7 rum

[TwoMore]

I am shooting a 7 rum AI and I shoot the wc 872 powder(lil over 6 dollars a pound) and the 195 berger, but i have also shot the 180s very well with it. now my barrel is 30 inches and it has a bore rider throat but it pushes the 180 well north of 3300 , my reamer is a .260 freebore . the 872 burns pretty clean once you get it up to pressure

 

[Lefty7mmstw]

https://www.longrangehunting.com/threads/7mm-rum-coal-problem.46588/#post-320965
well, I found my issues in a post from ten years back... directional ignition... retumbo is too fast of a powder for my 7rum as it sits...

I'm starting to doubt directional ignition... I will go with a bit slower powder than retumbo anyway.
I took a look at the throating and it seems to be a bit shorter throated than the last rifle but I can still get to 3.9-4 inch oal with most bullets before I jamb up.
The biggest thing I'm seeing is the chamber neck. My fired rounds are barely accepting a bullet. There is no gap at all with a slip fit to a bit of pressure required to insert a bullet into a fired casing. I guess I'm reaming brass... Inside reaming or outside turning? What's best for this rifle? I am using standard dies with a button expander...

 

[Lefty7mmstw]

I am shooting a 7 rum AI and I shoot the wc 872 powder(lil over 6 dollars a pound) and the 195 berger, but i have also shot the 180s very well with it. now my barrel is 30 inches and it has a bore rider throat but it pushes the 180 well north of 3300 , my reamer is a .260 freebore . the 872 burns pretty clean once you get it up to pressure

I have a bit over a keg of wc872 on my shelf and a half keg of aa8700... Once I figure out this case neck stuff I'll be moving over to rl50 or one of the 50bmg ball powders...
On my old 26" bbl I was around 3150 fps on a 26" bbl with retumbo; this barrel isn't much longer...

 

[TwoMore]

my reamer is a no turn tight neck (.3164), I do turn necks(O.D.) but I am .003 under my chamber with a loaded round and my bullets dont go into a fired case real easy

 

[TwoMore]

I just checked a few pieces of brass that have a few firings on them , (3 rem brass and 3 Bertram) all 6 were .3145 fired, so it looks like it is springing back close to .002 from my .3164 chamber

 

[Lefty7mmstw]

I'm running .315" sized, .317 loaded, and .320" fired... I am not turning necks but I'd bet as close as I'm running I need to as a thick neck might be an issue...

Is the rcbs handheld unit any good?

 

[TwoMore]

i use the K&M stuff with a drill but I am sure the rcbs will do fine.
my loaded size is .3135 with necks turned to clean up. my necks are just under .015 thick

 

[Lefty7mmstw]

i use the K&M stuff with a drill but I am sure the rcbs will do fine.
my loaded size is .3135 with necks turned to clean up. my necks are just under .015 thick

just ordered a rcbs turner and a 7mm mandrel... we'll see soon if it helps... a powder switch to something a bit less hyper than retumbo is also in order

 

[Lefty7mmstw]

I'm running .315" sized, .317 loaded, and .320" fired... I am not turning necks but I'd bet as close as I'm running I need to as a thick neck might be an issue...

Is the rcbs handheld unit any good?

I took another look at my necks and it looks like there's a couple thousandths taper on this chamber right at the mouth... I'd bet that's where I'm getting issues...

 

[TwoMore]

sometimes my brass will spring back more at the mouth so my brass will seem to be tapered but it is just the brass

 

[TwoMore]

IMO the throat is pretty short. on factory barrels, at least the 2 I have had, I couldnt reach the lands , they were both around .400 freebore and everything I have seen on the 7 rum says that any closer and the pressures got screwy and would get volatile quick so the slower powders helps that. this one I am shooting now I had a bore rider throat done on my reamer where it reams half of the rifling to .002 instead of .004 for the first .949" of the throat and I am able to run my bullets in the lands .005 and my pressures are very contestant and the rifle will drive tacks

 

[Don A Parsons]

I cheet when it comes to fitting brass into Chambers,,, normally I cut the neck back shooter then factory spec,,, yes I know why would I do that,,, simple answer is that it leaves room for the brass to grow and prevents any possibility of neck jam...

Another rule breaker for me it trimming the necks to 0.012 to 0.013 thou,,, pretty thin one would think,,, but it serves 2 ideas,,, less chances of building up a donut on the inside of neck to V,,, and it allows for more consists neck tension...

I just stared playing with this idea,,, how to check for inside neck donut,,, its simple,,, once the cartridge has been shot,,, a new boolit should slip into the neck with no restrictions where the V shoulder meets the straight wall of the neck...

"""If there is any felt restrictions,,, this is a sign that the brass is flowing forward as it piles up at the upper neck & Shoulder V,,, you will know what it feels like once the brass starts to pile up... Ha...

And yes,,, be careful with jam,,, don't get your boolit stuck,,, especially if the cone in the throat is tappered,,, its to bad you didn't get the spec on the remmer as it would of been handy to fall back on for sizing your brass...

Of course this is nothing major since you can season a hand full of your brass in your rifle to come out with a measurement,,, I'd try some full length brass with powder charge and corn meal to see of the tip of the brass neck is tappered. LOL...

There are lots of ways to skin a cat,,, using the tools we have with ways to find out whats going on... Run about 3 to 5 full length brass corn meal changes to see if the same V/ tapper is appearing at the tips... That way you'll know for sure...

PS: Use a ball mic to get a more accurate reading on your neck thickness,,, well seasoned brass will give you clues on what's going on,,, measure,,, measure,,, and measure,,, double check your measuring tools to make sure that they are reading correctly... Ha...

Half of a horse tail is still half of a horse if you know what I mean... LOL

Good luck going forward my friend.

 

[Lefty7mmstw]

Well, took the rifle to the range and had zero over pressure issues a few days ago. The rifle eats charges that are about 10% below book max. and seems full pressure at those levels. Three combo's were sub moa with the 183 sierra showing real promise with 82 retumbo under it. 140 sierra with rl25 seemed good too; been there, done that on a 7rum before (a bit more powder though last time). A few more groups to prove accuracy, speed, and poi and she's going hunting.
As to cases, I am turning the necks to clean them up and also trimming shorter... It seems to be working, so I'll just continue.