6BR velocities... what I see vs. what I read...

[memilanuk]

,originally started to post this in Jackie's testing thread, but decided it was too long and not entirely applicable to just his thread)

OK. I'm a tad confused here. After reading all these glowing reports,not just this thread) here and on Benchrest Central about these guys wringing 2950-3000+ fps,and looking for more) out of a little 6mm BR, even w/ a 30" tube... I was expecting somewhere in the mid-2800's, maybe on up to 2900fps from a 27" tube. If I'm reading this right, Jackie's testing shows about 8-10fps difference per inch from 28" on out... so one wouldn't think that the range I was looking for to be too unreasonable.

Reality... more like 2700fps. Needless to say, more than a tad perturbed. In talking to some other HP/F-Class shooters they seemed to echo my experience... 2700-2750fps, *maybe* 2800 w/ a 30" tube and one heck of a hot load. This is w/ Lapua 105's or Sierra 107's, somewhere btwn 29-30+gr Varget, Lapua brass, and usually CCI 450 primers. I'm currently running 107gr SMK's 0.020" off the lands over 29.5gr Varget... 30gr gave bolt wipe and sticky bolt lift.

My setup isn't anything special... Savage 10FP w/ a SSS,Douglass XX) barrel w/ a .272" neck, Redding Competition seater and Type 'S' F/L bushing die,though I've got and have used a Wilson seater and neck sizer along w/ a Redding body die... no significant difference). Others are using fancier custom barrels from 'top' name manufacturers, custom actions, etc. etc. etc.

So the burning question in my mind is "What's responsible for the difference?" 2700-2800fps is quite a bit off 2900-3000+. The 6XC and .243 run right in that 3000+ range... using quite a bit more powder, but you get the idea. What is the key here? Is it the ultra tight chambers and custom dies? If so, will someone explain to me the mechanism by which a tighter chamber alone in the same cartridge generates 200-300fps more velocity at the other end of the barrel?

 

[Forum Boss]

Monte,

What's your Freebore, cartridge OAL, and brand of chrono?

Are you using Moly-coated bullets?

First, borrow another chronograph. We've found typical variances in Shooting Chrony units of 30-40 fps or so.

Second, you might want to go into the lands. In my gun, with a .080 Freebore, jumping even .010 resulted in HIGHER pressures,stiff bolt lift in particular) than with the same charge .015" into the lands.

Also, the Savage bolt design is part of the culprit IMHO. It has to do with the toggle bolt head. Send me a PM and I'll try to explain--I can't really confirm what's going on, but I can give you my experience in my Savage and my theory, which has to do with headspace. All I can say is I think you will be able to run higher loads without the stiff lift if you jam. It has to do with headspace. The bolt wipe is another symptom that may disappear with a jammed load.

Third, I'd suspect the barrel. I have a Savage 10FP with a 3-groove Pac-Nor, and I run right about 2900 fps now, with 30.3 gr of Varget. I tried 30.5 but it was a little "stout" on hot summer days. The Lapua factory ammo chrons at 2830 in my gun, and I know the same stuff has chron'd 2780 in other guns. Lapua rates that ammo at 850 m/sec or 2789 fps from a 26" barrel.

My chamber is certainly tighter than SAMMI but I wouldn't call it super tight.

In your set-up a .010" jam will move the bullet .030" up the neck. In this little case, you might find that makes a big difference.

Last thought--it could be you have a very fast lot of Varget. Suggest you try some IMR4895 or RL 15.

NB: Now it could be that my chron is high while yours is low, but my comeups at 600 are within 1 click at 600 yards when I plug 2900 fps into the ballistic software, and my bullet impact was high.

One other specific answer to your question--Jackie's Krieger has a .237" land diameter. Your barrel is probably a .236.

Putting it all together,and these are just guesstimates) if you're losing 50 fps from the barrel,compared to some others), if your chron is 40 fps low, and if you can pick up 20 fps from changing the seating position, that's 110 fps.

You may also want to read this thread about recent "hot" lots of Varget:

http://www.snipershide.com/ubb/ultimatebb.php?ubb=get_topic;f=8;t=000892

The Varget I use is over two years old.

