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Help - developing 7mm stw load - questions

 
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  #1  
Old 11-24-2011, 11:12 PM
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Help - developing 7mm stw load - questions

HELP! Been trying to develop a new long distance capable loads for my 7mm STW.
Have chronographed a number of test loads and cannot get my feet on the ground.

Rifle: Shilen DGA-M, new 26in, 1 in9" stainless barrel under a S&B PMII 5x25 DT cm scope. Have shot in new barrel with over 75 shots w/ correct cleaning process. Gun shoots consistent 1/2"MOA @ 100yds. Having problem getting FPS up over 3000 fps. Load specs: Federal 215 Lr. Mag Primers, Fireformed (once fired) Rem Cases, Retumbo Powder and Ber ger 168 gr. VLD bullet set off lands @ 0.030"

Test bullet used: 168 gr Berger VLD Hunting

Have chrono'd 5 shot groups as follows:
7MM STW BERGER 168 GR VLD ----AVG FPS COUNT
String 1 --78.1 GR ----Retumbo ----------2924.8 ----5
String 2 --78.3 GR ----Retumbo ----------2814.7 ----5
String 3 --78.5 GR ----Retumbo ----------2817.6 ----5
String 4 --78.8 GR ----Retumbo ----------2868.3 ----5
String 5 --79.0 GR ----Retumbo ----------2942.5 ----5
String 6 --79.8 GR ----Retumbo ----------2919.8 ----5
String 7 --80.5 GR ----Retumbo ----------2896.5 ----5
String 8 --81.0 GR ----Retumbo ----------2904.5 ----2

My objective is to push load up over 3000 fps. Note String 1 load has high 2924.8 avg. fps, String 5 load is highest but still can't get bullet past 3000 fps.

Shot in barrel using several boxes of commercial HSM Gold Trophy (same) 168 gr. Berger VLDs, chrono'd HSMs loads at 3195 avg. fps (20 rounds).

Pushed powder load to big time max in String 8, but more Retumbo doesn't seem to push 168 gr. Berger any faster using 2 grains of addtional powder?

CAN ANYONE GIVE ME SOME ADVICE ON WHY?
Have prepared new test loads using other powders, RL22, IMR 7828 and 4831SC. Just need to get down to the range to test and chrono.

ADVICE WELCOME! Anyone had such a problem!
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Old 11-25-2011, 12:42 AM
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I've heard of MV maxing out, but haven't experienced it myself. Are you seeing any signs of excessive pressure: bolt face impressions on the base, popped primers, stuck cases, etc.?

Based on my Barnes and Lee manuals, the hot powders for 160-175 gr bullets in this caliber seem to be RL25, Magnum, H870, IMR7828 and Accurate 8700. The first two should get you to 3100 fps with those Berger 168 gr bullets.

FWIW, I don't invest as much in a single powder on my first pass as you did. I usually shoot a string of increasing charge, but only one load per charge weight. I repeat this for at least two more powders. When I shoot these strings, I look primarily for MV and pressure signs. I also watch impacts to identify the high and low positions.

Then I select a couple of powders and develop loads for 5-shot groups, each group with a different charge. I usually only shoot 4-6 such groups on the second pass, looking primarily at group extreme spreads. I usually find what I'm looking for without needing a third pass. If not, I then start to vary seating depth, change powders, or change bullets.

Good luck.
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Last edited by bruce_ventura; 11-27-2011 at 08:35 AM.
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  #3  
Old 11-25-2011, 12:53 AM
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Re: Help - developing 7mm stw load - questions

bruce_v

No signs of excessive pressure, primers all look good, etc. I originally started using Retumbo in a my Shilen DGA-M .300 RUM barrel and was very pleased with MV shooting Berger 168 gr. VLD. Found I could push the VLD to 3400 fps, just got tired of getting pounded at the recoil end of my rifle.

Dropped down to 7mm STW and have seen great groups. I start off shooting for sweet spot group combined with most MV. Once I'm in the range of desired MV, I drop to 3 shot groups, pick the best group then start to work on bullet COAL.

Thanks for the info. will report back with results of RL22, 7828, etc. I have some H1000 and H5010 I may try also.
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  #4  
Old 11-25-2011, 10:04 AM
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Re: Help - developing 7mm stw load - questions

In my STW I have used both RL -19 and H-1000. The most accurate loads are typically a couple of grains over max. I have an older Hodgons that shows H-1000 loaded at 82 grains with the 160. Work up carefully and cautiously.
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  #5  
Old 11-25-2011, 04:12 PM
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Re: Help - developing 7mm stw load - questions

80 grains of h1000 for me with a 162 grain. 3000 fps isn't even pushing it. A 7mag
will do that. With your barrel you should see 3150 or so. You may have to change bullets
as well. Bearing surface has a lot to do with speed as well. All that said, a stw was really
designed to shine with 140 grain bullets. So don't expect the kind of efficiency you would
get from a 300wmag with the heavier bullets.
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  #6  
Old 11-26-2011, 07:01 PM
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Re: Help - developing 7mm stw load - questions

I have played with two different 7 STW's. The first was nothing more than a parts gun put together with a 26" take off Sendero barrel. That rifle has a long throat and with the 162 Amax seated to just off the lands my oal is in the 3.9" neighborhood. I use IMR 7828 to push those Amaxes at 3240. I found the max listed load in my manual resulted in a gain of about 70 fps over my 24" barrel 7 RM. So I slowly worked up over book max, watching velocity and for the typical signs of excessive pressure. I started to get a bit of increased bolt lift at 2 grains over the load I settled on. The MV also stopped increasing at a linear rate at about the load I chose and then jumped up to about 3300 at the point of increased bolt lift. I have been shooting this load for quite awhile now and my W-W brass has shown no ill effects after 6 or 7 firings. This load also shoots in the .3s with regularity.

The second STW was built on a Stevens 200 that I lengthened and tubed with a 26" factory Savage varmint weight barrel. I used some Sierra 168 SMKs and H1000 with R-P brass for break in loads for that rifle. I never cronographed any of those loads as I just loaded 40 rounds for a baseline, and then made changes to the rifle to see what differences they would make (things like bedding, and recrowning). I did end up with that rifle shooting that random load into 1/2 moa at 500 yrds.

So I would say from my limited experiences that good accuracy isn't too hard to find, and at least some of the loading data doesn't fit well to all rifles. Work up carefully!
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Old 11-26-2011, 09:06 PM
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Re: Help - developing 7mm stw load - questions

Is there a reason for the heavy bullets? What are we hunting? Or are we just looking for good groups? I use 130gr Sierra Matchkings and US869 and get very good groups. MV is probably around 3600. Dropped a 250lb Mulley with it and only ran 35 yards.
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