6mm RAT powders for NRA HP

[bpm990d]

I have a 6mm RAT that I'm shooting for NRA HP. I've used R-15 for all my fire forming loads so far, but it is very dirty. I'm still fire forming so have not settled on a load but this is what I'm going to shoot OTC.

70gr Sierra @ 200
95gr Sierra @ 300
107gr Sierra @ 600
I also have 500 or the new Hornady 105 AMP bullets I'm going to try at 600.

Any recommendations for powders? I'd like to keep my loads to the same powder and something I can dump for the 200 & 300 yard ammo. Mostly concerned with function for short line loads and accuracy and velocity for 600. Your thoughts on:

IMR 8208
AR COMP
CFE 223
H or IMR 4895
N140

Thanks in advance.

B

 

[NateG]

I used R15 last season and 8208 this season with 80Bergers at 200, 90 Bergers (and I should probably move up to at least 100s, if not 108s) at 300, and 105 VLD hunting at 600.

As to function... I did have functioning problems for a while with the gun short-cycling with all but max loads (or an extremely oiled bolt carrier). Swapping out buffer springs fixed it, and the problem was with both R15 and 8208. But, with that fixed, it cycled just fine, even with the 80s over the same charge I was shooting with the 105s.

I haven't tried any of the other powders you mentioned, but I have been happy enough with 8208 that I probably won't.

 

[jscandale]

Nate,

Paul Irvin told me that you are the guy to talk to about 8208, so I just wanted to know what you thought of the powder. I have been developing loads to a cartridge similar to yours for the AR (6mm WOA Improved) that holds about 30.0 grains max of RL-15. With that load, I got 2860 fps with a 107, AR comp also looks like a good candidate providing more velocity with less powder. So, what are your thoughts on 8208? I understand you are very happy with it.

Thanks,
JS

 

[flatlander]

Nate,
I've been working with a couple of 6RAT rifles, both with 24" bbls. One has the Les Baer bolt, while the other has a LMT enhanced bolt. I think I need to switch buffer springs, based on what I'm seeing with both of these rifles, compared to casehead appearance in a 28" MR upper. IIRC, I used a Tubb/SSS flatwire buffer spring with the MR upper - what spring did you go to?

 

[flatlander]

BPM - I've got the same complaint about RL15 being dirty. Have used 8208, but mostly in FF loads using 85/87/90gr bullets. Didn't find any particularly accurate loads with 8208 until I backed off what appeared to be max loads a bit. I need to try 8208 with some of the 105/107/108gr bullets, but haven't done so yet. It meters plenty good enough to allow using thrown charges for 200/300yd loads, and no doubt burns cleaner than RL15.

I'm now experimenting with Alliant's Power Pro 2000MR. Got some very nice 600yd accuracy with S95MKs and 2000MR, but the initial test load produced only 2626fps. There's still plenty of room left for more powder, and I've got more test loads ready. Just need some decent weather to get out and try them over the chrono.

BTW - the current upper I'm working with is more of a tactical version, with a 24" Krieger, 1:8tw, .237" bore. However, my 1st RAT upper had a 28" Bartlein. I tried N140, H322, H4895, RL15, 8208, AA2520, and a few other ball powders that were too slow. Still looking for a ball powder that'll work as well with 70s & 105s alike, but so far, the best accuracy with the heavier bullets has been with RL15 & H4895.

 

[NateG]

I really like it.

I think the barrel I had is a bit on the slow side--I wasn't able to reach the higher loads that I've seen online--I think I used 28.5gr Re15 under a 105 VLD when I was using R15.

Most recently, I've been using 28.0gr 8208 under an 80 Berger BT for 200, a 90 BT for 300, and a 105 for 600, and it's worked great. With a WOP barrel (I think 26" Krieger 1:7.5, but whatever "standard" for the 6RAT is, in case I mis-remembered), I was getting almost exactly 2800fps (2796, I think) with the 105. I could go up a bit higher on 8208, but that load shot better than the warmer loads. The last match I shot with that gun (I've been playing with bolt guns this fall) was a 200-14X in the Crowell, where I got Creedmoored out of third by Cooper shooting a service rifle. Doh!

