7mm RSAUM questions?

[TAZMAN]

I rarely post here but I have read almost every thread I can find and I still have some issues. I had SAC build me a new 7mm SAUM on a long action and using a proof barrel. It's throated for the 180 Berger and it shoots them lights out but I am seeing pressure signs with H8831sc with only 58.5 grains and H1000 at 61.5 grains. I am using Nosler brass necked down from 300 SAUM and I have turned the necks to .319 which is what I was told to do. The best I can do is 2750fps before pressure signs which makes no sense to me. I have checked everything I know to check and read every post I can find but not sure what is going on. I use 215 primers in all loads and I am .010 off the lands according to my OAL gauge. I have no issues closing the bolt which makes me think I am OK on the brass prep but maybe not?
I am considering switching to H4350 to see if I can get it to have some velocity. I'm sure it something simple I am missing but I figured I would ask.

 

[toddc]

Strange, my Savage 27" Mcgowen is running 175ELD-X at 3150!!!! with 64.5 gr of H-1000.
Chrono is cross checked on other guns AND with other powders in the 7 SAUM and seems on the ball.
My headspace is set to 0 essentially and COAL is very long as it's a LA.
I was reallllllly surprised by the speeds I am seeing and I am 1 gr under book max and 0 pressure signs.
Your speeds seem low for a SAUM and mine...IDK , still kinda freaked out by it. In theory I am over RUM velocity so I am very cautious as to what is going on at this point.

 

[toddc]

I would get a way to check your fired brass dimensions. I'm using a RCBS precision mic as I don't trust the Hornady system. I would guess your issues are tied to the brass. Get some Norma 7 SAUM and try it. I am guessing something is going on with the 300 to 7mm operation.

 

[TAZMAN]

My COAL is 3.020 and the barrel is 24 inches plus the break for a finish length of approx. 25.8. I am getting a slight ejector swipe on the brass but no bolt lift issues. I may see if I can locate some 7mm brass and test that. The barrel has approx 35 rounds through it.

 

[Edd]

I don't think that is too far out of line. I have a 7mm SAUM in progress and am expecting to get 2800 fps from 175-180 gr bullets.

I'd be interested in knowing your chamber specs.

 

[toddc]

My COAL is 3.020 and the barrel is 24 inches plus the break for a finish length of approx. 25.8. I am getting a slight ejector swipe on the brass but no bolt lift issues. I may see if I can locate some 7mm brass and test that. The barrel has approx 35 rounds through it.

Even with 3" of extra barrel there is no way I should be running 400FPS faster even accounting for different bearing surface a 5gr less weight.

My tests STARTED at 61 which went 2892.

61 2892
62 2943
63 2963
64 3019
65 3042

This was the first 20 rds out of the barrel. Once it broke in, it runs 3150 M/L with 64.5. This is SMOKING out of a SAUM so take it with a grain of salt. In fact I had a thread on here about it being too fast but cross checked everything and I believe it is accurate.

Wish you luck and wish I had an answer, I'm still scratching my head over the TOO HIGH velocities I am seeing. I am usually in your boat so don't feel bad. Being too fast scares me way more than too slow. I may drop back to 63 just to feel better. Strange though since our longer COALs SHOULD give us more potential speed. IDK

 

[TAZMAN]

The loaded round neck measures .316 which seems to be right in line with others I have read up on. Seems like my velocity is still really low as compared to others. It shoots really good but I would like to see at least 2850fps.

 

[toddc]

I don't think that is too far out of line. I have a 7mm SAUM in progress and am expecting to get 2800 fps from 175-180 gr bullets.

I'd be interested in knowing your chamber specs.

I was prepared to ACCEPT 2800, hoping for 2900 and have no clue where in the heck 3150 came from. Seems impossible even with 70k. I'm being cautious with this thing it scares me.

I know my chamber is at minimum spec and I am probably going to lengthen it a tad and see if it slows down. Never had this problem before lol. Probably oughta quit worrying and enjoy but I don't believe in free lunches.

 

[toddc]

This is the link to my other thread. Not much help as everyone seemed to say be happy with no real data. Then the darnthing picked up almost 100FPS after break in.

http://www.longrangehunting.com/forums/f28/7mm-saum-big-surprise-179924/

 

[can1010]

check the neck on fired brass then check a loaded round for clearance you should not see pressure at those charges unless it is a tight neck chamber. I also neck down 300 brass mine loaded is .316 fired brass is .320

26 inch benchmark 60.5 rl-26 2930

 

[TAZMAN]

I am .319 on the fired brass. It doesn't seem like a tight neck and if I put the brass in and out of the chamber after firing it doesn't seem to bind or show any issues.

 

[eshorebwhntr]

If you have access to an accurate micrometer check the diameter on the VLD's. I heard rumor a while back that they had some leave that were .2845. Could add some to the pressure. Maybe try another bullet and see if your results are consistent with what you've seen so far.

There are also quite a few shooters out there that monitor chrono's pretty tightly during break in and claim that cut rifled barrels will speed up from 50-100 fps after the first 100 rounds are fired.

Are you full length sizing when you reload? If so, how far are you bumping your shoulders back?

I agree that .003-4 clearance on the neck should be enough and not create issues but just for the hell of it maybe cut another .001 off a few cases and see what that does.

From what I've seen there are fast barrels and slow barrels that people get every day. I know that isn't a fun answer but may be the only one that ends up making sense in the end.

Good luck tracking it down.

 

[TAZMAN]

I have a good micrometer so I will check them. I am out of the 180 Bergers so I ordered some that should be here in a couple of days. I am also using 215 primers and I have read that others are having better luck with the 210.

If the barrel would pick up 100fps after break in then I would be OK with that but the pressure at low charge weight doesn't seem to make sense. I would like to find a few comparable a-max bullets to try r the SMK at the same weight. Never had an issue like this before but it happens I guess.

I appreciate all the help, like I said....I don't post much but shoot as much as I can but usually can figure out issues.

 

[TAZMAN]

The bullets I have measure exactly .2845? Is that an issue? That's with a digital micrometer. Checked it a second time with my Central Tool Mechanical micrometer and it reads the same?