The 6UM

[Ryan Avery]

Thanks for sharing, Ryan and formi.

I appreciate the outside the box thinking compared to preconceived notions that exist in the hunting community. You've got improvement aspects in terms of internal, external, and terminal ballistics all rolled into one project.

And Ryan, I thought that you were a medium bore magnum proponent?!

I like to think I’m open minded and there is no doubt that under 1000 yards you give up almost nothing with a 6UM AND 115 NR Dtacs in terminal performance. But you gain an easily controlled rifle through the whole shot process.


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[WeiserBucks]

This has my curiosity, I'm going to rebarrel a WSM Kimber Montana and looking for good performance and low recoil. I wonder if UM would do a Kimber, it's not a very popular platform for most gunsmiths.

 

[Ryan Avery]

This has my curiosity, I'm going to rebarrel a WSM Kimber Montana and looking for good performance and low recoil. I wonder if UM would do a Kimber, it's not a very popular platform for most gunsmiths.

I’ve seen a few Kimber’s in the shop getting work done.


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[PathFinder]

What stock is that your running?

It's a Stocky's. Overall seems like a good stock but the inlet is way tight. Like tap everything in with a rubber mallet tight. They absolutely need to be relieved and bedded.
Got out to 835 last night to verify velocity. Velocity looks to be stable at 3450 according to AB. Going to do the bedding tonight to fix the horizontal stringing, the way this fit into the stock it's got to be the culprit. I had to force it in with a mallet and the shank of the barrel definitely has some pressure on it. Should have bedded it once I saw that but I got a bit ahead of myself.
I may try H1000 and N568 this summer when my dies show up, but N570 has been so easy it's hard to move away from it.

 

[Ryan Avery]

It's a Stocky's. Overall seems like a good stock but the inlet is way tight. Like tap everything in with a rubber mallet tight. They absolutely need to be relieved and bedded.
Got out to 835 last night to verify velocity. Velocity looks to be stable at 3450 according to AB. Going to do the bedding tonight to fix the horizontal stringing, the way this fit into the stock it's got to be the culprit. I had to force it in with a mallet and the shank of the barrel definitely has some pressure on it. Should have bedded it once I saw that but I got a bit ahead of myself.
I may try H1000 and N568 this summer when my dies show up, but N570 has been so easy it's hard to move away from it.

What BC did you use?

 

[Travis Bertrand]

It's a Stocky's. Overall seems like a good stock but the inlet is way tight. Like tap everything in with a rubber mallet tight. They absolutely need to be relieved and bedded.
Got out to 835 last night to verify velocity. Velocity looks to be stable at 3450 according to AB. Going to do the bedding tonight to fix the horizontal stringing, the way this fit into the stock it's got to be the culprit. I had to force it in with a mallet and the shank of the barrel definitely has some pressure on it. Should have bedded it once I saw that but I got a bit ahead of myself.
I may try H1000 and N568 this summer when my dies show up, but N570 has been so easy it's hard to move away from it.

How do determine stable velocity with AB?


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[PathFinder]

What BC did you use?

The one that AB had in their library. .591 G1/.302 G7

 

[PathFinder]

How do determine stable velocity with AB?


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I should have clarified. According to my data from AB, it's in the neighborhood of 3450. My assumption of stability is based on ~2" of vertical dispersion at 835 yards.
I'll pick up a chronograph in June and get some actual data.

 

[Tullis94]

I should have clarified. According to my data from AB, it's in the neighborhood of 3450. My assumption of stability is based on ~2" of vertical dispersion at 835 yards.
I'll pick up a chronograph in June and get some actual data.

Maybe I missed it, but what is your barrel length? Rifle looks great!

 

[PathFinder]

Maybe I missed it, but what is your barrel length? Rifle looks great!

Barrel is a 22" 7tw 6 groove Osprey with an SRS muzzle brake. Chambered etc by Unknown Munitions. Thanks! I'm excited to get it all finished up but there's bear hunting to be done first.

