7 Mashburn tomorrow

[joelkdouglas]

I don’t have it in my possession until (scheduled) tomorrow.

Here’s a pic the gunsmith, Kevin Weaver, sent:

I have done a terrible job keeping detailed notes. I anticipate starting with Retumbo and either 160 ABs or 175 PTs. I have one notecard detailing 160s with Retumbo.

I will be keeping details! What do you use to keep load notes?


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[DrMike]

Very handsome, Joel. I keep my raw notes in bound volumes for each cartridge/rifle. The data is transferred to an Excel program on my computer.

 

[sask boy]

Congratulations on a beautiful rifle, if I remember right Scotty should have some information on that particular calibre.
I am looking forward to a couple of range reports with photos I hope :wink:.

Blessings,
Dan

 

[SJB358]

Beautiful rifle Joel!

Maybe try some 175 Partitions loaded out to mag length and started with Retumbo. If it’s the same reamer as mine you can load them long and still be a hood way from the rifling.

 

[FOTIS]

Very nice rifle!!!

 

[joelkdouglas]

Spent some time today thinking about starting points for the 160s and 175s. I have some history with 160s (and mostly pressure signs), but none with the Mashburn and 175s. I also made a spreadsheet (which I will continue through load development for this rifle) so I could look at the info all in one place.

I looked so far at Nosler, Hodgdon, and Hornady data. My Swift and Berger books are at home. I haven't brought myself to purchase the Sierra book yet.

The Mashburn is a touch bigger than the 7 Rem Mag. Comparable cases, the 7 Weatherby and 7 Dakota, could be an indicator of 7 Mashburn velocities (not necessarily charge weights though).

All for 175 grain bullets
Retumbo (pretty limited info):
Highest charge weight for 7 Rem Mag: 68 grains
Fastest velocity in 7 Weatherby Mag: 3050 fps
Start point for Mashburn: 70 grains, stop at 3050 fps

IMR7828:
Highest charge weight for 7 Rem Mag: 63.5 grains
Fastest velocity in 7 Weatherby: 3100 fps (only one, all others 3000)
Fastest velocity in 7 Dakota (supposedly same case capacity): 3000 fps
Start point for Mashburn: 66 grains, stop at 3000 fps

H1000:
Highest charge weight for 7 Rem Mag: 65.5 grains
Fastest velocity in 7 Weatherby: 3000 fps
Start point for Mashburn: 66 grains, stop at 3000 fps

Thoughts?

Other Mashburn shooters, is this on par with what you expect?

My plan is to load 1 round per half grain charge weight and shoot over the chrono. And maybe because I've seen in my other Mashburn that 75.5 grains is good to go with 160s, I might load some 175s up with 74 grains just to see how it goes. Maybe I'll get lucky and be done with load development right there!

 

[SJB358]

73-74 grains of Retumbo should be on point for the 175 Partitions.

75-77 grains of H1000 with 160’s.

 

[longrangehunter]

Wow...... That's a thing of beauty for sure Joel, and it should be a real blessing to have in the field! I hope it treats you very well for many years to come!

 

[TXbaldhunter]

Beauty

 

[joelkdouglas]

First trip to the range, only 6 shots fired. I knew it would be quick, just identifying safe parameters to start working!

When I got home also measured the throat length with sharpie method. 3.521 OAL to lands. Magazine is 3.70 so no limitation there.

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[SJB358]

That’s great speed and I’m glad you’re not seeing any issues. I’d be you’ll find magic somewhere in that 3000-3100 range which is exactly what the Mashburn is meant to do.

 

[joelkdouglas]

Update:

Based on Friday's input I loaded up 6 more rounds for today, and hopefully more I'll load at the range.

All rounds are 7 Mashburn, Retumbo, 175 Partition, CCI250 primer, Winchester brass.

I loaded 71.3 grains to 72.3 grains Retumbo in 0.2 grain increments. Looks like this:

71.3
71.5
71.7
71.9
72.1
72.3

Hopefully there's a relatively "flat" velocity node in that range. I already suspect it's a safe powder range to work with based on Friday's results. Of course if I see any pressure signs I'll call knock it off.

For this test I moved the PTs out 0.01. Now they are 0.02 off the lands.

