7mm SAUM Help

[lokent]

Yesterday, I went to my range and got some very confusing results that I need some help with. Here are the details:

-Date: 7/14/2012
-Atmospheric Pressure: 30.00 Hg
-Temp: 90 deg F
-Humidity: 50%
-Altitude: 300 FT
-Winds: SE@6MPH

Brass: Nosler 300 RSAUM necked down and fired about 3 times
Bullet: Berger 7mm 180 VLD Hunting
Powder: 57.4g of H4831sc
Primer: Russian Mag

I ran an OCW during spring (a little cooler ambient temperature) and my chrono showed 2816 for 57.4 grains of H4831sc (my OCW). This 57.4 OCW showed no sticky bolt lift. A 58.3 g load showed a little stiff lift on some of the shots and some very slight ejector marks so I was happy that the 57.4 was my OCW and no pressure signs and I felt good that it would give me good case life since it was a good bit under the 58.3 g "hot" load.

Since running the OCW I have been attempting to find the best seating depth. I ran one session with big adjustments per Berger's advice and found a depth with this charge that yielded about 0.5 MOA (I recall this was about a 0.030 jump to the lands). The rest of the depths ran about 0.75 to 1 MOA. I ran another test adjusting depth depth by +.010, +.005, 0, -.005, -.010 from where I left off in the last session in an attempt to fine tune this load. My best group was now .010 closer to the lands and was about 0.3 MOA. The rest were in the 0.5 to 0.75 MOA range. I didn't shoot any of these seating depth test over a chrono.

Fast forward to yesterday and I was trying a new lot of H4831sc. I loaded up 10 rounds of the old lot at 57.4 grains and the seating depth I did best with last time and 10 rounds of the new lot everything else the same. There was no significant difference between lots. However, the load is now reading about 2775 with a range of 2807- 2750. I also had 2 or 3 shots out of the 20 with very slight sticky bolt lift. Accuracy suffered too... all loads were just under 1 MOA. I figured if it was hotter and I was getting some pressure signs that my muzzle velocity would have been much higher. My previous chrono readings for this load were 2816 in cooler conditions.

I am wondering if I have a neck clearance issue that could be messing with peak pressure. I neck turn my brass. My PTG reamer indicates that my chamber neck is 0.3169. My loaded neck is 0.3135 with around 0.0005 runout. My fired neck is 0.3145 (I would have expected this to be larger with a 0.3169 chamber neck). My re-sized neck (bushing die) is 0.3115. Bullets will not easily slide into a fired case. Should I be concerned about this?

Is there anything else that I should look at? Thanks in advance for the help!

 

[GLC]

Hello Lokent

Something's not right, 57.4 grains of h4831sc is an extremely light load, in fact this will be the go to reload in a .284 shehanne.....

I shoot 61.5 grains in my saum, 30" barrel 300 norma necked upto to 7mm 314 loaded neck, zero pressure and very good repeat ability and brass life, give me around 3000-3040 depending on temp, I have been as high as 62.5 grains.
I have shot this load at +80 degrees however we do not get the really hot temps.

As a suggestion try some Norma brass, also try some 210 match primers, your neck clearance seems ok however not sure why your fired cases are not larger?

One question, is your freebore +200 thou?

Your rifle should be capable of .20 or better groups,mine will shoot tighter than
I can with the same combo (however I am shooting hybrids which are worth a
try)

Regards
Gary

 

[lokent]

My freebore is .216. I tried the hybrids and noticed no difference in group size, but still have 80 or so left I can mess with.

Yes., I would expect my fired case necks to be .315 to .316. Maybe my chamber is dirty? I just cleaned my bore and shot about 5 or so fouling shots before I started. My barrel is a rock creek 5R 8.7 twist. Fired and reloaded cases have little runout.

Not sure what this could be.

