Extreme Spreading

Extreme Spreading

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forum.accurateshooter.com/threads/what-is-an-acceptable-extreme-spread.3780056/
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Thread starter
Austy

Start date
Oct 25, 2010

Help Support Long Range Hunting Forum

I was wondering if anyone had any suggestions for reducing the extreme velocity spread when reloading. I am shooting a 7mm STW, using RP Cases, Reloader 25 powder and Fed 215 powders with my current set up. Any suggestions would be greatly appreciated.
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Mar 21, 2010

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Idaho again Praise God!

I just tested my loads for extreme spread. I did all the case prep that I could trim, annelling, deburr, and uniform primer pocket. worked a good grouping load (1/4") but my extreme spread was 100fps.
I went back to the bench and tried only sizing the neck about a quarter and went back and got 23fps es. So if you have all the case prep down try playing with sizing depth.

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Mar 15, 2009

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I have found that if I apply too much neck tension when I neck size my brass that it can cause erratic velocities.

I do have some more questions for you

Are you neck sizing or full length resizing.

The brass that you are reloading, have they all been reloaded the same amount of times, or are you comparing velocities of rounds that have been reloaded several time to brass that has only been reloaded once.

Have you confirmed your crony reading to long range targets? I have seen on more than one occasion where the chronology was saying there was a large deviation; however when we inspected the 1000 yard target it became obvious that the chrony was giving bad data
The best ways to reduce ES is with neck tension and seating depth. I am going to assume that all of your brass is from the same mfgr and is the same age. I weight sort mine and do the usual match prep.

Seating depth......Are you using regular hunting bullets or VLD type, as in Bergers? First thing to look at is what kind of room do you have in your mag/clip....can you actualy get to the lands and still fit in the mag well/clip. I shoot VLD bullets, which like to be jammed into the lands. Be carfull here....to much jam with not much neck tension puts you at risk of sticking a bullet in your chamber should you decide to unchamber a loaded round. The action usually ends up full of powder. I start (with VLD bullets) at full jam....which ends up around .020 - .030 thou INTO the lands. I work my way shorter. If you are shooting regular bullets i would start at about .020 OFF of the lands.

Neck tension ....If you are worryied about ES and you do not have bushing dies....get them...both a FL and a neck die. As far as which bushings to use....measure the neck diamiter of a couple of loaded rounds....If it's .312 get a .310, bushing 308 bushing and .306 bushing. .314........ .312, .310, and .308. ect... Play with them.

I recomend shooting your tests at longer ranges...300 yards of more. Shoot everything over a chrono.

Good luck, and have fun!!!!

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Building on what was just said, if you jam your bullet too far into the lands it can cause erratic velocities as well... As well as potentially exsessive pressures in some cases

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I have heard that federal 215 primers will give higher extreme spreads, try changing primer. In my 7mm mag I am going to try the Winchester WLRM next time. I might also try the Federal 210 primer as well.

Stu.

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Latest: philipbrousseau
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Start date
Apr 22, 2007

Help Support Long Range Hunting Forum

What do you look for when your looking for extreme spread. I ran some loads thru the crony today looking for a node. Not looking for group but looking for the smallest extreme spread. Its worse than looking for the right combo of load, bullet, Col.
of the # rounds I fired I got the following info.
#1, 3210
#2, 3142
#3, 3177
#4, 3190
#5, 3182
#6, 3160
#7, 3174
#8, 3150
#9, 3148
The crony didn't record the actual #5 so I ended up with only 9 acutal recorded round.
3140- Low
3210+ High
3170 Average
68.36 Extreme spread
21.00 SD
yesterday I shot 10 rounds thru the gun, A 700 Remington, blue printed, 26" Hart barrel .300 Ultra Mag with all the bells and whistles and I ended up with an 82.XX ES 93 grains of Retumbo, Nosler AB Federal 215M primer and Remington Case.
I'm using 93.3 grains of Retumbo, Federal 215M primer and a 200 Nosler AB. Maybe I'm looking for the holy grail but I'm trying to get my ES down to at least single digits. Am I dreaming. I'm getting a bit over 1/2" groups and am trying to get them down to 1/4" if possible but its going to take a single digit ES to do it. Is Retumbo the wrong powder to use or would differant primers do the trick. I sure would like to get this thing dialed in before the barrels gone. /ubbthreads/images/graemlins/crazy.gif
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Blackfoot, Idaho

I was in the same boat as you except with a 338 RUM.

