Bullet Seating Depth??

[jimbires]

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I wounder if I should try three rounds at the SAAMI max length of 3.340" and see what they shoot like for a group. And then adjust from there. Does any one know if this extreme length past SAAMI max is alright? Does my method of finding the length that is just off the lands makes sense?

you can make the length anything you want , it ONLY has to fit YOUR gun . you should have one caliber size of the bullet seated into the case . an example is ; if loading a 30.06 the bullet diameter is .308 . you should have at least .308 seated into the case neck ..... if loading a 7mm , bullet dia is .284 , you will need at least .284 seated into the case neck . if loading a 243 win , you need at least .243 seated into the case neck .

the way you found your max overall length is how I do it . only difference is I use a fired unsized case from this gun , so the brass fits nice .

on hunting guns I start my COAL at magazine length that feeds well , or at my max chamber length minus .010 , which ever is shorter . you do not want a bullet getting jammed into the rifling on a hunt . trust me on this , I have one . then I work away from this max length in .040 intervals . you will find the sweet spot , then work around the sweet spot if desired .

here is a link to berger bullets . read the last paragraph on the VLD type bullet .
http://www.bergerbullets.com/Information/

seating depth will really bring a group around , it's well worth the effort . A few years ago I did a reduced recoil load for a young shooter . I picked the powder charge for light recoil . the only thing I played with was seating depth . you'll see I goofed , one target is only .030 COAL different .

 

[Guy Miner]

Sometimes there is little that can be done.

For instance, a short action Rem 700 in .308 typically has a Very Generous throat, and I've never seen one that can actually be loaded long enough to touch the rifling (or even come close) and still function through the short action magazine. So... I learned to just load them to 2.8" and call it good. Interestingly such ammo shot very well, despite a long, really long, jump to the rifling.

When I've had new barrels chambered for the .308 Win, I had the chamber cut specifically to take the 2.8" cartridge, loaded with a 168 grain conventionally shaped match bullet, Sierra or Nosler. This worked out real well too, producing even better accuracy.

With a long action, or with the single shot Rugers I'm so fond of, I've got all kinds of room to work with overall length and OFTEN load much longer than specified in any manual. For instance this .375 H&H round is loaded for the Ruger Number One, which has an extremely long throat. It won't even fit in the magazine of my Model 70!



A buddy and I traveled to British Columbia for a rifle match. He discovered that he'd brought some ammo he'd loaded long, and that it wouldn't even fit in his magazine! It was however, quite accurate. He had to sort out his ammo the night before the match, into two groups, that which would fit his mag, and that which wouldn't. BTW, this wasn't the only time he did this... :roll: Still, the man could shoot, and we did well in the competition.

There's often a lot more going on than just determining the distance to the rifling. It's got to actually fit in the rifle and work through the magazine - at least in many cases. With a hunting rifle, I'll take ammo that functions with 100% reliability over ammo that's too long to cycle well. Every time. Even if the longer stuff proves to be more accurate, which may or may not be the case.

Regards, Guy

 

[DrMike]

I wounder if I should try three rounds at the SAAMI max length of 3.340" and see what they shoot like for a group. And then adjust from there. Does any one know if this extreme length past SAAMI max is alright? Does my method of finding the length that is just off the lands makes sense?

SAAMI is a reference for manufacturers; it is the standard by which chambers are cut and ammunition is manufactured. There are tolerances that describe a range of measurements, which means that precise chamber dimensions don't often hold. Custom cut chambers may vary according to the smith and according to the throat allowance on a given rifle. Magazines are more standardized than are the chambers. Hence, many people have to load to the magazine, using charge weights to accurize the load. Others have generous magazines that allow them to alter overall length to accurize. You have options.

 

[nosler06]

I am so happy to be learning so much from others who know alot more than I do. One thing my grandfather always said to me was "there is never a dumb question as that is how you will continue to learn as life goes on".

I know that the old Browning BLR has a limited length detachable magazine. Some of you may remember the rounded metal detachable magazines on the Belgium made BLR's. I did have to use that as my guide. Running a long bullet into the chamber closing the action then backing off slightly still would not fit into the magazine. I had to use the mag length and then slightly back from that for it to cycle properly. My 30-06 Win mod 70 has a fair amount of magazine length to play with. Even with a teflon pad to reduce bullet tip deformations.

 

[tjen]

As was stated start long as you can and .020" is a safe distance since bullets can very by .005-.010" easy (even noslers). Pressure will be at its highest the closer to the lands and will decrease as you shorten the OCL.
If you did your work up to max pressure loads while touching the lands you will have a lighter charge than if you determened max charge .020-.030" off the lands. Lengthing the OCL of a max charged load can be dangerous. Shorting the OCL is not.

