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338 Snipe-Tac - Load Evaluation Wanted

 
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  #1  
Old 06-16-2008, 12:34 PM
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338 Snipe-Tac - Load Evaluation Wanted

Hey guys, finally got to do some load work-up this morning. I'm shooting a 338 snipe-tac made by Dave Viers (specs posted down in Gun Photos). I used H50BMG powder, 300gr SMKs (boron coated), and WLRM primers. I waited about 3 minutes between shots, putting the rifle and ammo in the shade between shots. Shots were made round robin, i.e. one 135gr, one 136gr, etc. It was sunny (mirage was pretty bad so you gotta cut me a little slack for the group size ) with a light (est. 2-5 mph) left to right breeze. Temperature ran from 45* at the start to about 50* at the end and elevation of 2621 (no humidity reading, forgot the Brunton). Distance to target was 235 yards and I used an Oehler model 35P chronograph. Group size is center to center.

135gr
1 3113fps (sighter/fouler shot)
2 no reading
3 no reading (shots 2 and 3 almost touching)
4 3134fps
es = 21fps
group size = 1.7" or 0.72moa

136gr
1 3134fps
2 no reading
3 3128fps
es = 6fps
group size = 1.52" or 0.65moa

137gr
1 3157fps
2 3150fps
3 3169fps
es = 19fps
group size = 1.38" or 0.59moa

138gr
1 3171fps
2 3174fps
3 3179fps
es = 8fps
group size = 1.62" or .69moa

139gr
1 3193fps
2 3208fps (1st two shots touching)
3 3208fps
es = 15fps
group size = 1.05" or 0.45moa

140gr
1 3218fps
2 3225fps
3 3232fps
es = 14fps
group size = 1.17" or 0.50moa

I thought about fine-tuning the upper spectrum, say 138.5gr, 139gr, 139.5gr, and 140gr. Maybe 5 shots each to gather a little more chrono data? The load at 139 sure looked promising to me, except for the first shot being 15fps slower...

Any thoughts or comments? Thanks! -- Don
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Old 06-18-2008, 05:45 AM
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Did you have a problem with your 35P, as it missed a few of the early shots?

How were the various load group impacting the target in relation to each other - as in vertical dispersion between the various load groups (e.g. 138 gr 2" above aim point, 139 gr 3" above aim point)? There are lots of ways to do load development, I try to do it with as few rounds down range as needed.

I agree that the upper range looks promising, and that 5 round groups in this area will give you a bit more data to determine ES and SD for your load.

I've talked to two different folks who said that 3,200 fps was the accuracy node for their 338 Big Baer (338/408), so your 139 load is verifying what they had to say.

JeffVN
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Old 06-18-2008, 06:03 AM
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Can you post pictures of the targets?
Where is the bullet seated in relation to the lands?
Have you been taking measurements of the case at the base to measure growth over a virgin piece of brass?
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Old 06-18-2008, 04:12 PM
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JeffVN: Regarding the missed readings on the early shots, I was shooting at six different targets and it took me a few tries to figure out to slide over a little on the bench so the bullet would get read - operator error. Hopefully the photo is clear enough so that you can see the impact shift from group to group.

Joel: My COL is 4.140, which is about .015 from the lands I believe. I did not take any measurements of virgin brass. The brass that I have I bought already fireformed from Dave Viers. To be honest, I'm not real sure of what you are referring to, which I hope means you are going to educate me.

Thank you to both of you for your interest and help. If the photo isn't easy enough to read (I took it with my phone) let me know and I'll use a better camera. I've got the rest of the data now for the half-grain differences on the upper end that I'll post next... -- Don
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Old 06-18-2008, 05:04 PM
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Let me get this straight, you would shoot one round (say 135 grs.) then pick the rifle up and it move it to the shade, wait three minutes come back and shoot one round with 136 gr, and repeat the procedure till all the different powder charges were shot, then start back at the lowest powder charge and do it all over again ?

Mirage at 45* are you sure it was not heat off the barrell?

Nice rifle btw,

John
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  #6  
Old 06-18-2008, 05:26 PM
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This photo is of the second day of shooting. I wanted to check the upper node to see if I could narrow it down. All of these shots were in the shade, without mirage, at early morning with minimal wind. Kind of thought I'd get a little tighter groups. Guess that's what I get for thinking...

Anyway, here is the data to go along with the photo.

138gr
1 3191fps (sighter/fouler)
2 3189fps (second sighter/fouler)
3 3164fps
4 3196fps
5 3185fps
6 3209fps
7 3217fps
ES = 54fps
group size = 1.91" or 0.81moa

138.5gr
1 3197fps
2 3184fps
3 3185fps
4 3209fps
5 3217fps
ES = 26fps
group size = 1.93" or 0.82moa
w/o flyer = 1.06" or 0.45moa

139gr
1 3213fps
2 3225fps
3 3198fps
4 3213fps
5 3215fps
ES = 27fps
group size = 2.60" or 1.10moa
w/o flyer = 1.60" or 0.68moa

139.5gr
1 3205fps
2 3210fps
3 3216fps
4 3238fps
5 3223fps
ES = 33fps
group size = 2.60" or 1.10moa
w/o flyer = 1.68" or 0.71moa

140gr
1 3232fps
2 3210fps
3 3225fps
4 3251fps
5 3243fps
ES = 33fps
group size = 3.8" or 1.62moa
w/o flyer = 2.1" or 0.89moa

I reported group size with and without the most extreme shot. I do not think I pulled those shots; don't really have any explanation to the flyers...though the flyers for the last three groups were the first shot in each group (in the 138.5gr group it was the third shot). I also noticed that the average velocity was running a little higher from the previous day (18fps on the 138gr, 10fps on the 139gr, and 7fps on the 140gr). The only thing environmentally different was shooting in the sun on the first day and in the shade on the second day.

Any ideas to reduce the extreme spread would also be appreciated. Dave Viers did recommend GM215M primers but I can not locate any so I'm using my WLRM primers for now. I'm fairly consistent with my reloading - not saying I'm great at it but I've been reloading for several years now all the while gleaning handloading techniques from this site. Sure is expensive applying what one learns from here!

Thanks again! -- Don
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  #7  
Old 06-18-2008, 05:56 PM
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Marine Sniper: Our local range is stuck right up into a draw, which gives a shooter some time past sunrise to still shoot in the shade. I saw a lot of mirage on the first day (shooting in the sun) and none the second day (got there an hour earlier and shot in the shade).

I set up my bench and chrono right off the side of the parking lot with my truck about 10' away. But yes, on the first day I picked up the rifle and set it in the shade of my truck each time in a vertical position to aid in the cooling down. Seemed to work ok, the barrel was never hot but never totally cooled down either. I do very little shooting from benches and really don't have a clue what proper protocol is, just what feels right, you know?

I shot the load workup round robin as it gives me a little more comfort factor. If I mess up a shot (which I try not to do ) I'm reasonably confident that the others will be correct, that I can hopefully make some assumptions off the aggregate, as well as chrono data.

Thanks for the compliment, btw. -- Don
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