Im not sure you guys are a good influence on me.

[stralia]

I tend to question, measure and remeasure everything since discovering this forum, I think I may have contracted reloading OCD. Last week I reloaded about 40
rounds of .260 for my Savage 12 LRP. As per the books I used a measurement of 2.780. After reading about finding your guns specific needs to have the bullet .010 off the rifling I decided to give the method of the loose bullet in the chamber a whirl. I did this 15 times and 12 of those times the test cartridge came out at 2.864, the other three were extremely close to that number.

My questions are.

A. Why is there so much difference between the two numbers?

B. What effect would this have had on past accuracy?

C. Should I now be reloading to a length of 2.854?

D. Should I grab a bullet comparator and which is the most accurate?

Cheers.

 

[KDX]

A. The reamer used to cut the chamber.
B. It may get better with the new measurement.
C. It is definitely worth a try.
D. The comparator is more accurate but both methods work well from what I have seen. You won't need 15 tries with the comparator.

 

[SND]

I'll let you know what the .260 LRP I have on the way measures whenever I get it. I've been hesitant to start reloading anything for it for that exact reason.

 

[Obtunded]

The difference has to do with how deep the throat is cut by the rifle manufacturer. The books tell you to load to a common spec (SAAMI) that is lawyer-proof, but rarely ideal. Factory throats are all way too long and are cut to accomodate every conceivable factory ammo out there.

Effect on accuracy is impossible to quantify in absolutes, but itr is very likely the mismatch in seating depth to throat length has had a deleterious effect on your accuracy.

As to relaoding depth, I would start loading 15 thou INTO the lands, and move back by 5 thou increments until you find a seating depth it likes best. (Results depend on the bullet and the individual gun)

As to a comparator, YES!! Simply measure your bullets now without one and see for yourself... there can be huge variation between bullets because of the irregularity of the meplat. Comparators measure at the point of the ogive. That is what counts most.

 

[stralia]

The difference has to do with how deep the throat is cut by the rifle manufacturer. The books tell you to load to a common spec (SAAMI) that is lawyer-proof, but rarely ideal. Factory throats are all way too long and are cut to accomodate every conceivable factory ammo out there.

Effect on accuracy is impossible to quantify in absolutes, but itr is very likely the mismatch in seating depth to throat length has had a deleterious effect on your accuracy.

As to relaoding depth, I would start loading 15 thou INTO the lands, and move back by 5 thou increments until you find a seating depth it likes best. (Results depend on the bullet and the individual gun)

As to a comparator, YES!! Simply measure your bullets now without one and see for yourself... there can be huge variation between bullets because of the irregularity of the meplat. Comparators measure at the point of the ogive. That is what counts most.

Thanks for the post. So your saying I should start my loads at 2.879 then back down to 2.854? Any recommendations on the brand of comparator?

 

[Ganderite]

I agree with Obtunded, but the other way around. I suggest starting 30 thou off the rifling, and then try 10 thou increments closer to and then into the rifling.

Use the powder charge that got you the best results before. As you get into the rifling, the pressures may get too high, so be prepared to stop and try the test with a milder powder charge.

A given bullet in a given rifle will probably show a clear preference of seating depth. Most of my rifles prefer the bullet to be well clear of the rifling.

Once you know the seating depth, you can try other powder charges and other powders - all using the same seating depth.

 

[stralia]

I agree with Obtunded, but the other way around. I suggest starting 30 thou off the rifling, and then try 10 thou increments closer to and then into the rifling.

Use the powder charge that got you the best results before. As you get into the rifling, the pressures may get too high, so be prepared to stop and try the test with a milder powder charge.

A given bullet in a given rifle will probably show a clear preference of seating depth. Most of my rifles prefer the bullet to be well clear of the rifling.

Once you know the seating depth, you can try other powder charges and other powders - all using the same seating depth.

Thanks Gander.

I have some 5 shot loads varying from 43.50 up to 44.0 grains. My plan is to test these all at .010 (2.854) off the rifling to find the best powder load then adjust the seating depth from there from there. Thoughts?

 

[Cleftwynd]

Personally I would start at 50 to 30 thou off the rifling and move closer, as long as the rifle isn't limited by magazine length. If none of those work, I move out from my starting point. Then play with charges again, etc....