I determent my max OCL than work up my max charge. Now I know whats safe. As long as I have a charge thats shows both suffient velocity and has the best grouping I pick it and then shorten the OCL to find a sweet spot to improve accuracy a bit more. I have picked a charge say 1-1.5grs above the best accurate charge that was still aceptable and then worked to find the best OCL for accuracy in order to keep the velocity up.

 

[nosler06]

As was stated start long as you can and .020" is a safe distance since bullets can very by .005-.010" easy (even noslers). Pressure will be at its highest the closer to the lands and will decrease as you shorten the OCL.
If you did your work up to max pressure loads while touching the lands you will have a lighter charge than if you determened max charge .020-.030" off the lands. Lengthing the OCL of a max charged load can be dangerous. Shorting the OCL is not.

I determent my max OCL than work up my max charge. Now I know whats safe. As long as I have a charge thats shows both suffient velocity and has the best grouping I pick it and then shorten the OCL to find a sweet spot to improve accuracy a bit more. I have picked a charge say 1-1.5grs above the best accurate charge that was still aceptable and then worked to find the best OCL for accuracy in order to keep the velocity up.

Do doing the method that described, I did have pressure signs with the .308 up near max loads. I also had the worst accuracy, so I backed down and found the best. I will now have to shoot more ( which I have fun doing) to lower the OCL to fine tune this load. Thanks so much for the advice.

 

[Wincheringen]

With match rifles I will play with seating depth, but for hunting rifles I just start at max mag length that also functions reliably and then I will shorten them up if accuracy is unacceptable. I only have one hunting rifle that is picky about seating depth, where I have to use a micrometer seating stem. It is insanely accurate at that setting, but shotguns with much variation.

 

[nosler06]

Well I have reloaded some more rounds and have 3 shots of each.
.308 is 2.800, 2.780, 2.760, 2.740, 2.720 and 2.700
30-06 is 3.380, 3.360, 3.340, 3.320 and 3.300

I am hoping these should get me close to where the sweet spot is and then if I feel like it I will run some splitting the best two groups. Just need a little range time to do it.

 

[nosler06]

Just curious if anyones think pressure will be an issue with running short lengths? For instance as I posted .308 is OAL of 2.800" and have laddered down to 2.700" and 30-06 OAL is 3.380" down to 3.300". I thought that the pressure should go down or am I mistaken?

 

[jimbires]

by shortening the COAL you are making the case volume smaller , which does increase pressure . by seating the bullet long so it is jambed into the rifling, or just touching the rifling , this also increases pressure . by increasing pressure you will be increasing velocity . this is another place a chrony comes in useful . if you are not at , or above a max powder load I think you'll be alright . just remember a reloading rule , always watch for signs of pressure when making any changes , and make changes in small steps . just as you are planning to do .
I see you are only working shorter than SAMMI specs , is something limiting you from loading longer ? I like to start out at my max length . sometimes it's the magazine length , sometimes it's contacting the rifling that determines my starting length .


there is a very knowledgeable fellow on another forum that says he finds his bullet seating depth first . he picks a mid range powder amount and works seating depth only . after he finds his seating depth he then works his powder charge . his way of thinking is the bullet will prefer the same jump to the rifling no matter what the powder charge is . I think I'm going to try this on a new rifle , just to see if it's a quicker method . it's probably just another way to skin the cat .

 

[nosler06]

by shortening the COAL you are making the case volume smaller , which does increase pressure . by seating the bullet long so it is jambed into the rifling, or just touching the rifling , this also increases pressure . by increasing pressure you will be increasing velocity . this is another place a chrony comes in useful . if you are not at , or above a max powder load I think you'll be alright . just remember a reloading rule , always watch for signs of pressure when making any changes , and make changes in small steps . just as you are planning to do .
I see you are only working shorter than SAMMI specs , is something limiting you from loading longer ? I like to start out at my max length . sometimes it's the magazine length , sometimes it's contacting the rifling that determines my starting length .


there is a very knowledgeable fellow on another forum that says he finds his bullet seating depth first . he picks a mid range powder amount and works seating depth only . after he finds his seating depth he then works his powder charge . his way of thinking is the bullet will prefer the same jump to the rifling no matter what the powder charge is . I think I'm going to try this on a new rifle , just to see if it's a quicker method . it's probably just another way to skin the cat .

