White-tail-deer

I recently caved to the magnum craze and purchased a 7mm RUM. One problem with the 7mm RUM there is not much load data available for this caliber. After determining my max OAL I loaded several loads and bullets and test fired them in 4-shot groups to try and close in on a load for this caliber last weekend. I loaded three bullet and powder combinations. Hornady Interbond 139 gr with Alliant MagPro, Barnes 140 gr. Triple X with Hodgdon Rotumbo and Nosler 140 gr. Accubond with AR25. I worked up these loads in 1/2 grain increments from 2-3 grains below max to max, while watching for pressure indicators.

The best load for the day was a Hornady 139 gr. Interbond 91.0 gr. with MagPro powder. Velocities ranged from 3351 to 3442 fps.



The load that was very interesting because of higher velocities and good accuracy was Nosler Accubond 140 gr. with 97.0 gr. of AR25. Velocities ranged from 3614 to 3679 fps.



I want to now experiment with the AR25 with the Hornady and Barnes bullets. My question is related to pressures and reading excessive pressure. How can one be sure they are operating within the acceptable presure ranges for a particular gun? I was told by a Barnes representative to use a micrometer to measure the case diameter just in front of the ejection ring on the case. When the case expands .0005" you are at max pressure for your rifle and should drop your charge down from there. The max any of my cases expanded was .0004". Is this a good practice for reading pressure levels? What indicators do you all look for? Any help would be appreciated!! Thanks!!

mossy33oak

3600 fps.......wow man, you got that thing hummin'......I have no experience with the 7 rum, but I do shoot a 300 rum, and mine is only clockin in at ~ 3150-3200 ! Other than watching your brass/primer for pressure signs, (is your bolt hard to open after firing?) the only other thing I have heard of is using the Stoney point overall length guage to measure your throat, and check occasionally for throat errosion. But thats kinda after the fact checking.

Briman

Its about the best way to determine safe pressures available to handloaders. You should be OK. Look for other signs that MossyOak described also. Looks like you found some pretty nice loads, and nice shooting also.

drinks

There is a co. that sells a stickon strain gage, about $300, and you need a laptop to connect it to.
I know someone who has one, he uses it very little , just more bother than it is worth most of the time.
Don

handloader1

The one thing I like to use as a high pressure indicator is primer pocket expansion. When you reinstall a new primer into a fired case, does the primer fit looser than the previous installed primer? If it does, back off the charge by .50 gr. to 1.0 gr. and recheck. Good luck.

Vapodog

Sorry friend.....without a pressure barrel you can't!!!! Reloading requires you watch a long list of pressure signs.....and velocity is one of them and so is keeping within the reloading book specs.

You can do that.....but it's simply not true.....I also measure it but it don't do anything except to confirm other pressure signs.

In reloading circles it's called CHE...or case head expansion and was widely regarded as a good thing to do.....and it don't hurt to do it.....but in fact it's just one of many factors to take into account.....in and of itself it means nothing!!!!

vangunsmith

Keep your loads within the printed limits.Anything going that fast wont kill any better than bullets going slower.VELOCITY does not mean accuracy!!! Accuracy has a lot of many factors involved. You don,t need to be pushing the envelope on this big blow hole. And you don,t need to use all the high priced bullets either for cutting paper.Try some other types as well,and us the primo ones for hunting,when you get your loads dialed in like you are doing. vangunsmith. BE SAFE

Roskoe

I would agree with Handloader1 - if there are no overt pressure signs, like hard bolt lift, extractor mark, case head expansion, or really flattened/cratered primer - then check the primer pockets. I do a lot of reloading for calibers that are not in the loading manuals - particularly Ackley Improved's. Any load that doesn't show any of the aforementioned pressure signs, and can be reloaded three times without a loose primer pocket; is good to go. Just be careful if you are doing your testing when its 20 degrees outside - and then do some shooting on a hot summer day . . . you may wind up with a box of ammunition labelled "cold weather loads". Roscoe

White-tail-deer

Thanks for all the help guys!! I appreciate it!!