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> Practical load development question
Practical load development question
@ 06:33 am (GMT) |
Rob Hughes-GamesBeen doing load development for the 7mm and my drops and groups seem to be larger than they should.At 100 I can print clover leafs but when I went 285 the group was 3". The group center was 10" low. According to the crono I'm driving the 180 bergers at 3013 with ES in the teens. I thought it would be close tho the 8" drop mark. Apart from maybe being a shit shot what would be the cause of groups opening up. I was looking for around 1.5" groups hopefully. Thought?[b] |
Replies
@ 10:28 am (GMT) |
Jim MoseleyRe: Practical load development questionI have more trust in my drop chart than with my chrony. Drop chart doesn't lie. As for your shooting, I suggest you back down to 200 yds and see how tight the group will be. What are you using for a rest? |
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@ 02:23 pm (GMT) |
Rob Hughes-GamesRe: Practical load development questionWas using a feed sack of sand front and back for rests. |
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@ 06:23 am (GMT) |
Rob Hughes-GamesRe: Practical load development questionThe drops just don't make sense to me. If I correct the velocity to match the drops is recons I'm getting 2770ftps with 180gn. Maybe I'm way under loading. I'm using 72gn h1000. I have a tight barrel. Using a different crono with 76gn h1000 and 168gn I was getting 3230ftps supposedly. Never tested drops.If I'm only getting 2770 I might as well almost be using a 7-08 |
@ 08:11 pm (GMT) |
Nathan FosterRe: Practical load development questionHi Rob, the powder charges you state should be giving the velocities you state. The 76gr / 168gr load is on the hot side and may not be safe in summer temps.So if the velocities are coorect (even if inaccurate, I estimate they could be no more that 60fps out), then something else is wrong. Check- 1. What is your actual scope height versus the scope height you inputted onto software. 2. Did you sight in on a hard bench, then move to the feed sacks. As Jim alludes to, if you initially sighted in over a hard rest, then moved to a soft rest, you will be at least 1 MOA lower. 3. Was there any change in technique (same problems as 2). Eye position- parallax. Does the rifle have an added cheek piece which may be forcing your eye out of alignment (eye too high). 4. Is your 100 yard range measured exactly- silly point but still pays to check. This may not account for a 2" extra drop but its another factor to check. 5. Down drafts when test shooting? 6. Environmental inputs. Freezing cold weather will cause a low POI via a combo of both ignition problems and changes exterior ballistics compared to warm days. One point- you are handicapping your 7mm quite badly with your current zero, whether the drop is 8" or 10" low. You should be dead on at around 270 yards, not low. My .308 has a better trajectory than this. The actual group size is not highly relevant as environmental factors will be at play. Group size at range can be addressed later with practice. Summary- check inputs, check technique and parallax. Have a think about zeroing the rifle at a greater distance (recommend setting 3" high at 100 yards). The above are all just ideas, some points are near to being irrelevant, others are major factors. |
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@ 02:35 am (GMT) |
Rob Hughes-GamesRe: Practical load development questionthanks for the reply NathanI measured my scope height with calipers from the center of the rings to center of action so that should be right. All the shooting has been over feed sacks so far and Ive tried to be conscious of keeping the same technique. I do have and adjustable cheek piece. im adjusting it until i get a clear sight without having to use muscles to hold my neck up. The range ive just been measurig with a range finder so +-1y. Ive been shooting in similar conditions over the last few days so environmental is pretty similar. all places have been flat so shouldnt be any down drafts. i understand the sighting in high thing to make your point blank range better but the bullet trajectory will be the same no? cant you just know the drops for close shots and just use the retical. so if its grouping good at 100 then it should just be environmental evvecting the groups at further distances? |
@ 05:05 am (GMT) |
chris murphyRe: Practical load development questionHi Rob what sort of target are you using a mate of mine was shooting at a square he drew and was getting 1.5" group at 100. I told him to aim at the corner of the box or use a cross and his group droped to .8" (factory ammo howa 308). By the sound of it your on to it with that sort of set up bit just a thought. Also are you South African? My Prather has a family friend called Rob Hughes-games |
@ 05:13 am (GMT) |
Bob MavinRe: Practical load development questionHi RobWhen you say your groups are 10" low, what height are they at 100m. If on at 100m Sierra infinity says 10.5" low at 285m. What twist rate is your barrel? I think it will need around 1:8" to stabilise that pill. Cheers Bob |
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@ 02:36 pm (GMT) |
Nathan FosterRe: Practical load development questionA 1.9 1/4 twist does stabilize the 180gr VLD OK out to long ranges. A 10 twist might be a problem. A 1:9 twist is optimal for all round work.I can only take guesses without having the rifle in hand. Hopefully something simple. |
@ 09:43 pm (GMT) |
john mitchellRe: Practical load development questionQuote: The drops just don't make sense to me. If I correct the velocity to match the drops is recons I'm getting 2770ftps with 180gn. Maybe I'm way under loading. I'm using 72gn h1000. I have a tight barrel. Using a different crono with 76gn h1000 and 168gn I was getting 3230ftps supposedly. Never tested drops.
If I'm only getting 2770 I might as well almost be using a 7-08 |
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@ 09:48 pm (GMT) |
john mitchellRe: Practical load development questionQuote: The drops just don't make sense to me. If I correct the velocity to match the drops is recons I'm getting 2770ftps with 180gn. Maybe I'm way under loading. I'm using 72gn h1000. I have a tight barrel. Using a different crono with 76gn h1000 and 168gn I was getting 3230ftps supposedly. Never tested drops.
If I'm only getting 2770 I might as well almost be using a 7-08 I'm using 72g h1000 with the 190 matrix and it's moving at 2980fps , it's a 28 in. Barrel but your velocity seems way off. |
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@ 04:32 am (GMT) |
Rob Hughes-GamesRe: Practical load development questionChris- was aiming at the corner of a square at 100. At 285y I was just aiming at a 1/2min square.And yes I'm South African. Only Rob H-G in nz. Must be me. Where you based. Who's your friend? Bob- I have a 1in9 twist 27" barrel. I'm also at 285 yards not meters so that will make a difference. |
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@ 01:09 pm (GMT) |
chris murphyRe: Practical load development questionMy partners name is Christine Martin (also South African) she was in Auckland but we now live in Blenheim. |
@ 02:37 pm (GMT) |
Mike DavisRe: Practical load development questionRob it seems others have answered your question for you but I thought I might add this for clarification as I think its what others were driving at.way back when Adam was a cowboy some clever fella (possibly a Chinaman as they seem to be credited with most handy things lol) worked out a rough guide for sighting in scope sighted rifles with a velocity of around 3000 fps that works pretty darn well across the board. its called the "rule of three" and works unless you have dicky great high see through scope mounts if you sight in so bullets impact target 3" high at 100 meters your bullets will be traveling a path somewhere along these lines 7mm mag with 150grn bullet 1.3" high at 50yards 3"high at 100 3.4"high at 170 yards zeroed for 290 yards hold dead on to=4"low at 325 yards hold 12"over at 400 yards now that came out of book published in 1968 so its not a new theory and even with new fandangled equipment available today it works for us old farts who dont dial up and generally dont stretch barrel much over 300 yards hope that helps |
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@ 02:54 pm (GMT) |
Rob Hughes-GamesRe: Practical load development questionChris. Yup I've known Christine since I was about 7yrs old. I used to hang out with her sister Kate a lot but haven't since we left Africa really.Mike. I like that idea but with a scope that can dial I also like the idea of just having a 100y zero so you can neck shoot close in and then dial once ranges start going past 200. Should have more time once an animals further out |
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