Barrel length question

[Mulligan]

Those of you with quick load, will H-1000 or the slower burning powders help o this end?

 

[Joe R]

Mulligan said:
Those of you with quick load, will H-1000 or the slower burning powders help o this end?

IMO I believe you're wasting time with H-1000. I don't believe you'll have enough case capacity.

I tried H-1000 with a 6mm 105 grain Berger Hybrid (.109 freebore) and the best I could get was 2950 fps. I doubt you'll have enough case capacity to push a 7mm 180 grain to mid 2800s. You could try it, like Ben said, with .235 freebore and if it doesn't work you could back-up to Varget, if that doesn't get you there then IMR 8208 will definitely get you there.

Another way would be to start with a shorter throat and use IMR 8208, once you find the node that works for you, then you could try some H-1000 and see what velocity you get with your barrel. Than using QL you can use that info to get a reasonable estimate of the amount of H-1000 that you would need to put in a case and OAL that you would need to get you there. Once you know that you could than use a Uni-Throater ( http://pacifictoolandgauge.com/throat-and-neck-reamers/5226-17-cal-uni-throater-kit.html ) to ream the freebore out to meet your needs.

Like my Dad used to say "With enough time and money, you can solve most problems."

Joe

 

[Sheldon N]

Those of you with quick load, will H-1000 or the slower burning powders help o this end?

Like Joe said, you'll run out of capacity with slower powders. My comments posted above were Quickload predictions, here's some additional details.

Throat the gun as long as possible and you'd get an OAL cartrige length of around 3.05". This is max usable case capacity with a 7mm-08 and a 180 hybrid.

50g of H4831 SC is a 113% compressed load, QL predicts 73k PSI and 2850 fps with a 30" barrel.... Too hot, too full of a case IMO

48.5g of H4831 SC is a 110% compressed load, QL predicts a safer 65k PSI and 2760 for velocity. Still very compressed, but safer pressures.

Since the case is already full, slower powder like H1000 just get you slower velocity and lower pressure. QL predicts mid 2500's for a full case of H1000. The only real other options are going faster up the powder burn rate chart, but the faster burn will hit pressure limits faster without giving as much velocity as H4831SC. Here's what faster powders would look like, assuming that you went all the way to 65k PSI.

H4350 45.5g 106% compressed 2736 fps

Varget 41.3g 98% compressed 2697 fps

IMR 8208 XBR 39g 90.7% compressed 2657 fps

A double base powder looks like the best option.... You'd have the issues of temp sensitivity, but you'd get more velocity.

RL-17 45.4g 100.7% compressed 2824 fps

Might also look into 2000MR, but I don't have that in QL. Seems like the 308 guys are getting good velocity with heavy bullets with that powder.

 

[Joe R]

H4350 45.5g 106% compressed 2736 fps

I think Sheldon N is very close. If you can get 50 grains in there you'd be right on the node. See below:

Or you could go with IMR 8208 and only fill 92.4% of the case and that will also put in 1.368 node. Although QL shows that in red at 70K psi I hang out in that neighborhood as a norm.

Joe

 

[ShootDots]

Sheldon N, I have a question.. If you refer to the Hodgdon Loading manual, for a "regular" 7mm-08 (as in NOT the A.I. version) it shows that using a 175gr Nosler Partition (which has a L-O-N-G bearing surface) seated to 2.800, can safely run 49.0grs of H4831.. It shows that it's velocity is 2516f.p.s. from a 24" barrel and generates 49,400C.U.P. (not P.S.I.) .. Now if Hodgdon shows 49.0grs as safe with a 2.800 C.O.L. out of a "regular" 7mm-08, how can the A.I. version, using a MUCH LONGER freebore, with a bullet only 5grs more and a shorter bearing surface, generate 73K of P.S.I. and be going 2850f.p.s.?? I did not realize that Hodgdon, using pressure testing barrels (with whatever pressure gauges they use) would print as safe, something that Quickload states has dangerous pressure..