So, I really like 8208. It does seem to clean nicely (I haven't noticed any real difference between Varget/R15/N140/N540, but 8208 does clean noticeably quicker), and it's very temperature stable. Cooking a round in the chamber didn't seem to have much effect, so in the Crowell this year, twice I waited for over 5 minutes for my condition to come back. Both times I left a round in the chamber and shot an X when the wind flopped back over. I would have pulled that round out had I been shooting R15.

If you PM me your email, I'll send you the data I've got on the 6RAT with R15 and 8208.

I haven't played with AR-comp, but it sounds interesting (and probably a wash with 8208, honestly) and if I didn't already have a good load with 8208 and a good supply of 8208, I'd try it, too. 8208's definitely on the fast end of what works in HP, but it punches well above it's weight class. (I shoot it in a .223, 6RAT, 6BRX, .308 for Palma) AR-comp sounds like it's a similar wonder-powder, but with a burn rate better matched to HP. But, I'd still be surprised if it's better than 8208, as well as it's worked.

Another thing I noticed with 8208 in the Palma gun is that the recoil's slightly less than with other powders--you use about 5% less powder than Varget, and since it burns faster, there's less pressure at the muzzle--less gas escaping at less pressure means (slightly) less recoil. It's not a big change, but even a little could make a difference at the end of the day.

 

[NateG]

Nate,
I've been working with a couple of 6RAT rifles, both with 24" bbls. One has the Les Baer bolt, while the other has a LMT enhanced bolt. I think I need to switch buffer springs, based on what I'm seeing with both of these rifles, compared to casehead appearance in a 28" MR upper. IIRC, I used a Tubb/SSS flatwire buffer spring with the MR upper - what spring did you go to?

I went to a standard buffer spring and changed the hammer spring in my Geissele to a more "normal" one. I'm not sure why, but that Geissele had a much heavier spring that the others I've got. Putting in another one (combined with swapping out the WOP buffer spring--which is quite heavy--for a regular one) set everything right. Well, there was still the bloop tube problem I had to fix right before Perry...

 

[rcw3]

I am looking at this thread and a couple of side thoughts come to mind:

1. As to complaints about things running "dirty", if you have an extended gas port set up on your barrel, then things typically will run a good bit dirtier. Many shooters seem to feel that an extended port is the way to go and that there are no downsides to an extended port, even though there clearly are, and a rifle that tends to run dirty is one of them. The "dirty" aspect of things may not exactly be related to the powder but more to the gas system set up you have.

2. As to the noted issues of potential short stroking and need to tinker with buffers and buffer springs, the same thing follows if you have an extended gas port. A powder like 8208 is very much on the fast side of a burn rate for an extended port AR upper and the pressure curve of that powder drops off fast (not good for an extended gas port AR upper unless you have a pretty big port in the barrel). Like I suggested before, there are downsides to an extended gas port in an AR barrel and having an extended port does not always equate to a positive gain or the ideal situation - it may just provide a narrower window that you need to work in for things to be optimum.

Robert Whitley

 

[bpm990d]

Thanks for all the replies.

