How deep to seat bullets for greates accuracy?

E

Ed Willers

New member
I have a dilemma. I just ran out of my supply of 140gr. Sierra Match Kings in 6.5mm. I thought this would be easy. Just order some more and load them. However, Sierra tossed a monkey wrench in that plan. They changed the shape of the bullet since I bought the others. This new one is more streamlined and longer, by about 0.10".
To load with the bullet base in the same place as before, to keep the load pressures the same as before, puts the bullet about 0.40" off the lands. To put the bullet where it was before, in relation to the lands, leaves only about 1/4" being gripped by the case neck.
It's obvious I'm going to have to work up a new load but which is more likely to give me the greater accuracy? Seating the bullet deeper so I get the greater stabilizing and straightening effect of having more bullet in the case neck? Or, having the bullet much closer to the lands?
The rifle is a Choate stocked Swedish Mauser in 6.5 x 55. Using the old load it shot 0.80 - 0,90" groups at 100yds from a rest when I developed the load. I'd like to be able to duplicate that if possible, & who wouldn't like to exceed if <g>.
I use the rifle in our local 300 yd F-class matches and at the local 300yd scoped prone match. I'm not competitive against the guys with the custom F-class rifles but I do well against the other guys shooting essentially stock rifles. It's fun shooting good groups at 300.

Thanks for all help.

Gregg Gammie
 
How much bearing surface?

I'm guessing that you mean 1/4 inch of the bearing surface being gripped by the case neck? If .250" of the bullet's bearing surface is being gripped when seated out like you like it, then using the 1 caliber rule of thumb for neck engagement, you'd have to back off the lands an additional .014" to get .264" engagement. That might not be such a bad thing. I would start there and try it. If you mean 1/4 including the boat-tail, then yes, things sound pretty wobbly in that case.
 
Personally, I do not view one caliber of bullet grip as a rigid requirement. If you have good neck tension, I don' think that there will be a problem. As far as which route to go with a new load goes, I think that you will have to do some testing to find out. What kind of shooting do you do with this rifle?
 
Couple things -- Sadly, there is no way to predict what will give you the best accuracy with the new bullet. You'll just have to test it. If you're single-loading, rather than using the magazine, I wouldn't worry too much about how much of the bullet is in the neck. Check out the Wolf Pup, which shoots quite well (to put it mildly):

http://bulletin.accurateshooter.com...al-short-necked-wolfpup-for-hunter-benchrest/

The other thing is to PM a BR Central participant named Greg Culpepper. He's done a lot with an 1894 Swedish Mauser in 6.5x55, including winning some 1,000 yard matches in the factory class. Believed he's used the 142 Sierra, which is likely the bullet you now have.
 
vtmarmot said:
I'm guessing that you mean 1/4 inch of the bearing surface being gripped by the case neck? If .250" of the bullet's bearing surface is being gripped when seated out like you like it, then using the 1 caliber rule of thumb for neck engagement, you'd have to back off the lands an additional .014" to get .264" engagement. That might not be such a bad thing. I would start there and try it. If you mean 1/4 including the boat-tail, then yes, things sound pretty wobbly in that case.
Click to expand...

Yes, 3/16 - 1/4" of bearing surface. Does not include the boat-tail. I could not feel any movement when I tried to 'wobble' the bullet seated there. No idea of bullet run out though, or how much it varies out there.
 
Boyd Allen said:
Personally, I do not view one caliber of bullet grip as a rigid requirement. If you have good neck tension, I don' think that there will be a problem. As far as which route to go with a new load goes, I think that you will have to do some testing to find out. What kind of shooting do you do with this rifle?
Click to expand...

I use the rifle in our local 300 yd F-class matches and at the local 300yd scoped prone match.
Neck tension is pretty good. No bullet set back after being fed from the magazine.
 
Charles E said:
Couple things -- Sadly, there is no way to predict what will give you the best accuracy with the new bullet. You'll just have to test it. If you're single-loading, rather than using the magazine, I wouldn't worry too much about how much of the bullet is in the neck. Check out the Wolf Pup, which shoots quite well (to put it mildly):

http://bulletin.accurateshooter.com...al-short-necked-wolfpup-for-hunter-benchrest/

The other thing is to PM a BR Central participant named Greg Culpepper. He's done a lot with an 1894 Swedish Mauser in 6.5x55, including winning some 1,000 yard matches in the factory class. Believed he's used the 142 Sierra, which is likely the bullet you now have.
Click to expand...

I'll try to contact Greg and see what he thinks. Thanks the suggestion.
I'm using the 140 gr bullet, the 142 wasn't out when I was testing and I thought it is the same weight the rifle was designed for.
Being a Mauser all cartridges have to be fed from the magazine, even the single loaded ones.
 
Ed Willers said:
Being a Mauser all cartridges have to be fed from the magazine, even the single loaded ones.
Click to expand...

Right. But there is difference between subjecting a bullet to being loaded from a controlled feed magazine than from subjecting it to the recoil from another (4) shots while it's in the magazine.
 
Most of the time the seating depth in relationship to the lands is the biggest factor in accuracy. I would seat the bullets to the same depth to the lands to start with.
 
Charles E said:
Right. But there is difference between subjecting a bullet to being loaded from a controlled feed magazine than from subjecting it to the recoil from another (4) shots while it's in the magazine.
Click to expand...

Hi Charles,
That's very true and it slipped my mind when I answered. Due to the rules of the competitions all rounds are single loaded.
 
Ed Willers said:
It's obvious I'm going to have to work up a new load but which is more likely to give me the greater accuracy? Seating the bullet deeper so I get the greater stabilizing and straightening effect of having more bullet in the case neck? Or, having the bullet much closer to the lands?
Click to expand...

Work up a load, then fine tune with neck tension and seating depth.

Only your barrel has the answer. The results of what it likes will be on paper.

Have fun.
 
ED Willers, I have had better luck for accuracy with the 142's. If you haven't tried them, I would give them a shot. no pun intended. rogina
 
It's easy to make a mauser feed single shot

If you radius the front of the extractor claw and put a bevel on it, it will slip over the rim with ease. Just go a little at a time until you get the feel you want. I have done many 96 and 98 mausers this way. The model 70 mauser was done this way. It's just a single shot 98 with no magazine cut out.

Richard Brensing
 
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