Opinions wanted on Cart. OAL?

[corey006]

I have a 7mm Rem Mag Ruger No.1 with quite a long throat.

The barrel is 26 inchs.

I am trying to work up a load with Retumbo and 160gr Accubonds.

I measured the OAL length using the bullet jam into the lands technique and the average came out to 3.520.

Should I start at 3.505 or 3.490?

Will I get more velocity closer to the lands or further away?

I know that pressure will rise sooner the closer I am to the lands.

Anyone have any experience on long throat chambers and if MORE distance to the lands increases velocity?

I am hoping to achieve 2950-3000 fps without pressure signs(of course with MOA accuracy). I know Retumbo would be better with heavier bullets but I wanted to give it a try anyways. I have tried H-1000 in the past but had trouble getting over 2900 fps without getting pressure signs. I also have some RL-22 but haven't tried it yet because of its "rumored" temp sensitivity.

 

[Divernhunter]

Usually with more jump you can get more speed and use more powder before you get higher pressures.

 

[quentin9595]

i get 3071fps with a 24 inch barrel and the 162s and H Retumbo

 

[corey006]

i get 3071fps with a 24 inch barrel and the 162s and H Retumbo

thanks for the input...but doesn't really apply to what I am asking???


just a note....according to the Hodgdon data 73.5 Gr of Retumbo compressed yields 2963 fps with a 162 Hornady SPBT.(your 108 fps faster than book numbers and appears to be unsafe load?) ...please explain how you can achieve 7mmSTW velocities out of a 7mm Rem Mag???

 

[quentin9595]

i get 3071fps with a 24 inch barrel and the 162s and H Retumbo

thanks for the input...but doesn't really apply to what I am asking???


just a note....according to the Hodgdon data 73.5 Gr of Retumbo compressed yields 2963 fps with a 162 Hornady SPBT.(your 108 fps faster than book numbers and appears to be unsafe load?) ...please explain how you can achieve 7mmSTW velocities out of a 7mm Rem Mag???

Sorry I should have put it more clear and with the specs of the seating depth as well. When I started with the 162 hornady interlocks I started right at the cannelure and did not worry about seating the bullet to touch the lands, and that seating depth is 3.330 With the H Retumbo I am only using 73 grains of powder and there are no pressure at all. We ran 5 bullets through the chronograph and that was the average speed at 15 feet. But just like Divernhunter said try the bullet with a little bit of a jump or pressure signs might spike up.

 

[woods]

All other things being equal, the further from the lands you are, the lower the velocity and pressure.

 

[rick smith]

Until you start jamming the bullet into the lands your pressure/velocity won't vary by more/less than normal for that round. As far as where to start, I normally seat my bullets 10 thousants off the lands and work with the powder charge. I will vary the seating depth once I find the best charge. Your goal of 3000fps should not be a problem. I get over 2900 with a 280AI and a 160gr bullet.Rick.

 

[old #7]

Until you start jamming the bullet into the lands your pressure/velocity won't vary by more/less than normal for that round. As far as where to start, I normally seat my bullets 10 thousants off the lands and work with the powder charge. I will vary the seating depth once I find the best charge. Your goal of 3000fps should not be a problem. I get over 2900 with a 280AI and a 160gr bullet.Rick.

I agree with that.
You stated you have a long throat. I wouldn't worry about touching the lands. Vary your COAL until you find a sweet spot. Load your rounds to fit in the mag box and seat deeper in .005 increments.
I would also give rl-22 a try in your 7mm mag. I think the temperature sensitivity of the powder is insignificant compared to the accuracy and velocity you can achieve with it.
You may end up with a winter load and a summer load.

 

[baltz526]

I would try rl22. your OAL question, I would set the bullet out as far as possible while still being .010 or more out of the rifling. The accubonds are long bullets, I would want every bit of case volume i could get by bullet seating. I can get 3000fps with rl22 with a 175gr sierra btsp game king in a 26" barreled 7mm rem mag. so 3000fps is a very reachable goal with a 160

 

[woods]

Pressure and thus velocity will decrease with deeper bullet seating. Reference this chart located in an article by Barnes

http://www.barnesbullets.com/resources/ ... -bullet-n/

This is a chart of different calibers and the pressure taken with the closest seating of .025" depth on the left for each caliber and increasing by .025" going to the right in most cases. The pressures generally show to decrease with increased seating depth

Here is what Hornady had to say

http://www.hornady.com/ballistics/internal.php

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.

You'll have to go to the website to see the illustrations. But the point is that seating deeper decreases pressure and velocity, probably up to a certain point.