 

[Sheldon N]

Sheldon N, I have a question.. If you refer to the Hodgdon Loading manual, for a "regular" 7mm-08 (as in NOT the A.I. version) it shows that using a 175gr Nosler Partition (which has a L-O-N-G bearing surface) seated to 2.800, can safely run 49.0grs of H4831.. It shows that it's velocity is 2516f.p.s. from a 24" barrel and generates 49,400C.U.P. (not P.S.I.) .. Now if Hodgdon shows 49.0grs as safe with a 2.800 C.O.L. out of a "regular" 7mm-08, how can the A.I. version, using a MUCH LONGER freebore, with a bullet only 5grs more and a shorter bearing surface, generate 73K of P.S.I. and be going 2850f.p.s.?? I did not realize that Hodgdon, using pressure testing barrels (with whatever pressure gauges they use) would print as safe, something that Quickload states has dangerous pressure..

I'm not sure on that either... Obviously Quickload is just an estimating tool so it's not gospel. The other factor might be what case capacity was involved. Quickload default is 55g of H2O capacity for the 7mm-08. A swing of a grain or two in capacity can make a big difference in pressure, especially at the limit where the pressure starts to rise exponentially. Another factor is that the Nosler Partition is 1.36" long and the 180 Hybrid is 1.529" long, which can really affect the usable case capacity.

I've noticed the same thing with Quickload and Hodgdon's data too. My 308 loads with 175g LRBT and IMR 4064 track perfectly with velocity predictions from Quickload out of my gun. However, Hodgdon's data for a safe load is almost 1.5g more than what Quickload says my max should be, although it's with a different 175g bullet and the shape/bullet length is not the same.

My own personal takeaway is that Hodgdon's reloading data is a bit on the aggressive side (confirmed when you compare with other data out there) and that generally I have confidence in Quickload when you can get really accurate measurements to feed it for case capacity, bullet length, etc, and you are checking the predictions against real world velocities.

The difference between CUP and PSI may also be involved, since duration of pressure affects the measurement units differently. Quickload is giving the peak PSI calculated pressure, which is only for a very short duration based on their pressure/time/velocity charts.

 

[savagedasher]

Before you get near max pressure of 60191 PSI your will find primers are giving up. Standard or Ackley.
260 AI uses the same case with the same problem. The on way I found to get more speed was without primer problems was change to Norma MRP. If you are starting from scratch I would recommend to go to Ackley chamber and throat it long. MRP will give you more speed at the same pressure then H4350. The felt recoil is less because of powder burning curve. Larry

 

[savagedasher]

Many use QL as I do . When selecting a powder I have found as QL stated Pressure used changes as the nears the leads. My rule of thumb is bullet jumping .020 nears QL pressures. Seating near or in always add 2 to 5 thousand more PSI pressure to QL reference. Larry

 

[Sheldon N]

I don't know if you'd lose primers at 60k PSI. My 308 loads in Lapua brass are at 65k PSI per QL and while I do notice a tiny bit of primer pocket loosening at 4 firings the brass is still fine with a lot of life left in it.

Agree on the issue of coming into the lands with the bullet. QL indicates that you need to add 7200psi to the Shot Start (Initiation) Pressure if you are contacting the rifling with bullet.

For the record, all the load estimates above are with the bullet OFF the lands.

 

[savagedasher]

I don't know if you'd lose primers at 60k PSI. My 308 loads in Lapua brass are at 65k PSI per QL and while I do notice a tiny bit of primer pocket loosening at 4 firings the brass is still fine with a lot of life left in it.

Agree on the issue of coming into the lands with the bullet. QL indicates that you need to add 7200psi to the Shot Start (Initiation) Pressure if you are contacting the rifling with bullet.

For the record, all the load estimates above are with the bullet OFF the lands.

Internal case volume is the key . Chamber size and head space enters . Along with the brand and how the brass is finished. That is the reason weighing cases doesn't work. When the extractor grove is cut it can very as much as one full gr or more. Lapua brass is the best I have tried for pressures and capacity's.
It still is not common to find several of the brass to have a full GR of capacity of volume with the same total weight.
100 new brass 60% will have the within .02 GR of capacity 15 % will be with in .03 % Gr Both light and heavy of the 60% The last 10% is not even close
Using 100 brass I have found I have 60% are good another 15% are ok the other15% are ok but must be grouped in light and heavy Both the 15% will shot faster or slower then the other 60%. Larry