240 SMK, H50BMG powder, 300RUM...anyone?

[jmden]

Anyone messing around with this combo? Be interested in your experiences.

Thanks.

 

[Michael Eichele]

Close. I have not tried the 240 but I toyed with the 220 and H50BMG for a while in the 300 RUM. I dont remember the exact velocities but the accuracy was very good. I do remember the velocities were decent. I dont know that you would get real good velocities with a factory gun but a tighter, smoother custom barrel will get decent velocities.

 

[jmden]

Close. I have not tried the 240 but I toyed with the 220 and H50BMG for a while in the 300 RUM. I dont remember the exact velocities but the accuracy was very good. I do remember the velocities were decent. I dont know that you would get real good velocities with a factory gun but a tighter, smoother custom barrel will get decent velocities.

Thanks, ME. I've had a lb. of it for several years. It just didn't produce good velocities with a 200g AB awhile back, but with a 240SMK, it might be right in there.

I had to go to a new 8lb jug of US869 and even reducing my load a bit while fireforming and shooting new cases, I got an ave. MV of around much lower 2940 MV and pressure signs unusual for that reduced load. Must be quite a bit faster burning lot unfortuanately. Thought I might give the H-50BMG another whirl. Would prefer to use and extreme powder anyway--might be less MV change with temp change than US869. I can fit 103g of H-50BMG in my RUM cases just below the neck shoulder junction. We'll see...

 

[yobuck]

have you ever done any mountainside testing to compare how the 200, 220, and 240 smks compare at 1500 or more?

 

[jmden]

have you ever done any mountainside testing to compare how the 200, 220, and 240 smks compare at 1500 or more?

Not sure if you're asking me or ME. I've only shot the 240 out to just over 1K. Haven't shot any other MK. With a 240 doing 2940 MV and a hard hold (no brake) I can barely spot my own shots at 1K if it's a dusty hillside. Shot some steel and milkjugs a couple of days ago. Steel at 880 had two out of 4 within 2.5 in of center and just left--ele right on. The other two shots hit, but I wasn't fond of feel of them as I pulled the trigger--about 6" off. Worked at jug at 816 and it stayed safe--couldn't spot my shots at that distanct and the milkjug was just in the shade so hard to see the hits anyway. Working on consistent prone form. Then shot a milkjug at 1017 yds. Fist shot skimmed just over the top, right over the middle. Second nailed the jug nearly dead center after adjusting down .25 MOA from what Exbal had reccomended. 2-3 mph 3 o'clock wind at my location--a bit stronger mid canyon and a wind switch somewhere as the dust on the far side of the canyon was not going the direction I thought i would've. Alot to learn about wind. Shot a couple of times at a jug at judged 1008 (Leica 1200 wouldn't get that far in the sun) and went right over the top middle a couple of times, then aout of ammo. Still working on my getting my prone shooting position 'feel' as consistent at possible--that time of year.

 

[jmden]

Well...went out and shot some H50BMG under 240's.

This was quick and dirty. Fired 'em all in less than five minutes up an old logging road. Good lighting conditions, so fairly confident in the chrono numbers. Chrono didn't miss a beat.

I've had this powder probably 4-5 years sitting in the shop. Used some old fired brass (some fired many times--don't have much nice new prepped brass and don't want to damage what I have carefully prepped in wild hair load development at the moment) I had lying around as seems like using new brass always results in less pressure signs showing and lower velocities--sometimes seems like new brass doesn't give the true picture.

Didn't start getting interesting until I got to 104g. Started at 98g in the mid 2700's.

Yes, compressed--haven't done much of that--any pointers?

300RUM, 26", 1-10", approx. 65 deg., ~3.775" COL, seated to lands, FED 215M:

(corrected MV using JBM ballistics for chrono 20' from muzzle)

104g--2932--small hint of ejector pin mark, primer cratered a bit
105g--same--no ejector pin mark at all, primer cratered a bit (almost makes me wonder if I loaded what I thought was 105 at 104, but I was pretty careful--maybe it's just a big node?)
106g--3007--definite ejector pin mark (partly shiny) and cratered primer

Have to get out and mess around with accuracy potential and velocity ES.

Use this info at your own risk. Maybe it'll help someone else out.

 

[Augustus]

92.5 gr of 50 BMG gave me around 2900 fps with the 240 out of a 28 in Broughton. This is about max in my rifle. 94 gr blowed primers. Be careful folks, there is no way my rig would have held togather with 104 gr. I shot 104 gr under the 190s and that was on the warm side.

