Need help deciphering my first OCW workup

[Widowmaker]

I just shot my first OCW test today and could use some help deciphering the nodes. I've been reloading for awhile but up till now, have always just went with what load shot the best at 100 yds. A little background information on the gun and the load.....

308 AR, CMT billet upper/lower, RCA BCG, JP Ent. Silent Captured Buffer Spring,18" Lilja barrel with 1-11 twist, SLR Sentry 7 adj. gas block, JP Ent compensator, Larue MBT, Fortis Switchrail, Larue A-Peg grip, Larue SPR scope mount and Vortex PST 6-24x scope. Rifle has approx. 700 rounds thru it.

Specs on the ammo used to shoot this OCW.....
*2x fired IMI 7.62mm Match brass (neck skim turned, annealed, full length sized, trimmed, flash hole deburred, PP uniformed)
*Powder used was Norma 203B
*CCI 200 LR primer
*175gr SMK bullet (sorted base-ogive, meplat trimmed and seated to magazine length 2.810" O.A.L.)

All rounds were shot round robin style at 100 yds. Started to get light ejector marks at 42.7gr.....

 

[jwood1284]

It looks like 40.6 - 40.9 - 41.2 is a node. Looks like the best grouping while comparing POI. Little vertical among the three as well. 41.5 is where the POI starts to rise. Load at 40.9 and adjust seating depth to fine tune.

 

[Macmathews]

I would choose 43.0 and fine tune seating depth

 

[pell1203]

I think you have a lower node around 40.9 and most likely a higher velocity node at/near 43.0. Both recommendations above are right on!

Chrono and seating depth tests next.

 

[Rprecision]

I think you have a lower node around 40.9 and most likely a higher velocity node at/near 43.0. Both recommendations above are right on!

Chrono and seating depth tests next.

Solid advice

 

[spife7980]

I think you have a lower node around 40.9 and most likely a higher velocity node at/near 43.0. Both recommendations above are right on!
Chrono and seating depth tests next.

Agreed, both of the next points higher and lower of 40.9 & 43 impact in roughly the same area so you know that if you miss your charge weight by a grain or two or the temp warms or cools it wont push it off the edge and turn your load to crap.

Since you found 2 potential nodes I would load up 5 of each and see if one of them has velocities that seem way out of wack. Then if you cant find you answer like that do some seating depth tests for both and see if the groups tighten up any. I would chrono first because its less work and cheaper to chrono 5 shots of each charge and rule one out than to run a seating depth test for both nodes. (also make sure they fit in your mag)

Keep in mind while youre doing this to keep an eye out for pressure indications and make sure that the 43 gr charge isnt chewing up your brass. If it does go for 40.9

 

[padom]

Seating depth tests with 40.9 and 43 to see which one you can shrink the smallest then load both up again and shoot over the chrono. See which ones has the lowest SD's.

 

[padom]

One of those 2 charge weights may have the best accuracy and lowest SD's making your choice easier.

 

[Widowmaker]

Thanks for all the feedback guys! I'll load some more up at 40.9 and 43 and run a seating depth test first. Since this first round of testing all the bullets were seated at magazine length (2.810" OAL) all I can do is seat them deeper at this point. What increments do you recommend setting them back at? .005"? .010"? Also, what's the shortest you would go on the OAL? 2.780" to short?

 

[padom]

Thanks for all the feedback guys! I'll load some more up at 40.9 and 43 and run a seating depth test first. Since this first round of testing all the bullets were seated at magazine length (2.810" OAL) all I can do is seat them deeper at this point. What increments do you recommend setting them back at? .005"? .010"? Also, what's the shortest you would go on the OAL? 2.780" to short?