I also got my range reloading kit together and I anticipate loading more rounds at the range and saving a trip home and back. I have already-primed cases (did that last night), a Lee Dipper kit, a trickler and beam scale, extra 175 PTs, a custom Wilson seater and arbor press. The die is set for 0.02 off already. Ideally I will see a flat spot in the velocity range, I'll load 5 or 10 in the middle of the powder charge flat spot and shoot for record.

Of course it could also all fall apart and I'll come home and readdress!

 

[joelkdouglas]

That’s great speed and I’m glad you’re not seeing any issues. I’d be you’ll find magic somewhere in that 3000-3100 range which is exactly what the Mashburn is meant to do.

I'll never know but will always wonder what difference the Nitriding makes on velocity. I'm liking it so far!

 

[SJB358]

Could be, the 25" tube doesn't hurt much either.

Looking forward to seeing how it shakes out though.. You could have that sucker ready for Wyoming if you keep up this pace!

 

[JD338]

Joel,

Beautiful rifle!
Even if if shot so so, it would be a winner.
Looks like your load development is coming along nicely.

JD338

 

[joelkdouglas]

Departed direct for the range early this morning.

First I shot the 6 rounds of Retumbo with 175 PTs.

71.3 gr 2972 fps
71.5 gr 3017 fps
71.7 gr 3045 fps
71.9 gr 3032 fps
72.1 gr 3073 fps
72.3 gr 3046 fps

None of the charge areas have a big wide velocity node. I picked 71.8 to try, between 3045 and 3032.

I shot a 5-shot group, 175 PTs loaded 0.02 off the lands, 71.8 Retumbo. Results were so so, the not-abnormal 2 in, 1 out. Maybe 1.5 inches. I figured seating depth would fix it, so I started seating the PTs deeper by 0.005.

Turns out this was the best group of the morning. I know 3-shot groups don't tell you much, but in this case it told me the rifle doesn't really like something.

The good news when I got back home was primer pockets were still tight, and I wasn't noting any pressure signs, so I feel the load is safe. Web expansion was 0.001 to 0.002; not confident how reliable a pressure indicator that is.

Got home and ate lunch, kind of disappointed.

 

[joelkdouglas]

Since I only had a couple hours before I had to pick up the kids from school, I decided to abandon the 175/Retumbo combination for now and try the 160 Accubonds.

I started the 10-round velocity test where I stopped with the 175s, figuring that would be safe because I was dropping a couple bullet weights (if you count 168s). I also switched primers from CCI250s to GM215Ms, just because.

7 Mashburn
160 AccuBond, measured 2.963 CBTO/3.61 OAL to the lands
Retumbo
Winchester brass
GM215M primers

Velocity test:
72.2 gr 3128 fps
72.4 gr 3078 fps
72.6 gr 3121 fps
72.8 gr 3140 fps
73.0 gr 3156 fps
73.2 gr 3158 fps
73.4 gr 3182 fps
73.6 gr 3182 fps
73.8 gr 3196 fps
74.0 gr 3207 fps

While I was shooting and waiting for the barrel to cool I saw the 73/73.2 area and thought that was going to be it. Until I kept shooting and saw the big node at 73.4 to 73.8. 73 might be another node too.

I picked 73.6 to work with. I loaded up 4 rounds, 160 ABs at 2.913 CBTO/3.565 OAL, 0.05 off the lands.

As soon as I pulled the trigger on the 4th shot I knew I flubbed it (it's the one low right). I didn't have good follow-through, and I pulled up instead of staying through the shot. Pretty sure I moved just too soon.

Anyway, the first three look good!

 

[joelkdouglas]

I'm headed back out tomorrow. Hopefully the results are as consistent, or somewhere in the ballpark, as this group! I've had loads fall apart on me on day 2, I'm sure we all have.

Here's an image of the 160 AB 0.05 off the lands.

 

[SJB358]

Joel, to me the node looks pretty darned good right at 72 for the 175’s. I think with those I’d try them .025, .050, .075 and .100 off just to see if anything looks good. You’re getting great speeds with the 175’s and it’d be interesting if it respond to any of those better. It wouldn’t be the first time I’d seen it work.

You’re 160 load looks great to me. Right on the 3200 mark or close enough and excellent accuracy. I’m real impressed how yours is shooting right out of the gate. Plus, it’s nice to finally see normal Mash speeds.

 

[joelkdouglas]

Thanks Scotty! I loaded some more 160s last night to try this morning but I haven’t given up on the PTs. They are great bullets!


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