 

[PathFinder]

Looks like bedding straightened things right up. I felt like I broke the 3rd (top) shot a little high. At any rate, the rifle is ready to bear hunt for the next few weeks.
This is the first time I've seen serious issues prior to bedding a stock, but all of mine moving forward will be bedded first thing.
These three were at .090" off the lands, the rest will be at the .060" off like Ryan has been doing. After bear season I'll shoot more on paper to see if that tightens things up a bit.

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[Ryan Avery]

Not bad splash for a little 115-grainer at 1149 yards. The rock is about a 1/4-ish MOA.

 

[RoseAllen]

What's the difference between 6UM & 6mm Sherman Short Tactical? Is 2.90" coal to long for aics short mags?

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[Ryan Avery]

What's the difference between 6UM & 6mm Sherman Short Tactical? Is 2.90" coal to long for aics short mags?

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6UM has a 40 degree shoulder 6SST has a 30.
Best I can tell the 6UM holds 5 grains more h2o.

2.90 will fit in a aics short mag

 

[khuber84]

I did some case capacity testing a while back between Saum, max, sst, prc cases.
65 max 75.1gr
65 Saum 73.1
25 sst 71.2
65 prc 69.6
These were all fired ADG cases not sized, filled with 80/20% h20/alcohol mix to small manisicus bubble. Everyone's results may be a lil different, but these are pretty close. I was thinking a fired 6UM would be around 73-73.5

I have a friend shooting a 26" 6prc and another friend a 24" 6saum, both running dtacs well at 3320-3340, Rl23 in Saum, rl26 in prc. These are quite a ways from psi.

First hand 115 dtac data(not nose ring cut) from my 7.5tw 6gt prs rig. G7 to get proper dope from 400-1k yards is 0.315, to get proper drops at 1300y, g7 needed dropped to 0.310, this was at mv of 2875. The ab custom curved lined up well as long I ran my mv at 2900. The Kestrel 4dof needed form factor of 0.96 to get proper drops at 1k and in, but at 1300y required the form factor to be at 0.98.

 

[hdc77]

Quick question @Ryan Avery, are you running your 6.5 SAUM brass through a 6.5 Saum die with a .243 bushing? If so, what size bushing are you using? I’d like to plan for a 6mm UM build and trying to get my ducks in a row before committing. Thanks

 

[Ryan Avery]

Quick question @Ryan Avery, are you running your 6.5 SAUM brass through a 6.5 Saum die with a .243 bushing? If so, what size bushing are you using? I’d like to plan for a 6mm UM build and trying to get my ducks in a row before committing. Thanks

I used a 300 WSM IMP dies with a .270 bushing the first time. The second time we had 6UM die from Whidden and used a .271 die. UM should have dies in stock very soon.

 

[hdc77]

I used a 300 WSM IMP dies with a .270 bushing the first time. The second time we had 6UM die from Whidden and used a .271 die. UM should have dies in stock very soon.

Thanks!!
I’ll make sure I keep an eye out to get a set!

 

[Ryan Avery]

Thanks!!
I’ll make sure I keep an eye out to get a set!

They have a few and I me two in stock right now!

Whidden Bushing Full Length Die Set - Unknown Munitions

All die sets are bushing style FL sizing die and Micrometer bullet seater. Each die sets include a Full Length Sizer, a Micrometer Seater and a Shoulder Bump Gauge. Bushings are not included in the set. Seating Dies include a Standard seating stem.

www.unknownmunitions.com

 

[hdc77]

They have a few and I me two in stock right now!

Whidden Bushing Full Length Die Set - Unknown Munitions

All die sets are bushing style FL sizing die and Micrometer bullet seater. Each die sets include a Full Length Sizer, a Micrometer Seater and a Shoulder Bump Gauge. Bushings are not included in the set. Seating Dies include a Standard seating stem.

www.unknownmunitions.com

Great, just bought the last set! Thanks again,
H