another bullet seating question.

[grundy53]

So now that I solved the OAL inconsistency (bought the hornaday bullet comparator and they were actually all seated the same) with my 25-06 rounds. I've started to figure out seating for my .300 win mags. The first one (REM 715) went fine but then I did my REM 700 Sendero and its giving me a seating that's about .025 over the maximum OAL. If I bring it down to under the max OAL will it effect the accuracy much? BTW at the over max OAL it still cycled and fed from the magazine. Thanks again for all of the help. Us newbies are very lucky to have you experienced guys around.

[grundy53]

Oh ya I'm using 200 gr accubonds

[sakoshooter]

If you're working on seating close to the lands for accuracy, COAL is mainly determined by what will cycle thru your rifle's magazine. Max lengths are guidelines. Rifles vary, magazines vary.

[GregMcFadden]

Let me preface this with the following "this is my opinion and make sure you are safe"

Unless I am A. Loading for multiple rifles with the same round, or B. loading to fit in a magazine that is constrained, I do not pay any attention to the Cartridge length specification.  What I pay attention to is the maximum length (for me, measured from base to ogive) that will fit in the rifle with the bullet just touching the lands and whether that round will feed from the magazine of said rifle.

Every cartridge combination(bullet, powder, primer, brass) and every rifle has a particular jump that will give you the smallest group size.  I've had some that liked to be rammed into the lands for best accuracy.  some wanted to be seated back 0.030 thou.  some folks have reported jumps as high as .125-.150 with some bullets in some rifles.  It is something that you must experiment with while watching for signs of over pressure (watch the primers in particular).  Personally, I always start my load development as close to the lands as possible, preferrably just touching them.  With that I generally start below the recommended starting load in the books, as touching the lands can run up the peak pressure.  Once I get a round that works well there, I seat the round farther back and see what/if there is an effect. 

[grundy53]

Thanks guys. When I was determining seating depth I also checked to see if it would cycle and it did. Thank you again! You guys really are a huge help to new reloaders.

[sakoshooter]

GregMcFadden gave a very good explaination. Pay attention to his mention of increased chamber pressures from 'touching' the lands.

[GregMcFadden]

thanks sako!

One more thing to note, just in case you are wondering if it is worth the trouble to change seating depth.  My pre-64 M70 featherweight 30-06.  Seated to the lands, 5 shot group size is .9 inches at 100yds and 2515 fps. I proceeded to seat back .028 inches from the lands.  same speed on the chrony but the group size dropped to .5 inches.  I stopped there and deemed it good enough.

[carpsniperg2]

If you're working on seating close to the lands for accuracy, COAL is mainly determined by what will cycle thru your rifle's magazine. Max lengths are guidelines. Rifles vary, magazines vary.

x2

[Bob33]

GregMcFadden gave a very good explaination. Pay attention to his mention of increased chamber pressures from 'touching' the lands.

Hornady expains it very well here: http://www.hornady.com/ballistics-resource/internal

To illustrate the effects of variations in bullet travel before the bullet enters the rifling, we'll compare a standard load with adjustments made only in the bullet's seating depth.

In a "normal" load with the bullet seated to allow about one 32nd of an inch gap (A) between the bullet and the initial contact with the rifling, pressure builds very smoothly and steadily even as the bullet takes the rifling. Pressure remains safe throughout the powder burning period (B), and the velocity obtained - 3500 fps - is "normal" for this load in this rifle.

Seating the bullet deeper to allow more travel before it takes the rifling, as in these next two illustrations, permits the bullet to get a good running start (C). Powder gases quickly have more room in which to expand without resistance, and their pressure thus never reaches the "normal" level. Nor does the velocity; with the same powder charge it only comes to 3400 fps (D).

When the bullet is seated to touch the rifling, as in the accompanying illustrations, it does not move when the pressure is low (E); and not having a good run at the rifling as did the other bullets, it takes greatly increased pressure to force it into the rifling. As the rapidly expanding gases now find less room than they should have at this time in their burning, the pressure rise under these conditions is both rapid and excessive (F). Velocity is high at 3650 fps - but at the expense of rather dangerous pressure. Many rifles deliver their best groups when bullets are seated just touching the rifling. Seating bullets thus can be done quite safely if the reloader will reduce his charge by a few grains. The lighter load will still produce the "normal" velocity without excessive pressure.

[grundy53]

Thanks again guys! I just got my hornaday electronic powder thrower/scale and loaded 40 rounds for each of my .300's (5@64.0grains, 5@64.5, 5@65.0, and 5@65.5)x2. Going to see what my rifles like this weekend. Everything went smoothly. Thank you again for all the help.

[KNOPHISH]

Don't be disappointed if those rounds don't group like ya want em to. Keep trying different weights, powders, or bullets. I finally got some 180 partitions under 1/2" but only 3 shots, 2 holes. Will try some more. Good luck.

[GregMcFadden]

Yepo, it just takes time and for some of us we enjoy the challenge