Lots of interesting information. The question about cleanliness mostly had to do with my barrel and chamber. The cases themselves came out reasonably clean (the necks did get a little black), but the barrel was filthy. It took 40~50 patches to get the carbon out. I was using Break Free Carbon Cutter and it has worked very well in my service rifle with R15, but it just kept getting black patches after black patches. I scrubbed it a little with a plastic brush but it just took forever to get the carbon out. The reason I'm concerned is that this is what I would consider a tight chamber. A fired case will hold a bullet. It takes a lot to get it in there, but it will go with finger pressure. I think there is about .003 clearance (total) between the neck walls and the chamber (according to the print). I'm not sure if this is because the AA Grendel brass changed, or if this is by design. In my mind there should be a little more clearance, but so far I have not had any functioning problems while fire forming cases. I think I have fired a total of 70 shots rapid fire so it's not really an exhaustive test. Accuracy has been tremendous with the 95 Sierras. The first rapid fire I shot with it at 300 yards while fire forming cases, I had a clean with 8 Xs with dumped powder charges of R-15. The two other strings I've shot with it at 300 had very nice baseball sized round groups.

Id like to find something that is a lot cleaner and produces good accuracy with dumped charges. I just have visions of alibis with all the crap in the barrel and neck.

B

 

[jscandale]

Boy, you want to remove carbon fast? I've never seen a carbon cleaner better than this:
http://www.kgcoatings.com/cleaning/kg-1-carbon-remover/
When you drip it on carboned up gas gun parts, it melts the carbon like pouring hot water on ice. Great stuff.

JS

 

[bpm990d]

Thanks, I'll order some tonight.

B

 

[Matt Pitchon]

My experience comes from 223 shooting heavy bullets for XTC. I have used RL-15 for many years, and now am using AR-Comp and 2000MR.

AR-Comp is a very good powder, and in my opinion, a definite improvement over RL-15. It has been accurate in every combination I have tried, is very clean burning, and does not seem to exhibit temperature sensitivity. I have used this up to 80s but could shoot 90s.

2000MR is also a very good powder for very heavy bullets. I shoot 90s at 2800 in a gas gun and 2900 in a Palma gun. It is accurate, but does exhibit some temperature sensitivity at near max loads. It is slow, very dense and has high energy, thus the high velocities. The drawback of this powder in a gas gun is high gas pressure at the port(my gas port is in the standard location). The result is it almost rips the rim off the case. I haven't figured out how to solve this problem without either relocating the gas port (new barrel) or an adjustable gas block (Ugh). Neither is good.

My guess is that AR-Comp would give almost as high velocities as 2000MR without ripping the rim off, but I haven't tried this.

Maybe none of this relates to the 6RAT, then just another data point.

FWIW

 

[bpm990d]

Thanks Matt,

A heavier buffer might be of use to you. I have a couple of Tubb CWS that I have used. They do tame overgassed guns and reduce the rim lifts. The neat thing is they can be adjusted to work for your load. The semi-auto bolt carriers do weigh a lot less than the M16 carriers.

B

 

[jscandale]

Matt,

I won the Porter Cup in 02 as well as multiple shoot offs for the Porter and Farr trophies with the service rifle and 90s. I remember having the same type of pressure problems. I have also used a Tubb carrier weight. It may have worked but I can't prove it. I have bushed the gas holes on a few barrels that work pretty slick. When I bush them, you can't even tell that it was done.

JS

 

[Matt Pitchon]

Guys:

Thanks for the thoughts on the CWS and bushing the port. I did try the CWS and it did help, but not enough. I also put in a heavier buffer spring, which also helped, but not enough.

Unfortunately, my current barrel is nitrided, which makes any kind of machine work on the port near impossible. The only good news is that it has 5500 rounds through it and shows very little wear.

I'm thinking about either changing powders, or designing a reliable and easy to use adjustable gas block.

I hate it when it gets this complicated.

 

[jscandale]

Hi Matt,
I understand about the nitride coating and the exterior hardness, but bushing the port can still be done pretty easily. When I have performed that task, I always used an 1/8" carbide end mill to go .200" deep, then turn a piece of ss with a .070" pilot hole to fit the hole with a press fit, then trim and finally indicate the OD of the barrel in the lathe and finish trim the new plug exactly to the barrel contour, then drill the final gas hole.

The carbide end mill will go right through the melonite coating which is oly a few tenths. When the job is complete, you can't even see the plug unless you use a magnifier to see the seem.

