|
|
|
Discussion Forums
Forum Index
> Precision long range hunting and shooting
> sudden accuracy loss
sudden accuracy loss
@ 07:58 am (GMT) |
markHi Guys,I have a custom 7mm rem mag that I had built last year at true flite, it was bedded by them and load development was straight forward, I got 3 different bullets working nicely. The Berger VLD was the easiest, I think I just got a good COL by chance. It was shooting consistently .4 MOA or less. (which seems about as good as I can do at the moment) I used it in 2 competitions and it shot really well. At the 250 round count I gave it a scrub up with maroon poly pad and have been polishing it after each shooting session. I suspect the accuracy loss may have coincided with the throat scrub (though cant be sure) Since I knew my VLD load was good I didnt test it before the next competition. That competition i shot poorly and when checking it at the range after that the same load was shooting just over 1 MOA at 100m and 3 inches at the 200y range yesterday. Ive checked the scope mounts, rings, action screws, checked cleaned & re-greased bedding. All seems fine. Gun smith had a look at the throat & crown all looks fine. next 2 options I will have to try is another scope.... perhaps the nightforce nxs just decided to sh#t itself, anyone heard of NXS issues? Or perhaps the berger VLD is so finicky on jump that with throat erosion & polishing has increased the jump sufficiently to blow accuracy..... are they really that finicky? Cheers, Mark |
Replies
@ 08:39 am (GMT) |
Nathan FosterRe: sudden accuracy lossHi Mark, Heavy (comp) shooting sessions are a catch 22. If you do nothing, the throat will erode and accuracy can be lost. If you polish to prevent severe erosion, the tolerances may still change to some extent and you may still have to rework loads.One also has to take the individual bore into account. The more heavy the rifle fouls, the harsher we can be with each session. But on a highly polished match bore, it can pay to be more gentle in our approach. Much depends on how the bore is used each session. If shots are fired quickly in high volume and the bore has been allowed to get quite hot, then this is when we need to really get into polishing once every so many rounds. But the guy who only fires a couple of shots here and there, then cleans his rifle carefully, may get up to 300 or 400 rounds before we see any signs of wear. In this case, just an occasional light polish with rag and autosol is fine. Its really all about usage. In either case, if you are still hovering around 1 MOA, then it is likely that the scope and platform are fine. If your smith has scoped the bore and found it to be OK, then all should be well and good. I would suggest that your load has simply lost some velocity, perhaps 40 to 60fps, losing its harmonic sweet spot. You may therefore have to work up another grain to find your sweet spot. But do take the time to re-measure your max OAL. This will also tell you whether your shooting and polishing has produced significant growth. Normally, a Rem Mag will show signs of craze cracking at 250 rounds after high volume shooting so again, its a bit of a catch 22. Do nothing and the cracks will simply get deeper. When you get a chance, could you please quote the load you have been using, the bullet weight, OAL, the powder type, powder charge and velocity. |
|
@ 10:20 am (GMT) |
markRe: sudden accuracy lossLoad is 72.5g 2225, col 88mm velocity 3030fps from 27 inch barrel.Fed match primers Norma brass. 168 grain Berger vld. The last comp I did we had mostly 5 shots at each station. However at 1 or 2 I had 10 consecutive shots due to a problem with electronic targets, she got pretty hot then. It's a no 4 contour. |
|
@ 10:23 am (GMT) |
markRe: sudden accuracy lossIt shot pretty similar velocity over pro chrono the other day, doesn't seem to have dropped much velocity I got 3006/3016/3030 from 3 |
|
@ 02:16 pm (GMT) |
markRe: sudden accuracy lossBy the way thanks for the prompt and comprehensive reply Nathan.I'll give the jump a measure tonight, see if I can discern any difference. I normally keep the barrel cool for practice, only comps get successive shots. Round count is about 330 now. I polish the throat after most shooting sessions that are over 5-6 rounds. Thanks again. Mark |
|
@ 07:54 am (GMT) |
