.308 dope, just guessing bullet BC ...


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Snakum
February 17, 2010, 04:54 PM
I'm shooting a lot of PMC Bronze and Silver Bear .308 ammo to nail my scope dope and prepare for hunting season in the Fall. But I can't find the BC of the bullets anywhere, of course, nor could I find the velocity of the Silver Bear. So I made a first pass at the tables using an online calculator and the bolded info for each cartridge. Could someone take a second to look at my BC and velocities to see if I'm even close? I don't want to go out and burn up ammo without some valid starting point. I took the PMC velocity and trajectory from their site and backed into a BC. For the Silver Bear SP I'm pulling it from my butt.

PMC Bronze 147gr FMJBT BC = .401 Velocity 2780fps

Silver Bear 140gr SP BC = .343 Velocity 2650


I'm using this data to calc my trajectories and come-ups and windage clocks as a starting point. But bullet data on the cheap stuff is hard to come by. Any help at all appreciated.

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rcmodel
February 17, 2010, 05:02 PM
Published BC and drop tables aren't accurate enough to depend on them for long range hunting or target shooting.

The only actual way to find out the BC & drop of any bullet at a specific velocity is go shoot some at 100, 200, 300, and 400 yards and measure the actual drop on paper out of your rifle.

From there, you can reverse engineer the bullet BC from published drop tables if you really want to know the BC that bad..

rc

Snakum
February 17, 2010, 05:50 PM
I'll be shooting thru the entire table, just need a starting point. the BC is needed only to put together a table to take to the range.

Zak Smith
February 17, 2010, 08:01 PM
Probably as reasonable as anything given you don't post a barrel length. Go buy a $100 chronograph, it'll pay off in a couple shooting sessions.

Snakum
February 17, 2010, 08:18 PM
My bad ... totally forgot the barrel length. It was 22" and I deducted for it. Anyway I found the info on JBM. Just needed a general idea of the BCs so I could generate a starting table before heading to the field Sunday. I know real world is going to be different, but I needed to start somewhere.

Chrono is the next purchase after reloading kit. If this keeps up I'm going to have to actually get a job. :(

627PCFan
February 18, 2010, 11:53 AM
I would have an issue with bullet choice on the Silver Bear side although Im not familair with the PMC but I wont touch that.

I get large velocity deviations using Silver Bear ammo, after I sort them by OAL. FWIW Im shooting 223 in a bolt action so I assume that could translate into 308s as well. When you pay 3.50 per box of 50, you get what you get.

Snakum
February 18, 2010, 06:31 PM
The Silver Bear is just used for practicing my come-ups and shooting from positions. It doesn't have to be accurate for that. Before deer season I'll be redoing the table with Federal PowerShoks or with Sierra GK handloads, maybe both.

R.W.Dale
February 18, 2010, 06:45 PM
According the my Iphone ballistic app the BC's you seek are as follows

.369 for the 147grn PMC load @2751fps

however the only steel cased load I have is 150grn Wolf, so nutz on the silver bear

If you need a table for the PMC stuff I can conjure one up for ya if you have the zero and scope height data

Snakum
February 18, 2010, 08:32 PM
Thanks Krochus. I'm zero'ing at 200 and scope height is a measured 1.5". Shooting conditions will be 300' MSL and standard atmosphere is fine. Wind 10mph, of course. I appreciate it.

On the Bear SPs I used BC = .343 and an avg velocity of 2650 from a 22" barrel. You think that's close enough for a start point? Any advice at all is certainly appreciated.

Somewhere in a box I still have my drag bag from school with my Dope and Range Cards, notes, FMs, and my prayer wheel, but I can't find it anywhere. Might be able to get my old brain unfogged on this stuff if I can find it. :erm:

hogshead
February 18, 2010, 08:37 PM
Please let us know how this stuff groups at 300 yards.

R.W.Dale
February 18, 2010, 08:44 PM
ask and ye shall receive

http://www.thehighroad.org/attachment.php?attachmentid=115969&d=1266543836

~z
February 18, 2010, 09:33 PM
seems difficult to determine the actual data with estimated velocity, estimated BC, and ammo you admit is not that accurate. Best of luck but a word of caution: as prefect practice makes prefect, the converse can also be expected.

I echo other comments, buy a chronograph, and add that accurate ammo will help with the practice. if you intend to hunt/shoot with 'better' ammo, use that for practice...just my $0.02
~z

Snakum
February 19, 2010, 05:40 AM
Thanks, Krochus. Much appreciated.

Snakum
February 20, 2010, 09:35 PM
Finished a simplified card to take tomorrow along with the targets, boxes to put the targets on, three bolt guns, sandbags, bipods ... a full trunk load of stuff. Should be enough to get started. Thanks for the help with it.


-------------------------------------------------------
http://i92.photobucket.com/albums/l16/snakum/LRDope.jpg


Wind Effects
2-4 mph - feel on face, leaves and tall thin grasses jostling
4-8 mph - leaves and grasses begin whipping, mirage tips 45 deg
6-10 mph - moves tips of trees, loose paper, and dust
8-12 mph - small brush and tree limbs bend
10+ mph - trees swaying, marage flattens
* Open air moves faster than air close to the ground,


Wind Dir Comp
70 to 90 degrees - full value
40 to 60 - half value

Snakum
February 22, 2010, 12:03 AM
Worked like a charm. After one run thru and associated corrections we could get first round hits 100% of the time out to 400 yards. Even the Silver Bear shot minute-of-pie-plate at that distance so long as we loaded up the bipod correctly. Sweet. :D

Remo-99
February 22, 2010, 12:48 AM
BTW Krochus, your phone battery will need to be recharged soon. lol.

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