7 mm SHERMAN SHORTMAG vs 7 SAUM

[jraulsten]

Have you checked neck clearance? I have never had a slow Bartlein. Anything is possible. I am sure if you sent it back they could slug it and see if it meets spec. All the Barts I have owned actually took more pressure and powder than other barrels. I am shooting a 7 Saum with RL23 and 59.5 is 2910 in 26" barrel. Went all the way to 61..7 before pressure. Case volumes are close. Is it bolt lift or ejector marks your seeing?

I've owned several Bartleins and never experienced this with any of them. I'm seeing both sticky bolt lift and ejector marks. I immediately stop when this happens and pull the bullets on remaining loads. This was all virgin brass that I resized (without touching the shoulders) and trimmed to length (1.95") before loading and firing.

Another way I know pressure was excessive is the fact that I separated that brass and tested in the gun by removing the firing pin and ejector. The bolt would not fall and they had to be bumped back .002 after one firing! That is either crazy high pressure or ADG brass isn't what everyone claims it to be, All brass that showed no signs of pressure after the first firing had head space growth of .005 from that of virgin brass, and did not require setback.

 

[jraulsten]

I'm on my 5th 7 SS barrel (four 8.25tw Bartlein and one 8tw Schneider) shooting 190 A-tips mostly, some 190 and 184 hybrids. The ADG brass is very tough but if you hit it hard on the first firing and expand the body at the .200" line, just above the web, your sizing die may not be able bring the diameter down enough to prevent heavy extraction which will be manifested by a heavy bolt lift and a definite "click" at the top of bolt lift when the extraction cam breaks the case free. This is often confused with excessive pressure. I've had this happen. Two solutions, short of starting over with new brass, is either having a small based die made or, the easy way, having the lower 1/4 of the chamber opened up with emery cloth of an appropriate sized wood dowel with the barrel spun in a lathe. I'll repeat @Rhovee question….what are you seeing that suggests excessive pressure?

Please see my response to Rhovee. This is carefully prepped virgin brass.

 

[Rhovee]

I would not be running pressure tests on virgin brass. I always hit them with a moderate load on first firing while breaking the barrel in

 

[Rardoin]

^^^ particularly on these short mag 'fat' bodied cartridges. If your brass is a bit short of the chamber's shoulder and the load is not light on the first hit the brass can slam back against the bolt face producing ejector marks. The brass will also 'swell' at the base above the web and produce heavy bolt lift and clicking. I suggest dropping the load a few grains and shooting a couple of pieces of new brass twice then trying the loads that had the problems and seeing if it reoccurs. If it does then I'd investigate the barrel/chamber neck.

 

[jraulsten]

I would not be running pressure tests on virgin brass. I always hit them with a moderate load on first firing while breaking the barrel in

I would not be running pressure tests on virgin brass. I always hit them with a moderate load on first firing while breaking the barrel in

Wasn't really testing for pressure. I loaded them thinking they should be well under pressure based on the experience of others.........Bad move.

 

[Chase723]

@jraulsten for perspective, my 7SS loads were developed in the middle of summer in GA (95-100F). Not sure that I'm ever going to shoot in anything hotter and so I would consider them safe in my rifle. They are max loads though, no question. Just happens to love them. My barrel develops pressure in a very reliable fashion, faint/half ejector, full ejector, change in bolt lift. Never pierced a primer, never had difficult extraction/ejection (other than increased bolt lift force, but I only test to that level when pressure testing). I also shoot suppressed, but that only adds 10-20fps. I would expect your barrel to speed up 50-80fps over 100-200 rounds, and am kind of surprised that it hasn't sped up at all. Hope some of what a few of us have mentioned helps you out. I love the 7SS. It's does everything I hoped it would.

 

[jraulsten]

Another option, you could either get your gunsmith to do it or buy a PTG unithroater, and cut a little more freebore into it to where you're jumping 40 Thou at 2.96 if your mag will accommodate it. Your pressure will come down from both the increased freebore and you'll be able to load a little longer increasing case volume. You'd then be able to get a little more powder in the case. With that, you might not get all you're hoping for, but my guess is you'd get a bunch of it.

After 120 rounds my paperweight suddenly got much better. Did my first pressure test today with once fired brass and switched to CCI 250 primers.
Loaded 180 Hybrids with H1000 and RL26.
Went to 62.5 grains of H1000 with no pressure at all and got 2815 fps.
Went to 61.5 grains of RL26 with no pressure and got 2948.
Go figure...........I'm a happy camper now

 

[jraulsten]

After 120 rounds my paperweight suddenly got much better. Did my first pressure test today with once fired brass and switched to CCI 250 primers.
Loaded 180 Hybrids with H1000 and RL26.
Went to 62.5 grains of H1000 with no pressure at all and got 2815 fps.
Went to 61.5 grains of RL26 with no pressure and got 2948.
Go figure...........I'm a happy camper now

H1000 was 2871 with 62.5 grains, not 2815. Got 2815 with 61.5 grains.

The 10 shot groups of each powder had a spread of 5 full grains and stayed in a one inch group. I would have thought they'd be more spread out.

 

[Rardoin]

If you can find some N165, give it a go. It is very kind on the freebore and I was able to push 190's up to 2860 fps before getting stiff bolt lift. It should push a 180gr in the mid/upper 2800's without taxing the brass.

 

[jraulsten]

If you can find some N165, give it a go. It is very kind on the freebore and I was able to push 190's up to 2860 fps before getting stiff bolt lift. It should push a 180gr in the mid/upper 2800's without taxing the brass.

Midsouth has N165 in stock now.......

 

[Chase723]

I think I may have posted these pics elsewhere but since this is the 7SS thread it seems appropriate that they should be here. 190gr Berger LRHT. 64.1gr N565 (max load). 2815fps. 22" K&P barrel. 1005 yards.

 

[elkaholic]

Nice shooting right there! One of the many good things about a 7 SS is how well they perform with short barrels.

 

[Stuntman Jeff]

If you can find some N165, give it a go. It is very kind on the freebore and I was able to push 190's up to 2860 fps before getting stiff bolt lift. It should push a 180gr in the mid/upper 2800's without taxing the brass.

Care to share any load data for N165? I'll be shooting that and Sierra 183s, and a starting point would be a big help.

Thx,
Jeff

 

[Copper Basin]

Care to share any load data for N165? I'll be shooting that and Sierra 183s, and a starting point would be a big help.

Thx,
Jeff

60g N165	2.168	2801​
60.2g N165	2.168	2819​
60.5g N165	2.168	2845​
60.8g N165	2.168	2857​
61g N165	2.168	2860​
61.2g N165	2.168	2874​

Ran these last month. Nice easy load in one I built. Could push it more too. Running a 24" tube. Berger 180g Hybrid Targets. Base to Ogive is the 2.168. I changed my insert to measure .277 inside diameter so your BTO could be different. COL 2.920.