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> Crude Ladder Test
Crude Ladder Test
@ 03:34 pm (GMT) |
Jim MoseleyNathan,I finally got around to pushing the 7 mag with the high end load of H-1000 with 72.0 - 73.4, in increments of .2's that you had suggested. I used Fed GM210 primers instead of the 215m. I hope the photo of the target will post. Anyway you'll see the 72.0 and 72.2 are in the same hole. As others started to spread, the 73.0 came right back to group with 72.0-72.2. Measure 1/4 inch @100 yds. for the 3 rds. I'm hoping you are going to tell my that the harmonics are the same with that group and that either of the loads should work. I only loaded one round each which was intended only to show me signs of pressure and not waste loading a lot of rounds past the pressure threshold. Lucky, no signs of pressure through out the string. I know this is a crude test at best, but what are your thought or anyone else?? |
Replies
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@ 05:24 pm (GMT) |
Jim MoseleyRe: Crude Ladder TestI think I've got it now.
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@ 05:27 pm (GMT) |
Nathan FosterRe: Crude Ladder TestHi Jim, those photos are on your computer so they won't appear here. You need to upload the pics to a hosting site first. That way, when you insert the blurb , it will show the photo on the host site.
It is either that or it could be that you are clicking on 'copy image' rather than clicking on 'copy image location'. That probably is what is happening. Sorry Jim,I know it can be confusing if yoiu are not used to it. I remember joining a forum a few years ago and thinking what the heck is this. The ladder tests sound good. Next step is to establish ES. A low extreme spread of velocities from shot to shot is the focus now. You'll want to try and get under 20fps, low 10's would be great but we don't want to turn this into an exercise in frustration. What bullet jump did you go with Jim? |
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@ 06:30 pm (GMT) |
Matt ReidRe: Crude Ladder TestHi Jim,As you have mentioned its a fairly crude test so hard to draw definitive results from. What you have done is closer to a optimum charge weight test (OCW), with ladder tests usually being performed at 300y. Assuming your shooting was good for each shot, the group around 72gn looks good. If it were me I'd test at 71.8,72,72.2 again with 3 shot groups over the chrono. The higher charges seem to be moving you out of the node. I have read of and experienced a 'scatter node' where groups really open up, kinda the opposite of an accuracy node. This phenomenon means that single shot tests have potential to be misleading (although obviously fine for pressure testing). Accuracy nodes tend to fall a 1.5% charge weight either side of a scatter node. Full credit to Dan Newberry for his work on this. Part of the thinking behind load development is finding a really stable load as well as accurate and low es. In your case, if the loads either side of 72gn group well with the same point of impact, this means by running with 72gns, small variations in the reloading process, case capacity, temp etc aren't going to throw your accuracy out the window. Just a few thoughts, hope it helps, Matt |
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@ 07:42 pm (GMT) |
Nathan FosterRe: Crude Ladder TestWell you can really see the effects of harmonics there, the bullet leaving the bore at different points of the 'whip'.So we are seeing what I would call a highly sensitive barrel. You used the word crude and I think that ladder testing can be crude, just as you suggest, as evidenced by the sensitivity of this barrel. I am working on a Sendero at the moment. I initially tricked it up a few years ago, now it has come in for a birthday as groups have opened up to .6" (shocking isn't it). It has probably had about 400-500 rounds through it. Changes within the bore are not completely uncommon in this regard. I have been doing three shot groups, working up in .2 grain increments. I got to 3086fps, then hit a plateau. At 75 grains H1000 (please nobody try to duplicate this- it is way over max), velocity is still 3086fps, but with the odd 3120fps and the pressure is too highwith scuff marks on the case heads. Groups are similar to yours, left right left. I cant down load this one. The trouble is, if I load to 2960-3020fps, the accuracy is excellent but the ES is so poor that we are looking at a minimum 6" dispersion at 1000 yards. Add shooter error, temp error and up/down drafts and we could be looking at a 12" group or more. So what to do. Well, the next step for me is seating depth. I will pick a load (74 grains for 3086fps and ES 3fps) and then play with seating depths. I have been sitting on 10 thou jump so next step will be 20 and then 40 thou and maybe 60 thou (.2mm .5mm 1mm 1.2mm). By doing this I will attempt to alter accuracy (when the bullet leaves the bore / harmonic whip / node / timing) while maintaining the ES I want. It may or may not work- such is the rifle accuracy game. We just have to try these things. It may become a 7mm Practical if it does not behave! It will eventually anyway. It will take me hours and hours by the time I have finished. We have a goal of .250-.3" so I will have to keep at it. I know you already have an accurate load Jim so if the velocity experimentation gets to be too much, I can well understand if you want to leave it. I think 3 shot groups will be the way if you want to keep experimenting. Usually I can get to 3125fps with ease during experiments with the A-max. Some rifles will like this, others won't and may need to be loaded around 2960fps. I try to test the full range just to make sure I have a full understanding of the individual barrel. But its quite a disparity if you think about it, 165fps. Good input thanks Matt. It does need to be a stable load as you say, if a bore is sensitive, the last thing we want is a sensitive load that cannot handle .1 grain off the mark. So true. |
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@ 08:15 pm (GMT) |
Jim MoseleyRe: Crude Ladder TestThanks Nathan and Matt for the input. I'm seating the Amax .010 off the lands. I'd be happy with 3050 to 3070 fps as long as I can get the accuracy. Hope to test this week, but the weatherman is calling crappy weather....snow and wind!Nathan, I keep reading your article on the 7 Practical and it continues to intrigue me. What's the expected number of rounds for the barrel life? @Matt My chony has never been very good. It will always give high MV readings. I just set up my "tall target" at 600 yds and read the mv off the drop. This also tells me how well it will group at long range. I still start at 100 yds, zero the rifle at 300 and drop chart at 600. Once I get to 1000 yds, I can tweak the MV if needed. Thanks again guys! |
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@ 08:28 pm (GMT) |
Matt ReidRe: Crude Ladder TestSounds good Jim. I figure, regardless of what your chrono is saying it's what vertical dispersion you are seeing on the target out at field ranges that will be the decider.Be great to see some follow up pics of targets etc once you get it all nailed down. Matt |
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@ 08:59 pm (GMT) |
Nathan FosterRe: Crude Ladder TestIts a funny thing Jim in that the barrel life of the Practical (and other similar magnums) is highly dependent on cleaning methods. If the pores in the steel of the throat are kept closed via polishing, throat erosion is (in my case) .1mm (5 thou) per 350 rounds. On the other hand, by avoiding polishing (due to a fear of abrasion) and using solvents only, throat wear is .5mm per 350 rounds (20 thou).In other words, abrasive polishing prevents throat wear, not increases it. String counts also make a big difference too. Lots of 12 shot strings will heat up the steel, open the pores and allow material to cut away. I am picking 1200 rounds will be about right for my rifle but it could go a lot more. It depends on whether it will be used in heavy sessions between cleanings. The Practical is a simple fix for a worn 7mm RM barrel. Simply rechamber, recrown, buy a 50 count of .300 Win Mag and as long as you already have neck dies, off you go again. I thinks its a good thing especially if you have a bore that you already trust and has proven itself to be a good shooter, but gradually lost accuracy. the rechambering can bring the old 7mm RM barrel back to life for another 1200 rounds, plus another 100-200fps etc into the bargain. |
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