 

[dreever]

Milanuk,

You've got to consider you are shooting a Savage factory action which cannot/will not take the kind of pressures that a custom action will. In my heavy Hart 1AS action I can push the BIB 95 to 3000 and beyond. I don't shoot it there because accuracy and brass life are much better in the 2950+ range. This is with a hefty load of Varget with the bullet .020 into the lands.
The 105 VLD's will run 2940, again seated well into the lands, with a hefty load of Reloader 15. Freebore makes a huge difference you cannot get these kind of velocities with a "do all" .050 freebore chamber. Also my reamer is a good bit tighter than Sammi spec's. that alone makes a big difference.
If you want to chase the "velocity rabbit" your actin/barrel/chamber combination makes a huge difference also you have your reamer ground for a particular bullet in mind, no compromises. There are always tradeoffs.
The F-class and Palma guys do not need or want super tight chambers,they need reliable magazine feeding, functioning in a dirtier enviroment, etc. Different game different expectations.

Velocity isn't everything. Accuracy is first and foremost. It dosen't matter if your running 3000+ if you can't put them in the ten ring. In my game the tenrings 1 1/4 inch and we shoot 200/300/500 meters so accuracy is where it's at, not velocity.
If your rifles shooting bug holes at 2800 be happy, and don't chase that Velocity Rabbit.

 

[chino1969]

I've run into differences in velocity by going from one lot of Varget in one pound containers. The difference was approx. 200 ft/s. When I looked at the containers closer, I saw that one was made in Australia and one was made In the U.S.. The one made in Australia was the hotter of the two. I bought an 8lb. container made in Australia and solved that problem for awhile. Be aware that Varget was made in both places and this could account for the difference.

 

[JeffT]

Monte,
My first 6 BR was a Remington 700 w/Hart 1-8" with a standard .060" free-bore. I got pretty much the same results you are getting, around 2750-2800. The accuracy was excellent though, and a shooting buddy just had to have it, so I sold it to him and bought a Nesika K, another Hart 1-8" and had some free-bore added to the new chamber. I can now get 2900-2975 easy, these numbers are backed up by come ups at 500,600, and 1000 yards shooting f-class. My best load is 34.5 H4350 w/bare 107 & CCI450,,2975), but when it gets 95 outside it's to hot, with 30.7 Varget I get right at 2900, with no problems regardless of temperature. My chamber has the boattail junction app. 2/3 down the neck, or another way to look at it, the boattail is just barely in the case. The odd part of mine is the 4350 load wants to jump .030" and the Varget load wants to be crammed into the riflings .030"


Jeff

 

[Forum Boss]

Jeff,

I'm actually not surprised by the jam/jump preferences of the two powders. Between .030 jam and .030 jump is .060". That's enough to alter the pressure significantly.

As noted in my previous post, with this short 6BR case, moving the bullet down the neck significantly will raise pressure. Conversely, going a long ways into the lands, can actually reduce pressure,compared to say .005" jam) by increasing case capacity. I suspect what you're accomplishing with the seating depth changes is to tune the pressure,Up for H4350 and down for Varget).

We're all still learning things about this case and every barrel is different. We've also observed that not all lots of Varget behave the same.

 

[rhino]

Perhaps get a Tikka M 595 action as your platform for the 6 br.

1. It has a flat underside which is better for accucracy and bedding.

2. It has the smoothest bolt throw of almost any factory action.

3. The trigger can be upgraded by Mac Tilton.

4. Have Mac or GAP face,mill) your reciever and install a pinned lug.

5. Install a quality barrel with quality tight reamer. You may want to turn necks.

6. Slap it into A McMillan if they will still inlet for them. Some custom stock makers will if you ask.

7. Shoot with that big grin on your face as bughole and your friends marvel at the smooth bolt throw!

Well this all hinges on finding a stock. I got a Mac for mine...might be a one time deal.

Yes, the Tikka M 695 M 595 actions are slick as snail snot on ince!

RHINOUT!

