ULD's, ES & nitpickin

[ss7mm]

Been doing some shooting, load testing and checking drops lately because of an 11th. hour barrel change courtesy of APS Right off the bat this tube seemed like it was gonna try and get along with me so I've been a little pickier and a little more anal than normal .

This time I tried loads more to the upper and lower extremes and found that I can easily push it to 3400 but the J4s just really really don't like it up in that stratosphere and tend to get a little flaky. so then I went in the other direction. Just like focusing a picture in a camera this thing slowly "came into focus" and at speed a little lower than I'd been shooting with prior tubes but found that I'd finally found a sweet spot and the ES put a smile on my mug. I've heard all kinds of comments about group size, ES etc. but I firmly believe that you can't have a super accurate looong range gun with out low ES.

Take your favorite group and load. With the ES of that load, go to your friendly ballistics software and looking at 1000 yards and on out, vary the velocity by the low to high variation you have in your favorite load ES and notice the difference in elevation at the longer ranges. If you factor in the normal variations in group size due to mechanical/steel/human variations then I believe you have an opportunity in ES to help reduce your group sizes at extended ranges. Why not eliminate as many variables as possible?

The load I'm currently running is turning out to be verrry accurate and also seems to help immensely in the vertical dispersement department.

We were out doing some shooting today and set up a target at 811 yards. Winds were pretty steady at 5-8 with gusts to 12-15 from 3:00. I made no allowances for the wind as I knew the horizontal would be exaggerated because of the wind. I was mainly interested in vertical, as I know it's horizontal will match the vertical under ideal conditions, and I was also checking drops for data confirmation.

We were shooting across the top end of a canyon that dumped the winds out of the canyon into our line of fire at about 250-300 yards and the whole range, from where we shot to the target was out in the open and exposed to the winds. Talk about some real world practice. Sure glad I don't live in Wyoming.

Except for the called third shot, the group turned out pretty good. A couple of guys driving by stopped at the bench and asked me a few questions after the second shot. I just didn't have my mind where it should have been for the third shot and I knew where it was going when I broke it. You can see what I feel is the result of a very accurate load with an ES in the mid single digits in a case that burns 100 grains + of powder .

If we'd had time to put out wind flags and fully utilize the R2 reticle it might have ended up being a half way descent group. It's done better but this is a good representation of it's potential.

 

[AJ Peacock]

Nice shootin'

Beautiful!

 

[royinidaho]

that's some kind of good.

Flaky even in the 5R, eh @ 3400?

What is your velocity?

 

[TMR]

I found similar results in my rifle....30" Lilja 6 groove, 1-9 twist, Nesika M....At 3400fps, accuracy was ok, but not great. At around 3320fps, accuracy was very good and es was low. At 3200, accuracy is also good, but es was a little higher than I like. I am also doing some 11th hour testing. Guess we should have left well enough alone. What velocity are you running her at now?

Good shooting, by the way. Those muley's are in trouble.

 

[ss7mm]

Roy and TMR:

The velocity of this load is running 3140 fps. I'll take accuracy over top speed any day. I feed her what she likes. We seem to get along better that way.

Dialing the clicks is easy so 100 fps really doesn't make much difference.

 

[gamedog]

Very nice work ss7mm. That round sure has my attention. Have you had any chance to use it on any game yet?

 

[ss7mm]

Very nice work ss7mm. That round sure has my attention. Have you had any chance to use it on any game yet?

I've killed 3 deer and one elk with it. The longest deer, if I remember correctly was about 860 yards and the elk, again if I remember correctly, was about 690 yards. All one shot kills. None of the bullets for the deer were recovered but the elk was a full body length shot and I recovered the bullet after it went through 4' or more of elk. They were all dead before they hit the ground.

 

[gamedog]

The accuracy and results sure speak for themselves. I'm really interested in Kirby's Magnum's he's building. If you don't mind, what made you choose the 7mm over his other creations? To me it sounds like the perfect combo for long range deer & elk. Thanks

 

[ss7mm]

The accuracy and results sure speak for themselves. I'm really interested in Kirby's Magnum's he's building. If you don't mind, what made you choose the 7mm over his other creations? To me it sounds like the perfect combo for long range deer & elk. Thanks

I'd been tracking Kirby and his work developing the AM rounds. As soon as I heard him say "7mmAM", and knowing what Richard had planned, I immediately started bugging Kirby to get the 7mmAM up and running. I think I gave him a little heartburn for a while there.

I love the 7mm to begin with and, like you said, I considered the 7mmAM, especially knowing what Kirby and Richard had planned and what the planned results were, to be the ultimate long range big game round for me.

When we started the 7mmAM project the only AMs available were the smaller brothers of the 7mmAM. The big stuff came later but even now, I'd still pick the 7mmAM for long range hunting. I've had a little 100# woman shoot it and she loved it. Said it sure had a lot more horsepower than her .243. If Richard can get some shop time this winter the round is going to get a whole lot better by next spring.

 

[royinidaho]

With the 200 RBBT in the 7 AM and the 195 in it's itty bitty little brother I figure anything over 3000 is gravey.

I shot the 195 @ nearly 3200 but ran into problems (Lilja bbl but I don't know the number of grooves)

Have settled on the 169 @ 3300. Still very impressive numbers at long distance.

We'll see beginning on the 10th and 15th. Will have two great AMs side by side. Should be fun.

I'm gettin' pretty pumped.

 

[ss7mm]

With the 200 RBBT in the 7 AM and the 195 in it's itty bitty little brother I figure anything over 3000 is gravey.

You got that right and I like "AM Gravy".

We'll see beginning on the 10th and 15th. Will have two great AMs side by side. Should be fun.

I'm gettin' pretty pumped.

I don't know how you guys can get excited over a big game hunt. Have fun and we'll be looking for the pictures and writeup.

We start here the 13th. My buddy couldn't make the trip to Idaho this year so we'll be hunting here. Washington sucks compared to Idaho.

 

[Ernie]

If Richard can get some shop time this winter the round is going to get a whole lot better by next spring.

Boy, is that an understatement

 

[Fiftydriver]

SS7mm,

Looks like "MAYBE" we have that girl behaving again????

I hate to even post a reply about my AMs after the tongue lashing I got recently about that being all I do on LRH but screw 'em!! I mean that with all due respect.

In the case of the 7mm AM, I have found very similiar results to what you just have posted. My personal heavy 7mm has nearly the exact barrel as yours, only 30" finish length. I could horse the 200 gr ULD RBBT to 3400 fps if I really wanted to but that was not the most accurate load in that barrel. Turned out it was also a bit off max at aroud 3265 fps.

In my lightweight rifle, its preferred load is down to 3155 fps on average but it is also a 27" barrel.

Accuracy of the light rifle has been 1/2 moa to 500 yards, 3/4 moa out to half mile and around 1 moa from there to 1200 yards or so. I think this may have as much to do with the shootability of the lighter rifle(9 lbs) as much as anything.

My heavy rifle, very similiar in weight with your rifle has proven capable of 1/2 moa out to 1000 yards in good conditions when my head is in the right place while shooting.

I tend to not be quite as critical as many extreme accuracy minded long range shooters as far as E. S. is concerned. Obviously if I have a load that is giving me 75 fps spreads, this will not be really good at long range. But, if I can get a load into the low to mid 20 fps range for ES for say a 10 shot average string, I will be plenty happy with that and have yet to have any problem hitting big game at the ranges I have shot to so far.

That said, I certainly can not argue the fact that the tighter the extreme spreads the less vertical stringing you will see down range. That true with any chambering.

One very nice thing about the 7mm AM is that you have a pretty wide performance window you can search for your preferred load in. By that I mean, it has the case volume and ability to push 3400 fps in any barrel length 30" or longer easily. Often times this not the most accurate but I feel this is a bullet jacket issue and that will be changed very soon!!!!!

But even if you have to down load a bit, your still right there at the very top of the performance ladder for 7mm rounds. The 7mm STW will get you around 3000 to 3050 fps with this bullet weight. The 7mm RUM will get you 3100 to 3150 fps with this bullet in the barrel length you are using but needs very high pressures to get to this level of velocity.

In comparision, 3140 fps in the 7mm AM with a 32" barrel is such a mild load, I would suspect the cases would rechamber after firing and rechamber easily from the lack of high pressure.

When the right bullets come available, then we can throttle up and see what she will really do!!!

WC872 also seems to have very distinct vibration nods and also a relatively narrow pressure range where the powder will burn really consistantly. I think that is why we see accuracy drop off on the lower end of pressure as well at times and certainly can see some velocity spreads increase.

Anyway, take away that third shot and it looks like your playing with 1/4 moa at 1/2 miles. Not to bad at all!!!! Can not wait to see how you two boys do in Idaho!!!

One of these years I need to come down and play with you as well. I could bring a 338 AM, you your 7mm and roy his 270 and we could really have some fun!!!!

Again good post,

Good luck this season.

Kirby Allen(50)

 

[ss7mm]

Looks like "MAYBE" we have that girl behaving again????

I hate to even post a reply about my AMs after the tongue lashing I got recently about that being all I do on long range hunting but screw 'em!! I mean that with all due respect.

I know what you mean. We also shot the 270 at the same time and the wind fluttered the little Accubond around pretty good although it was still a very good group under the conditions. I didn't post the picture of the 270AM group because of the recent arguments over boolits, big and small.

In comparision, 3140 fps in the 7mm AM with a 32" barrel is such a mild load, I would suspect the cases would rechamber after firing and rechamber easily from the lack of high pressure.

When the right bullets come available, then we can throttle up and see what she will really do!!!

They do rechamber very easily. They'll last a long time at this rate. Hopefully by spring I'll be able to crank up the pressure on some new brass and run her hot enough to "melt some aluminum".