Taking apart 97 rounds of 6mmBR--updated after range trip

[carlsbad]

Just went to the range with my newly built 6mBR norma, 30" barrel, 1 in 8 twist. I took 100 rounds loaded with berger 108s, loaded to sit on the lands.

Couldn't find any varget so I'm working on a load for 8208xbr. Not nearly as much data out there but I found quite a few guys using 29.5 grains or so of 8208xbr with good luck.

I lowered it to 29 for my longer barrel but it appears that may not have been nearly enough adjustment. Fired three rounds. severe cratering of the primers and one perforation.

Previous owner of this barrel says he used 27.1 grains of Varget but was getting a pretty low velocity (2600 or so). I was shooting for 2800-2900 ft/sec as a starting point with this round.

Living in CA, it is a pretty good trip to the range so I'm hoping to get it pretty close on the next trip (friday). So I'm hoping someone has a good load recommendation or a good way of adjusting a load based on barrel length.

If I don't hear from anyone I'll start with 27 grains next trip.

thanks,
Jerry

 

[fdshuster]

Re: Taking apart 97 rounds of 6mmBR

jerry: What primers are you using?

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

Remington 7 1/2 BR.

 

[fdshuster]

Re: Taking apart 97 rounds of 6mmBR

O.K., then I don't see primers as the problem. The Rem. 7 1/2's have a .025" cup thickness. Have to wonder though if the CCI 450's or BR4's would be tougher with the nickle plating? Try just 3 or 4 rounds?

I had much of the same problem when I chambered a 6BRX on a Remington 700 receiver. Sent the bolt to Gre-Tan and had it bushed. Problem (also removed the burn holes in the bolt face) solved, until the primer pockets started to loosen after only 4 loadings. Then had to reduce the load by 1 grain.

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

I have some very tough CCI 41s for use with the AR15s but I like the 7 1/2 BR for bolt action.

Pretty sure it is just a load problem. Wish I could have gotten chrono data but didn't want to play with any more over-pressure rounds. Just good range safety practice.

--Jerry

 

[Erik Cortina]

Re: Taking apart 97 rounds of 6mmBR

Start low and work up a load properly!
You already tried a stab in the dark and you want to do it again. If you had started working up a load on your first trip like you are supposed to you would be much closer to finding a load and would not have to pull all those bullets.

There are no shortcuts to any place worth going.

 

[effendude]

Re: Taking apart 97 rounds of 6mmBR

Why not load at the range? In 5 or less test rounds, you will know your max charge. Then you can load up promising charges at the range?
Scott

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

Can be kindo windy to load at the range. Good thought though. Wonder if the range safety officer would have a problem with that. Today there were 69 shooters registered when I got there. During the week there will be at least 20.

trying to find a good starting load is not a shortcut. Took 30 minutes to take the rounds apart while watching NCAA golf championships and now they are ready to reload waiting on a civil answer to my question. I did take some 28.5 and 29.5 with me but decided I wasn't close enough that the 28.5 was worth shooting.

I highly recommend the RCBS collet puller. I polish the ID of the collet with fine emery paper on the lathe and it doesn't leave a mark.

--Jerry

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

OK. I've come up with the following: Using 8208 data from IMR load data sight and linearly interpolating between the two loads given, I get 60 fts for every grain added. Found a reloading manual with some guidance for barrel length saying in the 2500 to 3000 fts range, velocity will increase 20 fts for each inch of barrel. So my 6" longer barrel is worth 120 fps.

So 120 fps/60 fps/grain = 2 grains, suggesting that I should reduce load by 2 grains for 6" longer barrel.

Seems like a lot. Anybody have comments on this analysis?

thanks,
Jerry

 

[Erik Cortina]

Re: Taking apart 97 rounds of 6mmBR

OK. I've come up with the following: Using 8208 data from IMR load data sight and linearly interpolating between the two loads given, I get 60 fts for every grain added. Found a reloading manual with some guidance for barrel length saying in the 2500 to 3000 fts range, velocity will increase 20 fts for each inch of barrel. So my 6" longer barrel is worth 120 fps.

So 120 fps/60 fps/grain = 2 grains, suggesting that I should reduce load by 2 grains for 6" longer barrel.