 

[aJR]

Because of the complexity of transporting gunpowder from ADI in AUS to Hodgdon in the US it does not go in the little bottles ..It goes in 5 tonne vats and 100s of tonnes at a time,then is processed into small containers..I have seen lab reports siteing changes of an up to 600 psi diff in 2 following batchs of H4350 while at the same time having a 400 fps difference when fired from a 50 gn capacity,H2O)case in the same temp/humidity controled environment..ie it's just a different batch..JR..Jeff Rogers in AUS

 

[memilanuk]

About the custom action thing...

1) Thought I mentioned that other people that I've spoken w/,HP shooters mostly) were also getting markedly less speed than what is bandied about here... using custom actions,RPA, Barnard, Hall, etc.)

2) Will someone please explain the mechanics by which a custom action allows a cartridge to generate an extra 200-300fps at the other end of the barrel? What specifically is the key here?

About the seating depth...

If I'm following this right... you're saying that I need to seat the bullet out *further* into the lands, thereby causing the pressure to spike sooner and thereby avoid the over-pressure signs I'm getting at a 'mere' 2700fps... seems a little counter-intuitive, at least on the surface... I'm not adverse to playing w/ this a bit though... after a Prone/F-Class match on Saturday I think I'm out of matches,or working weekends) for the next three weeks or so...

Thanks,

Monte

 

[Forum Boss]

About the custom action thing...

1) Thought I mentioned that other people that I've spoken w/,HP shooters mostly) were also getting markedly less speed than what is bandied about here... using custom actions,RPA, Barnard, Hall, etc.)

2) Will someone please explain the mechanics by which a custom action allows a cartridge to generate an extra 200-300fps at the other end of the barrel? What specifically is the key here?

About the seating depth...

If I'm following this right... you're saying that I need to seat the bullet out *further* into the lands, thereby causing the pressure to spike sooner and thereby avoid the over-pressure signs I'm getting at a 'mere' 2700fps... seems a little counter-intuitive, at least on the surface... I'm not adverse to playing w/ this a bit though... after a Prone/F-Class match on Saturday I think I'm out of matches,or working weekends) for the next three weeks or so...

Thanks,

Monte

Monte,

#1, I'm getting a usable 2900 with a Savage 10 action, CCI Primers, Lapua 105s, and Varget. With Norma 203B,Similar to RL15) I can go higher.

#2, Barrels do make a difference--50fps more/less is not unusual even with the same maker. 100 fps is not unheard of with different bore dimensions, land configurations, and degrees of hand lapping.

#3, The custom action won't crater the primer as readily. Part of this advantage can be had by bushing the firing pin. Re the Savage action--it is a little hard to explain, but the toggle-bolt design, in my experience, generates stiff bolt lift,from excess headspace on fired round) at lower pressures than with a custom action. I really don't want to espouse this as some kind of proven theory--it's just something I've seen with the Savage.

#4, Yes, going from 0.0" contact to .005" in to the lands will raise start pressure. However, if you compare .020" jumped to .020" jammed, the reduction in case capacity,when jumping) actually raises pressure. You can see this predicted by QuickLOAD, and we've also seen it in Jackie's testing. I suggest you try your 29.5gr Varget load .010" into the lands and see what happens. You may, then, have to add powder to get your velocity back up, but ultimately you may end up with more velocity. There's no question in my mind, for example, that a guy with a .120" freebore seated into the lands will be able to get more Velocity than somebody with a .060 Freebore who is jumping, at least with the heavy bullets.

I know it seems counter-intuitive. You can also just extend your throat with a throating reamer--then you can increase the case capacity and reduce pressure without jamming the bullets. What is your Cartridge OAL right now? I think optimal V is achieved, with a 107, with the bottom of the bearing surface about 1/2 way down the neck, i.e. with about .150 of shank in the neck.

It is a relatively simple matter for a good smith to move the throat out a bit. The equivalent of .090 to .120 freebore seems to be a good place to be with the long bullets, although the Berger 105gr VLDs, with their shorter bearing surface will work fine with a .080" FB,using Kiff-style measurements--Hugh Hendriksen would quote you different numbers for the same throat).