If you need help, send me a pm.

JS

 

[spclark]

I've had great results with 8208XBR too in 6RAT this past season. Same for Palma & even 6XC for mid- and long-range. Original 6RAT chambering seems to vary some depending on who ran the lathe. I know two shooters' whose chambers are reported to be 0.005" shorter than my WOA upper. Sizing Grendel brass down will increase neck thickness so I neck turned from the get-go. Point of fact, I found 0.011" neck wall thickness to be super accurate in my 6HAGAR upper & work towards the same thickness on my 6RAT cases, in two steps three to four firings apart.

Chamber dimensions revised a bit in what's called the FATRAT now but I don't have specifics. Supposed to reduce potential some folks have seen for pressure issues.

Had short-stroking early on too, cured with new buffer spring. My 6RAT upper's a hybrid: AA billet upper body & bolt carrier, WOA-sourced Krieger barrel & "improved" bolt. As I'd messed with the 6.5 Grendel for awhile early on then found 6HAGAR to be MUCH more satisfactory but a PITA when it comes to brass, I had a Grendel upper rebarreled by JH last year to save 6HAGAR barrel life. I had LOTS of Grendel brass on hand....

 

[old_gasgunner]

As a group, 4 of us bought 6Rats together last year. We all did much testing and 2 of us shot them at the Nat'ls. We all discovered early on that they were very accurate, but had some problems. The biggest was bad pressure indications when shooting bare 108 Bergers with RL15 pushing them at 2825+ fps. Some brass was only lasting one loading and we had many cycling issues. We could not shoot the loads listed for it or the 6AR Turbo40 (which looked to be the same). We had no problems with lighter bullets and were able to reduce the pressures by neck turning or Moly coating......neither which we wanted to do. With the help of Lee Wells, http://www.accurateandreliablerifle.com ,who built the uppers, we designed a new reamer/chamber which was named 6mm Fat Rat. Initial testing has shown that this has greatly reduced the pressure issues and neck turning or Moly should not be necessary. Even with these improvements tho, we believe the combination of bare 108 Bergers and RL15 pushed hard is not reliable and have seen much more predictable results using H4895 and Varget with 105-107 bullets at 2825+ fps with very good accuracy and reliability.

 

[bpm990d]

That is interesting information. How much more neck clearance does it have in comparison to the regular RAT? The RAT print I have says it has a .274 neck and given the way fired cases come out of mine, I suspect that is the reamer that WOP used. Is the FAT RAT "open source" or proprietary?

Thanks again for the useful information.

B

 

[dfry]

Nate and Steve, and Gary Yuen have a lot more experience with the RAT than I since I have just started working up loads for it, I'm still shooting my 6mm WOA until I do a little more testing of loads. I didn't even try RL15 in my rifle, wasn't interested in shooting it in my rifle here in Phoenix. I have tried 8208, Varget and ARComp, still need to test H4895. Steve and Nate use 8208, Gary uses H4895 because he has a bunch of it. Varget has done much better than I thought it would, I get about 2800 with it with 107 SMKs, although this lot is very slow. 8208 has given me very suspect results, I need to chrono it again. ARComp is showing real promise, very tight groups and velocity a little over 2800 with 107s with no pressure signs. I really liked the ARComp load, it shot great, it also shows real promise in the 6 WOA and I will probably try it for the first time in a match this coming weekend in the 6 WOA.

I need to fire form some more brass for the RAT before I shoot it in a match, I just don't want to fire form that brass in rapids. My RAT has a 27" Krieger barrel in an upper from Holliger. This upper looks like it will be a real hammer, just like my 6 WOA has been. I also need to test H4895 in the RAT, but I'm hoping that ARComp will be the powder for me. I am really tired of dealing with Varget in the WOA, with this slow lot I can't get enough of it in the case to get my old velocity back, but it is very accurate, Dave