Thanks for the info. Yes I am limited to length as the rifle is a 1970 Browning BLR and the magazine will only allow so much length before it does not clear properly. I found max length by using a dummy round with bullet just in slightly then closing the bolt. This puts the bullet right against the lands. I then backed the bullet off by I believe 0.010" or 0.020". I have had a couple of rounds that did not feed correctly, so I want to shorten the round. Also this rifle in the past would routinley do sub 1" groups at 100yds with 5 shots. It is just under double that, so I want to play with the seating depth to find the sweet spot.

 

[nosler06]

Well I finally was able to get to the range today. Great day overcast with a temp of 4.0 degrees and no wind.
Here is the 30-06 targets sorry so big, but can't figure that part out yet. I think it is a no brainer at a length of 3.320". This is what I have been used to with this rifle. It has from day one been a tack driver.

30-06 at 3.340"



30-06 at 3.320"



30-06 at 3.300



Now the .308 is not as easy to figure out.

.308 at 2.800"



.308 at 2.780"



.308 at 2.760"



.308 at 2.740"



.308 at 2.720"



.308 at 2.700"



Open to any suggestions of the .308. I am sort of leaning towards the 2.760".

 

[SJB358]

It's really hard to tell but id reshoot 2.8 and 2.740". Let the barrel cool a lot between shots.

 

[nosler06]

It's really hard to tell but id reshoot 2.8 and 2.740". Let the barrel cool a lot between shots.

As I said 30-06 is a no brainer. The one problem I have with the .308 and the 2.800" is this length does not feed well as it is near the max length of the magazine. I was looking at the 2.740" and 2.720" and wonder if the out lyers are pulled. Both of these lengths fed really smoothly.

 

[Oldtrader3]

I use 3.340 with my .30-06 which is SAAMI length and get sub MOA groups.

 

[SJB358]

It's really hard to tell but id reshoot 2.8 and 2.740". Let the barrel cool a lot between shots.

As I said 30-06 is a no brainer. The one problem I have with the .308 and the 2.800" is this length does not feed well as it is near the max length of the magazine. I was looking at the 2.740" and 2.720" and wonder if the out lyers are pulled. Both of these lengths fed really smoothly.

Sure, I'd give them a whirl. I would reshoot to see if the same thing happens. It hard to changed the load with only 1 group. Reshoot and let the rifle cool alot between shots. Something may pop out.

 

[nosler06]

A friend of mine told me that when the holes line up vertically and one like the 2.720" target this is where the ideal OAL is. His reason behind this is the dropped hole is a velocity drop not a pulled shot. The 2.740" target shows the pulled round as the patern is started by the two rounds stacked on top of each other on the vertical plane with the one shot being pulled to the left. Is there anyone out there that can tell me if this is actually true or not? If this is true then an ideal OAL would be 2.730" for this rifle?? Yes/ no??

 

[rick smith]

I do not think the dropped shot is a velocity issue. That would have to be a large error in vel. to drop that far. The pressure you asked about in shorting the seating is not an issue. You are increasing bullet jump which drops pressure, think WBY Mags., Pistol rounds are another story. I have a manual that is just 30/06, in it all combinations of changes are pressure tested. Seating depth was one of those.
I have loaded for several BLRs including my own 308. First find a seating depth that functions from the mag box and is not jammed into the lands. Work your powder from there. In a 308 size case I vary charge by 0.5 gr. If nothing looks promising, change powder or bullet and start again. If you find a load that looks good then work by seating 0.005" deeper into the case. Since you already know any longer will not function, there is no need to go there. There is no magic being close to the lands, just a place to start with seating.Rick.

 

[jimbires]

shortening the COAL will increase your pressure . jamming into the lands will increase your pressure .

I just checked my 338 lapua on quick load . the only change I made is shortening the COAL , my pressure increased . the pressure keeps rising as I shorten it . my pressure raised 3839 psi by only shortening my COAL 0.100 , no other changes .
OAL ............................ psi
3.723 ..........................61723
3.700...........................62696
3.680...........................63413
3.660...........................64149
3.640 ..........................64898
3.623 ..........................65562


if nosler06 wants to see his pressure rise , he can give me his load and his COAL's I'll run it through quick load .

 

[RiverRider]

shortening the COAL will increase your pressure . jamming into the lands will increase your pressure .

Yup. Two entirely different things at work here.

If you play around with QuickLOAD is will show increases in pressure as OAL decreases BUT it also says to expect an increase on "start" pressure increase of 7200 psi if you seat to touch the lands. Interestingly enough that seems to not simply add into the peak pressure result. What I would like to know is how pressure is affected as the bullet is seated away from the lands in 0.001" increments. I've never seen such information.