 

[jmden]

Augustus,

That is amazing there would be so much difference. I wonder if it's because my powder is a few years old, just different lots...? How old is your powder? If it's new, I'm starting to wonder if a good portion of Hodgdon's powder is getting 'faster' for some reason. I think my newer 8# jub of US869 is a fair amount faster than my old jug, I've recently heard of faster H1000 going around and causing a bit of trouble here and there and now am wondering if you have a newer lot of H50BMG that's faster as well.

Just goes to show that you can't be too careful with reloading.

START LOW AND WORK UP POWDER LOADS SLOWLY AND CAREFULLY.

Thanks, Augustus.

Jon

 

[Augustus]

The difference is probably due to a combination of factors. The lots may be a little different, my barrel may be a little tighter than yours and you may be throated longer. The 240 has a very long bearing surface and pressure will go from OK to UNOK very quickly, I like the combo, its just needs to be handled carefully.

 

[Autorotate]

Shot from rifle that is spec'd here:
http://www.longrangehunting.com/forums/f52/611-yd-34-nm-oryx-44827/

Temp: 86F
PA: +4000'
OAL: 3.800 (.020 from lands)
Powder: H50BMG
Muzzle to Chrono distance: 15'

Charge in grains / Velocity in fps
89 / 2839
91 / 2865
92 / 2875
93 / 2914
94 / 2922
95 / 2941
96 / 2990
97 / 2989
98 / 3031 slight ejector mark
99 / 3059 ejector mark and bolt lift

Me thinks JMDEN has a fast one

As observed from the shooter, it's been my experience that the 240's hit steel down range significantly harder/with much more authority than 210 VLDs and 200 NABs for sure. Recoil is upped a notch or two as well with the 240s.

If the 210 VLD didn't shoot so well for me, and have such a well established track record for hunting applications, I would've invested more time investigating the 240s.

 

[jmden]

Thanks for the good info, Autorotate. I've got over 1100 barrel burning hi-pressure rounds through the pipe on this thing, so that may have a thing or two to do with it. Still getting good accuracy by chasing and seating at the lands though. Nice to have the 4" Wyatt's box. I wonder if the powder I have is a little slower than some of the new stuff as well.

That's one reason I've got parts headed to Kirby for a 338AX...

Haven't shot the 210's, but at 1/2 mile, the 240's put a 3/16" to 1/4" deep crater on my 1/2" mild steel plate. I think they'll still kill an elk at that distance... I remember how I paid $50 to have this nice, flat 18" square plate cut for me. First shot that hit it warped the whole thing. Wouldn't sit right on a flat surface anymore. Oh well.

 

[Autorotate]

1100 rounds with good accuracy....I will be elated if this happens for me. I did use the Gun Juice treatment after the first 100 rounds, so we'll see. I took some Stoney Point measurements with the unfired rifle regarding distance to lands, and am at the 400-450 round point and have seen the Stoney Point ogive/lands distance grow approx .007. Seems like I might have a measurement issue, as one would expect much more, but I've been checking that dimension after nearly every range session. I'm skeptical, and this is still inconclusive at this point, as it seems I learn 10 things everytime I go the range. Yesterday's dummy is todays' genius

A 338 AX by Mr. Allen....that will be tough to beat. Have you posted on this thread about it yet?
http://www.longrangehunting.com/forums/f19/tell-us-about-your-2009-custom-rifle-build-37991/

You might be able to "straighten" out your bent plate with a 300 SMK from your 338 AX

 

[jmden]

The rate this build is going, it'll have to be in the 2010 version of the same thing. I think I put in in that post or one like it as I recall. 30" finished Rock Ck. fluted med. palma 10 twist barrel with lightweight PK brake. Manners T2 (90% carbon version with a different filler in the area the DE adj. cheekpiece will be), jewell trig, PTG Al bottom metal, BAT HRPIC receiver with 20 MOA integral rail and integral recoil lug and specially machined to accept the 4" Wyatts mag box. That's about it. Trying to go as light as possible for a carry gun. Still holding off on the scope to see what, if anything, happens to the Leup Mark 4's this year. Supposed to be some changes that we might like. We'll see. I would've had it for November elk hunting but BAT Machine is months past when they said the HRPIC action would be delivered to Kirby. Not much you can do...

"as it seems I learn 10 things everytime I go the range. Yesterday's dummy is todays' genius" I hear you there!

 

[jmden]

BTW, I mentioned using this combo to Kirby and he related that H-50BMG seems to be very temp stable. Good to know if it works for you otherwise.