use another example, I might notice that two load recipes, identical except for powder type, give nearly identical precision. But one recipe produces a 50 fps higher velocity with the same calculated barrel time. I'm likely to use the powder giving the higher velocity. You get the point.

The old-school dog-eared notebook makes this kind of analysis nearly impossible, so I much prefer using my computer. But in the interest of full disclosure, there is still enough mystery in this game to keep things exciting. My carefully gathered data often shows variations and deviations that I can't explain. I'm constantly filled with doubt about how to produce the best ammo.

Bottom line: The path to getting better is never easy and using a computer certainly doesn't guarantee results, but a more scientific approach to load development might just help you beat the joker next to you on the firing line

 

[500Stroker]

I believe that neck tension equals pressure. You mentioned "various neck tensions", are you sorting for neck tensions? When you are shooting across the chrono are the rounds all at the same neck tension?
Some of my best groups were shot with brass that had terrible flash holes, if the brass can hold a primer I shot them.

 

[montana_native]

You seem to be devoting some effort to improve your load precision and that's good. However, you also say "If I recall correctly........." and "My notes are not good enough..........". That tells me that you might consider spending a little more time and effort when gathering and analyzing your data.

I can't imagine this barrel has much life left in it. It's got between 2300 and 2400 rounds on it. When I rebarrel, I plan to use a 0.075" free bore reamer. Heck, I might even create a proper load development book.

I believe that neck tension equals pressure. You mentioned "various neck tensions", are you sorting for neck tensions? When you are shooting across the chrono are the rounds all at the same neck tension?
Some of my best groups were shot with brass that had terrible flash holes, if the brass can hold a primer I shot them.

I've tried various neck bushings. Seating pressure seems to be very consistent.

 

[carlsbad]

.040 freebore seems very short for the long bullets. Are you compressing your loads?

My 6slr was worse than yours. I cut it off once and rechambered it. I was shooting H1000 mild loads. It shot decent for about 100 rounds. Then the throat cracked in a 1000 yd match where bad info from the pits had me off paper trying to get back on before going 20 rounds for score. After that it was a headcase with ES of 100 or so.

I cut it off and rechambered it. No improvement.

I moved to 6xc and never looked back.

--Jerry

 

[74Bronco]

my last loads of 105hybrids, 43.5gr 4831sc, new ww brass, 270 neck bushing, br2 primers, had a es of 14 sd of 6. only thing i did extra was inside/outside chamfer the necks , have you checked your scale for consistency by chance? only variable no ones seemed to have brought up yet .

 

[500Stroker]

I've tried various neck bushings. Seating pressure seems to be very consistent.[/QUOTE]

"seems to be" I take you do not use an in-line seater with an arbor press that measures seating force.
I also suffered from poor ES, until I got a handle on conditioning necks and precisely controlling neck tension and seating depth.
Some food for thought.
Good Luck

 

[savagedasher]

The first thing you need the internal volume of the case to be the same. Weight of the case has no relationship to the internal volume . Same with case volume you still have to know how much your using . Good quality brass helps but it's not perfect.
First thing whe blue printing a engine we do is make the combustion chamber in the head perfect . Combustion chamber-in a engine is the same as case in a gun . Larry

 

[Milo 2.0]

I can't imagine this barrel has much life left in it. It's got between 2300 and 2400 rounds on it.

Most 6slr don't live this long.