Seems like a lot. Anybody have comments on this analysis?

thanks,
Jerry

It so does not work this way at all!

Load from 25.0 gr. and work up to 29.0 gr. and go to the range and shoot them incrementally. Stop the minute you see pressure signs and look at your groups on paper. The target will act as a translator and tell you what your gun likes. Some barrels are faster than others due to bore differences. Chamber dimensions also play a huge role on cartridge performance. Not to mention powder lot differences, bullet differences, primers, brass, etc.

So, no more shortcuts, you have to do the work if you expect results. The definition of insanity is doing the same thing over and over and expecting a different result.

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

Eric,
I understand what you are saying but as a scientist, I want to understand more than just the experimental brute force way of getting to the answer. For example, for 308 there is so much data out there that I can estimate my load very accurately. I'm trying to find the starting point with some basis behind it.

So you picked 25 grains as a starting point. Was that by subtracting the 2 grains from the 27 grains I was toying with? That's about where I'm ending up. I just want to understand how I got there. Before I did this analysis, I was thinking 26 would be a good starting point.

--Jerry

 

[Erik Cortina]

Re: Taking apart 97 rounds of 6mmBR

The rule is thumb is to start 10% lower and work up. They would be 24.3 if we use the 27 gr figure you came up with. I myself think you will end up so webers around 28.0 gr, which would yield a starting load of 25.2 gr. using the 10% rule.

If you want, split the difference between you and I and start at 24.5 and work up. I personally like to cover a wide range so that I can clearly where the node starts and ends.

 

[snowpro440]

Re: Taking apart 97 rounds of 6mmBR

He might just get it if he keeps stabbing it in the dark long enough..... I would load 3 rounds of each , No need to waste ammo there.

 

[blvedere]

Re: Taking apart 97 rounds of 6mmBR

I would check your powder measure. I shoot 29.5 gr. 8208, with 66 grain Barts, and 71/2 Rem primers, .010 off the lands with no problems. Maybe you are jamming the bullets to much? Although 29.5 is more than likely to heavy a charge with 108's.

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

I'm using an RCBS chargemaster that seems to throw very accurately for 308 loads. I'm thinking it is accurate.

Perhaps 29 wasn't as much too high as I thought, there is quite a bit of clearance around the firing pin on the bolt. I'll bush that. But still, it was too hot.

friday when I go back I'll get there in time to set up my chrono. This past sunday, I was late because I had to drop my son off at 9am so they were already shooting means no chrono data. #singleparentproblems.

This thread has been useful to me in that I moved my start point lower than I thought I needed to. Thanks to all for your help.

--jerry

 

[nosualc]

Re: Taking apart 97 rounds of 6mmBR

Loading 100 for a new rifle, case, powder, bullet, primer combo off hearsay, is frankly, reckless.

Start 10% lower than a conservative target range. Load a single rounds with 1% increments. Stop immediately when you get any pressure signs, call that your MAX. Write it down, never go there again.

I would have started at 26.5, and increased in 1/3 grain increments. 26.5, 26.8, 27.2, 27.5, 27.8, 28.2, 28.5, 28.8, 29.2*. Less than 9 rounds to get to know your real MAX (all you know right now is that 29.0 is too hot), likely without a blown primer. Worst case, you end up pulling 8 bullets, 1-2 more likely.

Also, remember that your chargemaster is only accurate to +/- .1 grains, which is 2/3 of the 1% increment I mention above.

-nosualc

 

[carlsbad]

Re: Taking apart 97 rounds of 6mmBR

What made you think I was using heresay? I found a successful shooter, I believe in the "favorite loads" section here, using 29.5 with low velocities and so I used 29.0. There isn't a lot of data on 8208 xbr so I didn't have the multiple sources to check that I usually have but I didn't just go with "heresay".

I loaded 100 because when I drive to the range to test a round, if it is ok, then I want to have some fun progressing up the hill to 900 yds. If not successful, I take them apart and get rocks thrown at me from people who would have done it differntly. I tested I came home. What was reckless about that?

--Jerry

 

[snert]

Re: Taking apart 97 rounds of 6mmBR

carlsbad,

I was reviewing this thread. This site is a wealth of helpful info and the shooters here are genuinely thoughtful, for the most part, and desire to help. With that in mind, I thought I would make a couple observations to give perspective to your experience with your BR.