I tried all of the combinations of bullets and typical powders for the cartridge.

Just for fun or desperation or just plain bull hardheadedness I tried US869 w/300 SMKs. WaaLaa. Five shots: 2732/2732/2731/2732/3731.

A possibility would be some 869 and some 240 gr bullets. If the load gets the ES/SD down the extra BC would more than compensate for the lower velocity.

Also I'd consider setting the target at at least 300 yds to let that long bullet go to sleep somewhere along the line. Plus you'd be more apt to see the vertical spread do to the velocity differences.

Just a thought.....

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Couple things not clear here.

1. How accurate are the charge weights? Are they each weighed and on what?

2. Accuracy of the chrony? What type chrono or are we talking chrony chrono?

3. Try different primer first for 5 shots to see if ES comes down. I would start with a F210, then CCI. Many times it will even though not a mag primer.

4. Different powder next. I have not used the U869 but it might be the ticket. If you can find some MRP2 (Graf and Sons and Black Hills are stocking it), I know a standard primer will normally beat the mag in that and it is equivalent to RL25.

You must have uniform charge weights for uniform MV and your chrono has to be accurate within its own range. The chrony chronos are touch and go when comparted to an Oehler, so you might have problems in eithe one of those areas.

BH

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work up the charge a bit. The first 2 shots gave you a large enough extreme spread. 5 shot test if the first 2 are close would be enough to know if further development is an option......
Thats what I was thinking (Moving up the charge and changing primers) This barrel is FAST. Kind of suprised me that it was getting that kind of volocity average. I was getting approx .50" groups with both loads tried so far and for the initial lower load I tried working my way up but everything shoots great so I bought the crony cronograph to try and see is was easier to pick up the accuracy node by watching the extreme spread and then working with primers and COL to adjust from there. If 96 grains of Retumbo is max I'm not sure what kind of volocity this thing will get once I get there. Might hit a peak and go back down before I get there. I started loading it at the lower end hoping to find accuracy and maybe get a bit longer barrel life. /ubbthreads/images/graemlins/crazy.gif
Thanks for the info guys. Will try the heavier load and maybe some Remington primers next.

Also yes the loads are all weighed on a beam scale. A Pacific and its adjusted to zero correctly. All my cases were weighed and picked to be all within 1 grain. Flash holes debured. Neck thickness checked and made uniform with a RCBS neck thickness turner.

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BillR

Not sure that you can ID node by watching extreme spread, just never heard of that and not sure how that works. Maybe you hit in the middle and maybe you hit at one end.

Normally a node can be ID'd by a ladder with sequential incremental charges fired and normally 3-4 rounds will have very close MV while the rounds before and after will take dramatic jumps again. If the charges are say .2-.3gr apart that will show you the node start and end. Start tuning in the middle.

Would recommend you change one thing at a time and work powder first. Ie stick with increasing charges of Retumbo if 96 is a safe level and leave primers for last IF you need to go there.

Your weighing etc looks to be good, so no issues there. The chrony might be questionable. I would say at some point in the future set up your chrono and a someone elses and check them together, particularily if the other is an Oehler. That way you can have some degree of confidence in it and comparison. I had an older PACT that was very uniform in its readings but just a little slower than my Oehler, but at least I knew it was consistent and that is the key.

BH
I checked it against an Oehler and its right there with it. I was having a bit of problem that day due to wind. Also the reason I didn't post a target. Wind kept blowing everything over so I just went to trying to narrow ES. I had a total of 3 false readings due to clouds and wind conditions. Even locked down the wind would spin my Chrony around. /ubbthreads/images/graemlins/ooo.gif I don't think the wind ever quits out here. If it did everyone would fall over. /ubbthreads/images/graemlins/crazy.gif
I have another day later in the week and IF it quits blowing long enough I'm going to try a ladder.
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