 

[memilanuk]

Interesting... I wouldn't have figured that w/ that much air space in the case that moving the bullet forward some would have that meaningful of an effect on case volume in terms of pressure. If the case was packed full...sure. But when the powder has room to slosh around it surprises me a little.

I'll try to get to the range on Friday on my day off,have some other load work to tend to) and see if I can run a few different seating depth tests. Most of the SMK's I've shot worked well either jumping a bunch, or jammed. Jamming isn't a problem per se, but I feel a little uncomfortable having to add a cleaning rod and a can of compressed air to my range kit for a match

About the firing pin on the Savage... the primer isn't the problem,yet). I get ejector wipe and sticky bolt w/ perfectly shaped primers.

 

[Forum Boss]

Interesting... I wouldn't have figured that w/ that much air space in the case that moving the bullet forward some would have that meaningful of an effect on case volume in terms of pressure. If the case was packed full...sure. But when the powder has room to slosh around it surprises me a little.

I'll try to get to the range on Friday on my day off,have some other load work to tend to) and see if I can run a few different seating depth tests. Most of the SMK's I've shot worked well either jumping a bunch, or jammed. Jamming isn't a problem per se, but I feel a little uncomfortable having to add a cleaning rod and a can of compressed air to my range kit for a match

About the firing pin on the Savage... the primer isn't the problem,yet). I get ejector wipe and sticky bolt w/ perfectly shaped primers.

Variations in seating depth DO make a BIG difference in pressures in this small case. A .040 difference is a big deal with this case. Trust me there.

QuickLOAD Estimate for 107 SMK with 30.0gr Varget, changing ONLY the seating depth .040":

COAL Pressure
2.400"----60,637 psi
2.360"----62,386 psi

Nearly 2000 psi difference!!

Data based on 38.00 grain H20 capacity--your cases might be slightly less or more. I've found QL to be pretty accurate in these predictions except that it OVER-estimates the pressure effect of land contact.

With the Savage bolt, when you're not jammed, the bolt head is not fully compressed against the spring washer that separates the bolt head from the bolt body. I really hesitate to try to give more of an explanation,because I may not be understanding what is really going on) but I can tell you that when I went from Jammed to jump I saw stiff bolt lift that wasn't there before.

Also--did you ream your Flash-holes? I've found that can cause the case to pressure out earlier.

One last thing, do try RL15 and borrow a different chronograph. Shooting Chronys are notorious for wide variances in outputs from one particular unit to another. Also don't confuse ejector shaving,mechanical cutting from rough edges on the ejector hole even at low pressures) with brass flow into the ejector hole. Two different things. The brass flow will be a distinct round spot on the rim. Many Savages will rough the rim from burrs on the ejector hole edges as the bolt closes on the round.

 

[memilanuk]

Hmmm... don't think the chrono is the issue. I tested it against another CED Millenium in the past... long story short, there was about 23-24fps difference btwn the units,don't remember which was which), but other than that the readings were within 2-3fps of each other, every time. Very consistent. 'Course, that was then,first half of '05) and this is now. But I think I'll continue on the assumption that the chrono isn't the problem for the moment.

Re: seating depth/length... I'm running about 2.350" w/ 107's w/ the meplats uniformed. SMK's seated to the lands,jam length) are 2.830",Stoney Point comparator). Capacity is 38.8gr.

Never touched the primer pockets or flash holes. Thats why I pay extra for Lapua brass

 

[Forum Boss]

Hmmm... don't think the chrono is the issue. I tested it against another CED Millenium in the past... long story short, there was about 23-24fps difference btwn the units,don't remember which was which), but other than that the readings were within 2-3fps of each other, every time. Very consistent. 'Course, that was then,first half of '05) and this is now. But I think I'll continue on the assumption that the chrono isn't the problem for the moment.

Re: seating depth/length... I'm running about 2.350" w/ 107's w/ the meplats uniformed. SMK's seated to the lands,jam length) are 2.830",Stoney Point comparator). Capacity is 38.8gr.

