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Posted: 6/18/2008 11:11:02 AM EDT
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Guys Went to the range today with my fist 308 loads, Here is the info: LC 74' Brass (all within 1.0-2.0g of each other in weight) All resized to fit case gage between high/low and all trimmed to 2.005" All charged with a 150 FMJBT seated to 2.775" ( not seated to cannelure ) All with Fed 210 primers and 39.0g of IMR 4895 All with a approx .002 crimp I only made up 20 to test for function and all did but they were all shooting high but seemed to group ok for my first loads so I made a scope adjustment and continued, they still were off 1.5-2.0" groups and then on my last (3) this happened ? the last group dropped alot and shifted right and came together but they were my last 3 so I could not continue I wish I could give you a answer on how but cannot as all were made at the same time and all the same components with the same weights, would you have any suggestions on my next loads to make up By the way thanks for everybodys help in answering my questions and concerns on OAL, Crimps and everything else  |
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If the scope or rings aren't loose, it's possible the scope's guts are. Bore sight that scope again, and reshoot your loads. Try shooting a box to test the scope; that will tell whether it's done in. Someone else can explain the procedure for shooting a box if you don't know, I have to log off. |
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Yes this was shot @ 100yrds Can somebody explain shooting a box? does he mean shoot a box of commercial ammo ? I will say that at 39g of IMR 4895 that the action seemed to cycle slow and had almost no recoil at all, is it possible that I need to bump the charge up 1-2g and I have checked several resources and most say to seat to 2.800" for a 150 FMJBT and I was seated at 2.775" is it possible that I am not getting enough pressure developed in the round. My Speer Manual along with Loadbooks say OAL is alittle short at the 2.775" but the low group was very tight, the scope has alway proved well and is never mishandled and I just had it out last week shooting some BH 175 Match and it shot very tight groups at about 1" |
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Box Testing for Repeatability (from www.6mmbr.com The number one internal scope problem most shooters encounter is unreliable tracking, not poor glass. Therefore, with any scope it is vital to test the full range of windage and elevation adjustment. Our box test consisted of a central aiming point and four separate one-inch diameter impact circles. Each circle is 4" apart vertically and 6" apart horizontally. My testing showed the scope's tracking to be positive and repeatable throughout the adjustment range--performance many scopes can't deliver. I also found that each click was positive. Unlike many other scopes, there was no lash problem. With the S&B you dial two clicks and you get two clicks of reticle movement. You don't need to click beyond your chosen setting and then go back a click or two. During the box test I ran out of 155gr Scenars and switched to the 170gr Lapua Lock Base. The ammo change altered the baseline zero a bit (lower POI), but the tracking remained dead-on. When I dialed in 4 moa "up", for example, that's exactly how much the bullet impact moved. Four clicks gave me 1 moa change, whether moving vertically or horizontally. |
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You need to work up loads, not pick a charge out of the air! Take your max load from a reliable source. Then decrease the charge 10percent. IE Max load 42 gr so your work up from 38. 38.5 39. 39.5 40 40.5 41 41.5 42 I load six of each. I fire one to check for pressure signs in a stair step approach and function in the gun, especially semi autos.....these rounds also act as fouling rounds! Then I will use at the OCW load development firing method to look for the best results. OCW That will let me zone in on a load that is accurate safe and functions the rifle. |
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Yes the OCW theory works well and will produce a optimum load for your rifle. I don't like the 10% drop from the max load though. Almost all the time dropping 10% from the max recommended load will put you UNDER the recommended START charge weight. So if you don't feel comfortable with a middle weight in the data sheet start at the minimum charge weight...JMO... Do a box test on your scope and you might find your problem. |
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I did not know this was called a box test and yes it has been done when I installed the scope and did a laser bore sight on it with my Site-Lite SL-150, I basically benched the rifle and fired at a target and then raised/lowered Elev to check click repeatability along with the windage and it all came out good, I did however notice as I was going thru the fired cases that there were some mixed headstamps all were LC but different years some how I got these mixed up,I will have to start over to see if there is a problem. I may try the OCW Method but after looking at several sources including here I am going to start with a charge wt of 41.0g of 4895 and a OAL of 2.780" the range for a FMJ BT is 41.0-45.0 and the OAL is 2.780-2.800" at least from my sources I will load up at least 30-40 for a proper test and compare it against some Commercial Ammo of similar wt. and post my findings |
The idea during "shooting a box" is to shoot at one aiming point, the moving the scope reticle to determine whether the scope returns to the initial point of impact. The procedure it to shoot at the aiming point, then click up, say 8 or 10 minutes at 100 yards and shoot a group while holding on the original aiming point, then add right wind the same amount and shoot a group, then down and shoot a group, then left wind and shoot a group. Hopefully it will fall on top of the first group. If the scope's internals are loose, causing a wandering zero, you'll likely find out before shooting the entire box. If it's really bad, each shot will fly into the target in a seemingly random location unrelated to the point of aim. This is pretty easy to discern by taking a shot, then banging on the scope with your hand and taking another shot; they should be close if the scope is okay and your bench method is good. |
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