Finding your rifles Sweet spot

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Mikeyman

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Hi all, I was curious how to find the optimal OAL when reloading for my tikka t3 6.5x55. I have read that a key component to accuracy is proper seating depth so that the bullet is just off the rifling. Thus far I have just been following the hornady manual which calls for OAL of 2.905" with the 140gr SST bullets I am using. I have been getting average of 1 MOA but I have noticed that out to 200 yards it spreads out to closer to 2 or 3 moa(could be just my shooting:D). The rifle likes IMR4350 using 41.5grains. Just wondering if my groups at longer distances would tighten up with optimal seating depth.
 
I am far from an expert, but after I loaded my .280 to a COAL that had it just off the lands, as per the nosler manual, my groups REALLY tightened up. The rifle shoots factory ammo very well, but the custom COAL to that rifle really woke it up.
 
"...how did you know..." One way is to load a DP cartridge with a long, loosely, seated bullet, chamber it, measure the OAL(record it), then reduce the OAL by 10 thou and try a mag load or two of your IMR4350 loads at that length. Repeat using different OAL reductions from the recorded OAL. 5, 15, 20 thou, for example.
 
Ajusting OAL is considered "fine tuning". There are more fundamantal parameters such as bullet weight, powder type and charge that warrant investigation first. FWIW my various 6.5 X 55's seems relatively insensitive to OAL - I'm generally 30 thou or more off the lands, and my rifles are shooting fine. (I shoot several rifles with the same load, so I have to set the OAL to my minimum chamber - in this case a Ruger 77 Mk 11)
 
The improvement to accuracy you will observe by adjusting the seating depth of your bullet will not take a 2 MOA group and turn it into a sub MOA group. All the same, here's how I determine the seating depth of my bullets:

The first step is to determine the length from the closed bolt face to the lands. The system I like is to make up a dummy cartridge because this gives me something tangible I can refer back to. Take a flat based bullet and seat it nose down in a resized case with no primer or powder. Chamber this cartridge, gradually increasing the force you apply to the bolt, don't jam it closed or that may cause the bullet to be pushed further into the neck and your measurement will not be precise. It may take a bit of effort to close the bolt as the bullet is pushed into the case but it will eject easily. Once you have ensured that the bolt handle is pushed to the bottom of its travel, eject the round. The ejected round is now a mirror image of the length from the closed bolt face to the lands.

Next make up a second dummy cartridge with the nose of the bullet point forward. Now press the nose of this bullet into the muzzle of your rifle and turn the cartridge in your fingers so a line is scribed by the rifling around the circumference of the bullet. Smoking the bullet with a match makes the line easier to see The scribed line marks the forward edge of the bullet's bearing surface, and its position on the bullet is going to be the same for all the bullets of that style and weight from that manufacturer, regardless of the condition or manufacturing variances of the nose of the bullets you load. The seating depth off the lands can now be easily determined by seating the bullet deeper into the second dummy cartridge, and basing the finished length from its base to the scribed line on the bullet.

Once you have the length you seek, lock down the seater stem of your die and you're good to go. Adjusting the seating depth can be done easily from this point if you know what the value is for one full turn of the seating stem of you die. For example, RCBS uses 28 turns per inch on their seater stems thus a quarter turn equals .009" a half turn equals .018" a three quarter turn equals .027" and a full turn equals .036".
 
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