 

[Preacher]

A bullet that your using should slip right back into a fired case with very little pressure, if not, your brass may be work hardened and is not springing back like it should..
If your neck is exactly 316.9, a fired case neck thats around 314.5 isn't to bad considering.
Temps in the 90's will cause pressure problems that wouldn't show up in 70 degree temps..
Your also showing 2 different loaded neck dimensions....

 

[lokent]

Preacher, The bullet definitely will not easily slip back in the fired case. Perhaps the necks have work hardened as they have been fired around 3 or 4 times. Maybe that and the 90 degree temps were what was causing the pressure to spike? Still can't figure out how I am loosing muzzle velocity though.

Thanks for pointing out the two different loaded neck dimensions. I corrected that in my original post. The 0.3115 neck is the re-sized neck dimension prior to seating the bullet.

To summarize:

Chamber neck (based on reamer) - 0.3169
Fired Neck - 0.3145
Loaded neck - 0.3135
Re-sized neck - 0.3115

I have lost 41 fps muzzle velocity. Gone from no pressure signs to slightly sticky bolt lift on about 3 of the 20 rounds. All with the same 57.4 g charge (each individually weighed). Groups have gone from 0.5 MOA to 1 moa.

Potential Causes:

-90 degree ambient temperature
-case necks too tight/work hardened case neck
-seating depth change
-shooter?? not ruling that out

Thanks!

 

[MrMajestic]

Fast forward to yesterday and I was trying a new lot of H4831sc.

Is there anything else that I should look at? Thanks in advance for the help!

Maybe?

 

[lokent]

I loaded up 10 of the old and new lots of powder. They both shot the same.

 

[lokent]

Hello Lokent

Something's not right, 57.4 grains of h4831sc is an extremely light load, in fact this will be the go to reload in a .284 shehanne.....

I shoot 61.5 grains in my saum, 30" barrel 300 norma necked upto to 7mm 314 loaded neck, zero pressure and very good repeat ability and brass life, give me around 3000-3040 depending on temp, I have been as high as 62.5 grains.
I have shot this load at +80 degrees however we do not get the really hot temps.

As a suggestion try some Norma brass, also try some 210 match primers, your neck clearance seems ok however not sure why your fired cases are not larger?

One question, is your freebore +200 thou?

Your rifle should be capable of .20 or better groups,mine will shoot tighter than
I can with the same combo (however I am shooting hybrids which are worth a
try)

Regards
Gary

Gary, This is what I got from Berger for 7mm SAUM with the 180g VLD:

Powder: H4831 sc
Start Load: 55.5
Approximate Start Velocity: 2646
Max Load: 58.3
Approximate Max Velocity: 2782
Fill Ratio: 97.80%

Hodgdon shows a max load (62,900 PSI) of 58.0 grains with a 175 GR. HDY SP. The above is with a 24" barrel and standard COAL. I am sure that longer free-bore than standard will allow for more powder (and a 30" tube will definitely yield more MV), but I am surprised that it will allow for that much more. How many firings do you get before you see loose primer pockets? Anyway, having trouble seeing 57.4 as extremely light based on this data.

Anyway, I need to start keeping better records, but my original OCW may have been with virgin brass. Maybe virgin vs 3 times fired brass and moving the bullet seating depth out 10 thou could account for my MV drop. Still scratching my head over the sticky bolt lift on the couple of rounds. I'm going to give the barrel a good cleaning and re-do the OCW.

 

[GLC]

Hello again

I did some work on Quickload with the hybrid and got less pressure than you are indicating, my freebore is long around .275 and I do have a 30" barrel, my cases are all still good after 5 firings some up to 62.5 gr, the Hornady bullet is pretty different to the 180 Berger.
Now usual disclaimer applies safe in my rifle/barrel but may not be in yours or anybody else's.

Now I found at least 50-60 fps difference with new unformed brass (quicker) than fired brass so I drop the load for new brass this maybe the answer to your question regarding velocity difference, also the 8.7 twist may slow it up a tad as well, mine is. 1:9.