In reviewing the BR loads suggested by many shooters, you will likely note that they appear to be "hotter" than the loads listed in the manuals. I am not going to take a stand on that, but rather make some observations. First, the powder/bullet makers have access to and use test instruments every day to arrive at recommended loads. Of course, engineering, tolerances, atmospheres and maybe moon phases (not really) have effect on that data. BUT, it is wise to stick with it and not depend on "scientific" observations of cratered primers and bolt stickiness to tell you that you are "too high", cause by then, YOU ARE TOO HIGH. But I think you know that, as you are pulling bullets. And, since the very real possibility of a lost eyeball or brain matter exists when being OVER, it is wise to avoid that. Not preaching, just perspective....

So, use the manual as your guide, not the "good reloader said" approach.

Secondly, when running the long and heavies, even a slight goof in OAL can get you into the lands faster than you think, or too deep in the case, pushing pressures.

Thirdly, 8208 XBR appears to show velocities (in the manuals) in the higher end spectrum, and remember, velocity increase equals pressure increase. There is no free lunch.

Fourth, (and I am NOT a math guy) pressure does not increase in a linear fashion. It does not increase "two grains" because we add two grains. Frankly, I think pressure sometimes rises exponentially, so don't just assume a bit more is JUST a bit more. Sometimes it is BOOM more.

Fifthly, a Rem 700 is NOT a BAT. The 700 is a fine action, strong, etc etc. But it does have a fat pin, and the BR tends to crater primers because guys run them hard and wonder why they get primers that look like swiss cheese.

I understand you are travelling and want to spend your time shooting. I certainly would not like to be loading at a bench where 60 others are waiting for me to make a cartridge! BUT, as has been said here by folks responding to your post, you will be safer, and will get things sorted out if you spend an evening re-reading the load manual, sticking to the data found, and choosing a powder (yes, none of us can find it!) that is proven with much data. Load conservatively and test carefully. If you want a mega-zapper that spits bullets at warp 9, then buy one. A BR is NOT that cartridge. it is a fine round, very capable and darn fun.

Lastly, i like 8208 XBR in my BR, and I use 70 grain bullets, WSR primers and a 700 clone. But I am below the recommended max, and am getting fine groups. Oh, and the woodchucks can't tell 3100 FPS from 3300 FPS!

Glad you are having fun, keep shooting that BR and it is great to have you here

Snert

 

[gotcha]

Re: Taking apart 97 rounds of 6mmBR

Hi Carlsbad! Just as an aside. For my new 6BR I made up some rounds based on info I got from this site. I made the mistake of ASSUMING the data provided here would be bullet proof. ( I also enjoy puns) In the name of safety & common sense I reduced the load a full grain from that published. The web of my Norma case grew by .004" after firing ....... So, I had to return home and use the Hornady bullet puller too :-[ That evening I e-mailed Berger for data on my bullets and powder. Lesson learned, trust Berger not some of the outlandish loads found on the net. And, work up in small increments like .3 or .4 gr. You'll be glad you did. Just didn't want you to think you're the only one suffering the wrath of the Gods

 

[nosualc]

Re: Taking apart 97 rounds of 6mmBR

What made you think I was using heresay? I found a successful shooter, I believe in the "favorite loads" section here, using 29.5 with low velocities and so I used 29.0. There isn't a lot of data on 8208 xbr so I didn't have the multiple sources to check that I usually have but I didn't just go with "heresay".

I loaded 100 because when I drive to the range to test a round, if it is ok, then I want to have some fun progressing up the hill to 900 yds. If not successful, I take them apart and get rocks thrown at me from people who would have done it differntly. I tested I came home. What was reckless about that?

--Jerry

I equate all load information I read on the internet to be hearsay. I have no direct evidence that they're correct, or even safe. I cross reference all load information with other trusted data sources (e.g. - reloading books, powder manufacturers.) Caveat emptor.

Reckless is duplicating loads from people on the internet (however successful), and assuming they'll be safe in your rifle.

Reckless is shooting three of these rounds when the first gave you trouble signs.

Reckless is ignoring the common advice of start low, work up.

Not a big deal, you just have to pull 97 bullets. Could have been much worse.

-nosualc