7mm RUM with 180 VLD loads

[effendude]

I just had a 7mmRUM built on a Stiller action with a Broughton 1-9" fluted barrel that finished around 27.5" before the brake. It sits in a McWoody A3 sporter stock and is a piece of gunsmith's art. I shot 5 rounds of factory ammo through it for a slight break-in. I then did my normal, look at the book, pick a powder and load up one each in 1/2 grain increments to look for pressure. Started at 93 grains of H50BMG and went to 97. No pressure signs. I went form 97 to 100 grains and still no pressure signs. 100 grains send the 180 at about 3250fps. I am at ~103% case capacity, slight crunch at end of seating. Accuracy through the 7 grains all landed in a hole 1/2x1/2". Don't knwo where to go next. Shoot 3 of a few charges to look for best accuracy and ES over the chrono?

I am wondering if anyone has any experience with this powder. I am temped to go to H1000 for a try. With a rifle like this, I don't want to shoot 100 rounds developing a load. Maybe I found it already, just looking for others experiences. Anyone have any experience?
Scott

 

[BradY]

I would follow Erik Cortinas method. Shoot 3 shot groups of varying charges looking for ones that are hitting the same POI vertically. Look for low ES as well. Adjust seating depth to bring in group size and then go shoot it!

 

[eric32]

Just curious what distance did all seven of those charge weights go into a 1/2 inch?

If you did this test with anything beyond 100 yards i would have to say look for the load with the lowest ES/SD since they all grouped in the same POI.


From what you have described it seems you have a hammer of a hunting rig.

 

[TonyR]

I just ran this through QL and, according to QL, your max load is way over pressure. It estimates that 50BMG is one of the best powders for that bullet/cartridge combination but you should be close to the max rated pressure for the case somewhere around 3000 fps. There are always lot-to-lot and barrel to barrel variations with QL, but it is usually a pretty good indicator of loads with too much pressure. If you have access to a blade micrometer, you could measure the case-head expansion in the extractor groove to see what the growth is with those top loads or you could just pop the spend primers and seat some new ones. If they come out easy and the new ones go in soft on one firing, you are definitely into excess pressure.

 

[effendude]

Tony,
Thanks for the information. I have measured the case head expansion as part of the process and they haven't grown but I know I am close. This is a custom chamber in a hunting rifle with an extended length box. The bullets are seated to this rifles mag length as spec'ed to the gunsmith which allows much more capacity than SAAMI. I am not trying to fill the case and scrape off the excess but I want to get the most accurate, safe performance out of the case. Running hard, I don't expect great brass life. As a hunting round, the 100 pieces I have should last as long as the barrel ;D

Every other hunting rifle I have worked up 1/2-3/4 MOA loads for were pretty easy to find the top end. Ejector marks, cratered primer, case head expansion all are signs I watch for. My first step is to always find the upper safe powder charge and then back off a little. Usually the ultra mags perform best when pushed a little. The very conservative Berger manual lists 93.8 as the top load.

I guess I have some chrono work to do.

Thanks,
Scott

 

[nastynatesfish]

I'd like to find some 175s or 180s. I'm running 108gr US869 and a 130 sierra. It's a freakin laser and hits steel hard. I have to work on aol. I cannt touch lands with the 130 or a 162 amax. Mine is a 26" sendaro barrel

 

[effendude]

Most factory rifles, especially magnums, have long throats for safety reasons. I would recommend you run whatever bullet you want at mag length and see what accuracy you get. You might be surprised.
Scott

 

[ebb]

Don't worry about 162 Amaxs I couldn't get them to make it to the target. A 7 RUM is tooo fast for an Amax, I clocked some at 3600 fps . I like the berger 180 grn hybrids and the 175 grn Match kngs.

 

[effendude]

Here is the latest. I have settled on 98 grains of H50BMG with the 180 VLD. This gives me one hole groups at 100 yards and 1/4MOA elevation at 300. The 99 and 100 gr loads had the slightest ejector marks on the second test at 90* temp. I also loaded up 5 of the Barnes 168gr. LRX bullets at 96 grains of H50BMG which gave me a 3/4MOA 5 shot group at 300. I believe that with the 5.5-22X scope at 22X, I can't hold any tighter than that anyway so both loads seem to perform really well. I will chrono them and run drop charts but total load developement took 35 rounds.
Scott

 

[eric32]

congrats that is a fine shooting rifle