Nathan FosterRe: sudden accuracy lossHi Mark, sorry I was away from the computer for most of the day.The load and velocities sound about right. A check on the max OAL's will be useful. It looks like the throat was already long on this one so its using about a grain more than normal. But then again, it could just be that batch of bullets so take my previous comment as being a possibility, not an absolute. Being a match bore and being that you are keeping it cool for the most part, it may be time to back off polishing for a bit. Use a tight rag and autosol every 100 rounds (or after comps) for the next 300 rounds and monitor results. If you get a chance, try the 180gr ELD-M in your rifle. Drop down 5 grains and test up to 69 grains or possibly 69.5gr 2225 but do be careful of pressures with this bullet. The sweet spot is normally 3.5 to 4 grains below the sweet spot for 168 and 162gr pills. But before you reload this, check that there are no donuts inside your brass from previous long seating. Run a piece of wire or very small screw driver down the inside of the case neck and see if it hits a bump. If there is a bump, you may need to ream the inside of the brass before experimenting with heavier bullets. K&M make a neck turn tool with a donut cutting carbide mandrel, very handy. |
|
@ 09:45 am (GMT) |
markRe: sudden accuracy lossNo worries Nathan, I really appreciate your input.Yes I have a box of the 180 eld m's to try and the k&m neck turning gear with cutting mandrel. That gives me plenty to work on! Thanks again |
|
@ 02:48 pm (GMT) |
markRe: sudden accuracy lossHi Nathan & others,I havent got an OAL gauge, previous max OAL I measured using the partial neck size technique which now that I am measuring against my previous results I see there is/was room for a fair bit of error. Poor form on my part. I changed to the cleaning rod method with a drilled out case which seems to give more consistent results. The berger 168 VLD measurement is barely different to what I had originally measured. I would put that down to error explained above. my original 162 ELD X max OAL was 87.65mm, now appears to be 87.8 162 AMAX max OAL was 87.65mm, now 88.25mm looks like the 180 ELD M will be max at 89.5mm So not particularly helpful data due to my poor method, that error aside it does seem the throat may have lengthened slightly perhaps by .15mm. I'll load up some 180s and see how that goes. Cheers, |
|
@ 09:42 am (GMT) |
Nathan FosterRe: sudden accuracy lossThanks for the update Mark.OK, it appears this reamer was .65mm longer in the throat than the basic factory rifle reamers (may be due to a more gentle leade angle). Since then it has crept forwards by a normal amount - but possibly enough to alter harmonics. If the 180gr reads max at 89.5mm (double check it because it might be 89.2 or 89.3), try .3mm jump and see how you get on. Hopefully a new pet load. |
|
@ 12:46 pm (GMT) |
markRe: sudden accuracy lossBeauty, thanks so much Nathan, yes Grant did a bit of a custom throat on it rather than straight SAMI spec. It was set up to shoot the 162 AMAX/ELD s but I found them a bit harder to shoot well than the bergers.I checked several cases for doughnuts, I cant discern any, I sized them, expanded them on the k&m mandrel then run the cutting mandrel through them, they went smoothly with no sign of gripping or cutting. I'll get loading some 180s, see how I go. Cheers |
|
@ 07:44 pm (GMT) |
markRe: sudden accuracy lossYou'd be spot on as usual Nathan!Measured a few more times with my glasses on 89.2mm Cheers |
|
@ 06:12 am (GMT) |
markRe: sudden accuracy lossHi Nathan,Got down the range yesterday, Back on track! 69 grains at 2820fps 20mm @ 200y. A little bit of fine tuning and I should be away again. Thanks again for your superb advice. Mark |
|
@ 07:18 am (GMT) |
Nathan FosterRe: sudden accuracy lossGood to hear Mark. From a 26" tube there may be a sweet spot just up a bit from this (2850 to 2900fps) but this last 70fps is not really worth chasing if the rifle is already grouping well and if the ES is complimentary. Also, I do find that this projectile produces higher pressure than others so again, it may be in optimal form now. |
|
@ 08:28 am (GMT) |
markRe: sudden accuracy lossCheers Nathan,Other groups were only slightly larger so It could be just short of that node, i only tested to 69 grains so far. ES was 2 at 2820 and 1 at 2860 but sun came out for that one. It's a 27inch barrel so maybe I could squeeze a wee bit more speed out of it. Thanks. |
|
@ 04:54 pm (GMT) |
markRe: sudden accuracy lossHi All,The 180eld m has been going great in my rem mag, thanks so much to Nathan, tested 69.3 g today which went very well 8mm at 100m even with one shot I felt the foreend slip just slightly. Probably just luck but 3 velocities identical at 2867fps, I have never had that level of consistency with my chrono. Interesting thing was that when I tried 69.6g the velocities dropped slightly 2855 & 2849 & 2861. One would immediately think I mixed up my labelling but I'm 99% sure I didn't. The group was slightly better, all shots felt good, bolt lift normal and primers look ok. I've seen flat line velocities before, approaching or at maximum but do they sometimes drop or is it more likely just reliability in the chrono with current light conditions etc. It was a clear sunny day today, which has given me weird readings in the past. Cheers Mark |
Please wait
ABOUT USWe are a small, family run business, based out of Taranaki, New Zealand, who specialize in cartridge research and testing, and rifle accurizing.
|
KNOWLEDGEBASE |
KNOWLEDGEBASE |