Regards
Gary

 

[pmarauder]

Nosler 300 SAUM brass is made by Norma. You can see it pictured in the Norma catalog.
Do you have a reamer print? A 7SAUM chamber length is 2.040. If you measure your necked 300 SAUM brass....I bet they will measure out at 1.998-2.003. Right in there.... So that leaves about .040 before the actual leade. If you are positive that your chamber neck is .3169...... then i bet you are all carboned up on that .040 gap. If you have access to a bore scope, that would confirm. If you dont have a bore scope.....then i would take a 8mm bronze brush on a chamber rod and spin that about 1000 times in your chamber with some Pro-shot and maybe IOSSO. Then take a loaded round, and fire it.....now measure your OD on your fired neck. Problem solved I bet.....

 

[lokent]

Nosler 300 SAUM brass is made by Norma. You can see it pictured in the Norma catalog.
Do you have a reamer print? A 7SAUM chamber length is 2.040. If you measure your necked 300 SAUM brass....I bet they will measure out at 1.998-2.003. Right in there.... So that leaves about .040 before the actual leade. If you are positive that your chamber neck is .3169...... then i bet you are all carboned up on that .040 gap. If you have access to a bore scope, that would confirm. If you dont have a bore scope.....then i would take a 8mm bronze brush on a chamber rod and spin that about 1000 times in your chamber with some Pro-shot and maybe IOSSO. Then take a loaded round, and fire it.....now measure your OD on your fired neck. Problem solved I bet.....

I do not have a reamer print but I have the reamer and the neck diameter is marked on it and I have confirmed it to the best of my ability to measure it. I trim my necks to 2.000 and have noticed some neck sooting. I have never cleaned my chamber other than a little light mopping. I think you may have nailed It. THANKS!!!

 

[lokent]

It has been a while since I have had the time to shoot. Here are my results after giving the bore a good cleaning and cleaning the chamber with IOSSO:

-Date: 9/15/2012
-Atmospheric Pressure: 30.007 Hg
-Temp: 86 deg F
-Humidity: 38%
-Altitude: 300 FT
-Winds: nne@5MPH

Brass: Nosler 300 RSAUM necked down and fired about 4 times
Bullet: Berger 7mm 180 VLD Hunting
Powder: H4831sc
Primer: Russian Mag

I shot around 5 fouling shots before I started shooting these groups...

58.6g | 5 shot AVG Velocity 2782.2 | 5 shot extreme spread 35 | 5 shot group size @ 200 yards ? (Didn't get group to print as I left the elevation of my scope set for 500 yards )
58.3g | 5 shot AVG Velocity 2774.0 | 5 shot extreme spread 11.5 | 5 shot group size @ 200 yards 2 inches (3 shots in one ragged hole and 2 unexplained flyers)
58.0g | 5 shot AVG Velocity 2762.8 | 5 shot extreme spread 23 | 5 shot group size @ 200 yards 1.75 inches (fairly evenly dispersed group with POI about 1.5 inches down and left of the 58.3 g group)

Although I had absolutely no pressure signs, my fired neck size is still 0.3145. I am thinking that the chamber cleaning with the IOSSO may have cleared up some carbon fouling in the neck area that could have contributed to my pressure issues last time. Still don't know why my fired neck is 0.0024 under my chamber neck dimensions... oh well.

I still can't seem to get these Berger VLDs to group well. I think I will try shooting 5 shot groups with 58.4, 58.7 and 60.0 to see if I can get a consistent POI and reasonable extreme spread with no pressure signs. If that works I'll once again start playing with seating depth.

My original loads with the virgin brass on a cool day indicated most consistent POI and groups with 57.4g and a velocity of 2816. Not sure why 58.6g @ 2782 is still 34 slower? Maybe I was being impacted by the carbon in the neck area then and didn't realize it? Those unexplained flyers with the 58.3g load are really messing with my head. I keep asking myself if the 3 in a ragged hole were just luck or if I pulled them...