I assume thats because your using PMAGS. Get yourself some KAC or Larue LR308/SR25 SS magazines which will allow you to seat COAL out to 2.871". You can also try the ASC SS magazines which allow 2.865+. I have a few I run in my AR15 for long COAL and they are great. Havent tested ASC's 308 pattern magazines but for $25 you cant go wrong.

http://www.operationparts.com/kac-kn...r25-with-clip/

http://www.larue.com/larue-tactical-...ound-magazines

http://www.ammosc.com/308-sr-25-20-rd-magazine/

 

[Widowmaker]

Thanks padom, I'll check them out! May hold off on testing the seating depths until I can get a few in hand. And you're correct, I'm using PMAGS right now. What size increments do you use when testing the seating depth? .005", .010"?? Dan Newberry's site recommends testing in .010" increments......I guess that would point you in the right direction and you could always fine tune the seating depth even more if you chose at a later time. And I assume loading up 3 rounds at each seating depth would be adequate?

 

[Macmathews]

Thanks padom, I'll check them out! May hold off on testing the seating depths until I can get a few in hand. And you're correct, I'm using PMAGS right now. What size increments do you use when testing the seating depth? .005", .010"?? Dan Newberry's site recommends testing in .010" increments......I guess that would point you in the right direction and you could always fine tune the seating depth even more if you chose at a later time. And I assume loading up 3 rounds at each seating depth would be adequate?

I do further load testing .005" at a time and 5 shot groups. out to at least 300 , I actually prefer up to 600 Yards. IMO - shooting 100 Yard groups is sometimes hard to tell what load really shines over the next. This method requires more loads , but for me thats part of the fun.

 

[Conrad]

Work between 42.7 and 43 and load in 0.1 increments. Then decide if you want to tweak seating depth. You have a very wide node here that should be quite forgiving. Forgiving translates to quicker loading and not being anal on powder measurement, at least for practice rounds. This is huge in my opinion.

 

[padom]

I seat in .003 increments. There is always a group the is obvious and stands out from the rest.

 

[Widowmaker]

I went ahead and ordered 5 of the ASC 308 SS magazines and picked up 4 of their 223 SS magazines while I was at it! It will probably be a couple weeks before I get the magazines, load up some new rounds and get back out to the range. I'll update this thread when I get the seating test finished and post the results. Thanks for all help up to this point!

 

[Macmathews]

I seat in .003 increments. There is always a group the is obvious and stands out from the rest.

.003 ehh..
I seem to be about that variance between say 20 or so rounds.
maybe closer to .002.
Using a co-ax and forster ultra seating die.

Kyle

 

[padom]

Here's an example of a seating depth test I did for my new 6.5x47L and 130 ELD-M in .003 increments. Im also loading on a Forster Co-Ax and using a Forster Ultra Micrometer seating die with Lapua brass.

 

[STI_1911_Guy]

I agree with Macmathews .003 is to small of increments for me. Your picture above from the seating depth test doesnt show much in means of justifying .003" increments. All groups are look good on size and location except for the one but thats right in the middle of very good ones one either side with similar POI also. That one group is most likely attributable to shooter or other factors. It has been argued over and over that everybody has a 1/2 moa rifle yet in reality most (not all) turn out to be a little above 1/2 moa on average with many very good groups thrown in the middle. Sometimes i feel the fact that we accept our rifle will shoot around a 1/2moa yet we analyze our targets to make corrections by .00X" is a little contradictory to itself (if we know at any point we could be .25 moa in any direction from POA i dont need to analyze data that has a difference of less). Just my opinion. I try to use the law of averages when playing with rifles otherwise i find myself chasing my tail and getting frustrated instead of just shooting and having fun. To the OP I agree with everyone else, somewhere around 43 looks good and if you want to go .003" seating depth adjustments have at, I feel more comfortable adjusting by .010 or going by something closer to bergers seating depth adjustment recommendations.

 

[Widowmaker]

Update....I was able to get some rounds loaded up and shot today to perform a bullet seating depth test. I concentrated on the 40.9 gr powder charge for this test. Bullets were seated from 2.801" OAL up to 2.828" OAL in .003" increments. All rounds were fired round robin style again.....2.822" OAL gave the tightest grouping. I loaded up 20 more rounds at this length and will be shooting them tomorrow over my Magnetospeed V3. Plan on shooting four, 5 shot groups. I'm able to mount the Magnetospeed on the bottom of my rail in front of the bipod. So I can shoot for groups and not worry about the chronograph affecting them. I'll let ya'll know how it turns out! Pics of target and rifle....