Never touched the primer pockets or flash holes. Thats why I pay extra for Lapua brass

Monte, OK. we can rule out the chron. Otherwise, I think we're in business. My friend John Southwick recently put a 6BR on his Borden custom rig. He was seeing the same thing you did--stiff bolt at relatively low,2800) Vels with Varget. He switched to N540 and punched up his velocity 100 fps. Problem solved. Mind you, he won a 100-yard match with his "slow load" of N540, but was able to ramp it up another full grain and he's right under 2900 fps now with the Berger 105s.

Setting my comparator at 2.830",to match yours) that's about .030" past ogive contact for me. So that makes sense--I have a .080 FB, you probably have about a .110" Freebore. Right where you want to be with the heavy bullets.

Seat your bullets .015" into lands,past just touching) and you should be in good shape.

Your 38.8 Capacity is also on the high side, which is good. Start with 30.0gr RL 15 and work up towards 31.3 RL15 MAX. If you aren't seeing the V gains you like, switch to Lapua 105s,which are .0005 smaller diam.) or the Berger 105 VLDs, which have a shorter bearing surface,less friction). Don't mess with the meplats on the Bergers or the Lapuas for now.

Also, take some fine crocus,sp?) cloth and polish around the edges of the ejector hole to make sure there are no burrs.

But with the numbers you gave me, it looks like your throat length is good. I predict we'll get you up in the 2850 range, maybe even 2880.

As a baseline, my gun runs 2830 fps with the Lapua Factory ammo,COAL 2.330") and Jackie got 2812 if I recall correctly.

FYI: With a 2.385" COAL,I think that would be .015" jam for you), 30.5gr RL15, 38.8gr capacity,Average), 28" barrel, QuickLOAD predicts 2896 FPS at 58,314 psi.

I'm very curious where you end up.

 

[Asa_Yam]

Monte,
Repeat after me:

Accuracy first, speed second.

The practical effect of an extra 100 FPS is pretty minimal, when it comes to wind drift. Given a 10 MPH crosswind, Standard Day conditions, and MVs of 2750 and 2850 FPS, you need 1/2 MOA less wind correction at 1000 yards with the faster round. ,8.36 MOA vs 7.87 MOA.) With either load, you are still around the upper edge of the transsonic region,Mach 1.17 versus Mach 1.2) at 1000 yards.

If you want to be able to get more speed safely and reliably, USE A BIGGER CARTRIDGE. People have blown up rifles by trying to hotrod rounds, when all they needed to do to get the extra speed was to go to the next largest case.

 

[Forum Boss]

Asa Yam's point is very important and should probably be reiterated on this board daily.

And I do not advocate pushing for higher Vs at the loss of accuracy. But with this cartridge, there's a lot of guys finding their best accuracy comes at a relatively high V. Likewise, the ES and SD often declines as you get to a higher load density and operate at higher pressures.

Terry Brady collected 4 world records last year shooting about 2900. Harold Seagroves has won the Hickory shoot multiple times running about 2950 with Danzac-coated bullets.

Talk to the PPC and 30BR guys and they'll tell you speed and accuracy go hand in hand--up to a point.

I am reminded of what Al Nyhus has said: "pressure is your friend". By this he meant, learn to tap the benefits,low ES/SD) of higher pressure loads. But obviously you don't want to be victimized either.

Whether you run fast or slow, we also always have to remember, the wind will still kick your ass, if you don't "tune" your marksmanship skills while you're optimizing your load.

 

[outlawsix]

Mr. Moderator, you mentioned the Savage spring washer. Has anyone to your knowledge taken it out? Then replaced it with a correct thickness washer/shim?

This seems as though it would give you the same spacing each and every time.

Just a thought.

 

[jb1000br]

#4, Yes, going from 0.0" contact to .005" in to the lands will raise start pressure. However, if you compare .020" jumped to .020" jammed, the reduction in case capacity,when jumping) actually raises pressure. You can see this predicted by QuickLOAD, and we've also seen it in Jackie's testing.

I have also seen this very NOTICABLY in a 300wby IMP

JB

 

[Forum Boss]

Monte, I just went out this morning and shot my Savage. With a load of 30.5 Varget, .020 into lands,2.355" COAL), it was running 2927 fps.

It also shot a 1.6" five-shot group at 610 yards, witnessed, preceeded by a 2.2", witnessed, so I don't think you'll be giving up any accuracy at those speeds. Air Temp about 65 F.

No stiff bolt, no ejector wipe, round primer edges.

Note, on an 80-deg day, that same load, at .010" jump, 2.325" COAL, gave me stiff bolt lift, with big craters and Vs over 2980 fps.

Got to love Pac-Nors and Wipe-Out though. One dry patch through the bore, one shot into the berm and my elevation zero was dead-on at shot #2. I still haven't put a brush in this barrel.

One interesting aside. My scope is a Leupold 8-25x. My buddy has a Nightforce 8-32 NSX. The NF was able to resolve bullet holes a bit better at 600. However, the colors and contrast truly were much better with the Leupold. The Orange sticker really popped when viewed through the Leupy while it was kind of dull in the NSX. Also the general view through the NF seemed grayer and more cloudy. It was really quite noticeable.

Right now I think Zeiss may have the best balance between resolution, color fidelity, and contrast. I'm convinced more than ever before that someone shopping for a premium scope MUST look through NF, Nikon, Zeiss and the S&B,if you can afford it) side by side in the same conditions--there ARE differences!

 

[AlNyhus]

Hi Monte. Man, where to start on this subject....

Monte, sometimes differences like you're seeing are the result of many small details in the entire package. This includes firing pin size, spring tension, pin-to-hole dimension, throat angle, freebore diameter as well as length, bolt-to-reciever clearance, barrel internal dimensions, rifling profile, the entire spectrum of chamber/brass/dies dimensional compatability..not to mention the commonly known and more easliy controlled stuff like powder lot variances, primers and bullets, plus all the other stuff I'm not smart enough to figure out.

Just last weekend, Randy Robinett and I spent the better part of 2 hrs. discussing this very subject.

Personally, I would take a really hard look at a couple of areas if this was my stick:
,1) I would have an accuracy 'smith that knows what he's doing bush the pin hole and make the firing pin around .058-.062 in diameter with no more than .001 pin-tip clearance and set the pin protrusion to around .052-.058.
,2) I would use a new, standard tension firing pin spring.
,3) I would have a serious look at the mechanical camming situation. Many times, we've seen what has been described as
"sticky bolt lift" be nothing more than a mechanical camming situation. Small changes here can have huge effects of bolt lift, sometimes giving the perception of excessive pressure.

As mentioned by Paul, the Savage bolt design does have significant drawbacks when you start working in the higher pressure ranges...one of these is that the bolt will give a stiffer 'feel', for lack of a better term, as you open it. This is also there at lower pressures, but as the pressures get higher the 'feel' increases by a greater percentage..hope I'm explaining this okay?

I'm going to put foward something here that will not be either popular or well accepted, but here goes....deep breath now Al, let it out slowly....:lol: Okay...here we go: It's my opinion, based on work I've done with two Savage rifles, that the Savage toggling bolt head design significantly contributes to out of square case heads on fired cases and that this becomes increasing noticeable in the upper pressure ranges in the form of increased bolt lift and wiped case heads. This becomes more apparent when there is excessive bolt-to-reciever clearance.

But all in all, it sure doesn't sound like you're far off the mark with your gun, esp. if you're getting the accuracy you need at the 2700 speeds. Again, I would check the three areas outlined above and see what improvements they offer. You probably won't spend over $100 for all the work involved, so it's a reasonable approach to take, IMO. Just make sure that you're working with a 'smith that really understands the subtle nuances of what we're trying to do with these rifles.

Occasionally we see some big differences even in our well worked out BR stuff...some combos of barrels/bullets, etc. just don't give us the same in all situations.

Hope this helps. Good shootin'. -Al

P.S. Yes, pressure is your friend:thumb:, but everything has to be working together to make this happen, regardless of the pressure ranges we're talking about.. I've pushed my 30BR with 118 BIB's to near 3,200 fps,3,180 and change) and the pressures had to have been nearing 75,000, but the bolt opened with my little finger. 'Course, the cases were thrashed......:lol: